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Goody
January 8th, 2009, 06:16 AM
I have noticed an alarming trend creeping in on this site over the last few years. I have been a member longer than it says on my avitar (I think I joined about 1998)
And in that time plc’s have become more and more ubiquitous.
So much so, that now it seems that even the milkman is having a go at programming them.

And this worries me!

PLC’s seem to be treat by some as though they are toys to play with and experiment. People with no electrical or engineering experience whatsoever are going into programming as if they were programming a personal computer.
Not only this - some are not even prepared to read the manual or if they do its all double dutch to them and so they come here wanting to get straight into a live working machine and alter things.

They do not want to waste time with a manual and a plc sat on their desk practicing with it!

And so we get a lot of questions that can be answered by reading page 2 or 3 of the manual or even a quick search of this site.
Just about everything that is asked today has been asked a 100 times before on this site and is searchable.
But this alarming trend of total novices wanting to get straight into the game has other consequences that is not often mentioned.

Machines controlled by plc’s can injure and kill people if something is not programmed right!

I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.
This sensor should not have done this until several other conditions had been met but due to terrible programming and no ‘event’ control - the conveyor started up although the conveyor system was off (not e stop - just the red stop button)
I am all for helping people to learn programming and I always give advice where I deem it proper and know what or where the poster is struggling.
But the plain truth is - some posters here should not be allowed within 50 ft of a plc controlled machine until they have fully understood the machine/plc and all the possible consequences of their actions.

tragically1969
January 8th, 2009, 06:49 AM
Is this a general rant or have you actually got a point ?

This argument applies to more than just PLC programming, it applies to nearly every job that involves handling anything more than a piece of paper !!

brucechase
January 8th, 2009, 07:24 AM
I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.


To me, the most alarming part is that this person was not locked out while working on a piece of equipment. That should always be the first line of defense. You should never rely on a stop pushbutton to protect your life. The reason he was thrown off the conveyor is because he did something stupid - work on a machine that could have killed him without locking it out. This had nothing to do with programmng.

I do agree that there seems to be a lot of people who try their hand at this new fangled plc stuff. I do wish more people would be mentored instead of jumping right into a situation. You have to wonder how much blame companies have for propogating this. Even though a person out of school is nowhere near ready to program a machine or design a safety system, many companies will not understand that. If you have a degree (or been to a tech school), then many managers will assume you can do it all.

monkeyhead
January 8th, 2009, 07:38 AM
I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.

The guy who got injured would be disciplined or fired for not properly locking out the system if this incident had happened where I work. Trash program or not, if the system had the power isolated and properly secured with a lock, this simply wouldn't have happened.

tacm
January 8th, 2009, 07:43 AM
the guy who got injured would be disciplined or fired for not properly locking out the system if this incident had happened where i work. Trash program or not, if the system had the power isolated and properly secured with a lock, this simply wouldn't have happened.

x2

Christoff84
January 8th, 2009, 07:49 AM
Even though a person out of school is nowhere near ready to program a machine or design a safety system, many companies will not understand that. If you have a degree (or been to a tech school), then many managers will assume you can do it all.

Being out of school for only 2 years now I can wholly agree with this. Coming out of school the company that hired me threw me right into re-designing exisiting machinery and adding new safety systems. I was completely unprepared for this, my program focussed on robotics, automation and process control but didn't touch on safety systems at all. There is just way too much to know before designing any type of safety system.

The other situation I find school doesn't prepare you for is fault handling. All the PLC projects I completed in school were your basic sequencers and of course the traffic light (creative teacher...do a complete intersection with only 2 timers), and the step7 DRUM FB (worst 2 weeks ever). None of it focused on what to do when the machine did something unexpected. Thats something I had to learn as I went.

Goody
January 8th, 2009, 08:28 AM
Is this a general rant or have you actually got a point ?

This argument applies to more than just PLC programming, it applies to nearly every job that involves handling anything more than a piece of paper !!

The subject IS plc programming.

you need to re-read if you dont see my point ;)

And the others that mentioned lock-outs and disciplining workers - of course I you and the guy know this - that is not the point either.

Accidents will always happen no matter what measures you take.
And if you always think ' well that wouldnt happen - a man wouldnt do that' you have not been in the game long enough.

I am on about too many people taking on programming without any experience of automation and controls with an attitude of 'how hard can it be'

muusic_man
January 8th, 2009, 08:52 AM
I had a CE who wanted me to make some operational changes to a Mitsubishi PLC for a disc polisher. I told him I would put it on my list, but this wasn't a good enough timeline for him. His exact words were, "Well just give me the program and I will make the changes myself." I asked, with surprise, if he had PLC experience. His response was, "How hard can it be. Just tell it what you want it to do." I agreed that it couldn't be that hard and he should give it a shot. The next day I delivered to him the software and a copy of the program, along with a COMPLETE printout of the program (about a 1 foot stack of paper). A month later it all re-appeared on my desk with a sticky note that said, "please make the discussed changes to the equipment when your schedule allows."

It is a pervasive attitude from CE's in my company that they can do anything, an sometimes it is necessary to humble them.

cjd1965
January 8th, 2009, 09:15 AM
I agree fully that the conveyor should have been isolated beofre any work was done.

However, I also fully agree with the op when he says that many 'amateurs' are creeping into the work arena without any engineering/controls background and are writing aweful and sometimes potentially dangerous code. I recently attended a job where an RTD had failed and the HMI indication was 0 degrees, and the PLC was calling for max heating. Obvious case where the failure of the sensor was not considered.

I dont agree with 'licences' so only the chosen few can do partiular work however I do agree that certain skils and experience is required.

I am always asked 'can you just........' when it involves a weeks worth of modifications and testing.

Ned_Flanders
January 8th, 2009, 10:02 AM
I thinksome plc manufacturers/training providers are guilty here. I have some colleagues who have been given some basic training - really only enough to get online and view the I/O, timers etc. However, the company assumes they now "Know" plc's!
i agree with the novice point. There was a post (Today?) which said "I need to fit an e stop but have not had much experience...any tips?" Makes you shudder!

Most people were kind and suggested assessing the risks, referred them to safety documentation etc.

odlaw
January 8th, 2009, 10:04 AM
I agree with the author of this thread. Anybody who can plug in to a PLC is now a "programer". The use of latch instructions (OTL) has become the standard. I even see people using the same output in multiple rungs. Try and debug that ****.
Why should we pay John with 20yrs experience when we can get Dave who took a class last year to do the same thing.
You can select Dave over John but sooner or later someone is going to loose a finger or worse.
Any idiot can change a timer or turn off a bit but it takes a lot of trial and error and a consideration of the big picture when changing or creating code, not just turn this on if that switch is made.

n9xcr
January 8th, 2009, 10:42 AM
I agree with you to a point. There are terrible programmers out there, but it's not just as the beginner level. I've seen terrible programming and little thought put into control systems from people of all experience levels.

Although thorough review and testing of a program should be done by multiple people, operators and technicians should never assume that a program is perfect. Operators need to closely monitor the equipment they're operating for anything unusual. Any person who will enter an area where injury could occur MUST isolate and deplete all energy sources before doing so. Lock-Out/Tag-Out exists for a reason.

Yes, there are situations where you need the equipment to be operational while working on it. I get that. I work with equipment like that. There are safety measures you can take in those situations as well.

That said...
Why should we pay John with 20yrs experience when we can get Dave who took a class last year to do the same thing. You can select Dave over John but sooner or later someone is going to loose a finger or worse.

I am a firm believer in,"You get what you pay for." Experience is more important than a damn piece of paper.

Chris

Ron Beaufort
January 8th, 2009, 11:17 AM
I fully agree with Goody’s point - but I do NOT have a solution to offer ...

as part of the discussion though, I can tell you what I’m seeing more and more of in my classes lately ... many of the students are younger now - and quite a few have what I call a “video game” attitude toward everything that they do on a computer ... they tend to click-and-drag and double-click and so-on and so-on with little or no regard as to what is going to HAPPEN when they “shoot from the hip” like that ... in a video game that’s fine ... (“Game Over” is probably the worst possible outcome) ... but in an industrial setting, that sort of nonsense might have “read-about-it-in-the-papers” implications ...

one simple case in point: the next time you have an offline project of RSLogix5000 opened up, try the little experiment shown below ... notice how incredibly easy it is to drag-and-drop something to those little green targets that light up even when you’re still SEVERAL INCHES AWAY from them ... for my money, it’s entirely too easy to make unintended changes to the program this way ... and those little “touch pad” mice things are the world’s worst for this “drag-and-oops” type of problem - especially when the “tap-to-click” feature is used in a sloppy manner ... notice that if you're offline, you don't even have to put the rung into the "edit" mode first to make a change to it ...

and - if you fail to notice the change to your logic before the next time you fire up the machinery, what will happen? ... this could fall squarely into the “BAD” column on the giant clipboard of life’s little experiences ...

anyway ... as I said, I don’t have a solution - but a few years ago I had one customer who seriously suggested putting me on his payroll - just to be the “old guy” in the office at the end of the hall ... his problem was that he was continually hiring new “computer programmers” fresh out of college - who knew NOTHING about PLCs and industrial control ... he was talking about paying me to just “hang around” fulltime and provide a little “experienced color” to the company’s operation ... the problem was that the office was located in a state up north in the “Land-of-Ice-and-Snow” ... any place with salt trucks on the highway department is no place for a southern dude like me ...

now on the other hand, if anyone knows of a cushy job along those lines that’s available somewhere down south, please let me know ...

yes, it’s scary now - and getting worse ... let’s all be careful out there ...

mystery
January 8th, 2009, 11:20 AM
I totally agree with Goody

Have you heard of the most important control relay,the Master Control Relay if programed correctly should disable all the reliavant output cards etc in affect killing all the movement or action of the equipment.

If you think a lock out system works then god help us (master keys,Managers and Control Engineers( Electricians with the Manuals).or you may think protection by use of guards (removed for access)and complete with warning label to reduce company liability .
As many a good Maintenance Electrician will no fault finding on electrical equipment controlled by a plc require entering the equipment to inspect proxy sensor etc etc with the power on hydraulic,air but with the output card's inactive .

The emergency stop, guard interlocks ,emergency pull cord etc controlling a Master Contol Relay isolating the supply to the output card ,motor contactors .

In every Allen Bradley brochure or manual I have seen from PLC2,PLC3,PLC5,SlC100,
SLC500 etc as a sample diagram .

A little knowledge is dangerous and so is a NVQ ( no valid qualification)

cjd1965
January 8th, 2009, 11:41 AM
If you think a lock out system works then god help us

A proper system WILL help. If you allow someone to remove fixed guards, bypass safety devices etc then you are guilty of contributing to any accident that may occur.

I understand that sometimes live working is required but this should be rare, fully authorised in writing by a responsible person (chief engineer or director/ceo).

I have never put myself in a position whereby I have bypassed safety devices, but i have seen mangled hands and arms where others have done so.

Cheers

dmroeder
January 8th, 2009, 11:42 AM
I went to a two year tech school (instrumentation) and I certainly felt unprepared my first day of work. It was a new plant and I was tossed right in the middle of a start-up (great experience). To make it even more interesting, there were 2 other controls guys directly out of the same school that made up the department and no other electrical/technical types in the plant (besides some contractors).

Luckily the school that I went to stressed that they could only teach us a sliver of what is out there in the controls world, so what we needed to be proficient at was finding the answers. Reading manuals, contacting manufacturers, whatever it takes to understand and make it work.

Fortunately for me, I knew and understood how inexperienced I was, so I didn't have an ego to get in the way.

Looking back on it, they plant was trying to get away with cheap technical labor (all labor for that matter). They hired kids right out of school at a low-ball wage. Dumb on their part I'm sure but I wouldn't have done it any other way. I learned a lot of things that I never would have otherwise.

brucechase
January 8th, 2009, 12:23 PM
I totally agree with Goody


If you think a lock out system works then god help us (master keys,Managers and Control Engineers( Electricians with the Manuals).or you may think protection by use of guards (removed for access)and complete with warning label to reduce company liability .
...
A little knowledge is dangerous and so is a NVQ ( no valid qualification)

If you work at a place that will allow a master key or anyone to remove YOUR lock, GET OUT NOW!!!!!!!!

If you think that is ok then your statement about a little knowledge is a dangerous thing definately applies.

If I was working on a machine and someone removed my lock, they would have to call the police because I would assume that person is trying to kill me and I will do everything to prevent that.

I really can't believe there is an attitude that this would be OK.

Steve Etter
January 8th, 2009, 12:32 PM
If you work at a place that will allow a master key or anyone to remove YOUR lock, GET OUT NOW!!!!!!!!

If you think that is ok then your statement about a little knowledge is a dangerous thing definately applies.

If I was working on a machine and someone removed my lock, they would have to call the police because I would assume that person is trying to kill me and I will do everything to prevent that.

I really can't believe there is an attitude that this would be OK.

My sentiments, exactly.

Steve

Ned_Flanders
January 8th, 2009, 01:10 PM
Mystery : I thought NVQ was "Not very qualified" Ha Ha!

Pandiani
January 8th, 2009, 02:09 PM
Hmm, I think most inexperienced people are comfortable with asking questions (both right and wrong) but I believe very few of them would actually try something on a real plant. I think that most "NVQ" people will not be so quick to write code or actually change existing code so easily. I waited more than a year before I actually changed code on running plant. During that time I read a lot and asked a lot.

Outrage
January 8th, 2009, 02:22 PM
My sentiments, exactly.

Steve

I Also agree.

If your system of lockouts doesn't work then thats a management failure and should be investigated and fixed. But just because the paperwork system fails you shouldn't allow that to put your life at risk - at the very least you could still turn off the isolator and put your personal padlock on it?

Getting back to PLC programming - I think That you have to have the electrical experience to understand the consequences of your actions and understand the machine, process etc from the ground up. But, everyone has to start somewhere in PLC it's just about going the right route. Personally, I Started in this carreer working for a systems integrator cadding up electrical diagrams from my pears and doing SCADA whilst spending time at college on an Electrical course. After completion of my course I was allowed to get into Electrical control design and progressed into PLC I think that was a good route to follow.

Cheers,

Lee

Sliver
January 8th, 2009, 02:38 PM
If you work at a place that will allow a master key or anyone to remove YOUR lock, GET OUT NOW!!!!!!!!

Bruce, I cannot believe in that all of your years locking out that you never forgot to remove your lock when leaving on a long weekend and that the plant doesn't have a 'lock removal procedure' to verify that the employee is not on site or if they can't be reached to do a extensive search of the equipment for the employee before bringing out the big blue key (also known as the boltcutters). Removing a safety lock should never be taken lightly but the procedure for doing it safely and documenting it should be in place.

Brian.

icky812
January 8th, 2009, 02:56 PM
All of the plants I worked in had a master key that was controlled by the Maintenance manager. It was almost an act of Congress to get them to unlock a lock. The Plant Manager, Safety Guy, Maintenance Manager, and two maintainence workers all had to agree to remove the lock. Consequently it was something that happened so rarely it was a non issue. Removing the lock without the approvals was a quick way to the exit, one way.

brucechase
January 8th, 2009, 03:46 PM
Bruce, I cannot believe in that all of your years locking out that you never forgot to remove your lock when leaving on a long weekend and that the plant doesn't have a 'lock removal procedure' to verify that the employee is not on site or if they can't be reached to do a extensive search of the equipment for the employee before bringing out the big blue key (also known as the boltcutters). Removing a safety lock should never be taken lightly but the procedure for doing it safely and documenting it should be in place.

Brian.


Yes, there are certain procedures that can be followed to remove a lock. Ours includes verify the person is not on the plant site using our swipe in access, calling them at home, calling their manager, calling the maintenance manager, and calling the security manager. My comment was specifically to this:

If you think a lock out system works then god help us

I think, and rely on with my life, that a lock out system works.

gas
January 8th, 2009, 03:48 PM
Must be the weather.
I am a maintenance guy…40+ years. Along with this site I look at the Welding Society forum, a maintenance forum, and several fluid power forums.
A similar rant has appeared in all. Outlaw welders, Hacks for mechanics, Buba and Cletis fixin a piston pump.
Much verbiage and many pages later another old guy said this:
“This is the real world out here dude…it ain’t perfect, so get over it and go back to work.”

TConnolly
January 8th, 2009, 03:55 PM
All of the plants I worked in had a master key that was controlled by the Maintenance manager. It was almost an act of Congress to get them to unlock a lock. The Plant Manager, Safety Guy, Maintenance Manager, and two maintainence workers all had to agree to remove the lock. Consequently it was something that happened so rarely it was a non issue. Removing the lock without the approvals was a quick way to the exit, one way.

IMO that is a good policy. But I learned the hard way that a determined production supervisor will still get that lock off without authorization.

Years ago at a place where I worked I was working a on machine where we did not have the replacement part. It was ordered and fed-exed in overnight. When I left for the evening I left the lockout/tagout on the machine. When I entered the building the next morning I was met with the smell of burned electrical gear, an irate supervisor who was fuming mad at me, and the plant manager. The supervisor had decided he needed the machine and cut my lock off and threw the disconnect on. Sparks flew and the machine caught fire. The supervisor wanted to blame me. I pointed out that he was the one that had removed the lockout with a bolt cutter and that he was the one who had signed the requisition to overnight ship a spare part, so he should have known that the machine would not have been operable. He was still determined to blame me for the destroyed panel. I asked for the safety policy book and turned to the page that indicated that anyone who cuts a lockout off without authorization will be terminated. The supervisor instantly changed his attitude and became quite penitent. Lucky for him, he was not fired (at least not then). It took about a week and a half to repair the fire damage, but he stayed away from me and did not hound me about hurrying to get it done.

That company stepped up lockout/tagout training after that so that everyone from the GM to the janitor to the receptionist knew about lockout/tagout even if the only power tool they operated was a solar calculator.

Tom Jenkins
January 8th, 2009, 04:15 PM
I don't think the problem is that there are more rookies programming PLCs. I was dumb as a rock myself at one point (and by some opinions still am).

I think the problem is that apparently many of the rookies are not being supervised properly. In some cases they appear to have a project thrown over the wall at them and they are left to flounder through as best they can. That is a failure of their supervisors.

The real problem that I see is their is apparently an unwillingness on the part of the rookies to admit ignorance ask for help from the appropriate quarters. Many of the questions we see here aren't able to be adequately answered on this kind of forum. They should be addressed to the boss or the local supplier or a more experienced co-worker. Particularly in complex automation systems there are many things that can't be conveyed properly without diagrams and immediate feedback.

Muzza
January 8th, 2009, 04:31 PM
These problems apply to most areas of industry.

There's Operators who haven't got a clue but are being expected to run a complex plant, there's maintainers who have had their training 'fast tracked' but have no idea about proper isolations and procedures and there's PLC programmers who've never seen a machine in real life that's more complex than a toaster.
All of the above are DANGEROUS but are encouraged by the 'faster / cheaper / better' mentality that is endemic throughout industry.

I recently priced an upgrade and the plant manager said "We've got a Graduate Engineer who's worked with the software for 3 months and knows all that there is to know about it - we'll do it in house"... a smary lad to be sure, but has ZERO experience in real word applications & failures.
I'm waiting now for the call to either fix what happened or perhaps even to go along to the Coroner's Inquest after someone gets KILLED.

Yes, people need to start somewhere. Sadly, overinflated egos (usually the result of a cut-priced engineering degree or having succesfully written some macros in Excel and now knowing it all) are everywhere out there but are not matched with real world experience and training.
What ever happend to walking before you could run???

Bah Humbug,
Muz

twu026
January 8th, 2009, 06:12 PM
I agree with Tom Jenkins comments.

Everyone starts out as a novice programmer.

The problem is, these inexperience programmers are allowed to work on (or thrown into) projects that are way over their heads with little or no supervision.

This is a failure on the part of the programmer's supervisor.

With experience you know your own limitations.

vettedrivr
January 8th, 2009, 08:05 PM
We have a problem with some of our maintenance guys that when a machine function fails or becomes out of adjustment from a prox sensor or limit switch getting moved (Ran into), they change the PLC program to comphensate. After all, when a machine that has been running for years suddenly changes it must be because the PLC program wasn't correct. Later when the real problem with the machine is located (Or not) and the defective component is replaced, now the machine works incorrectly in a different way. I've seen failed limit switches get over-ridden by having timers added to the program to allow the mechanical movement to be stopped by time instead of contacting the limit switch. As you can imagine this makes troubleshooting interesting. You don't need limit switches and prox sensors if you can write the PLC program without them, Right?!? This is why my laptop stays locked in my desk, so I always have a correct copy of the program to re-load into the machine.

mrtweaver
January 8th, 2009, 08:34 PM
I figured I had to my .02 in here. A situation that came up about 3 years ago. The company I worked for at that time went out and got quotes to design a machine because I did not have the time, we were in the middle of 7 other rebuilds. So along come a fresh college idiot and we also had some good integrators give quotes. Well of course the fresh college idiot got the bid because as MGMT said, it cant be that hard, and they liked his price as well. Well he made the machine, did the program and such installed it and got it running and gave training. About 6 months after the install a maintenance tech was working on the machine. There was a very sharp pair of sheres on the machine. Well even though the air was locked out there was still enough residual pressure that when his tool brushed against a sensor it caused the knife to fire and he ended up with 27 stiches. after investigation and the OEM saying that they did not have proper safety coding in place they still blamed the mechanic for improper work performance. I always wondered if they would have just spent the extra and had a seasoned professional do the work if this accident could have been avoided. Some of the things that would have made it better:

1. A positive dump valve that would have made sure all the air was dumped out of the machine when the air was locked out.

2. a series of safety measures that would have ensured that nothing could move unless all safeties were met and machine was in a run state.

3. Better training of the mechanic to ensure lockout/tagout. Mainly the electrical should have been locked out as well.

Paullys50
January 8th, 2009, 09:53 PM
......So along come a fresh college idiot and we also had some good integrators give quotes. Well of course the fresh college idiot got the bid because as MGMT said, it cant be that hard, and they liked his price as well. ..........

Obviously you don't have much patience for a college graduate....the reality is that the management is/was the idiot(s) for hiring him to do the job. If they have the impressions that controls work is "not that hard" and are influenced by the price that easily.......focus your attitude on the real problem.

twu026
January 8th, 2009, 09:57 PM
Pretty impressive for an fresh college idiot.

Did the guy do the mechanical, electrical, pneumatics design as well as write the PLC program?

Why didn't anyone check his work?

Jeev
January 8th, 2009, 10:23 PM
Why didn't anyone check his work?

Unfortunately in some small companies the fresh out of University Grad is the only Engineer of that type, and as such has no one to check their work. It's an unsafe practice and not only unprofessional, unethical, and irresponsible, but just plain dangerous. That doesn't mean it doesn't and won't happen....

On a side note, all our machinery is CAT3 or CAT4, and when undergoing service or repairs all E-stops on the machine must be pushed at absolute minimum. If it's electrical work the machine is usually isolated and unplugged too. Working for an OEM, during commissioning I often have the need to bridge out certain safety devices, to this day there has not been a case where I or any of my colleagues have been unable to safely work on a machine even under these circumstances.

zankorel
January 8th, 2009, 11:27 PM
Pretty impressive for an fresh college idiot.

Did the guy do the mechanical, electrical, pneumatics design as well as write the PLC program?

Why didn't anyone check his work?

Ive got to agree. If he was fresh out of college, its amazing that he was able to do that.

Actually... he couldn't. He must have had more experience than he is being credited for.

PhilD
January 9th, 2009, 01:10 AM
I felt I wanted to input my two cents here. This is kind of long so be warned.


I am a Journeyman electrician with over 20 years in the petrochemical and automotive industries and currently carry a high voltage certification for substation work which requires it's own special safety procedures. My emphasis currently is robotics, plc, and automation. I was once a dumb rookie plc programmer also. Still am depending on who you ask and when :) Anyway, the company I work for has provided many hours of training for me on plc, automation, robotics, hydraulics, system integration, safety systems, etc. It was several years after I started working for this company before I was the least bit comfortable in making an online change to operating equipment during production. Yes I do make changes to logic all the time to keep production running, but I also log them so they get fixed properly during regular maintenance. Yes, I have caused downtime, sequence issues and equipment damage over the years, but rarely.


I asked a lot of questions to the controls engineers I've gotten to know and still ask for their input and assistance on a regular basis. I have earned the controls engineers trust in that they know that I know what I am doing. The controls engineers now routinely give me major changes or additions to the plc logic that they need to do which lightens their load. These changes are to be input even during production. Testing is done of logic changes during break time for anything that could stop production and I am fully aware of what the machine is currently doing and what the new logic is supposed to do. There is still things I do not know much about, but it is mostly system design


The company also does extensive testing including safety systems on new production equipment. This is to ensure the safety system works the way it was designed to. All safety interlocks and devices are hardwired and redundant (runchain 0, runchain 1). Plc gets inputs from hardwire for indication but can not control the hardwire.


The company I work for also hires summer engineering interns. This summer I had the pleasure of working on a new project that was assigned to a couple of these interns. One was having trouble with getting changes made to a program and sometimes complained that her edits were not "showing up" for some reason. I wondered why she was having so much difficulty so I watched over her shoulder for a few minutes and discovered the problem. She did not know how to make online edits or do online programming, so she was going off line making edits then downloading them to the processor, doing this for even the simplest edits. Sometimes she forgot to download the edits. I took a few minutes to show her how to make online edits etc. and test them. She said she learned more in a few minutes about plc programming than in an entire semester at college. Point I am getting at is everyone needs assistance sometimes and that assistance does not always come from a book or the engineer who is supposed to mentor. So if you are new or are having problems, put the ego away and ask questions.




As far as the guy who was working on a conveyor when it started throwing him and his tools off, then it was at least partly his own fault. The other part of fault lies in the company he works for or is contracted to for failing to ensure the employee was following proper safety lockout/tag out and hazardous energy control. The same goes for the employee who was cut by the shear knife when residual air fired the knife. He should have properly tested the locked out equipment and controlled (blocked and tested) the potential energy hazard.


The company I work for (and previous one) provides lockout/tag out and hazardous energy control training every six months. Hazardous energy control is not simply "locking out" the equipment, but making sure that all stored energy has been removed from the equipment and all machine blocks and safety devices are properly installed. This company also has a gate lockout procedure for dealing with common equipment problems during production hours. Every single "gate lockout" box is hardwired into the cells safety circuit and has been very carefully checked and certified by an independent certification. No work may be performed with the gate lockout if the procedure is not listed on the gate placard. No work may be done during non-production hours using the gate lockout procedure.
There are also procedures in place that cover working on live equipment if it is absolutely necessary. These procedures must be reviewed, agreed upon, and signed by safety and everyone else involved before any live equipment is worked on. This procedure also includes a statement as to why the equipment could not be properly locked out and a list of hazards. Yea, this is somewhat CYA, but at least everyone is on the same page and are aware of the hazards.


Lockout locks accidentally left on are not to be removed except by following a certain procedure. Failure to follow the procedure will result in a minimum balance of shift, and 3 days off with lockout and hazardous energy retraining for all involved including supervisors. General procedure is to contact supervisor who will contact his supervisor, Maint coordinator, security and the union. A search will then be made of the locked out equipment for the employee. If the employee is likely not in plant (shift ended, weekend) or otherwise can not be found then security will call the employees home for an ok. If no contact can be made, then a search of the locked out equipment will again be made before the lock is removed by security.


I am ultimately responsible for my own safety.


It is something that has served me well over the years. Especially now when society looks to be a bunch of "don't blame me, it's somebody else's fault" idiots.

aikona
January 9th, 2009, 03:13 AM
Quite a few things discussed so far

1- Safety first but ... does a person who has to grease a conveyor know where and how this conveyor is safe , he most probably has to 'believe' what an electrician tells him.

I also had an accident where a robot throw me off .... the purpose of the job was to 'teach' this robot a few new positione etc.Due to a faulty cable and 'bad' programming this robot decided to move at full speed to its home position.Thats the space I occupied.

2- Bad Programming ... reading some of the threads ( its a treat to read) you can see that even the basic knowledge is lacking ( Bit ,Byte)but these people have to resolve complex problems .It must lead to bad programming.I am also a selfmade PLC specialist but it took a lot of manuals , lots of bench testing ,lots of rewrites , using preset progamming rules and some proper coaching when in the deep end of the pool

Bye

Eric

mrtweaver
January 9th, 2009, 07:24 AM
I realized once I posted the message that I forgot to mention that the project was only a rebuild. The frame and the machine were already there. All he had to do was put in a PLC, program it to do its job, commision it, and make sure it ran properly. Here is why I made the somewhat nasty comment about College Idiot. Yes he was out of school only 2 or 3 years, instead of going and working for someone else, cutting his teeth, and learning the trick of the trade, you know kind of apprentice work, he immediately sought self employment with the attitude that I went to college and I know everything, or at least that is the way he presented himself. He did not work for any integrator, any industry or anything prior to his schooling or after his schooling. I mean he was only 24 and said he had gone from HS to College then off on his own because he could make more money. In essence it is both MGMT fault for not understanding more about what is going on, safety administrations fault for not properly looking over machine and checking it out completely, and his fault for not doing all the things he needed to do. So yes the blame does fall on more than one, but if the comments made in this thread are any indication on schooling, then that makes things even scarier. The postings I am refering to are where comments are made that safety circuits and such are not being fully trained. I am sorry but with OSHA, Lawyers everywhere, and all that jazz, I would think this would be one the biggest and most fundamental things that should be covered and it should be harped on every year not just as side notes or something like that. When I was in college we had a professor whom I admired, at the time I dont think I did but for any of you TV watchers who watch NCIS, think of what happens to Denozo when he acts up. He gets smacked in the back of the head. Well this professor he would do this to you if you were unsafe. If he told you to do something and you did not know how or did not ask questions you got a crack. Talk about a wake up call. It was his way of saying dont forget to ask the basic questions of WHO, WHAT, WHY, WHEN, and HOW. And his and my father most important statement of all, THE DUMBEST QUESTION IS THE ONE NEVER ASKED. Well enough length on this note. Have a great day.

Ive got to agree. If he was fresh out of college, its amazing that he was able to do that.

Actually... he couldn't. He must have had more experience than he is being credited for.

tacm
January 9th, 2009, 07:47 AM
Quite a few things discussed so far

1- Safety first but ... does a person who has to grease a conveyor know where and how this conveyor is safe , he most probably has to 'believe' what an electrician tells him.



You could not be more wrong with this statement. LOTO and safety is EVERYONES responsibility. Anyone who works around machines can be in danger of losing their lives. Work is a job, there is no room for error when it comes to safety

randyk
January 9th, 2009, 08:44 AM
I have 2 years experience in PLC's and I know I don't know everything. I work for a company that has been using PLC's since they started and already had all the program's written. I make changes to them and my boss looks over everything I do letting me know if I can do something in a better way. When I read this post I got Deja Vue, my company is looking into using RFID along with proper lock out/tag out to keep the maintenance workers safe. My company is in the process of having the shop totally rewired electrically because we lost a friend of our a few months ago to a workplace accident. I would hate to see someone injured or lose their life because of something I did not take the time to check and make sure it was safe as it could be.

Killercal
January 9th, 2009, 09:06 AM
Maybe I’m wrong, but isn’t this supposed to be a “Help” website? Rookie programmers are going to be the ones with the most “Basic” questions because they are green. One thing that bugs me the most are “senior” programmers who think that everyone should know what they all know when in reality, they learned everything from experience or asking questions when they were rookies. Lets not bash new/green programmers or even experienced programmers who are now learning some new technology. I’ve experienced learning new technologies through manuals, test benches and asking experienced programmers, and I find that asking people who have experience to be the most helpful! Some manuals leave out some very important things that aren’t intuitive. If you only take one thing out of my rant here, please take this! Any programmer, new or old (experienced), that come across a program that you see will case issues, let the person who programmed it know. The person that programmed it either overlooked it, doesn’t know he programmed it wrong or had “fat finger syndrome” and needs this to be pointed out. This is how we all learn! That said, I know to check, re-check and check again all my programming before I deploy it and I’m just here to help out others and get help from others.

Matthias von Zorn
January 9th, 2009, 09:33 AM
I believe there are so many unqualified people here because there are so many new programmers that are the only people in the plant that have any idea about PLCs. Being an OEM, ive been in many many plants over the last 15 years; and, in every instance save a very few, there was either no PLC person, a maintenance guy with little plc skill, or an engineer from a different field having to do dual jobs. They may not have manuals, etc. They google search PLCs and find us. They see how awesome we all are, and post their questions. We help. Like it or not, we are that PLC expert that all these companies lack. ;)

matt

n9xcr
January 9th, 2009, 10:07 AM
he immediately sought self employment with the attitude that I went to college and I know everything, or at least that is the way he presented himself.

Gotta love the entitlement generation. I've worked with people on both ends of the spectrum. Some did excellent work and valued input while others thought they knew everything and didn't want any input. The same know-it-all individuals wouldn't hesitate to criticize the experienced workers, though. I really got ****ed when I saw them laugh at people who took the time to properly lace and label their wiring.

We had one seasonal employee who had no electronics background, but was perfectly capable of learning and performing the functions we needed him to. He had a great attitude and never made a mistake. He could follow wiring diagrams just fine and construct the circuits with no difficulty. He ALWAYS asked me to look over his work. It was perfect every time. Now this is where it gets funny...

Another experienced employee was always complaining about how people with little or no electronics background were being hired into the department all the time. He made more mistakes than they did!!! In fact, he miswired a couple of programmable relays and literally blew them up when he plugged it in. This was within a couple hours of one of his rants even! lmfao

He blamed it on a full-time technician that drew up the diagram. I looked at it and found that yes, there was a serious error in the drawing. The sad thing is that it was pretty obvious. If memory serves me correctly, 120V was wired across the NC contacts of one of the relays. The 120V also powered the relays.

Chris

BillRobinson
January 9th, 2009, 10:25 AM
Firstly an analogy about the logic vs the lock-out tag-out deal. Would you not put your seatbelt on if your car had an air bag? Or would you disable your air bag if your seatbelt was on? Both should have been done!

Here's what I think the PLC comunity needs to do.

#1 - Some regulated training needs to be done.

In certain areas of industrial work you need to be trained. You can't run a forklift without a forklift ticket. You can't go up scaffolding without a fall arrest course. And you should not be able to touch a PLC without some sort of certification. And I don't mean those 1-day courses that a PLC manufacturer gives you so that you can play with their software; there should be a regulated course which teaches and warns of the potential hazards and consequences of typical PLC situations.

#2 - PLC code needs to be written/approved by a certified proffessional

Because most training corses only last about 1 week in your head; I think this second step is needed. Ladder logic is a direct desended of relay logic, which used to be mandated to be stamped by an engineer. In most cases PLC logic is not. I'm not suggesting that PLC logic needs to stamped by an engineer; but rather someone who has significant field time and has passed some sort of standardized test.

#3 - A definitive line needs to be made between industrial PLC's and personal computers

Lastly this needs to be done because both worlds are slowly creeping towards eachother. PLC's are not PC's and the shouldn't be handled the same way.

creativepaper
January 9th, 2009, 10:29 AM
I'm actually one of the dual job engineers that Matthias spoke about. I have a chemical engineer background with no formal PLC training, but I know computers to where I'm the IT guy an write some C++ programs for the company (learnt it in my own time for fun) when required. My chem Eng degree had a LOT of safety aspects and forward thinking (you don't want to incorrectly size a safety valve or not enough bracing for water hammer).

We needed a major drive upgrade (16 drives 50-150hp) since our drives had a failure approx every month (some a board, some a blow up). We got quotes, but couldn't afford them (tried to get financing for over a year). I figured out a way to control our drives with a AB PLC (incase the PLC and spare died), got demo software and simulated them enough that we purchased a ControlLogix platform and little 10hp test drive. This worked, therefore the next stage was a piecemeal drive upgrade. We started on the winder and then every month moved onto a couple drives per shutdown. At present we have a sucessful 16 drive upgrade. This is my first program and first HMI design.

The reason I took on the challenge is that I know the system, the interlocks and we still couldn't get financing for the drive upgrade so instead of about 30 drive failures (and call-ins) last year we had 0.

My initial code was junk, but I think now its quite good, but it works. Best thing that I did was plan ahead, take things slow (I could have spent nearly 2 years solely on the project and the company would have still come out ahead) and write simulation loops to test everything and all scenarios (someone cuts a cable) to ensure fail safe.

Since this went well, my second PLC program I'm currently working on is a DCS overhaul to the AB ControlLogix platform (30 PID loop, 24 motor controls).

OZEE
January 9th, 2009, 10:56 AM
Maybe I’m wrong, but isn’t this supposed to be a “Help” website? Rookie programmers are going to be the ones with the most “Basic” questions because they are green. One thing that bugs me the most are “senior” programmers who think that everyone should know what they all know when in reality, they learned everything from experience or asking questions when they were rookies. Lets not bash new/green programmers or even experienced programmers who are now learning some new technology. I’ve experienced learning new technologies through manuals, test benches and asking experienced programmers, and I find that asking people who have experience to be the most helpful! Some manuals leave out some very important things that aren’t intuitive. If you only take one thing out of my rant here, please take this! Any programmer, new or old (experienced), that come across a program that you see will case issues, let the person who programmed it know. The person that programmed it either overlooked it, doesn’t know he programmed it wrong or had “fat finger syndrome” and needs this to be pointed out. This is how we all learn! That said, I know to check, re-check and check again all my programming before I deploy it and I’m just here to help out others and get help from others.

The problem isn't with the "green" programmers who are asking questions with the honest intent of truly learning and improving. The problem is with those who are looking for the shortcut or someone to do their work for them. The problem is with those who aren't willing to do their own research first, who won't do their own homework, who won't put in the effort. The problem is with those who think they know it all right out of the box because they have a piece of paper or because they can beat all their buddies on XBox. The problem is with those who don't really want to learn, or don't care about safety, or don't care about proper practice.

And TACM is right -- safety is EVERYONE'S RESPONSIBILITY. There are many of the pro's here for whom I have the greatest of respect, even though we've never personally met. But if we were working together, I would NOT trust their LOTO -- I'm going to put mine on anyway, and then I'm going to test it to make sure it's safe. I'm not going to trust them with my life.

Killercal
January 9th, 2009, 11:19 AM
The problem isn't with the "green" programmers who are asking questions with the honest intent of truly learning and improving. The problem is with those who are looking for the shortcut or someone to do their work for them. The problem is with those who aren't willing to do their own research first, who won't do their own homework, who won't put in the effort. The problem is with those who think they know it all right out of the box because they have a piece of paper or because they can beat all their buddies on XBox. The problem is with those who don't really want to learn, or don't care about safety, or don't care about proper practice.

I agree with your statmet!

jtn
January 9th, 2009, 01:49 PM
I don't have the time to read everything here so this may have been covered already. I think the problem is not with green programmers, because everyone is a green programmer at some point. The problem is with supervisors throwing green programmers into the fire with little supervision. I got my start in this field at a place like that, actually had the owner tell me once it was cheaper for to park at a job site for month to figure it out myself than for him to come down and help.

parky
January 9th, 2009, 02:17 PM
Even the "master control relay" bit worries me if you think a MCR in software is a safety device think again.
Switching off the outputs by removing the supply to them with a safety relay is the real answer
anyway I also get worried about untrained engineers messing with plc programs but not novices (these are just as we were many years ago) it's the ones that think they can program & decide to "do a quick Mod" that worry me more.
A novice is usually someone who hopefully is under some experts wing or at least only writing programs in the classroom & not on a live system.
I had a simular experience with an Engineering manager that reckoned he could load HMi's & do small mods.
One day while on holiday I got a call from him asking me for the logon to the "programming laptop" as he had a problem he needed to go on-line to find a problem.
After reluctantly giving him the password I continued on my well earnt rest with the phone switched off.
Next day when I arrived at work I was presented with my laptop & a mesage to the effect could I put the software right on the machine after the engineers have straitened out everything on it?.

andysherris
January 9th, 2009, 05:10 PM
I think the problem is that years ago before plc control it took a qualified Electrician to build control systems with good old relays, timers and contactors. Unless you had good knowlege of the relevant regulations how to wire safety systems this is a task that would be seldom attempted by a novice. Most Electricians moved on to PLC control with ease because they had a good background already.

dogleg43
January 9th, 2009, 05:42 PM
I think the problem is that years ago before plc control it took a qualified Electrician to build control systems with good old relays, timers and contactors. Unless you had good knowlege of the relevant regulations how to wire safety systems this is a task that would be seldom attempted by a novice. Most Electricians moved on to PLC control with ease because they had a good background already.

A lot of good points being made in this thread, especially the onces about how everyone was a beginner at some point. My 2 cents is that just because someone is a programmer, that does not make them an engineer, electrical-mechanical repairman, or electrical designer. It also doesn't mean they can't learn to be one of the above. It takes time.

One of the beautiful things about skilled trades is the apprenticeship program and how they should be learning their trade while working with a pro...and part of the journeyman's job was to teach the apprentice. I know it didn't always work that way but when it did it was a beautiful thing.

Ned_Flanders
January 9th, 2009, 05:53 PM
Parky I liked your tale about the laptop.

I had a similar experience with a robot. I am definately not an expert but have just lived with it for 3 years.(Background: I was not getting on very well with my boss as he wanted me to work shifts!!!) I was on holiday and found this out after I came back: It stopped and would not go. A number of my colleagues fiddled and it STILL would not go. My boss paid for an Engineer to fly down from Scotland to fix it. He cancelled the program, reloaded it and flew home.

"Why didn't you call me said I.....?":doh:

Derek
January 9th, 2009, 07:39 PM
Seasoned programmers never make dumb mistakes?

Killercal
January 9th, 2009, 11:08 PM
Seasoned programmers never make dumb mistakes?

Ha! I laugh at that comment!

nettogrisen
January 10th, 2009, 05:58 AM
I think the problem is that years ago before plc control it took a qualified Electrician to build control systems with good old relays, timers and contactors. Unless you had good knowlege of the relevant regulations how to wire safety systems this is a task that would be seldom attempted by a novice. Most Electricians moved on to PLC control with ease because they had a good background already.

Aye!
My boss want's me to teach our new apprentice PLCs cause "he's goon on computers" but as i told him; I would much rather teach one of the older apprentices that knows whats going on outside the PLC, but is not that great with computers.

dahnuguy
January 10th, 2009, 06:34 PM
yeah its a problem, but until emplyers ask for and require a proper certification for these jobs none will be neede.

I would be in favor of a license even. At least pass a test somewhere take a class official apprenticeship something.

This barrier to entry would weed out the non logical types and be a great way to add value to those doing the work legit.


If there were such a system I would join and be certified.

I almost took the CET test just to do something, but I never had time and no one ever asked for anything beyond an interview.

I have this thought between jobs frequently but then I get on with the next project.

Just imagine what it would do to our saleries if the non tech types were all booted?

Why do car mechanics need a certification but industral techs do not?

They work on a machine that you depend on for the safety of maybe 12 people if we count the ones you might run over. I have worked on PLCs that could kill over a hundred if things went wrong and poison thousands.

And the only time I have brought this up it was seen as a "rant". Maybe I use the wrong words or mention it at the wrong times.

Anyway this is not a popular issue with the masses.

Tom Jenkins
January 11th, 2009, 10:46 AM
I would be in favor of a license even. At least pass a test somewhere take a class official apprenticeship something.

This barrier to entry would weed out the non logical types and be a great way to add value to those doing the work legit.

I respectfully disagree. Licensing would help a little, but I don't think it would significantly alleviate the problem. I work with a great many licensed professional engineers that aren't worth a diddle.

Someone who is book smart can pass the test but not have the common sense, mechanical instincts, or process understanding to properly and safely program an automation system.

I don't have a good solution, but the best practicable one appears to me to start with the school system and have the instructors stress real world applications and safety considerations.

dahnuguy
January 11th, 2009, 02:40 PM
I respectfully disagree. Licensing would help a little, but I don't think it would significantly alleviate the problem. I work with a great many licensed professional engineers that aren't worth a diddle.

Someone who is book smart can pass the test but not have the common sense, mechanical instincts, or process understanding to properly and safely program an automation system.

I don't have a good solution, but the best practicable one appears to me to start with the school system and have the instructors stress real world applications and safety considerations.

You dissagree with the strangest things and in ways that lead me to believe you never understood the statement you are disagreeing with.

A system of education is part of the issue , a certification or license is part of the issue, weeding out the ones who are not right for the job is part of the issue, but until the employer requires something, none of it matters at all.

To drive legaly one is required by the state to take and pass a basic test and carry a license from the state.

This system does not prevent idiots from driving but it does leave a trail and a history of their offenses.

There are a long list of jobs that require some certification or license but any body with a PC can have a shot at PLC programming.

In the "old days" of relay programing the problem was less frequent because the work was work.

Now every new college grad is looking for a job that uses a PC and is in some air conditioned space. Thanks to progress? allot of jobs are going that way.

I have sat in a plant on a bucket beside a machine where it was loud and frequently 140 degrees F on the floor with all sorts of offending odors and moving objects for hours on end, programing a PLC. The field service engineers who came after me would never do such a thing. One in fact discovered the 50 foot limit of rs232 by trying to connect to a machine from the break room. He would look at the machine for an hour and then go to a room with AC and move bits around and try it again for a day or 2 and then they would call someone else to go "help" them.

I have learned from my insane curiosity and my need to find out why. I must find the problem, I have to. It is a compulsion. But I would have been much better if I had some structured course or apprentiship.

This is one thing I like about the Germans. Maybe the only thing.

But there has to be something that separates someone who is honestly on the course to doing this job and someone who is just playing around.

I lost an arguement with a engineer about the MCR and Estop issue.

He used the Estop as an input to the PLC and then used the PLC to stop the machine.

I argued that the Estop should control the stop condition directly and ALSO be an input to the PLC so the control knows why thing have stopped and can do a reset.

I lost this arguement.

They contacted OSHA and got the OK to do it their way. Or thats what I was told.

Even when you have standards they are followed when it is easy to follow them and then the result is covered up.

Anyway some system some safety some something....................what we have is close to nothing.

Peter Nachtwey
January 11th, 2009, 03:43 PM
You dissagree with the strangest things and in ways that lead me to believe you never understood the statement you are disagreeing with.

I think Tom understands and I agree with Tom. The problem is what would you test? All PLCs are different and program differently or have different networking capabilities. I would not even put PLC questions on the test. I think it is more important to get certified to work on a particular type of machine rather than the PLC. PLC knowledge should be a given. There is MUCH more to programming than scaling an input or output or figuring out how to toggle an output.


A system of education is part of the issue , a certification or license is part of the issue, weeding out the ones who are not right for the job is part of the issue, but until the employer requires something, none of it matters at all.

The employer is responsible for training on his machines.


To drive legaly one is required by the state to take and pass a basic test and carry a license from the state.

This system does not prevent idiots from driving but it does leave a trail and a history of their offenses.

Yes, but an employer can check that too.

A PLC is like a hammer. Framers use hammers to pound nails. It is important to pound the nails quickly but that is just the grunt work. Programming is like being an architect. The architect must make sure the whole house or building is sturdy.

We have a term at Delta. It is "high tech ditch digging". This is what we call the grunt work that engineers do. For instance "connecting the dots" on a board layout. Kids are trained from an early age to connect dots in their coloring books. The CAD programs can "connect the dots" for you if you let them. The big difference between a board designer and a computer or unskilled person is that the board designer will know how to "connect the dots" in the optimal way so that trace lengths are minimized or kept the same length. Analog and digital lines are kept apart. High frequency lines are kept in the inner layers etc. There is the bigger issue of picking the right chips and knowing what dots to connect. The point is that just because you can use a CAD program to layout circuit boards doesn't make one a board designer. The same goes for PLCs. A PLC is just a tool like the hammer and CAD software.

So just because a framer is certified to pound nails, that doesn't qualify him to design houses or buildings.

leitmotif
January 11th, 2009, 03:44 PM
Think i am gonna chime in based on 20 years in safety where I closely worked with Facilities groups and from 40 years (off and on) as electrician.

E stops functions
1. supposed to be used only for emergency
2. shut whole machine down
3. place it in mechanical zero energy state.
4. Upon reactivation (?) ie pull the E stop back out is not supposed to restart the machine all by itself (very very common)
5. Supposed to kill power to the PLC inputs and outputs.
6. The exception to 5 is where PLC (and or VFD) is needed to accomplish zero energy state ie bleed off cylinder on punch and place ram at bottom.
7. After 6 is done then power to PLC input and outputs is killed (along with VFD)

I am doing this not to be the guru but to make double dang sure I understand this whole thing.

As far as the other stuff here are my thoughts
1. CERTIFIED means you paid the class tuition and were there at end to get the certificate.
2. LICENSED means you had the money and finally passed the test.
3. TRAINED almost same as #1.
4. QUALIFIED somebody said you know what you are doing
5. DEGREED you were able to take all the classes, pay the tuition and remember enough to pass the test. I know -- I have an AA BS and MS.

The above are pretty pessimistic definitions I admit. But the proof of the pudding from the above is when you investigate an accident. Yes they have all the paper required but they still screw up
- part of this admittedly is from being human - we are never I am afraid going to eliminate this aspect.

COMPETENT means you really know what you are doing and also what you do not know and find out before you really mess up. It also means you test your work for proper operation before the work can be called done.

Dan Bentler

Tom Jenkins
January 11th, 2009, 04:46 PM
Thanks Peter - you expressed what I was thinking.

Tom

Jim Dungar
January 11th, 2009, 04:56 PM
A major problem of inexperienced and many expert programmers is that they usually do not know what they need to know. This is why specific industry experience is important when designing a process.

I believe we need to be teaching risk analysis, as in "how to figure out what bad things will happen if things don't work right". For example, if you have a crane using an electro-magnet to transport steel, should an E-stop really disconnect all of the power sources?

twu026
January 11th, 2009, 05:44 PM
With regards to safety. A machine should NEVER be designed to rely sole on software for safety.

A machine should be designed to be mechanically safe AND electrically safe AND programmed safe.

Unfortunately, it doesn't matter how well (safe) you design a system. If the proper procedures are not followed during normal operation or maintenance, people can still be injured.

leitmotif
January 11th, 2009, 07:02 PM
A major problem of inexperienced and many expert programmers is that they usually do not know what they need to know. This is why specific industry experience is important when designing a process.

I believe we need to be teaching risk analysis, as in "how to figure out what bad things will happen if things don't work right". For example, if you have a crane using an electro-magnet to transport steel, should an E-stop really disconnect all of the power sources?

Excellant example
1. One person cannot think of all contingencies permutations.
2. I worded in a steel mill magnets were used.
3. The last thing you would want E stop to do is turn off the magnet.

Not even sure I would want a PLC operating a crane in a steel mill after all. Lot to be said for that human in the cab or on ground with remote control.

Dan Bentler

dahnuguy
January 11th, 2009, 11:00 PM
I am not convinced that either of you actually dissagree with me.

My point is simple, we need something more than what we have.

None of the examples you give use less certification than PLC programming.

"I think I'll be an architect............"...oh wait that's not enough.

I am not sure what the solution is, but I have thought about it many times.

Why are car mechanics trained and certified so much?

I can rebuild car engines..........I can build a house........by myself even. I can weld. I can do lots of things, but not professionaly. Why is that? Is it because someone thinks these things need to be done carefully with some degree of training and accountability?

That's all I am saying. We got nothin.

Say you can............ and then do something that appears to work and TADA! your in.

As for the how or what or which.................well I am pretty good with general machine issues, but that does not qualify me to make standards for industry.

All you need is to be smart enough to figure it out as you go and have the balls to jump in and do it. And the nerve to stay in till payday.

If there were any real accountability in industry things would work out eventualy , but there is no accountability.

I used to be a calibration/ electronics specialist. I was traceable to NIST and audited and certified as trained and held accountable for errors.

BUt now, all I have to do is make it work and then help explain how the software doesn't change itself.

If I were less ethical or safety minded, I could be dangerous. Like many I have worked with.

I don't see how any of this is something to dissagree with.

What exactly do you dissagree with?

Do you argue that there is no need for any oversight or certification? Or just exactly which way it should be framed.

Or are we happy with the wild west?

I am doin ok with the way things are. I don't think any change would benefit me on a personal level.

I have met a bunch of graduates who are complete idiots. Some have been average some have been interesting to work with. No system will solve all the problems.

I have even had to explain simple mechanical issues to MEs.

My point is , nothing will be fool proof and make everything perfect. But I find it interesting that certain jobs have so many requirements and others seem to have none.

I just don't get it. Look what you have to go through just to sell houses, and nobody can die from a bad house deal.

dahnuguy
January 11th, 2009, 11:12 PM
A major problem of inexperienced and many expert programmers is that they usually do not know what they need to know. This is why specific industry experience is important when designing a process.

I believe we need to be teaching risk analysis, as in "how to figure out what bad things will happen if things don't work right". For example, if you have a crane using an electro-magnet to transport steel, should an E-stop really disconnect all of the power sources?

I just worked at a foundry that had 2 overhead cranes that carry over 10,000 lbs of steel over workers routinely.

While I was working on one of the cranes rebuilding the rectifier, I asked about the machine to determine exactly how it worked. I did not understand how it could be expected to hold steel when the rectifier failed.

I had never worked on an overhead crane and I suggested we call a crane specialist and have the crane certified OK by a reputible crane service company. Such companies are certified and licensed by the state.

No dice,

Then I discovered that niether crane had a UPS to hold the magnet in case of a rectifier failure. I brought this up and was told the cranes were not required to have a UPS because of their age!

All new cranes are required to have a UPS.

And I suspect if you call the crane service for repair they would require a retrofit to add a UPS to give the crane pass on safety.

The metal cabinet and guard rails looked like play doh after the bar fell off the magnet when the rectifier failed.

I have run into this at every job I have ever worked.

leitmotif
January 12th, 2009, 01:11 AM
I just worked at a foundry that had 2 overhead cranes that carry over 10,000 lbs of steel over workers routinely.

While I was working on one of the cranes rebuilding the rectifier, I asked about the machine to determine exactly how it worked. I did not understand how it could be expected to hold steel when the rectifier failed.

I had never worked on an overhead crane and I suggested we call a crane specialist and have the crane certified OK by a reputible crane service company. Such companies are certified and licensed by the state.

No dice,

Then I discovered that niether crane had a UPS to hold the magnet in case of a rectifier failure. I brought this up and was told the cranes were not required to have a UPS because of their age!

All new cranes are required to have a UPS.

And I suspect if you call the crane service for repair they would require a retrofit to add a UPS to give the crane pass on safety.

The metal cabinet and guard rails looked like play doh after the bar fell off the magnet when the rectifier failed.

I have run into this at every job I have ever worked.

I think this is why the concept of the service guy PLC guy electrician being trained certified is a bunch of BS.

MANAGEMENT should be inspected and certified for being rectal cranial inversion free.

NO battery backup for a crane magnet running loads over people? What kind of - ahh hell I already know
- the codes dont call for it
- costs too much
- Production God will be ****ed
- we have never had a problem.

Who cares if there is no code ? ACTUALLY there is - ie General Duty Clause which says "shall be free of recognized hazards" non compliance is more common than compliance.

I am so glad I am out of the steel business because of things like this and the same goes for the last job I worked at.

Struggling_forward
January 12th, 2009, 02:36 AM
2 points:
1.We were all dangerous novices once.
2. If you are relying on software and a PLC to make your system safe you are doing it wrong. All safety systems need hard-wiring. ( specific safety PLCs such as Piltz etc excepted)
3.What about us experienced programmers? I've done some howlers. Thats how you become more experianced.
4. two points wasnt enough.

parky
January 12th, 2009, 03:45 AM
Although I agree with formal training I'm against some kind of licencing.
Point 1. I have been doing this job for 25+ years, have formal qualifications etc. & at my time of life with my experience would not like to have to pay extortionate costs to pass a test I don't need.
Point 2. passing a test does not make you good at your job it is just a licence to say you have passed the test.
Take the Part P system in the UK, what a load of cobblers.
They came up with a test for electricians with a number of parts, but suddenly realised that kitchen & bathroom fitters also needed to install sockets, switches etc (this part of the test is more comprehensive).
So they came out with a simple test for them which means they can work in bathrooms & kitchens where a qualified 16/17th ed. electrician cannot without the more intensive course.
Again the costs of passing this is expensive unless you can get your employer to pay for it.
Incedently they changed the wiring colour code at the same time so any mods after the cutoff date would use the new colour codes(convienient).
It's not getting any easier in other trades, my brother is an HGV driver & after 20 years driving lorries he has now had to take city & guilds!. Madness.
As we have no manufacturing in this country now I suppose it's the governments way of creating jobs welcome to service industry brittain, unfortunately we will be a nation of trainers with no students to train becouse we have no manufacturing, perhaps we can all emigrate to other countries that will have a need for trainers.
Well... that made me feel better Iv'e had my go.

Struggling_forward
January 12th, 2009, 04:15 AM
I lost an arguement with a engineer about the MCR and Estop issue.

He used the Estop as an input to the PLC and then used the PLC to stop the machine.

I argued that the Estop should control the stop condition directly and ALSO be an input to the PLC so the control knows why thing have stopped and can do a reset.

I lost this arguement.

They contacted OSHA and got the OK to do it their way. Or thats what I was told.


Thats not good.
I don't believe they contacted OSHA.
Surely you can just quote the regulations to them.
In Europe we have the EN written standards to work to.

dahnuguy
January 12th, 2009, 09:16 AM
Thats not good.
I don't believe they contacted OSHA.
Surely you can just quote the regulations to them.
In Europe we have the EN written standards to work to.

Quoting regs will you get you to the front of the next "lay off". You become the new "smart@ss know it all". Once I shut down a whole plant for a safety issue. And 2 weeks later they didn't need me anymore.

In regards to the Estop/PLC issue.......I re-wired it to stop the outputs and inform the PLC of the stoppage.

Same as theirs but mine actually stopped the outputs, which on the machine in question would render it safe.

They never noticed the difference, because if all went well there would be no noticeable difference.............IF all went well..............

I try to imagine whats the worst that can happen ...............if the PLC out gets "stuck" on, or the isolation relay fails closed, or the Estop sticks. I have even had to fight the companies I worked for to add a redundant Estop circuit!

What do you think the second set of contacts are for on an Estop???

They were just jumping them together at the switch!!!!!!!!!!!

Oddly the safest machines I worked with were huge hydraulic presses that were capable of 1200 tons and 30 strokes a minute! Talk about scarry.

Textiles and chemical plants are the most unsafe places I have worked. Small margin low profit no protection and then "free trade". No oversight no regulation or no enforcement of regulation............OSHA is a joke in the south east US.

Tom Jenkins
January 12th, 2009, 09:40 AM
I am not convinced that either of you actually dissagree with me.

That's true - I stated that licensing would help. I just don't see it as a cure - more like providing a little relief.

Matthias von Zorn
January 12th, 2009, 09:59 AM
Does OSHA really allow the PLC to shut down the outputs on an estop? I thought they required estops to be hardwired and to remove power from outputs as needed (ie, on furnaces, we only shut down things in motion (belts, fans, etc)). Thanks

matt

OZEE
January 12th, 2009, 10:15 AM
Does OSHA really allow the PLC to shut down the outputs on an estop? I thought they required estops to be hardwired and to remove power from outputs as needed (ie, on furnaces, we only shut down things in motion (belts, fans, etc)). Thanks

matt
No, they do not allow the PLC to handle estop functions -- unless it's a specifically rated/designated "safety PLC". An EStop needs to put the machine into a "neutral energy" state.

milldrone
January 12th, 2009, 10:26 AM
The problem is what would you test?


Ooooh! Ooooooh! I think I already know the first question;)

Question 1) Explain the difference between Unitary, Modular and Rack PLC sytstems, include diagrams to aid your explanations.

Matthias von Zorn
January 12th, 2009, 10:31 AM
Thats what I thought. Thanks OZEE.

Struggling_forward
January 12th, 2009, 10:55 AM
I try to imagine whats the worst that can happen ...............if the PLC out gets "stuck" on, or the isolation relay fails closed, or the Estop sticks.


Or a novice programmer forces the output on and walks away forgetting about it.

icky812
January 12th, 2009, 11:38 AM
If so, then the second question would be about traffic lights... :lolis::lolis::lolis:

S7Guy
January 12th, 2009, 12:03 PM
I can see how shoddy programming could hurt production or even damage the machine. Heck, even experienced programmers can do that.

But if hundreds can die or thousands can be poisoned or fingers can be chopped off or bodies crushed due to a programming mistake, isn't the inherent design of the machine flawed anyway?

Looking at the various machines I have worked on (which are many), I couldn't write a function to hurt someone even if I tried. I mean, if someone has opened a door to work on a machine, how could faulty code make a shear pop up and cut his hand? Personally, I am much more concerned about the qualifications of the electrical and safety hardware designer than the qualifications of the programmer.

As for licensing, I guess it wouldn't hurt in theory, but reality is a different thing. For one thing, it's impossible to even get hardware suppliers to come up with a programming standard, let alone getting the programmers to agree. And who would evaluate the programmers? Some kind of government worker? If he knew anything about programming, would he be working for the government?

So, I think the most reasonable solution is to regulate safety and hardware (as it already is), and let individual plants decide on a programming standard.

Matthias von Zorn
January 12th, 2009, 03:30 PM
Some machines can be dangerous. Take an atmosphere furnace. Its only filled with hydrogen, and in a sealed chamber, at 1750F. What could go wrong? Can you say bomb? Its possible, just through incorrect operation to induce air intake into outer chambers. The PLC has code to try to make sure this doesnt happen. Maybe that tech there was annoyed with that delay that would not allow him to open a door till the air is purged and burnoff is established. He is in a hurry, he will just remove some of those interlocks to get that load in faster. A few forces here or there, and its gulping air. Air + H2 + Heat + compression. So,yeah, some machines are dangerous if misused.

n9xcr
January 12th, 2009, 03:50 PM
They were just jumping them together at the switch!!!!!!!!!!!

There are ways to put a stop to that. :)

PLC_Idiot
February 23rd, 2009, 11:21 PM
First time poster, enjoying the thread.
Certified does not make one qualified. There are some very bad electricians out there who the state has certified. Just as there are some very good electricians out there who the state has not certified.

You could set up a test, but then someone would start a two day seminar to teach you how to pass the test, not teach you what you need to know.
Is the certification to protect the public, or to protect our job?
By reading post, I've determined some of you folks are pretty sharp. But remember you once were a newbie, and dummer than dirt!
I might be very versed on GE and AB but put me in front of a Siemens, I'm going to be a "newbie" for a few days. I will be asking for help and from looking around here, it appears to be a good place to ask.

On Safety
Two phrases come to mind.
1) I am ultimately responsible for my safety.
2). I am my brothers keeper.
So basically we are all responsible for ourselves and everyone around us.

No you should never depend on a software EStop.
I am in my 50's, been programming awhile, I love Xbox, and have been known to call tech support instead of reading a manual. Sometimes because I'm lazy, sometimes because manual really sucks! (stereotypes don't always apply)

PeterW
February 24th, 2009, 08:08 AM
2 things that the resurfacing of this topic brings to mind.

Firstly I remember reading the OP post when there was about 2 replies, I was going to respond but was too busy at the time then it faded.

Secondly, seeing the name dahnuguy, what happened there?? he suddenly appeared and was all over the board like a rash, making long posts which led me to believe he was going to be the new 'Terry Woods', then zap.. vanish..


Regarding Goody's original post and in particular this bit

'I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor'

Its quite common for a sensor to wake a conveyor up from 'energy save', I've seen many versions of it, where a sensor can wake up a single or multiple conveyors that have stopped due to no action.

The reason to stop is to save energy, reduce noise and wear and tear.

There is normally no 'warning' sound on wake up (if there was then the reduce noise reason is gone). Usually the conveyors have signs around stating that the system is automatic and will start without warning. Saying that on initial start from a dead system there would normally be a start warning.

I prefer the individual conveyor type where every conveyor has its own time out and restart condition. I also prefer that the sensors do not wake up a conveyor unless the conveyor on which the sensor is fitted is running.

The company I work for usually uses the group versions and the conveyors do not need to be running, in the week that Goody wrote his bit, a worker where I was placed his tools on a conveyor, jumped on and was also taken for a ride, he was lucky, he managed to get off before he was fed into the X-ray machine.

The thing is, he should have known better than that, its down to the person to isolate anything before he decides to get onits his responsibility. The system is automatic after all and safety starts at home.

Goody
February 24th, 2009, 01:40 PM
With me being the original poster, maybe I should reply again.

I have liked the way the topic has veered and swayed between novice programmers and safety because I am an absolute believer that any safety discussion is never wasted time. Anything that tries to stop complacency (which I believe is one of the biggest factors in accidents) is a very good thing

At no point was it my intention to put off anyone trying to learn the art and craft of plc programming.
I read a few of the 'we were all new once and shouldn't be elitist' type comments and chuckled.
I also laughed at some of the top people here saying they were once plc dummies - and some still think they are, because thats the mark of a excellent engineer - one that knows that if they work for a hundred years they will still not know everything.

So any new plc programmers here, please keep posting and we will keep answering. The ones I dont like make themselves obvious in their questions anyway :)

just_lionel
February 24th, 2009, 03:40 PM
I agree with the posts here. I started out fresh coming from the computer programming background. I was lucky in the sense that my Dad is a Controls Engineer and helped me alot in my growth and development. I have came along ways from when I started, but I still have much to learn. This is one reason why I love this site. I might not post much, but I do read other people issues and learn from them as well. I have always taken saftey into consideration and I double check my work everytime because I know one small change can make a huge difference.

I just want to say Thank you to all here, it is a great place for all to gather and learn. Heck, I have even been able to help people as well!

lipalipa
February 25th, 2009, 05:16 AM
First things first. Hello to everybody. Excuse me for my English, I’m not an native English speaker. I’m new here and also in the integration field. I’ve spend a little time to read this post because of its tittle. I feel that is necessary to make some clarification or what I see as clarification. The integration field is far from an one-stand-job. If you know economics you can be an economist, if you know electric you are an electrician and so on. But what you have to know to program PLC’s? Well you have to know a lot. Is not enough to know programming, drag&drop, networking, electrical, mechanics, safety system, electronics, cabling, system optimization, system architecture. My point is what do you test for a young guy? Who make the test? You can not, it’s impossible to test all.
Regarding the example with the person who repairs cars or with the driver’s license. With the direction of automatizations the car, driving looking to be fully automated, the future mechanics will be PLC programmers? The future driving license exam will be analyzing, testing and debugging embedded programs? Maybe is to soon to search here the answer for this problems.
Reentering on topic, I found out that 1 week of hard work on site it’s often more teaching than 3 years in school without seeing an working machine. I thing the problems, both the safety an fresh-out-school programmers, are based in economy. We have economy studies and cut-cost directives and deadlines more and more shorter and practically isn’t possible to follow and retest a work.
Overall i find that for really programming an PLC in a automatism system is mandatory:
- a kind of expertise in one of the adjacent filed (mechanics, programming, electrical, .....)
- a good communication skill
- a first project where the "new-guy" does nothing, he learns, watch, ask,...
- a second project with daily supervision
- a 3rd project with overall supervision

and maybe after that he can do a project on his on....

PS Sorry for the long reply

silva.foxx
February 25th, 2009, 08:36 AM
First things first. Hello to everybody. Excuse me for my English, I’m not an native English speaker. I’m new here and also in the integration field.

Welcome Lipalipa, you're written English is fine and I'm a rag-arsed spark.

I once worked for a small company that manufactured paper napkins and cups. I went there having self-taught on Mitsubishi Fx. I took on a project of backing up the plant's plcs, over a hundred programs.

I had to research AB, Siemens, Omron, Keyence and Toshiba... to find the neccessary software, comms cable and battery requirements for purchase. I then had to learn a little of RSLogix/Linx, Step5, Step7, Syswin, CX-P, KVLadderBuilder to enable upload.

I went to night school for a 2 year course on AB-slc500, got a course at Siemens for Step5 and a local course for Step7 as a result.

I was about to suck the program out of the Toshiba EX100(?) when I got a shout from an operator. The machine was a paper laminating machine and the Halogen heaters, for drying the gluing process, were on and burning the paper that was webbed up.

The plc was in 'HALT'.

This was the original program. The heaters were through normally closed contacts on two relays in series and the program energised to turn off! Needless to say this was corrected for a fail-safe. Another fault I found on this machine was the 110vac center tapped tranny was only fused on one leg. One day a 110v sol. coil developed a -55v to earth fault and burnt up the earth wire all the way back to the tranny. Smmmokin!

I recently completed my first real 'machine' program as part of a controls upgrade from relay to programmable logic. We were just going to convert but chose to go from scratch with a Siemens S7-300 and Cat4 safety set-up. I'd say I am between novice and intermediate. The program worked fine straight away, I've just to add an interface signal or two then it's done.

My 'license' has been the opportunity to work with all these softwares, see many programs, the continual use of this website, the priveledge of books, working with others who have plc experience, time to learn and the vast data you can obtain from t'internet. I am so lucky to be a rag-arsed spark!

uptown47
February 25th, 2009, 01:12 PM
Reading through this thread I think I'm in agreement with the majority of posters in saying that if 'experience' and 'competency' were a pre-requisite for doing any work then how would newbies develop.

Training only goes so far. To develop properly you need to be in the 'thick' of it actually making changes, modifying code, coming across and then surmounting obstacles. This is how we as programmers, and as humans, develop and improve.

I think anyone who has been in PLC's for a while will have had that experience of being a bit 'out of their depth' but you work through it and learn from it.

The problem with 'licensing' would be that as soon as it was introduced it would become a requirement in order to comply with health and safety laws. This would mean that only the people who had attended the course would be in the programming roles.

I've been around long enough to know that just because you've done the course doesn't mean you can do the job!

I think it should be down to individuals to be able to ask for help if they need it or even get someone to check their code if they are unsure of anything.

And, to reiterate what has been said many times in the post, machine safety should never be reliant on the PLC anyway.

:site:

dahnuguy
February 25th, 2009, 05:17 PM
Secondly, seeing the name dahnuguy, what happened there?? he suddenly appeared and was all over the board like a rash, making long posts which led me to believe he was going to be the new 'Terry Woods', then zap.. vanish..






Don't know Terry Woods,

Sorry about the rash if I need to be.

No zap no vanish , no email alert that this thread had been responded to and my time has been consumed with applying what I have leared here and been able to figure out.

Basically, I was here allot due to being unable to proceed with my task. It is a point of sucess in the tutelage I received here that I have not been around much of late as I have been swamped with using this new knowledge.

I also have not received any emails up to this one today, so I was quite surprised to find this had grown to this length.

Lastly, I see everyone has a firm grasp of the questions and issues and we all agree there is no solution or none is needed.

As for the why of testing, there are people in charge who know nothing of programming or safety, these persons have hired someone who likes the look of this job and can spell PLC. The tech is pressured to say he can even if he cant to keep his job/ good standing/ pride/ ego. The boss is pressured to get this dangerous thing done without thinking through the after effects and the tech doesn't have the confidance or knowledge to convince the boss it may not be a good idea. So off we go down the "OOPS" highway.

I have been a witness to this , first hand. I was able to illustrate my point by just asking questions until they "figured it out and explained it to me."

"UM I was just wondering, what happens if that valve opens now? Is that bad?"

yes very bad.

"UM ok how is that different from what we are doing in this edit?"

well its completely ............um oh wait nonono that wont work , let me explain why and make it look like I am telling you.

The question remains , with processes that are unsafe if programed incorrectly who will make the changes and who will check the changes and who will say who should be doing it?

I am not so big in ego to get in over my head. And I am always trying to "break" what I write as a test hardening. Doesn't everyone do this? .........No everyone doesn't. Not everyone can even see what might go wrong.

My version of the machine is like a horror show where everything conspires against you and every component fails at worst moment, etc.

I often hear "What are the odds of that happening?"

The odds have to be very small and the danger must require multiple failures before I will even consider leaving it alone.

Even then it bugs me.

An extra valve costs 500 dollars? so............what is a whole batch of product worth? or someones health?

Well that's all I have to say about that..........................today.

bernie_carlton
February 25th, 2009, 05:40 PM
Regarding the remark concerning testing and just teaching to the test. As an Air Force instructor the objective for a test was such that, if they could pass it by memorization or whatever then they knew what was needed for the job. If sucessfully answering the test questions, while knowing nothing else, meant that the test taker was unqualified THEN IT WAS THE MAKER OF THE TEST WHO FAILED.

The question according to my Air Force instructor was 'I'm not a mind reader. What BEHAVIOR do I need to see to convince me that the person is qualified?' Answering that question defines the test. If passing a test based on the answer to that question does not make a person qualified then the question was answered incorrectly.

dahnuguy
February 25th, 2009, 06:33 PM
Reading through this thread I think I'm in agreement with the majority of posters in saying that if 'experience' and 'competency' were a pre-requisite for doing any work then how would newbies develop.



Newbies should develop under a qualified veteran, after qualified instruction, for a number of years. Yes I see the variables, these are not for me to decide and I am not debating how long training should be only that there should be some. As of now , none is required.




Training only goes so far.


but so far is better than none.



To develop properly you need to be in the 'thick' of it actually making changes, modifying code, coming across and then surmounting obstacles. This is how we as programmers, and as humans, develop and improve.



and if no one is in any danger , I agree with this hands on cavelier aproach. Jump in and get wet. Then discover if you can swim. I have been thrown to the wolves on many occasions, I enjoy the rush.



I think anyone who has been in PLC's for a while will have had that experience of being a bit 'out of their depth' but you work through it and learn from it.



and if you get lucky the first couple of times and no one gets hurt then you gain the confidence to go to bigger things. Maye that's good , sometimes it's not.



The problem with 'licensing' would be that as soon as it was introduced it would become a requirement in order to comply with health and safety laws. This would mean that only the people who had attended the course would be in the programming roles.

I've been around long enough to know that just because you've done the course doesn't mean you can do the job!



yep qualified and certified does not mean good

no training and little experience can't be better.



I think it should be down to individuals to be able to ask for help if they need it or even get someone to check their code if they are unsure of anything.



yeah, my english teacher used this logic on me "Why don't you look up the words you missplled?"

and I said "Why would I look it up in the dictionary if I think that's how it's spelled?!!!! Do YOU look up words you think you spelled correctly???????"

Do you ask someone to check your code if you tested it and it passes your testing and logic checks? What about through lack of knowledge or experience you miss something? and then something bad happens? I have noticed that when someone gets hurt the investigator is usually some guy that has no idea what's going on and gets snowed by the company into blaming the operator and never is the machine or the code ever questioned. And what if I could prove it was a machine defect that caused the injury / death? Who is responsible? The company? the boss? the programmer?

nope.

and that's why we have no certification/ education requirement.

You can't run a daycare without a license and training and inspections. But a 16 year old girl is frequently trusted with all the kids and the house for hours.

I have seen so many shortcuts in every part of manufacturing, and so many good people who were slowly "taught" to accept it due to lack of training.

Someone mentioned Air Force iinstruction.

The USAF will train you on a task until you can not screw it up through lack of knowledge or training and they document every step and have you and the trainer sign off on every task, so when you do screw up, you can be held responsible. You know the job inside and out BEFORE you are let go on your own. Maybe this system is why I feel so untrained as a civilian. Nobody signed off on my PLC training and I dont know what I don't know.



And, to reiterate what has been said many times in the post, machine safety should never be reliant on the PLC anyway.

:site:

No it shouldn't but it many machines it so is. If machine safety was not affected by the PLC I would only have a quality arguement and would drop the whole debate.
I have been drilling safety into every manager I have ever talked to, most don't want to hear it.

Job one is production............safety is rarely in the top 5. I think it should at least make the top 3.

dahnuguy
February 25th, 2009, 06:49 PM
Secondly, seeing the name dahnuguy, what happened there?? he suddenly appeared and was all over the board like a rash, making long posts which led me to believe he was going to be the new 'Terry Woods', then zap.. vanish..



It strikes me as odd that anyone noticed I went missing.

Most places where I speak frankly, I am not missed when I leave for a bit.

ziggys
February 26th, 2009, 06:20 AM
thanx for your input, I worked for a company that designed and built custom automated plc. machines, I've seen it happen with experienced programmers!

brucewoodrem
August 29th, 2009, 02:40 PM
I have read chapter 6 over and over of the manuel but still cant get an understanding of how to write the ladder to start a drum sequencer

ziggys
August 29th, 2009, 09:11 PM
If I was a programmer I would give you the answer, i bought the dvd's and books, phil melore tells me to practice, how do you practice when you don't know where to start! i think a machine crashes when safety's aren't built into the program!

Bitmore
August 30th, 2009, 02:27 AM
I would think those individuals entrusted with such,and had limited knowledge, would seek out advice or strive to learn. I think/hope all of us try to test our logic in a condition that does not endanger people.
I have ALWAYS breadboarded or simulated my logic before implementation. Even after trying my logic on the simulator or breadboard I would ALWAYS insist on testing equipment in real time without risking life or limb.

rustysmith52
August 30th, 2009, 08:39 PM
There has been quite a bit of excellant information posted here on this topic. Not so much on programming help, but consequinces of poor programming. I'm an instrument tech. with a very limited knowledge of plc's. I have assorted switches and relays and a temperature controller with an on/off output controlling my hot tub. I also have a surplus mitsubishi fxon 24 es plc which I plan on integrating into my system. With the help of folks on this site and others, I'm slowly developing a workable program. My point, which goes along with what a lot of you have talked about, is that this plc is sitting on my workbench with switches for inputs and lights for outputs. It won't go anywhere near my hot tub until I've checked and rechecked every scenario of what could happen. I have to be very careful combining water, electricity, kids and quite possible, a few drunk adults. I'm glad I read this post and all the replies, it reminded me of how dilligent I need to be to keep this safe. If I feel uncomfortable any at all, I'll probably just buy a new spa pack, but I enjoy projects like this and I'll make it work whether I use it or not.
Thanks for listening.

Rusty

arunsinha
August 31st, 2009, 07:35 PM
Quite a discussion Goody has started... I'm not sure if has been touched on in all the replys (I read a few only), but I think there is a larger issue of Automation & Controls education in America that needs to be addressed. For that matter, Engineering as a whole. I've been feeling this way for the past several years, and I see it finally popping up amongst "pundits" and business leaders. Basically, there seems to be a shortage of Engineering Graduates in the U.S., and the problem is much more magnified in our field/subset. PLC programming is not part of many Engineering carriculms(This is not so much the case in other countries, like India). In the U.S., most PLC programming is learned on the job, from manufacturers classes, and perhaps in some trade schools. Many of the "boomers" that are now retiring came up on relay panels, so in regard to ladder logic in particular, it was an easy transition for them. They are now retiring. Kids coming out of school know higher level languages like C, C++, VB (it was FORTRAN for me, back in 1990!)...and like one post I read (about the CE who gave the task back after a month)...these languages don't really prepare you for controls programming.

Answer/solution - Automation & Controls programming as part of Engineering school carriculum.

How to make this happen - I have no idea!

Goody
September 7th, 2009, 03:15 PM
I have re-read all the posts and nothing has changed my mind.

It's not education that is the problem, it's the attitude.

Some of the people that are trying to program PLC's believe they don't need training - or at the very least lots of practice on a plc training setup.

Just read a lot of the posts that come in daily on here.

even today some guy is wanting to automate a 300 ton press and it is obvious from his posts he hasnt a clue - and that is why it isnt a joke or a grumble - these guys are out there doing these things.

up_onus
October 13th, 2009, 03:12 PM
Hmmm,
Goody. I suppose you never were a novice, and when you were you probably looked right where you were supposed too, because PLCs were simple, didnt have 50 page manuals.
And I suppose you never made mistakes or asked stupid questions to your "senior" engineers.
This is a ridiculous rant.
You sound just like a begining engineer who refuses to look for the answer to your proposed problem and you just come to this site to "say how long youve been here".
Good luck with your whining.

504bloke
October 13th, 2009, 03:21 PM
Hmmm,
Goody. I suppose you never were a novice, and when you were you probably looked right where you were supposed too, because PLCs were simple, didnt have 50 page manuals.
And I suppose you never made mistakes or asked stupid questions to your "senior" engineers.
This is a ridiculous rant.
You sound just like a begining engineer who refuses to look for the answer to your proposed problem and you just come to this site to "say how long youve been here".
Good luck with your whining.

We were all novices at one point, i for one dont remember being lazy and googling "How do i program a 300 Tonne press" or even attempting to without the relevant knowledge.

Machines can be dangerous and some of the posters here as goody points out HAVE NO CLUE and shouldnt be dabbling with seriously dangerous bits of equipment, its one thing to program a set of traffic lights but quite another to desing a control and safety system for a press, rubber mill, spray booth etc

When i started with a Square D Symax PLC this had a Massive manual (More than 50 pages) and that was years ago, S7's, Omron, Mitsi and AB's are In My Opinion simpler than the older plc's were and far more powerful. We didnt have ASi years ago or PROFISafe or Safety PLCS.

Anyway thats my 2 penneth :dance:

dahnuguy
October 13th, 2009, 05:07 PM
Hmmm,
Goody. I suppose you never were a novice, and when you were you probably looked right where you were supposed too, because PLCs were simple, didnt have 50 page manuals.
And I suppose you never made mistakes or asked stupid questions to your "senior" engineers.
This is a ridiculous rant.
You sound just like a begining engineer who refuses to look for the answer to your proposed problem and you just come to this site to "say how long youve been here".
Good luck with your whining.

This is a perfect example of the point being missed entirely.

WE WERE ALL BEGINNERS AT SOME POINT YESSSSSSSS>

AND WEEEEEEE KNEW WHAT THAT MEANT. AND THAT IS WHERE WEEEEEEE HAVE AN ISSUE NOW.

When I was a beginner no one would dare ask me to build a PLC control for a dangerous machine with no help. And if they did ask I was quick to say it was over my head.

It seems this is not done these days.

"Can you program a PLC to make that press run?"

"Sure no problem, I'll look it up online tonight and start in the morning."

"Ever program a press before?"

"Nope"

"Ever program anything before?"

"I did real good in school with the sample problems."

"Ever use this type of PLC before?"

"Nope, I'll figure it out."

"Ever worked with safety of workers in an industrial environment?"

"Nope, but we talked about it one day in class."

"OH ok , sounds good, have at it."

This is what it looks like out here these days.

I pick up new PLCs but I tell the bodss there will be a time delay while I do it. And I still apply all the safety and logic I have learned in the time I have used the other types.

I don't see an issue with some one coming here asking for help learning. Or some one who has worked in indusrial situations and used other brands but has a question about a new brand.

Like I have used brand X for 5 years, but I have no clue about data types in S7.

Or I have used brand X for years, but I just hit a new process and I need some ideas, etc.

But when you want to figure it out for the first time and your intent is to expose operators to your learning curve with dangerous moving parts or chemicals, I have an issue.

I understand I am wrong to ask anyone to be responsible or show restraint.

I understand I am wrong to ask for any accountability.

I understand I am wrong to have such high expectations.

I know, I get it.

Just do what ever and apologize later.

I am amazed at the luck that stops so many people from getting killed in factories every day.

Why push it?

deemz
October 13th, 2009, 09:39 PM
I believe there should be some sort of mandatory certificate required to program machines/processes, above and beyond just having a degree/diploma, where you learn about fail-safe design, designing safety systems and have to show and prove that you understand standards like IEC 61508 through a project.

It's more than just programming.

I mean, you should need a license to do this work.

Paul B
October 13th, 2009, 09:56 PM
Stand on the plant floor and go through every aspect of the machine - always asking yourself if the end result is the right result. Its a judgement call for many many things.

That's why we make the big bucks is a great catch line - We also have job security.
Experience has no substitute.

Great thread!

PLC_Idiot
October 14th, 2009, 08:43 AM
I have been involved with electrical controls since 1976. Before PLC's there were relays. Alot of people who taught me were really good at the relay thing. Most of the things done in PLCs are relay logic. So for many of us, when the PLC first came out it was really more of a transfer of media, instead of mounting relays, we programmed them in. I installed my first PLC in 1982. I was new, and nobody there to teach me. But I understood logic. Does that make me dangerous? Hardly! I have taught many to make transition from hard ware to soft wire. Some do well, some do not. What I have seen alot is the instant arrogance involved once they make transition. As far as programming goes, you can either think logically or not. Doesn't mean you are smarter than someone who can't. It doesn't take long to learn to program. The think that takes time to learn is the equipment we are controlling, not what we are controlling it with.
We all bring different perspective to the table. I've learned from the old guys that are locked into there standard template. I've also learned from newbies who have no templates, and just figured it out. Old guys loose arrogance, new guys, learn.

demmons
October 14th, 2009, 04:59 PM
I would really like to see controls programming/Design taught in Vocational High Schools. I took 3.5 years of machine shop 4 periods a day. The advantages are :

No pressure to just get it done, learning is done at the students pace.
Good supervision.
Plenty of time to mess around and get the feel of what is going on.
Plenty of time to learn both theory and practice.
Usually a decent enough budget to get a lot of different equipment.
Co-op opportunities for OJT.

leitmotif
October 14th, 2009, 06:35 PM
I do not favor this type of instruction in High School for following reasons
1. the best instruction platform is with real world equipment 230 VAC and maybe 460 VAC.
2. High school kids are not mature enough to be around this stuff.
3. Many states will not allow under 18 in industry. There goes co op for OJT.
4. from what I saw granted years ago high school shop was just a glorified play room.

I do see the community colleges as a mucn better place for this type of program because
1. Older students
2. Not restricted to just high school age
3. Not as regulated as a school district is
4. More real world and no molley coddling - go ahead dont do homework - flunk - it is up to you.
5. Instructors are often as well educated as those in 4 year schools and are more dedicated - no research nor emphasis on publish or perish.
6. More able to have industry interaction than a high school.

Dan Bentler

robertmee
October 14th, 2009, 06:45 PM
I do not favor this type of instruction in High School for following reasons
1. the best instruction platform is with real world equipment 230 VAC and maybe 460 VAC.
2. High school kids are not mature enough to be around this stuff.
3. Many states will not allow under 18 in industry. There goes co op for OJT.
4. from what I saw granted years ago high school shop was just a glorified play room.

I do see the community colleges as a mucn better place for this type of program because
1. Older students
2. Not restricted to just high school age
3. Not as regulated as a school district is
4. More real world and no molley coddling - go ahead dont do homework - flunk - it is up to you.
5. Instructors are often as well educated as those in 4 year schools and are more dedicated - no research nor emphasis on publish or perish.
6. More able to have industry interaction than a high school.

Dan Bentler

Also at community college you are paying to learn so you are usually more motivated to do so. At High School you're just trying to score chicks :D

Clay B.
October 14th, 2009, 07:01 PM
I do not favor this type of instruction in High School for following reasons
1. the best instruction platform is with real world equipment 230 VAC and maybe 460 VAC.
2. High school kids are not mature enough to be around this stuff.
3. Many states will not allow under 18 in industry. There goes co op for OJT.
4. from what I saw granted years ago high school shop was just a glorified play room.


Not sure I agree here: I think High School is a real good place to introduce students to PLCs and automation controls.

1: Yes 480 VAC is most common for motors but most controls now are 24 vdc. Unless they are doing drive theory I do not see the need for high voltage
2: I am not sure what maturity has to do with it. If you do not do the work you do not pass the class
3: Agree here, a high school student would be useless for co-op reguardless of the regulations
4: That would depend on the teacher and the curriculum. We had drafting, wood working and automotive shop where I went to school and all were ran seriously.








I do see the community colleges as a mucn better place for this type of program because
1. Older students
2. Not restricted to just high school age
3. Not as regulated as a school district is
4. More real world and no molley coddling - go ahead dont do homework - flunk - it is up to you.
5. Instructors are often as well educated as those in 4 year schools and are more dedicated - no research nor emphasis on publish or perish.
6. More able to have industry interaction than a high school.

Dan Bentler


Biggest problem I see with Junior Colleges is how they are regulated. I have had several prospective employees come from a Junior College "PLC Program" that did not have a clue. Once again it goes back to the program. Alot of these colleges are using outdated equipment and even basic programming skills are being glossed over. Alot of these junior colleges are nothing more than paper mills where students buy their degrees.



In my opinion, it is up to the individual. He/she needs to make the call if they are qualified to do the job. Problem with this is the fact that you may not see what you are up against until your in it. Doing good research does help with the gotchyas but heck your going to go up against something that will stretch your abilities, it is just part of the trade.

The one thing my experience has taught me is how to ask better questions.

demmons
October 15th, 2009, 08:18 AM
My vocational high school education must have been different from you folks experienced.


We had to qualify to enter the county program.
We worked with top quality lathes, bridgeports, surface grinders, both manual and CNC.
We had a separate shop for electrical construction where high voltages were used, and these guys and girls were sent out to Co-op to work for electricians.
I personally went to work in a machine shop instead of going to shop for the last six months of my high school career under our Cooperative Industrial Education program, and I didn't turn 18 until a week after I graduated.
I was also taking extra classes in high school to prepare for college.
I guess what I am saying is...if vocational education is done right with motivated students and qualified instuctors, as it was done for me. It would be a good place to start.

icky812
October 15th, 2009, 09:28 AM
I'm going to do something I rarely do and weigh in on this one.

All high schools are different, but in the case of the high school where my daughter goes it works like this for extra credit/advanced classes.

As a company AutomationDirect sponsors the local FIRST robotics team (http://www.forsythalliance.com/). It consists of middle and high school aged kids. They learn safety, electronics, programming, critical and logical thinking, and troubleshooting skills.

As you can see from the picture on the first page the kids have fun. The amazing part is, when it comes down to working they dig in and go. Some of the projects that they have done are quite amazing.

So far in the four years of the program I don't know of a single major accident. A few minor cuts and bruises, but no lost fingers, eyes or other major body parts.

By the way. All of it is done by the kids. All the mentors do is keep the kids safe, provide instruction, and provide guidance. The kids do it all. Even the webpage I linked up top is done by the kids.

Most of the programs at the local schools are similar. My daughter is n JROTC. It works the same way. The kids do it all. The instructors mentor and guide. I've never seen the instructor do any of the inventory or other general clerical work. His thinking? Quote; "The kids are going to have to do this stuff when they graduate. They might as well learn now. I know how to do it. They don't."

Don't do your homework? You're out. Commit a crime? You're out. Underage smoking or drinking? You're out. The kids want to be there and it shows. Depending on the circumstance, the kid may get a second chance, but there is no shortage of kids wanting in the programs.

They are great programs and great kids who are in them.

TheStarr
October 15th, 2009, 12:17 PM
I have only been in the "industry" for a few years, my major experience came from the Air Force (Aircraft Mechanic).

Here is what I got out of all of this....

I started programming PLC because my company was in a bind, they needed things done NOW, and I figured it out. That was dangerous.

Luck played as much a part as thought, that I didn't hurt myself or anyone else.

It is sad to say, but most of my PLC knowledge comes from right here in this forum and from experimentation.

Should certification be required? Yes.

Should an apprenticeship be required? I think so. Just like a plumber or an electrician.

College courses, no matter how long or complete, can not prepare you for this industry. Only experience can make you safe.

And last... drum roll please......

Four sentences make a paragraph! Use the Enter key once in awhile!

I think I may be permenently cross-eyed after reading some of those novels!

Tech7
October 15th, 2009, 12:55 PM
Right on Goody! I guess the expert programmers are somewhat to blame for this "how hard can it be?" menatality. Sometimes we make it look way too easy to the layman or CE's. Don't worry though, as we get older it gets much more difficult. Heck, it's tough just getting out of bed and going to work some mornings

interd0g
October 26th, 2009, 03:13 PM
"The older I get, the better I was"

henry5674
October 26th, 2009, 03:59 PM
the thing that concerns me the most is this statement:

"Machines controlled by plc’s can injure and kill people if something is not programmed right!"

to clarify for any newbies reading this thread. a plc should have NO control over the safety systems of a machine, accept if it is a certified safety PLC. The worst case could be very expensive damage but no-one should get hurt. though your boss may beat the **** out of you afterwards!
What worries me is not the inexperienced playing with PLCs but the "i'll just wire my e-stops to the plc inputs and i'm done, whats a saftey relay anyway?"
Learning PLCs is only a small part of the overall role of controls and if you ask me should be studied after the basics of machine control and design especially safety regulations and requirement. Even a tech that is required to make small modifications should be fully aware of these before playing with the "Fun" PLC bit

CowDung
October 27th, 2009, 12:10 PM
the thing that concerns me the most is this statement:

"Machines controlled by plc’s can injure and kill people if something is not programmed right!"

to clarify for any newbies reading this thread. a plc should have NO control over the safety systems of a machine, accept if it is a certified safety PLC. The worst case could be very expensive damage but no-one should get hurt. though your boss may beat the **** out of you afterwards!
What worries me is not the inexperienced playing with PLCs but the "i'll just wire my e-stops to the plc inputs and i'm done, whats a saftey relay anyway?"
Learning PLCs is only a small part of the overall role of controls and if you ask me should be studied after the basics of machine control and design especially safety regulations and requirement. Even a tech that is required to make small modifications should be fully aware of these before playing with the "Fun" PLC bit

Perhaps in machine design, one relies on safety relays to keep people safe, but in process control, it's not necessarily that easy--improper programming can injure or kill people.

For example, a CIP (clean in place) system typically relies on prox switch inputs to verify that pipes/hoses are connected before allowing a specific circuit to be run. If the the incorrect address is used in the PLC for the prox inputs (or the programmer doesn't know enough to use them to inhibit the cycle), the pipe can be physically be open when the cycle is started and anyone in the area can be sprayed by hot caustic solution...

henry5674
October 27th, 2009, 02:45 PM
For example, a CIP (clean in place) system typically relies on prox switch inputs to verify that pipes/hoses are connected before allowing a specific circuit to be run. If the the incorrect address is used in the PLC for the prox inputs (or the programmer doesn't know enough to use them to inhibit the cycle), the pipe can be physically be open when the cycle is started and anyone in the area can be sprayed by hot caustic solution...

But surely if there is risk of injury from this, shouldn't those prox switches be keyed safety switches controlled by a safety PLC or safety circuit enabling the circuits? I only deal with the machinery directive which is a european directive so not a clue on the requirements in the US or on process control, I guess there is a whole different set of standards in that area.Surely when it comes to risk of injury or death the same basic ideas apply?

CowDung
October 27th, 2009, 03:15 PM
If that were really the case, why would they bother selling non-safety PLCs?

If the system is properly programmed and checked out thoroughly, those prox switches will do a fine job of keeping people safe without the added costs of safety PLCs and safety switches.

Pretty much any automated piece of equipment has the potential to hurt somebody. The idea is that the programmed system needs to be thoroughly tested and the inhibits/permissives verified before turning it over to the customer.

bernie_carlton
October 27th, 2009, 03:37 PM
Safety deals with people. If people are in proximity to functioning parts of the machine then it is the responsibility of all to ensure that actions which can harm those people cannot take place.

If the chance of injury or the probable degree of injury is slight then ordinary devices and logic can be used.

But as the risk rises so does the need to ensure that fail-safe devices and methods are used. With non-safety PLCs this means that the inhibit to the actions must take place outside the control of the PLC. Redundant safety switches and self checking safety relays need to be used in these riskier situations.

Let's also not forget that operator safety training and rigorous enforcement of safety procedures must be used. The 'forget the safety procedures - get production going' attitude must not be tolerated from anyone.

In the CIP system noted with the possible severity of malfunction as described, then probably keyed magnetic switches should be used leading to a safety monitoring relay. Only if all was in place would power be switched to the devices which can be switched on initiate the flow.

henry5674
October 27th, 2009, 04:15 PM
if there is a possiblilty of an inexperienced tech or newbie programmer causing injury from PLC changes then this should also be considered in assessing the safety requirements of the control system. there's always grey areas when it comes to safety control, even more reason for trainee students to be made aware that the safety control of a system should be studied and understood as well as PLC programming.

Scariest thing i every heard "don't worry about that power press , i'll change all those old yellow pilz relays for a neat little mitsubishi PLC"

Steve Bailey
October 27th, 2009, 04:26 PM
Scariest thing i every heard "don't worry about that power press , i'll change all those old yellow pilz relays for a neat little mitsubishi PLC"

Equally scary, in my opinion would be: "We don't have to worry about anybody getting hurt on that power press anymore. I just retrofitted it with safety switches and translated the program from the old Mitsubishi PLC into a new safety PLC".

Safety around machinery is a continuous, ongoing process. You are most at risk when you start to take the machine for granted and assume that you know it so well or that you've installed enough safety devices that you couldn't possibly get hurt around it.

Mrgumbo
October 27th, 2009, 04:33 PM
one simple case in point: the next time you have an offline project of RSLogix5000 opened up, try the little experiment shown below ... notice how incredibly easy it is to drag-and-drop something to those little green targets that light up even when you’re still SEVERAL INCHES AWAY from them ... for my money, it’s entirely too easy to make unintended changes to the program this way
and - if you fail to notice the change to your logic before the next time you fire up the machinery, what will happen? ... this could fall squarely into the “BAD” column on the giant clipboard of life’s little experiences ...

Ron, I actually watched someone "drag and drop" 2 rungs of logic into the recycle bin on the windows desktop from RSLogix5 without noticing it. :utoh: Always maximize the window, and don't be in a hurry. Lucky I was over his shoulder when that one happened.

henry5674
October 27th, 2009, 04:50 PM
Equally scary, in my opinion would be: "We don't have to worry about anybody getting hurt on that power press anymore. I just retrofitted it with safety switches and translated the program from the old Mitsubishi PLC into a new safety PLC".

Safety around machinery is a continuous, ongoing process. You are most at risk when you start to take the machine for granted and assume that you know it so well or that you've installed enough safety devices that you couldn't possibly get hurt around it.

obviuosly just wiring a safety relay in or translating a program to a safety PLC without thought or consideration for following correct assessments and standards can be just as dangerous which goes back to my point about training and understanding of machine safety requirements. The fact that people do take there machines safety for granted is why there is the need for proper safety systems,proceedures etc. And yes safety is ongoing hence regular inspections , re-risk assessments etc

Steve Bailey
October 27th, 2009, 05:10 PM
And that pretty much sums up the point of this thread. Based on some of the questions we get here all too frequently, too many people are being tasked with projects for which they lack sufficient training or experience. Either that or they think that a few hours on the simulator and a couple of posts on an internet forum qualify them to tackle the controls of systems that involve the transfer of large quantities of energy. Energy which can cause bodily harm and great damage if not properly contained.

If there is one leeson I would hope both the rookies and the experienced take away from this thread it is this:

There is no such thing as absolute safety. The best you can hope to do is to make your machine or less hazardous. Make sure you use the appropriate hardware and best practices that apply to your process, but don't be lulled into a false sense of security by having done so.

jlfrady
December 23rd, 2009, 01:49 PM
Amen to that!!! I have personnally seen the insanity that incompetent/untrained programmers can cause. It's amazing that companies don't see the liabilities of letting low/unskilled personnel program. I have seen a few very hazzardous conditions that were created by said novices. In one case a robot could very easily have reached out and "touched" someone, knocking them into their next life. the company said nothing even though I complained loudly when I was rectifying the situation. Can you say Lawsuit or Liability? There should be training standards in every factory or at least some sort of proficiency test before allowing someone to program on their own.

dwilson
December 23rd, 2009, 05:19 PM
This thread has been running for a while, and I haven't read it all.

But, we can't blame the newbies for all of s**t out there. Half a dozen machine in my last job were delivered with E-stop circuits running from/through the PLC, using NORMALLY OPEN contacts for the E-stop circuit ( as in, close contact to E-stop machine ).

That should make everyone cringe.

The integrator responsible is still in business. My boss at the time, an electrician, no less, agreed, but said it was too costly to re-wire the machines right now, they're in production, blah, blah.

They would have been delivered before Prestart Health and Safety Inspections became the order of the day, which has merely shifted the burden of compliance.

But I know that the people responsible for them now, are still tip-toeing around them to avoid opening the safety can of worms.

We had another machine come in complete with programmed PLC, from a sheet metal shop(!). There were no drawings, prints, backups, and, honestly, if they'd used a 'programmable relay', it would have gone un-noticed and probably worked better.

They used a MicroLogix 1000 that would fault every 1000 cycles or so because whoever didn't know what happens when your counter accumulator crosses the 32767 boundary.

jlfrady
December 23rd, 2009, 05:30 PM
That's funny. I was just asked to look over a set of prints from an "integrator" day before yesterday. The absolute first thing I saw was an "E-stop" wired with N/O contacts closing a relay (which had no seal-in)and the contacts of the relay wired in series with the power to the I/O cards on the PLC. I red flagged it and very carefully explained what could happen in that situation, then drew in how it should be wired in nice red ink. I told the manager that the guy who drew those prints was an amature at best and just plain ignorant in any case.

dogfart
December 23rd, 2009, 08:22 PM
baptism of fire

Mickey
December 24th, 2009, 12:16 AM
I told the manager that the guy who drew those prints was an amateur at best and just plain ignorant in any case.

And the manager said, "I drew those prints".

PhilipD
December 24th, 2009, 06:55 AM
Why does it matter if an E-Stop is wired NO or NC?

Thanks.

Jeebs
December 24th, 2009, 07:24 AM
Why does it matter if an E-Stop is wired NO or NC?

Thanks.

2 words:

Wire break.


Think about it and tell us what you've come up with.

PhilipD
December 24th, 2009, 07:42 AM
OK Jeebs,

I thought about this (and looked at a wiring diagram with a NC E-Stop) and I see why it should be wired NC. If a wire breaks it would be the same as pushing the E-Stop button and open the circuit -- the machine or process would stop. However, if it were wired NO and a wire breaks then nothing would happen. The circuit would be open, the E-Stop would be disabled and the machine or process would continue to run.

Sound good?

Jeebs
December 24th, 2009, 08:00 AM
It takes some people a few days, many drawings and lots of explanation to figure that out.

I've never had any classes on safety, nor anyone explaining it to me. I'm going mostly on my own views here.

The E-stop is a safety feature. It should work every time. If it doesn't work, the machine shouldn't be able to run. This is best achieved by using a NC-contact, for the very reasons you mentioned.

leitmotif
December 24th, 2009, 09:43 AM
2 words:

Wire break. Think about it and tell us what you've come up with.

The thinking of using a NO contact as a stop switch and considering a broken wire is a correct one. This is why stop switches are wired NC
HOWEVER
consider what I found with Cutler Hammer
the contacts were modular you just screwed on more contact blocks. A normally closed module is closed in the bin or box and it takes addition of an actuator ie stop E stop or whatever to make it switch to open.
SO in the case of an E stop where the actuator is damaged or jammed the E stop function would be defeated.

Dan Bentler

Lancie1
December 24th, 2009, 09:55 AM
The reason he was thrown off the conveyor is because he did something stupid - work on a machine that could have killed him without locking it out. This had nothing to do with programmng.I disagree. It did have something to do with programming. You are missing Goody's point. Sure, basic safety rules were violated. But the truth is that if the STOP control was in the STOP mode, then the conveyor should not have started. That was nothing less than an error in the programming. I see that all the time these days and it sacres me that newer programmers do not understand the need for a STOP function that does STOP the equipment and keep it stopped.

They rely way too much on the separately wired safety stops. I don not consider that a smart practice.

OZEE
December 24th, 2009, 09:59 AM
I don't usually disagree with you Lancie, but...

Without having the conveyor locked out, how would he have been protected from someone restarting the conveyor without knowing he was on it? You're right -- a STOP mode should be STOPPED. But when it comes to safety, you must not rely on programming and other people making right decisions. The only way to absolutely know it's safe is to hard-wire lock it out.

Lancie1
December 24th, 2009, 10:16 AM
Ozee,

I agree that the conveyor should have been locked out. But we all know that people do dumb things, like "this will take just a minute, and nobody else is around, so I am going to slip up there and adjust that sensor. The thing is stopped, so nothing is going to happen....".

In all Output rungs of a program for a machine, there should be a contact from the software Machine RUN that disables that rung logic if the machine is not in run mode. That sounds elementary to me, having first built relay logic panels where is was necessary to do it that way, but now very few programmers carry this over, instead relying on the legally required hard-wired saftey stop systems. IF safety is the goal, why would you put all your eggs into the Saftey Stop basket? What if it is not used?

Well, if you have all the legally required stuff, and someone gets hurt, you are okay, right? No blame can fall on you, but you could suffer just the same, lying awake at night thinking about that poor guy that would still have legs if you had put a few more instructions in your logic....

Legally safe is one thing, but guarding against the stupid moments of others, as you would want them to look out for you, is the way to make macines really safe in my opinion.

Why leave off some little instructions in a program that could prevent a injury? Preventing even one broken arm will justify the extra time. We know that if it can be done, someone will do it sometime.

OkiePC
December 24th, 2009, 10:29 AM
Ozee,

I agree that the conveyor should have been locked out. But we all know that people do dumb things, like "this will take just a minute, and nobody else is around, so I am going to slip up there and adjust that sensor. The thing is stopped, so nothing is going to happen....".

Where I work, we fire people for stuff like that. No exceptions, no 2nd chances. Everyone has a lock, and all machines have a readily accessible lockout point.

I don't disagree about having the PLC program keep things in a safe state as an additional measure of safety. One drawback to doing that, however, is that during safety checks performed by the operators, if there is a problem with a safety circuit, but the PLC monitor circuit stops the machine, the machine will act like it is supposed to when an e-stop is engaged, even though power could still be present. This can give a false sense of safety. So, you must be careful how the safety device check procedure is written to ensure that the actual safety circuit is validated, and not just rely on machine behavior.

Paul

OkiePC
December 24th, 2009, 10:35 AM
The thinking of using a NO contact as a stop switch and considering a broken wire is a correct one. This is why stop switches are wired NC
HOWEVER
consider what I found with Cutler Hammer
the contacts were modular you just screwed on more contact blocks. A normally closed module is closed in the bin or box and it takes addition of an actuator ie stop E stop or whatever to make it switch to open.
SO in the case of an E stop where the actuator is damaged or jammed the E stop function would be defeated.

Dan Bentler

I have seen that myself. E-Stop doesn't work, open the box and find the contact block dangling there behind the actuator...

That is one reason you are supposed to try to start the machine after pressing the e-stop button, and perform frequent checks of all safety devices...but those should never be relied on when performing maintenance...only minor adjustments and setup which is considered a part of normal operations..

I have also seen N.C. contact blocks that would open if they came loose from the actuator...don't recall the brand...

Paul

Lancie1
December 24th, 2009, 10:37 AM
Where I work, we fire people for stuff like that. No exceptions, no 2nd chances. Everyone has a lock, and all machines have a readily accessible lockout point.I think that is the normal punishment. But it works just like every other rule: the most frequent violators have learned how to get around the system, to not get caught, to do their bypasses when no one is looking, or at least no one that will turn them in. So don't kid yourself, unsafe acts are being done in your plant all the time. The key is not to depend too heavily on any ONE system, but use a combination of systems and PEOPLE working together.

I think the ugly truth is that many plants really don't care as much about the safety of their employees, as they do about meeting the legal safety requirements. Then when someone does somethig dumb like humans are likely to do, management can throw up their hands and and say, "not our fault, we had all the required safety systems in place." It is easier for a corporate board to enforce rules, but much harder for them to grow a heart.

OkiePC
December 24th, 2009, 10:53 AM
So don't kid yourself, unsafe acts are being done in your plant all the time.

Occasionally maybe, but no one is breaking the lockout rules. This place is the exception to the norm. We just gave away a 2010 Dodge Challenger for going 1,000,000 man hours without a lost time accident. That kind of incentive along with the one mentioned above tends to keep the safety culture here as close to perfect as I have ever seen. People will rat each other out over a $40000 prize! And everyone knows it...

Paul

Lancie1
December 24th, 2009, 11:10 AM
Paul,

Dangerous thinking. Nothing any risker than thinking everything is covered, and we are rewarding ourselves because we are so perfect.

Your plant is heading for a catastrophe, and everybody thinks the ship ain't got no holes....

OZEE
December 24th, 2009, 11:12 AM
Occasionally maybe, but no one is breaking the lockout rules. This place is the exception to the norm. We just gave away a 2010 Dodge Challenger for going 1,000,000 man hours without a lost time accident. That kind of incentive along with the one mentioned above tends to keep the safety culture here as close to perfect as I have ever seen. People will rat each other out over a $40000 prize! And everyone knows it...

Paul


CONGRATULATIONS TO YOUR PLANT, OKIE!! That is not an easy achievement.

Within our company, we have an ever improving safety culture, too. Yes, Lancie, I'm not so naive as to believe that every rule is followed every time -- Quite often, when there IS an injury it was due to not following the safety rules. But, we have several locations that have now achieved several years without a lost-time injury -- and that comes by working safely every time.

And, Lancie, I absolutely agree with you! As engineers/programmers/techs, we need to give the people who use our systems every possible chance to work safely. Though we've never met, I have a great deal of respect for your skills -- but I'm still not counting on your programming to provide for my safety. If I'm entering a danger-zone, my lock will be on the disconnect. And if you're working with me, so will yours.

Lancie1
December 24th, 2009, 11:28 AM
Quite often, when there IS an injury it was due to not following the safety rules.Good point, and that sums up my main point. Is it too easy of a cop-out to say "we got rules, and if you don't follow them you are on your own"?

Most accidents in the present time WILL be the result of not following the safety rules. The question is, how can THOSE accidents be prevented?

Certainly not by implementing more rules. More rules will simply mean that more accidents will fall into the category of "caused by not following rules". It is going to take a holistic approach, a lot of small things applied together. Education of employees about how an injury will affect their lives personally, how it will affect their co-workers, and so on.

But small changes in the PLC operating program are very easy and very cost-effective.

OZEE
December 24th, 2009, 12:04 PM
But small changes in the PLC operating program are very easy and very cost-effective.

... and not recognized by OSHA as being "SAFE"

TurpoUrpo
December 24th, 2009, 12:48 PM
But does it need to? just add more safety above the demanded by regulations.

Why to make dangerous programs, becouse some regulations dont demand you do safe programs?

OZEE
December 24th, 2009, 01:34 PM
No, it's not a problem to add MORE safety -- but you cannot absolutely guarantee that PLC code will keep somebody from getting hurt. Having PLC provide a STOP mode where stuff is absolutely stopped is a great idea. BUT it won't keep somebody from starting a machine that your walking on.

TurpoUrpo
December 24th, 2009, 02:02 PM
Ofcourse not, but its better tha plc not providing absolute stop when at stop.. As stated before, there will always be ppl using shortcuts.

Alan Case
December 24th, 2009, 06:01 PM
Congratulations on a million hours.
I hope your plant is not like one I went to once where they were proud of the no days lost record.
There seemed to be a lot of people hobbling around with crutches. Going to the hospital did not count as a lost day, then you had to return to work and count paper clips etc.
Regards Alan Case

Lancie1
December 24th, 2009, 06:37 PM
Right on, Plcs programs are not recognized by a government bureaucracy as promoting their goals. What credit could a government safety organization take for someone else's program? Many of the OSHA goals are first orginated by a company selling safety devices, thus the latest deluxe triple-redundant device is always better than last year's version.

As for protecting the guy on the plant floor, if you depend solely on a government-dictated program, you are never going to be safe, just legal. In many plants the safety program exists as a legal excuse to go ahead with business as usual, even though the training says "no, we are really worried about your safety". If they really are concerned about your health and safety, you will see the emphasis also outside the safety program, not just insdie it.

leitmotif
December 24th, 2009, 07:23 PM
Right on, Plcs programs are not recognized by a government burreacy as promoting their goals. Many of the OSHA goals are first orginated by a company selling safety devices.

As for protecting the guy in the plant floor, if you depend solely on a government-dictated program, you are never going to be safe, just legal.


Based on 20 years experience in safety and health work:
1. there were myriad rules and regulations and guidelines before OSHA came into effect in 1970. Some included ANSI, SAE, ACGIH, ASSE, etc etc etc.
2. MAny employers did not even know what they were much less follow them
3. OSHA was not pushed in by safety companies but was pushed in by labor.
4. New OSHA rules are not pushed by the safety equipment companies. As examples Mine Safety Appliance and Scott (maker of SCBA) were in business long before OSHA and still do not need OSHA to stay in business. A fair amount of their business is the fire departments who switched to SCBA in 1955 to 1960 era.
5. New OSHA rules are heavily fought by industry. Example the ergonomic standard - I gave up on keeping track of that.
6. Most OSHA inspectors know very little about electricity - same for state program inspectors. That was teh way it was in 1980 - I did most of the electrical fatalities in Portland OR and yes I checked recently here in Washington.
7. I completely agree with Lancie that compliance with OSHA results in mostly a paper tiger. the empahsis is on record keeping which is easy to inspect and easy to verify compliance. Besides the inspectors dont have to go out there in teh heat dust and dirt.
8. Employers squak about penalties. Here at a marina a guy got a leg burned off when contact 13,000. Penalty was 1000 for that and 9 thou for completely unrelated items. 10 thou for a leg?? I agree with my Dad they should have the doors nailed shut for 30 days and top management continues payroll out of their pockets. You would see safer work places if a few more Cxx's and Prez did some jail time for killing and maiming employees.
9. Yes employees do stupid things even when they know better. Lady I know chopped off a hand in a saw and still does not know why she did it after 5 years on those machines.
Yes I went to clear the exhaust chute on a running lawn mower - only felt the wind of the blade. Decided to shut it down and continue drinking my beer.
10. Having people come to work on crutches is in many ways a good thing - keeps insurance cost down, some really do want to work, and does keep them active and reduces depression. With good competent physicians writing good work releases overall it is a good thing but for sure can be abused by both employer and employee.
11. We had a safety awards program at Boeing but found after a year or so employees were not declaring injuries because crew would lose their safety prizes. So they stopped it only because the criteria of an injury when you get down to it was just a piece of paper and basically a worthless one at that.
I let a nurse write up one when I went to see a Boeing doc to get a fiberglass sliver from my boat pulled out of a finger - non work related I thought - there was hell to pay when the form hit our outfit probably because they could not figure out how to classify it oh Lawzy the consternation and confusion I caused.
12. E stops should be designed to protect the machine and to shut it down to reduce injury. Machine should slow and shut down as quick as possible and IF POSSIBLE AND SAFEST place all moving parts in zero energy state (bleed compressed air, put rams on bottom of stroke etc etc). E stops should dump all main power and interrupt outputs on PLCs where they can. Lock out tagout TESTOUT will prevent many injuries but not all. 13. Navy electrician school 1968 taught us to NEVER trust controls - tag it out ALWAYS.

Dan Bentler

silva.foxx
December 24th, 2009, 07:32 PM
This place is the exception to the norm. We just gave away a 2010 Dodge Challenger for going 1,000,000 man hours without a lost time accident. That kind of incentive along with the one mentioned above tends to keep the safety culture here as close to perfect as I have ever seen. People will rat each other out over a $40000 prize! And everyone knows it...

Paul

Hey... don't mean to be negative... but how many cover-ups and near misses got away from an LTA, especially when a fantastic record is on the horizon?

Maybe you work in cotton wool packing industry, I don't know.
.

leitmotif
December 24th, 2009, 07:35 PM
Hey... don't mean to be negative... but how many cover-ups and near misses got away from an LTA, especially when a fantastic record is on the horizon?

Maybe you work in cotton wool packing industry, I don't know.
.

SILVA

Please define cotton wool packing.

Dan Bentler

silva.foxx
December 24th, 2009, 07:55 PM
Maybe its a low risk environment...









I'm naive... maybe cotton wool, as soft and lush and fluffy and unoffensive as it is, takes lots of safety risks due to high speed high danger moving parts to put it into fragile soft plastic sleeves with delicate string ties.

dwilson
December 25th, 2009, 08:58 AM
I thought about this (and looked at a wiring diagram with a NC E-Stop) and I see why it should be wired NC. If a wire breaks it would be the same as pushing the E-Stop button and open the circuit -- the machine or process would stop. However, if it were wired NO and a wire breaks then nothing would happen. The circuit would be open, the E-Stop would be disabled and the machine or process would continue to run.

Sound good?
Exactly. But in the PLC case, it could be programmed either way, if someone uses the PLC as an MCR control (not good idea).
Think contact block coming loose from switch frame. In the PLC example, think blown control fuse and N/O stop contact( seen this one, machine keeps chugging along!).

No power (on control cct) = No stop signal.

On newer machines (in Canada, anyway), E-stops are supposed to be twist-to-reset now. How many have seen these switches, loose in their mounts because they weren't tightened correctly upon installation. Open them up and the wires are twisted into a knot, or the contact blocks are loose.

Jlfrady's example isn't as bad as it sounds, though I doubt it would pass safety inspection. At least it used a hard wired control of the PLC's output power. I think his point is that releasing the E-stop is not allowed to re-start the machine i.e. you should have 2 button control.

PeterW
December 25th, 2009, 09:10 AM
Going back to the original, there's no problem in a stopped line being automatically re-started as long as there are signs to state this and a warning sound before restart.

Anyone who decides to work on 'live' equipment in a gung ho way deserves what they get. Its the Darwin effect.

TurpoUrpo
December 25th, 2009, 11:32 AM
In Europe, after e-stop event, e-stop circuit needs to be reset from second button. It is not allowed to self reset when e-stop button itself is reset.

PeterW
December 25th, 2009, 11:44 AM
In Europe, after e-stop event, e-stop circuit needs to be reset from second button. It is not allowed to self reset when e-stop button itself is reset.


I was shocked when I first come over here and found the operators pressing an e-stop to walk on a conveyor (20 feet up) to clear a jam, then walk back, get off, pull the e-stop back out and the line restart. :scratch:


After any fault, the fault should have to be reset and the system restarted.

In normal operation though conveying systems can go into 'energy save' and restart without warning.

The systems are automatic after all.

leitmotif
December 25th, 2009, 05:51 PM
QUOTE I think his point is that releasing the E-stop is not allowed to re-start the machine i.e. you should have 2 button control. UNQUOTE

I believe every machine I have worked on was wired such that resetting E stop restarted machine. I have never liked that and believe it is indicitive of cheap short sighted management who really do not care about employee safety.

Dan Bentler

Alan Case
December 25th, 2009, 06:59 PM
Here the regulations state that re-setting an E Stop is not allowed to restart the machine. There shall be one reset button that should if possible be placed in a location where all the affected machines are visible. The E Stop needs to be reset then the operator needs to press the master reset button.
Regards Alan Case

S7Guy
December 26th, 2009, 08:27 AM
I believe every machine I have worked on was wired such that resetting E stop restarted machine.

It must be industry specific. I have worked everywhere north to south and east to west, and have never seen that. Nearly every installation I've seen uses something like a Pilz safety relay to make sure the machine's control power has to be explicitly reenabled and the machine restarted.

OkiePC
December 26th, 2009, 11:42 AM
. . .Your plant is heading for a catastrophe, and everybody thinks the ship ain't got no holes....

I have no idea what I said that would cause you to make a statement like that.

Hey... don't mean to be negative... but how many cover-ups and near misses got away from an LTA, especially when a fantastic record is on the horizon?

Maybe you work in cotton wool packing industry, I don't know.

It's a meat packing plant. We make about 900,000 lbs of burger and sausage patties per day.

There could be some near misses that don't get reported. I am not naive enough to think that never happens. Our biggest issues are slips and falls and repetitive trauma, but the production folks and safety dept. do all they can to minimize those. We also have cameras monitoring nearly all parts of the plant, so when there is an accident, they always can go back and review the footage to corroborate the reports. Everyone knows they're being recorded too, so that helps keep people honest and following procedure.

The point I was trying to make was that if you follow lock out tag out properly, then no matter how poorly the PLC program (or even the safety circuit) is designed, you can still safely work on it.

Okay, sorry for getting off topic.

Paul

Alan Case
December 26th, 2009, 07:27 PM
One thing that always worries me is the safety contactors.
Our regulations say that safety contactors have to be as far as practicable not easily defeatable. I have seen many contactors that claim to be safety rated that can be manually energised by pushing the contact block via the front panel. The AB ones can't do this but you can manually energise them by on the side .

Scenario:
Machine uses a Pilz system that drops out the 2 in series safety contactors.
This is done via a lockable isolation point at the machine.
Guy locks out machine and starts to work on it.
Electrician working in switchboard decides to power up a separate machine for testing by holding in the safety contacors. He makes a mistake and pushes in the wrong set of contactors therefore inadvertantly livening up the machine that is tagged out.

Where I work a lot of people call me anal but I always glue blanking plates over the side actuation points of AB safety contactors and will not use a so-called safety contactor that can be energised by a screwdriver from the front.

Regards Alan Case

leitmotif
December 26th, 2009, 07:38 PM
One thing that always worries me is the safety contactors.
Our regulations say that safety contactors have to be as far as practicable not easily defeatable. I have seen many contactors that claim to be safety rated that can be manually energised by pushing the contact block via the front panel. The AB ones can't do this but you can manually energise them by on the side .

Scenario:
Machine uses a Pilz system that drops out the 2 in series safety contactors.
This is done via a lockable isolation point at the machine.
Guy locks out machine and starts to work on it.
Electrician working in switchboard decides to power up a separate machine for testing by holding in the safety contacors. He makes a mistake and pushes in the wrong set of contactors therefore inadvertantly livening up the machine that is tagged out.

Where I work a lot of people call me anal but I always glue blanking plates over the side actuation points of AB safety contactors and will not use a so-called safety contactor that can be energised by a screwdriver from the front.

Regards Alan Case

If pushing a contactor manually will result in movement of a machine while someone else is working on it then lockout tagout was not properly done
OR
the disconnect does not disconnect all power. If so then machine should be labeled for how to completely put it in zero energy state including multiple disconnects for electrical, pneumatics, hydraulics, recirc water etc etc etc

Dan Bentler

Alan Case
December 26th, 2009, 08:15 PM
Hi Dan.
If you study a cat 3 or cat 4 safety circuit you will see that the disconnect from the power is 2 safety contactors in series controlled by a safety relay. Now with the isolator attached to the safety relay tagged out we would assume there is no way for power to get to the machine. Normally this is the case until someone with nothing more than 2 pens manually energises some so called safety contactors. The machine should not start but it will be energised ready to start if the start circuit is activated.
Regards Alan Case

PhilipD
December 26th, 2009, 08:27 PM
Alan,

I'm not sure about the standards and regulations in Australia. Here in the US we are covered by an OSHA (Occupational Safety and Health Act) standard. Part of this standard, with a few exceptions, is as follows:

1910.147(c)(1) (http://www.osha.gov/pls/oshaweb/owalink.query_links?src_doc_type=STANDARDS&src_unique_file=1910_0147&src_anchor_name=1910.147%28c%29%281%29)Energy control program. The employer shall establish a program consisting of energy control procedures, employee training and periodic inspections to ensure that before any employee performs any servicing or maintenance on a machine or equipment where the unexpected energizing, startup or release of stored energy could occur and cause injury, the machine or equipment shall be isolated from the energy source and rendered inoperative.


What this means is that it no matter how many buttons or contacters you push the machine cannot be started. ANY source of electrical, air, hydraulic or mechanical power must be removed.

Alan Case
December 26th, 2009, 08:54 PM
Hi. My point is "power is to be removed" can be satisfied by a safety relay controlled dual safety contactor setup. I think you will find that this setup will comply with your standards, though I am willing to be corrected if I am wrong.
What I am saying though is a lot of contactor manufacturers are claiming that their run of the mill contactors satisfy the requirements to be classified as safety contactors. ( the main requirements are that the auxillary contacts are positively guided) Part of the requirements of the standards (european standards) for a safety contactor is that it can not easily be defeated. (have a look at a pic of an AB safety contactor, the button on the front is only indication, pushing it does not move the contacts of the contactor)

For example a standard telemechanique/schneider contactor which in their docs claims to satisfy the requirements to be safety rated is a lot cheaper than an Allen Bradley safety contactor.
The Telemechanique contactor can be manually energised with nothing more than a pen or a screwdriver. The AB unit cannot be manually energised this way.
Now if the lockout/tagout system relies on these 2 contactors being de-energised then I am very duious about the integrity of the system when the system can be over-ridden by someone with 2 screwdrivers and 5 seconds to spare.

Regards Alan Case

leitmotif
December 26th, 2009, 08:59 PM
Alan
Will reply after each "little bit"

If you study a cat 3 or cat 4 safety circuit you will see that the disconnect from the power is 2 safety contactors in series controlled by a safety relay.
This in my mind what the Navy stressed highly
NEVER RELY ON CONTROLS. PULL THE MAIN POWER.
Even if the control circuit is still energized (which could be the case - for instance DC control power) with main power to motors pumps etc disconnected machinery will not run.


Now with the isolator attached to the safety relay tagged out we would assume there is no way for power to get to the machine. Normally this is the case until someone with nothing more than 2 pens manually energises some so called safety contactors. The machine should not start but it will be energised ready to start if the start circuit is activated.

Sorry I reserve the right to pull the main switch and kill all drive power and keep pulling switches until I am sure I am safe.
- you are NOT going to get me ground up in your machinery and end up in a cripple ward.
I dont care how many controls and safety designs you have. I have seen too many and investigated enough electrical fatalities - no thank you.

The above does not apply to testing and troubleshooting where you may have to have all or a portion energized - completely different set of circumstances and where in my mind you really need to know what you are doing and know the machine very very well. Have come a little too close on testing and troubleshooting a couple times.

A lot of peopl talk about OSHA here. What I find interesting is few mention that OHSA says employee has the right to refuse to do a dangerous task. That was a USA case that went to Supreme Court (I believe).

Dan Bentler

Alan Case
December 26th, 2009, 09:19 PM
Hi.
A lot of what I am talking about is related to Australia and may not be relevant to the USA.
If you read the European standards (on which our system is based) a 3 phase isolator does not count as a disconnect as a basic isolator is not able to be proven that it is off (if that makes sense)

I was at a sawmill once where the fitters were isolating a saw box via the 3 phase isolator before changing saw blades. I had to do something on the machine so I went to isolate it. The switch did not feel right. On investigation the switch was turning on the shaft and doing nothing. No idea how long it had been like that with the fitters changing blades with the saw box energised.
On my recommendation the trim saw box now has a Pilz PNOZ programmeable safety relay that monitors a 2 pole isolator.
When the isolator is off then the PNOZ de-energises the 2 series'd safety contactors that isolate the main power to the saw box. The PNOZ also looks at the positively guided normally closed set of contacts of both safety contactors and when it sees both of these contacts made and the isolator off it energises an indication lamp via a safety output of the PNOZ to indicate the machine is isolated. This method in A?ustralia is fairly standard for a cat 3 or 4 system. Where it can fall down is that someone can still manually energise the safety contactors if the correct safety contactors are not used.

There is another way here to do it and that is to have a 3 phase isolator that has a visible break between the contacts. The usually also have indication lights to show the disconnect status.

Regards Alan Case

leitmotif
December 26th, 2009, 09:29 PM
Think i am gonna chime in based on 20 years in safety where I closely worked with Facilities groups and from 40 years (off and on) as electrician.

E stops functions
1. supposed to be used only for emergency
2. shut whole machine down
3. place it in mechanical zero energy state.
4. Upon reactivation (?) ie pull the E stop back out is not supposed to restart the machine all by itself (very very common)
5. Supposed to kill power to the PLC inputs and outputs.
6. The exception to 5 is where PLC (and or VFD) is needed to accomplish zero energy state ie bleed off cylinder on punch and place ram at bottom.
7. After 6 is done then power to PLC input and outputs is killed (along with VFD)

I am doing this not to be the guru but to make double dang sure I understand this whole thing.

As far as the other stuff here are my thoughts
1. CERTIFIED means you paid the class tuition and were there at end to get the certificate.
2. LICENSED means you had the money and finally passed the test.
3. TRAINED almost same as #1.
4. QUALIFIED somebody said you know what you are doing
5. DEGREED you were able to take all the classes, pay the tuition and remember enough to pass the test. I know -- I have an AA BS and MS.

The above are pretty pessimistic definitions I admit. But the proof of the pudding from the above is when you investigate an accident. Yes they have all the paper required but they still screw up
- part of this admittedly is from being human - we are never I am afraid going to eliminate this aspect.

COMPETENT means you really know what you are doing and also what you do not know and find out before you really mess up. It also means you test your work for proper operation before the work can be called done.

Dan Bentler


Thought I would post this again

PhilipD
December 26th, 2009, 09:30 PM
Alan,

I'm no expert on this at all. However, in a totally isolated system (at least in the plants I have worked in, and that is not many) there is a mechanical disconnect that opens the incoming power. A padlock can be attached to this disconnect to prevent anyone from turning it back on. I don't think a safety relay could be used because there is no way to physicaly attach a padlock. The few safety relays I have seen in use have been attached to a door or gate to shut the machine off if anyone has to enter to clear a jam or make an adjustment.

PhilipD
December 26th, 2009, 09:33 PM
A lot of peopl talk about OSHA here. What I find interesting is few mention that OHSA says employee has the right to refuse to do a dangerous task. That was a USA case that went to Supreme Court (I believe).

Dan Bentler

Dan,

In the past 20 years I have only worked for three companies and none of them ever told me that. I would suspect it might be a fact they rather you not know.

leitmotif
December 26th, 2009, 09:39 PM
Alan
There is another way here to do it and that is to have a 3 phase isolator that has a visible break between the contacts. The usually also have indication lights to show the disconnect status.

I think we are discussing the same piece of equipment. Here in USA a disconnect often means a knife switch (I think you are calling this isolator) - more are coming on market with window to visibly see the blades are open. I open the disconnect to visually check them open after I had one with a welded knife - only seen it once in 30? years. the other means of de energizing power are circuit breakers of course. If remote operated I prefer to pull control power fuses and rack them out so they are physically separated from teh bus work. Pulling fuses is another way but I always had a hard time locking out fuse blocks so rely on tags.

Dan Bentler

leitmotif
December 26th, 2009, 09:43 PM
Dan,

In the past 20 years I have only worked for three companies and none of them ever told me that. I would suspect it might be a fact they rather you not know.

For damn sure you got that right. What is interesting is these complaints / cases are handled by US Dept of Justice (at least a while ago)

My feelings are if you cut my padlock (outside of a procedure) I am calling a cop for two reasons
1. to press charges - the cops I have talked to are not sure of charges either but appear to like reckless endangerment.
2. To make sure I dont beat you half to death with barb wire. Only half dead to let you recover so I can do it again to ensure adequate retention.

After that I may consider calling State Safety (Washington State).

Dan Bentler

Alan Case
December 26th, 2009, 10:08 PM
Dan. I agree with a lot of what you say (nearly all)
The visible disconnects are rare over here and a lot of machinery still just has a 3 phase isolator that the operators lock out. Under our regs due to what I mentioned earlier this does not really count as a lockout point.

Padlocks here can only be cut off under certain circumstances. Usually the following and it is a written procedure of the site.
a) The person who has placed it has left site.
b) He is unreachable to return to site to remove his lock.
c) His supervisor, the work area foreman and the safety officer agree that it is safe to remove the lock.
d) His supervisor is to advise him at the start of his next shift that his lock has been removed.

Phillip. On either a combination of safety relays or a programeable safety relay it is possible to fit a 2 pole isolator that feeds into the safety relay. This isolator that is placed adjacent to the machine is able to be tagged out.

Regards Alan Case

leitmotif
December 26th, 2009, 10:33 PM
Alan

What is good for USA does not mean it is good for the world. Yes we had Edison Westinghouse and Tesla but they were not the only ones developing electrical equipment.

Send picture of "isolator next to machine" please.

If you are able to physically insert something into a relay or contactor preventing contact closure and lock it out I would be real interested in seeing a photo of that.

Not all the bright ideas are USA made.

Dan Bentler

Alan Case
December 26th, 2009, 11:07 PM
Dan.
I probably did not explain it to well.
The isolator next to the machine is your standard normal 2 or 3 pole isolator.
I will relate the following description to the PILZ PNOZ Multi programeable safety relay.
The Pilz has 4 test pulse outputs called TP1, TP2, TP3 and TP4. These test pulses can be used as the power to feed the inputs.
(not the exact figures but TP1 is on for 30ms and off for 5 msecs. TP2 is on for 25msecs and off for 7msecs)

From the Pilz unit there are 2 circuits fed into the isolator and 2 returns to the pilz unit. These 2 circuits use a test pulse (each leg of the circuit uses a different test pulse) The programeable relay needs to see the correct test pulse at the correct input.
This ensures that water in the isolator or if a large chunk of steel drops on the cable and shorts all the wires together then the Pilz unit will fault and shut everything down.
Now we also feed the normally closed contacts in series of the 2 in series safety contactors into an input.
The Pilz unit has a dual in series monitored relay output.

Now if the Pilz sees that both safety contactors are off (by the input from the NC of the contactors) and it then sees the 2 inputs of the isolator become active with the correct test pulses and within a set time of each other ( this is to try and stop someone bridging out the isolator) it will energise the relay output. This relay output will pull in the 2 safety contactors and the Pilz expects to see the NC circuit open. (if it does not see it open it faults and shuts everything down)
When the isolator is turned off the safety contactors should open and the Pilz will again see the NC of the safety contactors. If a safety contactor has welded in then it will not open but the other one will.
This still isolates power but the NC of the safety contactors will not be seen by the Pilz. The Pilz will not allow the system to turn back on until the welded contactor is repaired and the circuit is seen.

Apparently the Europeans have done studies on the probability of 2 contactors welding in at the same time and the chance of that occurence is incredibly small.

I have been told that internally the Pilz uses 2 separate CPUs from 2 different manufacturers and the logic of both must agree before an output can be turned on.
There is actually nothing that fits into a contactor or relay to physically stop it energising.

Regards Alan Case

PeterW
December 26th, 2009, 11:28 PM
Talking of the fantastic North American E-Stop standards, how about the E-Stop zones!!!!

Another I could not believe (as much as the pulling out an E-Stop restarts the line).

Zones could be as little as 6 conveyors, E-Stops in a zone will only effect the zone. I've seen situations where an E-Stop is between two parallel conveyors and pressing it stops one set, the other continues to run.

I always envisaged some poor chap having his arm ripped off whilst some guy 30ft away goes between E-Stop and E-Stop, vainly trying to find one that stops the target one.

leitmotif
December 27th, 2009, 10:40 PM
Well a bit unrelated maybe but I think appropriate to the thread

Examiners from Britain's Health and Safety Executive, inspecting bowling alleys for hazards, considered recommendations (according to a November Daily Mail report) that included erecting barriers over the lanes to prevent bowlers from wandering the alleys and perhaps getting caught in pin-setting machines or, feared one inspector, bowlers injuring themselves trying to knock over pins by hand. The barriers would leave space for the ball to roll under. [Daily Mail, 11-30-09]

Dan Bentler

silva.foxx
December 28th, 2009, 12:07 PM
Examiners from Britain's Health and Safety Executive, inspecting bowling alleys for hazards, considered recommendations (according to a November Daily Mail report) that included erecting barriers over the lanes to prevent bowlers from wandering the alleys and perhaps getting caught in pin-setting machines or, feared one inspector, bowlers injuring themselves trying to knock over pins by hand. The barriers would leave space for the ball to roll under. [Daily Mail, 11-30-09]



Why are we protecting idiots and stupidity?

If Norman Numbskull wants to put his hand in a pin-setter, let him!

- Don't put your finger where you wouldn't put your pecker -

We still don't have finger-proof grilles over gas fires or a safety guard around gas cookers either. Let the pricks act as pricks and take responsibility for there own actions; they wouldn't do it twice! :mad:

Everything is "... let's blame everyone else but us!"

PeterW
December 28th, 2009, 12:21 PM
Why are we protecting idiots and stupidity?



On the North American continent no-one assumes responsibility for their actions, any accident has to be the problem of someone else, this I presume is down to the lawmakers giving out stupid compensations for people tripping over cracks in the road etc.

This is not a critisism of our American cousins, its just the way it is through no fault of the man in the street.

We've laughed at things we have seen over numerous years and cannot believe some of the payouts for gross stupidity of some people where they blame someone else for them doing something stupid.

The fault is with the lawmakers, wher in Europe some things would get laughed out of court, in North America they pay out large sums.

Someone said on this thread, no matter how stupid people are the programmer should ensure that certain things cannot happen (words to that effect, I can't be bothered to read back for it).

Programmers cannot take into account how stupid some determined people can be.

The emphasis for safety MUST START WITH THE PERSON DOING THE WORK.

silva.foxx
December 28th, 2009, 02:05 PM
Going a little OT here: I remember hearing about a US citizen tootling along in their motorhome, put it in cruise-control on the highway and went into the back leaving no-one at the wheel. This resulted in a crash. They got paid out because the manufacturers of the motorhome failed to put in the manual that you can't leave the driving seat when in cruise-control!!! What an a$$hole to think the thing could drive itself but what a to$$er the judge was to rule it wasn't his fault. I'm sure the lawmakers are in on the $$.



PeterW: http://www.skysports.com/football/league/0,19540,11687,00.html

harryting
December 28th, 2009, 02:37 PM
http://www.snopes.com/autos/techno/cruise.asp

PeterW
December 28th, 2009, 02:38 PM
Going a little OT here: I remember hearing about a US citizen tootling along in their motorhome, put it in cruise-control on the highway and went into the back leaving no-one at the wheel. This resulted in a crash. They got paid out because the manufacturers of the motorhome failed to put in the manual that you can't leave the driving seat when in cruise-control!!! What an a$$hole to think the thing could drive itself but what a to$$er the judge was to rule it wasn't his fault. I'm sure the lawmakers are in on the $$.



PeterW: http://www.skysports.com/football/league/0,19540,11687,00.html


I was going to mention that one, but was unsure if it was urban myth.

One that isn't was McDonald's being sued over someone tipping their tea over themselves, apparently it shouldn't have been hot.



6th going into the new year, that was not expected at the start of the season. Ref spoiled the game today for us, had to laugh at the blue cousins up the road though throwing away a 4 goal half time lead. :)

PeterW
December 28th, 2009, 02:39 PM
http://www.snopes.com/autos/techno/cruise.asp


:yeah:

PhilipD
December 28th, 2009, 05:53 PM
- Don't put your finger where you wouldn't put your pecker -

Reminds me of an old joke. Man comes home and tell his wife, "I got fired today." She asks, "Why?" He replys, "I put my pecker in the pickle slicer." The wife says, "Were you hurt?" "No.", was the answer. "What happened to the pickle slicer?", she inquires. "Oh, she got fired too."

By the way, not everyone who makes a mistake is an idiot. Even you pooped in your pants at one point in your life.

Lancie1
December 28th, 2009, 09:29 PM
The emphasis for safety MUST START WITH THE PERSON DOING THE WORK. I agree completely. When you write a program, you are the one doing that part of the work, so you should make it as safe as you know how, regardless of all the other safety features that may be (or may not be) added later....

Lancie1
December 28th, 2009, 09:47 PM
One that isn't was McDonald's being sued over someone tipping their tea over themselves, apparently it shouldn't have been hot.

Let us not add to the urban legends. It was in America, so it was coffee, not tea. We only use tea to have tea parties.

The fact that McDonalds coffee was (but not still) deliberately held about 30 degrees hotter than any other coffee AND the fact that they refused to initially just pay for the cost of Mrs. Liebecks medical bills made a big difference in how the jury saw the case.

http://en.wikipedia.org/wiki/Liebeck_v._McDonald's_Restaurants

In the American court system, where laws are written and applied by lawyers and judges who are ex-lawyers, and a jury is involved, a large "rich" multi-national company will always have to pay for events that otherwise would just be accidents.

It is interesting that the same type of charge against McDonalds (tea too hot) failed in the British courts.

PeterW
December 29th, 2009, 07:01 AM
I agree completely. When you write a program, you are the one doing that part of the work, so you should make it as safe as you know how, regardless of all the other safety features that may be (or may not be) added later....


When you write a program, you DO NOT write it with personel safety in mind (exceptions being perhaps when you are dealing with dangerous materials), when you design the control system you have safety in mind.

When you write a program, you have sequencing, interlocking etc in mind. As part of this you think more equipment protection, not allowing things that can foul up the equipment.

Safety of personel is achieved by physical protection or hard wired interlocks.

The OP chose an example of incorrect programming that could endanger someone, when the example he gave was of stupidity by someone who should of known better and what could be a valid piece of software.

I have worked on and designed systens that automatically restart themselves, both after a stop pushbuton has been pressed and when the system shut itself down.

They are after all AUTOMATIC systems.

Anyone working in areas must know the dangers in those areas and must act responsibly.

There is a difference in doing something we have all done, i.e. clamber over a 'live' conveyor and climbing onto a'live' conveyor to start working on it.

What I would say, where a system has been stopped by the pressing of a stop pushbutton, on automatically restarting, there should be a warning lamp and horn sounded, to let people know.

Where the line has automatically stopped (i.e. energy save), this can restart without warning and the appropriate signs should be displayed to warn of this,

People working in the areas have to be aware of dangers and act responsibly to their own safety.

Goody
December 29th, 2009, 07:04 AM
Just to remind people who are just starting to read this 'old' thread. It was not exclusivly about safety and E stops and 'locking' systems out.
Neither was it about seasoned programmers forgetting that they too were once new boys.
There seems to have been a lot of clucking and indignation about the above two subjects.
In fact the system and situation I originally wrote about had all the correct E stops and safety relays but in this case, the conveyors were just stopped by a normal stop button.

I know full well the safety implications involved but the point was that these conveyors were programmed wrong.
They were in stop mode but a sensor being actuated started a conveyor - thus causing an unneccesary accident reguardless of the fact that everything should have been locked out.

In fact the plc program was complete rubbish with some unbelievable errors in it.

Hence my post and title.

ydtech
December 29th, 2009, 07:32 AM
I suppose it's a conveyor where if a box is shoved onto one end of it, it runs long enough to deliver the goods on the other end and then stop. But yes, the sensor in no way should over-ride the stop condition. That's a major goof and should have been caught at the latest at set-up and test.

PeterW
December 29th, 2009, 08:13 AM
I suppose it's a conveyor where if a box is shoved onto one end of it, it runs long enough to deliver the goods on the other end and then stop. But yes, the sensor in no way should over-ride the stop condition. That's a major goof and should have been caught at the latest at set-up and test.


Not always true, the point I was making.

TurpoUrpo
December 29th, 2009, 09:30 AM
Peter, i see it this way:

Stop mode, everything stopped. No automatic restarts.

Auto mode, everything can either run or be in "stop".

Stop should mean STOP. No excuses on that.

ydtech
December 29th, 2009, 11:19 AM
Peter, I agree with Urpo. In stop mode it must stay stopped at all times, no matter what. If the sensor can start it automatically that's some other mode, call it auto or whatever, but not stop.

Anyone working in areas must know the dangers in those areas and must act responsibly.

Not necessarily. Even smart people can do silly things if they don't know all the details.

Someone seeing the switch in stop mode may think it's safe to clamber up on the end of the conveyor to rest his bum and ends up whisked away into the great unknown.

PeterW
December 29th, 2009, 11:35 AM
OK an example, actual as seen at an Airport near you..

Last flight all bags delivered, a local stop is pressed to shut down without waiting for energy save.

Morning comes and systems initiated, bags start to be loaded into the system, a bag requires a route to a flight where the conveyors are still stopped. On the bag approaching the area, a START is sent, the local sirens come on and lights flash, then after x amount of seconds, the conveyors start.

Passenger lands at holiday destination, happy his bag is with him.

PeterW
December 29th, 2009, 11:36 AM
Not necessarily. Even smart people can do silly things if they don't know all the details.


Then they should not be there.

Tom Jenkins
December 29th, 2009, 11:43 AM
If you make a system idiot proof, they just build a bigger idiot.

I believe that the system designer, the programmer, and the operator all have a responsibility to take reasonable precautions for safety - their own and the safety of others. To try to absolve any of the groups for responsibility is pointless.

The question is what constitutes "reasonable" precautions. That is a judgment call. A novice probably hasn't developed the judgement to anticipate reasonably probable safety or functional issues, or to determine reasonable preventive measures. Unforunately, that isn't preventing ignorant or irresponsible management from turning them loose in a dangerous world.

That, I believe, was Goody's original point.

It is true that the "kids" are not exercising good judgement, or even researching their systems properly. The main fault, in my opinion, lies with the management that puts them in a position of responsibility for which they are not close to being ready.

PcRider
December 29th, 2009, 12:09 PM
The last plant I worked at had a "master key" that the on duty maintenance supervisor controlled. It consisted of a 5 foot long pair of bolt cutters. We never found a lock it couldn't open.
PcRider

ydtech
December 29th, 2009, 01:38 PM
[...] systems initiated, [...] the local sirens come on and lights flash, then after x amount of seconds, the conveyors start.

I think we're thinking of entirely different systems. It still neeeds a maintenance mode where everything stands still until manually told otherwise. Anyway, it seems to me we're mainly having a difference in nomenclature.

What I figure Goody's talking about, and I have been on similar systems, is a conveyor where if something is placed on one end it starts up immediately, transports the goods to the other end and if no new material has been added stops after a time-out.

In my book that's auto mode, stop mode locks out the sensor and everything else. Otherwise the new material may be someone wishing to rest his bum and thinking the stop setting means just that.

Lancie1
December 29th, 2009, 05:22 PM
In my book that's auto mode, [where as] Stop Mode locks out the sensor and everything else. Otherwise the new material may be someone wishing to rest his bum and thinking the stop setting means just that.I agree. That is my whole point in a nutshell.

xetrov123
December 29th, 2009, 06:24 PM
My problem is a little different. I started as an apprentice in the shop and spent the first year asking ALOT of questions and testing. I wrote a program to replace a failing pump controller after eight months, and asked alot of questions. Now that I have been doing this for four years, I am writing most of the new programs for the plant and off site stations. But I am STILL asking questions and throwing ideas around to the shop.

Now, because of politics, industrial electricians with NO PLC experience are going to be able to program and troubleshoot programs. The electricians are SURE that the PLC is "just" an electronic relay system and that it would be no big deal to learn how to program.

It is amazing how a lack of understanding and the overwhelming desire for the "Easy Button" will cause so much harm. :hmmm:

coolasad14
February 8th, 2011, 07:54 AM
I have just Recently graduated & started working in an Automation Company where the guidance from seniors is great. Also this Thread has been a great disciplining ground for me and have made me aware of the responsibilities of an Automation Engineer regarding safety.
I have not started working on real life PLC programming yet & am working on logixPro software for learning simulation sand in my brief experience I have found Implementing Manual Stop to be the most Tricky and diffcult.

Goody
February 8th, 2011, 09:24 AM
Coolasad, I am glad you opened a 2 year old thread. maybe lots of people new to this site will read it for the first time.

I have re-read nearly every post again and was glad of the 'refresher' course. It should be read by eveyone who enters here.

Lancie1
February 8th, 2011, 09:38 AM
Goody, this thread is a classic, and should be refreshed again from time to time.

albertabound
February 8th, 2011, 01:30 PM
Hello all. I am new to the site, and found this thread interesting on many aspects, mainly because I might be considered a 'risk' as many see it.

My history is 25 years as a Journeyman Millwright, 4th year Electrical apprentice, with a number of years of supervision, maintenance management. My interests are varied, but I've spent many years on controls, embedded, drives, troubleshooting, and am very happy over the last few years to be diving into the PLC world. I've worked with GE Fanuc Cimplicity, AB ControlLogix and SLC500.

I'm a stickler for technical documents, more specifically for the understanding. I consider carefully the implications of my actions. But make I make no bones about the fact that I'm learning, and experience comes with fault.

There's a saying that I use occassionally, 'one man's logic is another man's frustration'. I personally love the cut and paste, structured text and data structure that closer resembles my native embedded 'C'.

In the end, what I wanted to say was that I'm a new PLC programmer, self taught at that. I am backed by a lifetime of industry on many levels, understanding the implications and interactions.

The other thing was that many of the posters declare Jman Electrician as a prequalifier to understanding the PLC and it's implimentation. That is equally dangerous.

Robb B
February 15th, 2011, 08:25 PM
I just wanted to add my bits in too. I am currently a 4th year Industrial Electrical Apprentice, and only recently have begun dealing with PLC's at work and school. My current employer began my introduction to PLC's by having me print off reports, do a bunch of descriptions on rungs and bits from paper copies, and establishing communications for the various PLC's and their cabling, drivers, etc. I have a strong background in computers and networking, and am very eager to keep learning this new world of controllers. I have a very strong respect for the work and learning that those who came before me have done, and are willing to pass on. I do agree with the general idea of some sort of structured learning for PLC's, though it maybe need not be mandatory, which covered at least some of the basics such as safety controls, interlocking devices/sensors/motors, and communications. As a new learner of PLC's, I find this sort of knowledge is priceless, and very difficult to obtain!

kwires
February 16th, 2011, 04:22 AM
Great thread!
tons of valuable info and interesting opinions!

MarkNightingale
February 16th, 2011, 08:45 AM
Just to add my little bit to this excellent topic.

I think the best knowledge people gain are from talking to people who have experience and lots of it. To me this is why this site is so good.

I read an article earlier about Rockwell Technical support. When i have phoned them up sometimes you get a guy just out of college or school and has not got a clue and cant help. Then you get the guys who have been working in the field for 30 years and know exactly how to solve your problem..........why..........because they have seen it themselves, and how did they find out the solution........by asking someone.

Knowledge is there to be shared and there will be not one single person on this site where at one point they havent had to ask for advice or got stumped by something.

Not everything can be learned from reading books and manuals. If they covered every eventuality that you may come across there would be an encyclopedia just for a SLC 501.

Mark

MarkNightingale
February 16th, 2011, 08:53 AM
Just on a side note, there have been a few occasions where I have needed to find something out, spent hours trawling through manuals etc, then posted my problem on here and 10 minutes later got exactly the response I wanted.

Tmknh
September 2nd, 2011, 02:05 PM
I agree with the author of this thread. Anybody who can plug in to a PLC is now a "programer". The use of latch instructions (OTL) has become the standard. I even see people using the same output in multiple rungs. Try and debug that ****.
Why should we pay John with 20yrs experience when we can get Dave who took a class last year to do the same thing.
You can select Dave over John but sooner or later someone is going to loose a finger or worse.
Any idiot can change a timer or turn off a bit but it takes a lot of trial and error and a consideration of the big picture when changing or creating code, not just turn this on if that switch is made.


What's so bad about OTL's?

Matthias von Zorn
September 2nd, 2011, 02:24 PM
I think he is referring to the use of them on actual outputs as opposed to using them in internal request bits, program flow control, etc.

matt

DamianInRochester
September 2nd, 2011, 04:28 PM
What's so bad about OTL's?


There are a lot of things wrong with using multiple OTL outputs, especially when directly referencing a specific physical output. I have yet to see one clearly written, well organized, and robust piece of software using this technique.

The problem arises because it is simply too easy to abuse set and reset coils and develop code by trial and error and evolution. Just keep adding sets and resets everywhere until you can get the machine up and going.

These are the programs that suffer from the "have to power down and back up again to reset it syndrome". Any little thing that gets it out of sequence, and the whole house of cards falls to the floor.

Not saying it can't be done in a fashion that is professional, only that far more often than not programs written with that technique tend to be disasters to debug or modify.

To me, the traits of good programming are

1) Things are as sequencial as possible. The program is written in a way that it CAN'T get out of sequence. Plug up every hole.
2) Things are broken up into routines with very specific and clear purpose. The routines should be as modular as possible with as few interconnections to other routines as practically possible.
3) The program can be easily modified without the fear of one small and subtle change having a cascade of negative effects throughout the rest of the logic.
4) The logic can be easily and cleary reset without resorting to having a large percentage of the code dedicated to reset coils for every bit in the program.
5) Physical output coils are referenced in one and only one spot in the program.
6) The code is written in a fashion that makes it very clear and obvious where things stopped and why they stopped.
7) Good comments go a long way toward quick understanding.
8) Use consistent naming conventions and meaningful descriptions. (ie. If it is a double solenoid spring return to center blocking valve, then say so). Don't label it "Brake", and not indicate whether it is energise to engage or energise to release. Don't just label it "estop" without indicating what the NO / NC state reflects.
9) If it seems to complicated, your probably over complicating it. Keep it simple.


If these things are done, I really don't care about style.

Jeev
September 3rd, 2011, 03:12 AM
Given the continual addition to this thread, we recently had something happen that concerned me quite a lot. In some of our machinery, I have started designing with Programmable Safety Controllers/Relays such as the Flexisoft. Many of these projects, I have commissioned the safety myself regardless of whether or not I am doing the PLC/HMI development. A couple of weeks ago I was made aware of an issue on an installation (One of my sparkies had done the safety programming) where under a certain condition one of the Safety Zones would not trip :eek:

Needless to say, someone got some talking to and I'm about to invest some time in training/education with my staff. I've also gone back to programming the safety myself.

If you want something done right...

Tmknh
September 3rd, 2011, 08:22 AM
Agreed, many things wrong with multiple OTL's. Actually I just finished rewriting a program someone had written using about 10 OTL and OTU instructions to operate the same physical output. Needless to say, the machine crashed continuously. No problem though, it made me some $$ :)

The original post seemed to be condemning anyone who used even a single OTL as incompetent. Like everything else, OTL's have their place, if used properly. You provided some good examples of using them improperly. I've used OTL's many times to latch an error bit, then reset by MOVing 0 to the entire error word(s) via reset button or first scan. Whether this is proper or improper to other people, I really don't care. It's my style, it's easy to follow, and I've never had a problem. There's always more than one way to skin a cat, people on here continuously raving and getting their panties in a bunch if you don't do it their way, the One and Only.

I like your list of traits, especially #9. This entire list should be published somewhere.

bce123
September 3rd, 2011, 09:05 AM
i agree totaly dude and what about that guy ben franklin he could of killed himself with that kite!!!! What are these Novices thinking doing somthing they have never done before. They may as well be making a bucket list.what would happen if beer, wiskey and cigarettes were not made safely. Someone needs to be in charge of thee people to make sure they dont hurt themself. Everyone is a novice at one point in time!! thats why there are fourms like this. Just my novice idea on the matter, Steve

Lancie1
September 3rd, 2011, 09:46 AM
Tmknh,

I have seen Latches used by novice programmers to turn motors on, with a logic path so that the motor then could not be turned off. If self-sealing relays had been used, the OFF function has to be put on the same rung and fairly obvious if it is missing.

bce123
September 3rd, 2011, 10:02 AM
I have seen so called pros put e stops in the manual rutine and forget to include any in the auto rutine etc.... Whats the difference novice or pro people make mistakes. all anyone can do is due dillagence: there will allways be more dangerous people than the safe ones can control. JUst do your best and try and teach others to do the same. like the great nike said: just do it!

DamianInRochester
September 3rd, 2011, 01:08 PM
I have seen so called pros put e stops in the manual rutine and forget to include any in the auto rutine etc.... Whats the difference novice or pro people make mistakes. all anyone can do is due dillagence: there will allways be more dangerous people than the safe ones can control. JUst do your best and try and teach others to do the same. like the great nike said: just do it!


I think the primary point is, there are certain professions where the consequences of your mistakes have a much greater degree of severity.

Yes, everyone has to start somewhere. But here's the thing. Where do you draw the line?

If you are a barber and you make a mistake, then someone may just look a little silly for a few weeks.

If you're a surgeon and you mess up, well...... you may have just ended someone's life.

If your designing automated machinery, depending on what it is, you may very well have someone else's life and well being in your hands.

And that is the point. And that isn't to say surgeons don't make mistake -- they do. We all do. And that isn't to say that everything a rookie programmer handles has potential to kill someone either. It is to say, however, that certain tasks by nature require a greater level of professionalism in order to help minimize the risks. I doubt many people would feel comfortable getting in a plane with a self learned pilot, who is just having a go at it, and giving it his best.

In these types of professions, the mechanism for minimizing the risks is long and arduous training. Part of this traing may involve working on things that develop the necessary skills, without the consequences involved. Some of it involves apprenticeship or internship. And most of it involves some sort of testing for a minimal degree of competency so you can be accredited or licensed.

That being said, I don't claim to know where we should draw the lines for engineers in our fields. We are definitely not surgeons, but we are not musicians either. There are consequences related to how well we do our jobs. Any task that involves safety and well being should be held to a higher level of scrutiny by nature. There are some things that just giving it a good effort isn't good enough.

So when the plant manager decides to save a few bucks by letting his electrican program that new dial table instead of hiring a professional to do it, you need to ask yourself why it is then also not OK for American Airlines to promote one of their mechanics to being a pilot to save a few bucks as well.

And I am sure we have all seen the results of someone getting hurt on a machine. And often times, ironically, it is not because the machine was not designed to be safe enough. It is because it engineered so poorly, that did not work very well, and required the operators to be constantly going inside to monkey with something to get it back and running. They then bypass guards and such to circumvent downtime.

But I do agree, knowledge is meant to be shared. And we should all be dilligent. And we should all try as hard as we can.

bce123
September 3rd, 2011, 02:56 PM
So when the plant manager decides to save a few bucks by letting his electrican program that new dial table instead of hiring a professional to do it, i cant speak for the rest of the world but in TX. you have to be a licensed electrical contractor to install a new plc in a plant many companies dont know this. I work at plants all the time where manegement thinks just because they have a electrican on staff he can do anything electrical.our state laws state that a maint. electrican can only repair existing equipment not modify or install new equipment. not even run 10' of pipe for a new outlet. However this still takes place. I Myself am a Master electrican and an electrical contractor with over 30 years in the field.I have been around plcs back when we would back up our programs with a cassette recorder.windows were what you looked out of. My point here is that I have seen vetrans and rookies alike do some pretty stupid things when it comes to all typs of equipment. i have seen 1 person decapicated due to lack of folling L.O.T.O. and 1 person die from falling 3' on to his head and 1 person step through a hole in the grating 18 stories up. all this said some of the best programers I know were novice when they started. I hate to say it but novice or pro has nothing to do with it some people are just STUPID

DamianInRochester
September 3rd, 2011, 04:38 PM
i cant speak for the rest of the world but in TX. you have to be a licensed electrical contractor to install a new plc in a plant many companies dont know this. I work at plants all the time where manegement thinks just because they have a electrican on staff he can do anything electrical.our state laws state that a maint. electrican can only repair existing equipment not modify or install new equipment. not even run 10' of pipe for a new outlet. However this still takes place. I Myself am a Master electrican and an electrical contractor with over 30 years in the field.I have been around plcs back when we would back up our programs with a cassette recorder.windows were what you looked out of. My point here is that I have seen vetrans and rookies alike do some pretty stupid things when it comes to all typs of equipment. i have seen 1 person decapicated due to lack of folling L.O.T.O. and 1 person die from falling 3' on to his head and 1 person step through a hole in the grating 18 stories up. all this said some of the best programers I know were novice when they started. I hate to say it but novice or pro has nothing to do with it some people are just STUPID


And I know people who had died from lung cancer who have never smoked. And I know people who have lived to 100+ that smoked like a chimney their whole lives. But I still don't smoke, because I know that the difference is the risk pool I would be putting myself in. It's not about certainty, it's about probability. And odds are much better that a professional is going to give you a much safer/better result than a duffer is going to.

Again, Yes, everybody starts out a novice. Even the best, and nobody is arguing that. But when I see a comment like.....

"Whats the difference novice or pro people make mistakes. ... just do it."

I'm sorry but "Just do it" doesn't cut it for me.

Your logic can basically be summed up as follows:

Since you can cite specific instances where someone perceived to be an experienced professional has made mistakes and since the pros goof up from time to time, lets make it free game for anyone.

Here is your same logic applied to a different scenario:

The surgeon who worked on my heart accidently nicked one of my veins. So next time, I won't bother going to a surgeon, I'll just have my son Fred do it, He's always wanted to be a doctor.



I would also like to point out that experience alone does not mean "good". Age doesn't discriminate. I have seen just as many really bad engineers with 30+ years of experience as I have with less. Only difference is the ones with 30+ experience have just been making other peoples lives miserable for longer. Experience is only part of the equation. And when I speak of letting a professional do something, I don't just mean someone who has been doing it for a long time. I mean someone who is actually good at it. Someone who not only tries hard, but also has the skill.

So you also have to define what you consider a "pro". Because by my definition if someone is "JUST STUPID" then I question the very notion of declaring them a pro.

If you go back to the orginal post:

"But the plain truth is - some posters here should not be allowed within 50 ft of a plc controlled machine until they have fully understood the machine/plc and all the possible consequences of their actions"

If you read the that whole post again, you will see that the people he was targetting are the ones who specifically come to this forum asking things that clearly indicate they are trying to do things without any bother of researching it themselves, reading a manual, or attempt to work it out themselves. It is not difficult to see where these kind of people could become very dangerous and it is not difficult to see why the original poster thought this was an item of concern

bce123
September 3rd, 2011, 06:19 PM
I think the primary point is, there are certain professions where the consequences of your mistakes have a much greater degree of severity.
My point is it dont matter if its a careless barber or doctor that cuts your neck your neck is still cut. so what im saying is would like some cheese with that WHINE. are do you want to just go on and on and on and on nd on and on complaining or do we try our best to teach people to think!

PeterW
September 3rd, 2011, 06:27 PM
My point is it dont matter if its a careless barber or doctor that cuts your neck your neck is still cut. so what im saying is would like some cheese with that WHINE. are do you want to just go on and on and on and on nd on and on complaining or do we try our best to teach people to think!

Important words there.

The point being you would expect a novice to be under some form of guidance until he reaches the stage where he can go it alone.

PeterW
September 3rd, 2011, 06:29 PM
i cant speak for the rest of the world but in TX. you have to be a licensed electrical contractor to install a new plc in a plant many companies dont know this. I work at plants all the time where manegement thinks just because they have a electrican on staff he can do anything electrical.our state laws state that a maint. electrican can only repair existing equipment not modify or install new equipment. not even run 10' of pipe for a new outlet. However this still takes place. I Myself am a Master electrican and an electrical contractor with over 30 years in the field.I have been around plcs back when we would back up our programs with a cassette recorder.windows were what you looked out of. My point here is that I have seen vetrans and rookies alike do some pretty stupid things when it comes to all typs of equipment. i have seen 1 person decapicated due to lack of folling L.O.T.O. and 1 person die from falling 3' on to his head and 1 person step through a hole in the grating 18 stories up. all this said some of the best programers I know were novice when they started. I hate to say it but novice or pro has nothing to do with it some people are just STUPID


Have you ever considered the 'new line' function.

Point being reading one long monotonous passage is difficult.

bce123
September 3rd, 2011, 06:52 PM
I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.
This sensor should not have done this until several other conditions had been met but due to terrible programming and no ‘event’ control - the conveyor started up although the conveyor system was off (not e stop - just the red stop button)
cant speak for the rest of the world but in my world the e=stop is hard wired and never relies on the plc or programer to make the system safe and yes even an e-stop can fail thats why we have L.O.T.O. and use it. If it not grounded it its still live if it has not been bleed off and tested it still has pressure ect..... the red stop button is not for safety, L.O.T.O. is. i have seen lots of answers to post here and on other fourms that do not include "preceed with caution" and some that do and just because you teach people to be safe does dot mean they will know how to. not all people are smart enough to use what they have learned in a safe way. it is very rare that one can not find a better way to write a program that someone else has wrote after all hind site is 20/20 now that im done ranting im going to find me some of that cheese to go with my wine L.O.L.

bce123
September 3rd, 2011, 06:58 PM
sorry peter i am often guilty of that. there was a very pretty girl in my english class never could stay focussed on that subject

leitmotif
September 3rd, 2011, 06:58 PM
It matters not one whit if you have 30 years in the trade, 19 licenses, or whatever
- the BIG question is are you COMPETENT

Maybe bigger
Do you know when you are competent AND
when you are not??

Dan Bentler

bce123
September 3rd, 2011, 07:00 PM
I think dan just sumed it up!!

bce123
September 3rd, 2011, 10:07 PM
OK enough soap box. It would be nice if Goody could post the program and details of the process on this fourm so we could look it over for safety concerns and discuss it here so that people might learn how to implement the ladder/code safely. this in my opion would be a great way to try and teach others what to do and what not to do. I know its been a long time since this post started and that exact program might not be handy. but im sure lots of us have other examples that could be used. Thanks, and thanks to Goody for his many posts here

williamlove
September 4th, 2011, 01:31 AM
It is amazing to me how many engineers and IT programmers are looking for work, and yet customers report having trouble finding programmers. I think the problem the original poster complained about will only increase if trends continue. This seems to be related to the topic of a lack of qualified process control talent coming up through the ranks, a topic discussed in editorials in some of the control magazines. I'll admit there does seems to be a contradiction, and I'm curious to know other's observations.

I'm not complaining about the lack of programmers because it keeps me gainfully occupied. In fact I'm slammed at the moment and would like to take a rest--I've been working like crazy all year. My concern about the lack of talent is if the overall economy suffers longterm because of it, thus affecting all of us.

Goody
September 4th, 2011, 06:58 AM
The original program is long gone! I was highly unlikely to save a dangerous faulty piece of programming.

Then I see 'it's my way' and 'I don't care' followed by 'and I have never had a problem'
The crux of the original post in a nutshell.

brucechase
September 4th, 2011, 08:30 AM
The original program is long gone! I was highly unlikely to save a dangerous faulty piece of programming.

Then I see 'it's my way' and 'I don't care' followed by 'and I have never had a problem'
The crux of the original post in a nutshell.

The original post described person who got thrown off a conveyor because he climbed on it with just the stop button.

Sorry Goody, I disagree that this is the crux of the original post. The problem was and always will be that he did NOT lock out the equipment before starting work. It matters not how anything was programmed or how many OTLs were used. The lesson (and LAW) is don't trust a program to protect you, lock it out.

DamianInRochester
September 4th, 2011, 09:23 AM
I think dan just sumed it up!!

Well now you have me confused because I was pretty sure you were arguing that this was something anyone should be doing regardless of their level of competence.

Again your words "Whats the difference novice or pro "

And I wasn't aware I was whining or complaining. Just trying to explain myself.

People whose professions involve a direct relation between how good they do their jobs and the life and well being of others MUST be held to a greater level of scrutiny.

I don't see how you can come up with any rational argument against this.

bce123
September 4th, 2011, 09:45 AM
People whose professions involve a direct relation between how good they do their jobs and the life and well being of others MUST be held to a greater level of scrutiny.

I don't see how you can come up with any rational argument against this.

If you get that chip off your shoulder you might could see that you may think YOUR profession is more important than others.

greater level of scrutiny
you must assume you are greater than others?

Is there a difference between a worker getting hurt because you make a mistake. and a bus load of school kids gitting killed because some truck driver is texting while driving and runs into the bus?

I think this is called prima dona syndrome or somthing you should have it checked out.

jdbrandt
September 4th, 2011, 11:05 AM
i agree totaly dude and what about that guy ben franklin he could of killed himself with that kite!!!! What are these Novices thinking doing somthing they have never done before. They may as well be making a bucket list.what would happen if beer, wiskey and cigarettes were not made safely. Someone needs to be in charge of thee people to make sure they dont hurt themself. Everyone is a novice at one point in time!! thats why there are fourms like this. Just my novice idea on the matter, Steve

The whole Ben Franklin/kite thing was busted :smas: on Mythbusters. Nice story , but it can't be true. :notrue:

bce123
September 4th, 2011, 11:17 AM
The whole Ben Franklin/kite thing was busted on Mythbusters. Nice story , but it can't be true.

yes rest assured you can trust anything you see on tv. and stay by the mail box your checks in the mail L.O.L

DamianInRochester
September 4th, 2011, 11:41 AM
If you get that chip off your shoulder you might could see that you may think YOUR profession is more important than others.


you must assume you are greater than others?

Is there a difference between a worker getting hurt because you make a mistake. and a bus load of school kids gitting killed because some truck driver is texting while driving and runs into the bus?

I think this is called prima dona syndrome or somthing you should have it checked out.


You insist on making this personal don't you?

No I don't think I am greater than others. It is clear to me that you do. You are guilty of everything that you are accusing me of my Dear Master Electrician of 30years.

Your not half as smart as you think you are.

You know absolutely nothing about me.

To answer your question, there is a difference, and your old enough to know better.

Your example of a Truck Driver texting is one of carelessness and disrespect for others, not competence or ability. I expect a truck driver to be scrutinized. I expect a truck driver to be competent in driving and to have been licensed to a class of operation relevant to what they are driving. According to YOU, there is no need for pre-qualifications for driving a truck, just have it. They make different license classes for just this reason!

I also very much so expect a school bus driver to be scrutinized. It is an extrememly imporant job. I expect the driver to be competent in operating a bus, and dealing with children. In fact, to a much larger degree than anything else we've discussed here.

I think the same for the security guy at the airport.
I think the same for the school nurse.
I think the same for the city police officer.
I think the same for the guy checking the tire pressures on the airplane.

I expect all these people to be competent in what they do, because their jobs impact the saftey of ours, not excluding people who program machinery.

Mistakes are made by everyone. Some are a result of carelessness, others are the result of competence, and some are just misfortune. You conveniently like to lump them all into the carelessness category.

If you ever want to get down off your soap box, your holier than thou pedastal, maybe you can live in the world the rest of us have to deal with.

bce123
September 4th, 2011, 12:05 PM
Mistakes are made by everyone. Some are a result of carelessness, others are the result of competence, and some are just misfortune. You conveniently like to lump them all into the carelessness category.
yes you got my point ,carelessness is carelessness no matter who comits it this was the fault of someone not using the proper L.O.T.O. and you or I can not make decisons for others. this is not about holding someone to a higher degree of scruinty just the same safety rules for everyone. If this had happend in the plants where i work the program in question would be on record as well as the operator manual and the L.O.T.O. procedure in place at the time of the incendent. There would have been an investigation done to find the cause and soultions to how to prevent this form happing again. you have to learn from mistakes else you repeat them. Steve

PeterW
September 4th, 2011, 12:22 PM
LOTO :huh:

bce123
September 4th, 2011, 12:30 PM
lock out tag out not game of chance

Mickey
September 4th, 2011, 12:31 PM
LOTO :huh:


http://www.osha.gov/SLTC/controlhazardousenergy/index.html

Goody
September 4th, 2011, 12:35 PM
Bruce, you are telling me what MY original post was about!

You'd have thought I knew too, ah well..........

bce123
September 4th, 2011, 01:08 PM
Goody, I think this is a good subject for a post. however the example in the post has lead everone off track including me. if your post had simply read:
Dangerous novices programming plc's

--------------------------------------------------------------------------------

I have noticed an alarming trend creeping in on this site over the last few years. I have been a member longer than it says on my avitar (I think I joined about 1998)
And in that time plc’s have become more and more ubiquitous.
So much so, that now it seems that even the milkman is having a go at programming them.

And this worries me!

PLC’s seem to be treat by some as though they are toys to play with and experiment. People with no electrical or engineering experience whatsoever are going into programming as if they were programming a personal computer.
Not only this - some are not even prepared to read the manual or if they do its all double dutch to them and so they come here wanting to get straight into a live working machine and alter things.

They do not want to waste time with a manual and a plc sat on their desk practicing with it!

And so we get a lot of questions that can be answered by reading page 2 or 3 of the manual or even a quick search of this site.
Just about everything that is asked today has been asked a 100 times before on this site and is searchable.
But this alarming trend of total novices wanting to get straight into the game has other consequences that is not often mentioned.

Machines controlled by plc’s can injure and kill people if something is not programmed right!

I am all for helping people to learn programming and I always give advice where I deem it proper and know what or where the poster is struggling.
But the plain truth is - some posters here should not be allowed within 50 ft of a plc controlled machine until they have fully understood the machine/plc and all the possible consequences of their actions.
instead of adding:
I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.
This sensor should not have done this until several other conditions had been met but due to terrible programming and no ‘event’ control - the conveyor started up although the conveyor system was off (not e stop - just the red stop button)
I think this post would have stayed on track .but hind sight is 20/20.
Thank you for your post I know the subject you wanted it to be about and it a valid one. Thanks, Steve

jtashaffer
September 4th, 2011, 10:34 PM
It sounds like the belt and sensors worked but the system should have been locked out reguardless of who programmed the PLC.

Christine1914
September 5th, 2011, 03:30 AM
But we must also admit that there are certain companies who's much preferred hiring a newly grad or a newbie than an experienced programmer due to "salary pay" issues.

They tend to look and think that they can save an amount by hiring newbies than paying high for the experienced ones.

Then these companies also expect that the newbie they just hired can perform well if not equally compared to the experienced ones. Without proper training regarding the system they are assigning to that person.

The sad part is, if this newbie (is going on-site alone) done something, instead of helping that person they tend to put all the blame to him and letting him solved that problem alone.

Goody
September 5th, 2011, 03:31 AM
I know that 90% of the readers on here have fully understood the point of my original post. The clue is in the title.

I suspect some have read a few answers and gone straight to the 'should be locked out' reply.

I KNOW AND EVERYBODY READING THESE POSTS KNOWS IT SHOULD ALWAYS BE LOCKED OUT.

But there are a lot of people wandering around industrial premises that dont know or don't care about the stringent safety rules.

If you don't believe that, you have not being doing it long enough.

So when you write a program and a normal stop button is pressed.
The machine should not be able to suddenly spring to life because a sensor has been triggered.

It's common normal programming practice - but as in the original case through sloppy and bad programming, it wasn't.

brucechase
September 5th, 2011, 12:12 PM
I'll play a little bit of devil's advocate for you.

Yes, we all know that stop means stop and a machine shouldn't just start by triggering a sensor.

But in our world, there are many situations and reasons for things that not everyone has access to. Take for example, some production manager (plant manager, new engineer, operator, etc) sees this machine and sees it stop when you hit the stop button. Then they come up some some great idea, to save time and money, to automatically restart the machine if someone puts a product into it. WOW! See, the operator doesn't have to go back to the panel and change screens on the HMI and hit the start (or walk all the way back and hit the start button). Safety guy (if by some miracle the plant actually has one) looks at it and says that the danger is minimal since anyone who works on it would be locked out (and of course he/she doesn't want to get in the political battle with some high level manager).

Now the programmer (be it an engineer or tech or some college student) gets told to change the program. If by some stroke of luck that person has any sense and refuses to make the change and keeps his job, then this wouldn't happen.

BUT ----- REAL WORLD HERE ----

He now has permission (or gets told to just do it) from the plant manager and safety manager and maybe even his manager and this change you describe gets done. Or worse yet, he refuses and they hire some contract engineer to come in and make the change. Now you have the situation that you describe.


Does this scenario happen? - Why yes, it does, many more times that most of us would like to admit or believe. Not many engineers or techs will refuse to make that change (if everyone above him tells him to) in today's economy (or any other day's economy either).

So it might not just be dangerous novices using OTLs that could cause a situation that you've seen. It could have been a 30 year engineer that was just told to do it and he felt he had no choice.


Goody, didn't mean to offend by telling you what your original post was about. The big problem of dangerous novices doing programming will always exist and there is nothing we can do about it. There are many on this board who after a couple of years know everything (most of it gotten off the internet too).

The only way I can protect my life is to NEVER rely on a programmer to do the right thing.

Sorry for the long post, I'll get off my soapbox now (you should have seen what I erased!!).

Lancie1
September 5th, 2011, 12:30 PM
The only way I can protect my life is to NEVER rely on a programmer to do the right thing.Yes, I agree that is the smart choice.

But at the same time, if I am that programmer trying to do the Right Thing, it is my duty to do my best to make it as safe as I know how, regardless of all the other external safety devices.

You also have to be able to recognize how safe you can make a PLC program. Reminds me of a PLC5 program I worked on for a decon plant for cleaning up the old biological weapons plant at the Rocky Mountain Arsenal in Denver. There were several layers of protection for the various levels of the plant, with sealed barriers at each level, and alarms if the mustard agent was detected in that level. We had alarm text that displayed for each level, and procedures to implement for each level.

The last barrier level was the operator control room. My question for the project manager was "what text should I display if we get a 3-minute alarm in the control room barrier?" He said, "Don't worry about it. The operators will be dead long before that alarm sounds." I could not think of anything to make it any safer, so I put a message in that said, "Bend over and kiss your @$$ goodbye!"

TurpoUrpo
September 5th, 2011, 12:30 PM
I'll play a little bit of devil's advocate for you.

Yes, we all know that stop means stop and a machine shouldn't just start by triggering a sensor.

But in our world, there are many situations and reasons for things that not everyone has access to. Take for example, some production manager (plant manager, new engineer, operator, etc) sees this machine and sees it stop when you hit the stop button. Then they come up some some great idea, to save time and money, to automatically restart the machine if someone puts a product into it.


I think automatic mode is just for that...

This all does not imply machine should not be locked out before working on it, but stop really should always mean stop and any programmer doing otherwise should be also held in some responsibility (or/and manager who might have forced him to do that).

brucechase
September 5th, 2011, 02:08 PM
We can all do the right thing, but if you don't agree and your manager and/or plant manager is telling you to do it - then you have only 2 choices

1. Do it anyway
2. Find another job

2. isn't so easy when you have a family to feed and bills to pay. Don't want to hear that there are plenty of jobs out there. There are NOT many and the ones that are, have the same bosses that would rather pay a college grad than a 20 year experience engineer.

weilerot
September 5th, 2011, 08:26 PM
Goody, I alway serch the forum before I post question. It also seems that people think the electrical trade in general is something that snyone can do. How many workers in the plant have a concern for fault current, proper overcurrent protection for the machines that you talk about. Working on energized electrical equipment is always an unsafe practice. What about arc flash? How many of us think about the proper overcuurent protection for IEC componets that are widely used in control panels today. There is a general trend that anyone can do electrical work period. I teach an electrical apprenticeship class for NJATC, and I always tell the students to not to show off, turn off the power before you work on it. If what you say is true about reading the manuals which I do, then there would not be any need for tech support offered by all of the PLC manufacturers.

Herb