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Old January 8th, 2009, 06:16 AM   #1
Goody
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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 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.
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Old January 8th, 2009, 06:49 AM   #2
tragically1969
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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 !!
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Old January 8th, 2009, 07:24 AM   #3
brucechase
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Quote:
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.

Last edited by brucechase; January 8th, 2009 at 07:26 AM.
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Old January 8th, 2009, 07:38 AM   #4
monkeyhead
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Quote:
Originally Posted by Goody View Post
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.
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Old January 8th, 2009, 07:43 AM   #5
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Quote:
Originally Posted by monkeyhead View Post
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.
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Old January 8th, 2009, 07:49 AM   #6
Christoff84
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Quote:
Originally Posted by brucechase View Post
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.
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Old January 8th, 2009, 08:28 AM   #7
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Quote:
Originally Posted by tragically1969 View Post
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'
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Old January 8th, 2009, 08:52 AM   #8
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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.
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Old January 8th, 2009, 09:15 AM   #9
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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.
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Old January 8th, 2009, 10:02 AM   #10
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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.
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Old January 8th, 2009, 10:04 AM   #11
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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.
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Old January 8th, 2009, 10:42 AM   #12
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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...
Quote:
Originally Posted by odlaw View Post
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

Last edited by n9xcr; January 8th, 2009 at 10:45 AM.
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Old January 8th, 2009, 11:17 AM   #13
Ron Beaufort
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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 ...
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Last edited by Ron Beaufort; January 8th, 2009 at 11:42 AM.
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Old January 8th, 2009, 11:20 AM   #14
mystery
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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)
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Old January 8th, 2009, 11:41 AM   #15
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Originally Posted by mystery View Post
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.

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