The nature of the Beast!

We have all kinds of equipment in our plant, from PLC controlled machines to machines controlled purely with relay logic. PLCs have been a huge leap forward.

However PLCs can also be frustrating. I have lost track of the amount of times, I have been asked to change how something on a machine works, only to find out that the change, has caused unforseen problems.

It seems like people think that since a PLC is involved, it is nothing to just run over there, tap away on a laptop and fix all of lifes problems. When someone (higher up) asks me if I can go over and change something, I always hum and haw and think about it (even though the change might by an easy change in itself), and yet I am always hit with "But it should be easy to change, hell anyone can do it".

How do yall deal with that?

I know there are people that will say a machines program should never be changed. Well our reality is that happens quite regularly.

Your post is not clear to me. I always opt to change relay to PLC. Yea thats why I have a job.
It is so fun to take 30 yards of panels down to one. No more clack clack clack.

Oh absolutely. I would take a PLC over relay logic any day of the week. My frustration comes from upper management not understanding that just because a PLC is installed, that should not just lead to changes being made to a machines operation willy nilly, without a full discussion and investigation.

With relay logic, changes to a machines operation generally took longer and so more thought is usually given to it, at least in my plant.

I am not sure I can follow your reply. I know I might spend more hours on fault logic than motion logic. Think, there is operational, data, and fault logic, to be done. at least for me.
I have to add that I have seen tons of fault logic that uses the sequence to deceit faults. They will not see the unknown. I simply use actual inputs and outputs. In my mind fault logic set you apart.

Think he's talking about:

Management: That red light, I don't like the way it's blinking, change it.
Management: Some of the dented products block the conveyors, can you make all conveyors stop when this specific error occurs?
Management: You know that change we had the machinebuilder do last week? Well it had some unintended consequences, can you fix them?
Management: We need a logging on how many times this exact fault has occured and the status of the relevant I/O's for each occurance.
Management: When the operator places the pieces like this, the machine crashes, change the program so it doesn't happen anymore.


Not only are they oblivious of the consequences, they believe it'll only take 5 minutes and all their problems will be solved.
Granted, in our case we might've planted that idea.....

You need to keep some records, like this:
"Last week, you guys asked me to change this blinky sequence to this blinky sequence.
The change took me 30 minutes of programming, and then anotther hour to find all the operators and make sure that they knew what changed.
I had to write up the change so 2nd and 4rd shift would have a clue whats going on.
The machine stopped 5 times during the first shift while the operators tried to figure out how to respond to the new blinky sequence.
Reprogramming the machine without some diligent investigation consumed a full shift of my time, caused extra machine stoppages (and here's the whopper) could have caused this unsafe condition"

I'm gonna guess that its safety checks/waits and interlocks that they are having you program around (sometimes?)....just a guess =)

The jokes about "this stuff is easy" have no good workplace answer (I can think of lots of sarcastic ones...). Either your boss really believes this, and is planning on laying you off soon (and he'll find out how useful you really are...), or he's joking and realizes that you are too useful in your current position - and he likes having a go to guy for PLC stuff- in which case you might be able to ask for more money if the time were right (or find a higher-paying job in another automation position...)

i'm agree with jonster, i face this kind of (It's easy to change) almost everyday but you have to make them undertand it's not always an easy doing...

You can do manny things with a plc program but peoples need to know that you can't do anything....You can't solve a mecanical issue by coding but you can help...A minor change can have disaster effect on the rest of the program if it as been made without considering every possible issues...

On my side i do initial start of equipements and i'm asked to change the sequence or minor things very often and i never do it the same day on the field. I make it work like it should and i try to have a night sleep before doing it to make sure i have evaluated the change on all the ways.
Doing changes without thinking have always lead me to troubles but sometimes you needs proof of experiences to have your boss understanding it...

Once my ex-boss demanded.......

Even if a sensor fails machine shall work....

My old boss purchased a large machine and i was supposed to have 4 HMI units on it but to save cost he had the oem give us a server with 4 thin clients and 1 thin client was in the same cabinet as the server as well as other controls.

Long story short "Bubba" installed a fuse on a circuit with a partial shorted heater which caused a fire in the pedestal cabinet taht got the server.

Boss tells me that even if we lose the server for any reason we still need to be able to run the machine so i say we can add pushbuttons and lights? Boss says No. I say we can do panelviews instead of the thin clients (Office grade Thin Clients BTW) and boss says no it will cost too much and tells me to "Just figure it out and do it cheap" "Make it Happen"

At this point i am like WTF? I figured it out alright. I found another job and left that idiot holding the bag.

manmeetvirdi said:

Once my ex-boss demanded.......

Even if a sensor fails machine shall work....

Click to expand...

Sounds like classic bruce Myers (My old Boss) to me.

Sheesh.

It's almost like stupidity is a requirement for being a boss in a lot of places.

I was recently working on a stacking machine at a lumber mill. The program had a lot of Latching bits in it. They where changing the location of the stack on the forks, and adding another stack size. Any changed rippled through the program horribly, and looped back on itself a number of times. A real pain to troubleshoot. I finally told them it would be easier to re-write a lot of the program.

Well everybody wants to make the machine run. No matter what you do. My Boss: do whatever you want I want this machine to run. Wtf. We had a fire and wires burnt. Boss want me to change program and make it run.

The thing people don't understand is that the program is stored in the memory and it will not change unless you change it. Plant runs for a decade with this program and one day something doesnt work. Blame it on the program.That is what happens

This is where very good verbal and written communication skills are required. Being able to explain technical things to non-technicals like bosses and supervisors is a necessary skill.
You must first have the technical skills to assess what is required to make the change, including being able to make the change without stepping on the rest of the process. How do you rate your technical and programming skills? Then understand what the cost will be in terms of material, downtime and man-hours.
Then explain this to your super in a consise way. If time permits, write or type up your estimate. Some places have forms for this like change order or work order forms.
Being able to document and explain the requirements concisely (they have short attention spans)should go a long way toward strengthening your position and getting buy-in from him.

When I am asked to change the behavior of a machine:

1) I never take away existing functionality, only add options, placing responsibility for selecting the settings on the shoulders of the production and quality assurance departments utilizing existing protocols for security of these settings.

2) I ask myself what are they going to ask for next, and I go ahead and put that in there too.

Without production none of us get paychecks, we are a service to them, and are required to adapt right along side them in order to compete. Sure, they'll make dumb decisions sometimes, and we must always act as verifiers of safety and common sense.

Know your machine well enough that you can push it to its limits and then give the keys to the operations dept.

Construct flexible code that does more than they asked for. Some of the more belligerent bosses will object "that wasn't in the scope", but if your changes include everything that they ask for and more, then you should be rewarded with fewer and fewer future modification requests and a nice review.

Paul