comparing Allen-Bradley to Omron ...

[DetlefP]

Hello Everyone,

I am the customer, Ron is talking about in this forum. I am Field Service engineer for equipment which is use to produce printing plates. Most of our equipment comes from overseas and is equipped with OMRON PLC....
My main target is to get an idea how to troubleshoot PLC problems. In the past I visited one or two classes for PLC programming, but this did not help that much.....
Actually I have a problem with an OMRON CPM2A60C. What happens randomly is, that the machine does unexpected things like draining a solvent tank which is controlled by an working level float ssensor and for safety an overflow float sensor. So far I checked all contacts and function. In manual mode everthing workd fine, but when it come to the auto mode the machine acts up.....As a last ressource to come over with this problem I ordered a new CPU from Europe....
Does somebody have any idea where else to look, if you need some more details...please let me know

 

[Lancie1]

What happens randomly is, that the machine does unexpected things like draining a solvent tank which is controlled by an working level float ssensor and for safety an overflow float sensor. So far I checked all contacts and function. In manual mode everthing workd fine, but when it come to the auto mode the machine acts up.....

I assume this is a working program that has been running correctly for some time. If so, then what has changed? If you can be sure that the PLC program has not been changed (on purpose or accidently), then it comes back to some physical malfunction - intermittent float switch (that overflow float sensor is a prime suspect), loose wire connection, partially shorted or grounded input wires to PLC, and so on.

If the program has only been running a short time, then it is always possible that it contains a logic error that only shows up under certain situations.

If you want to post your Omron program, ZIP it or print it out to a PDF file, then attach it to a post here. I am sure someone will be glad to take a look to see if any errors pop up.

 

[gtsuport]

Welcome to the Forum.

Short answer, when looking at the logic controlling the drain valve, what is the difference between the manual and automatic logic?

Do you have a CX-Programmer file for the plc program?

If you can post the program, and tell us what output the drain valve is wired to, we can take a look at the code and see if something jumps out.

gtsuport

 

[DetlefP]

OMRON CPM2A60C problems

I do not have the CX Programmer file at hand right now. But will get it as soon as I can....

To Lancie1
I totally agree with you to check the floats first, and I did it already. And indeed I found something strange on the overflow float sensor. So I took it out and checked the switch point and revised the contacts. But I did not check for grounded or partially shorted inputs. Thanks a lot for the answer.

 

[OkiePC]

I know nothing about Omron, but it is really really rare (if not impossible) for machinery problem to be caused by a PLC hardware issue and only screw up some of the time.

It is much more likely (99.95%) that the logic is doing exactly what it should be doing only some of its input data is now different resulting in the different behavior.

So, what I am saying, is that there is very little chance of the new CPU fixing the problem (but you should have a spare anyway). It is more likely that the symptom is caused by a faulty field device or that the logic needs some refinement to better deal with a signal or value that, in reality, does something a little different than the programmer originally planned for.

 

[BobB]

I know nothing about Omron, but it is really really rare (if not impossible) for machinery problem to be caused by a PLC hardware issue and only screw up some of the time.

It is much more likely (99.95%) that the logic is doing exactly what it should be doing only some of its input data is now different resulting in the different behavior.

So, what I am saying, is that there is very little chance of the new CPU fixing the problem (but you should have a spare anyway). It is more likely that the symptom is caused by a faulty field device or that the logic needs some refinement to better deal with a signal or value that, in reality, does something a little different than the programmer originally planned for.

I fully agree here - unfortunately the guy with the 'computer' programming the PLC usually gets the stares. Quite often when tracing faults I do not even get the laptop out of the car and finds the fault - but I know the system as I designed it.

I would suggest examining the software for differences between the 2 routines - manual may not use the float switches or other devices so the fault would not show up. I would be looking for a momentary contact closure triggering the PLC to perform its task. PLCs are very unforgiving if there is a fleeting contact closure - you could also put a timer on the suspect input to ignore a fleeting input for a short period.

 

[lostcontrol]

I wonder if the level tx is going under/over range, causing the signal to saturate & confuse the tank empty logic?
Are the unexpected things related to analogue devices specifically?
Some traps could be put in to detect this type of failure, as could limit checking on the scale functions.
The Omron scale functions do not clamp the signal!!

This is what okie was referring to.