Problem with SLC 500 PLC(AB)

[hegde10122]

I have a problem with SLC 5/02 1746-L524 PLC of Allen-Bradley.It is a 10-slot rack with the following configuration.
Slot 0-CPU.
Slot 1-IA16 100/120 VAC.
Slot 2-OA16 (RLY) 240 VAC.
Slot 3-IA16 100/120 VAC.
Slot 4-OW16 Triac .

The PLC enters Fault mode and the LED keeps blinking ONLINE.
The error code in S:6 was 351h which means a "STUCK" runtime error exists on an I/O module and the error is non-recoverable.
We decided to download the same ladder logic on a brand new set of 5/02 chassis with new I/0 modules.Everything seemed perfect until we discovered the same problem ONLINE and the PLC entered the fault mode.
Both the set of 5/02 PLCs are now showing the dsame problem.
Where are we going wrong?
PLEASE HELP.

 

[Tom Jenkins]

I guess the first thing I would do is go to the configuration of the I/O in RSLogix and verivy that the configuration there matches the physical I/O cards.

 

[Ron Beaufort]

from the "picture worth a thousand words" department ...

Greetings Hedge,

I think that if you’ll follow Tom’s wise advice you’ll probably come up with a solution ... the MINOR details that I’ve pointed out at items 4 and 5 below are probably just typographical errors that you made when you prepared your post ... BUT ... they indicate that you might have made some similar errors when you entered the modules on your IO Configuration screen ... check the model numbers on the sides of the modules CAREFULLY ...

[attachment]

true war story: I’ve seen one case in the field where the electricians had removed the doors from the I/O modules to make it easier to wire them up ... when the doors were replaced, some of them got reinstalled on the WRONG modules ... the next guys (the programmers) looked at the small model numbers printed on the inside labels of each door - and not at the model numbers printed on the sides of the modules ... and so they set the IO Configuration table up wrong ... after a day of frustration, they finally called in someone from outside (me) to make the system run ... it took less than a minute or so to point out their error ... then I left immediately to avoid the electrician/programmer fistfight that they promised me was coming up real soon ...

now I don’t think that a “wrong door” situation is causing your problem ... especially since you’ve gotten the same results with different hardware ... but the point is that you need to pay VERY careful attention to all of the details when you’re setting one of these things up ... the typographical errors shown in your post indicate that some minor details just might be slipping under your radar ...

also: for those who might be wondering ... the SLC-5/02 does NOT support the handy “Read IO Config” feature that would automatically populate the IO Configuration table for us ...

PS edit: and while we're on the subject of I/O for the SLC, here's somthing else that you might find interesting ... I SINCERELY doubt that it's got anything at all to do with your problem, but it's a trick that just might come in handy somewhere down the road ...

previous post about disabling SLC I/O modules

 

[Ken Roach]

"Stuck Runtime" errors happen when the I/O module can't communicate with the backplane chip. It can happen from a defective module or defective backplane, but you said you replaced both and have the same problem.

The only thing left is an installation problem. Usually this kind of fault comes from a very high level of electrical noise entering the I/O module. Output modules driving unsuppressed inductive loads are a common culprit, but input modules can do the same thing if there is something putting noise onto their wires. Motion controllers, welders, static discharge... there are a lot of sources for electrical noise.

The last "stuck runtime" problem I diagnosed was traced back to a conveyor belt on which several sensors wired to the SLC were mounted. The conveyor had a rubber belt and lacked a ground wire or grounded connection to other structures... we could draw 1/2 inch sparks off the thing with our fingers (ouch !).