Slc 500 cpu fault

superdave

Member
Join Date
Sep 2005
Location
Mich.
Posts
4
I recently replaced a old relay panel with a slc 5/02 processor and a small rack of discrete input and relay output cards.At first everything ran well but now I am getting a cpu fault stating fault on slot 3 which is a relay output card to solenoid valves a long way away. I thought about switching the relay card with a triac card to gain abit of isolation for a quick fix.
 
What is the fault? I've had an older used SLC processor want to remember it's previous configuration when powered off & on. Never did get that one figured out.
 
I believe it says rack fault slot 3. My thinking is that I'm getting some inductive noise from the solenoids thru the card onto to the backplane causing the processor to fault out ? That's why I thought replacing the relay output card with a triac module might help the situation.
 
Is the fault any more specific? I've never seen a device like a solenoid cause a fault in the backplane and processor. (That doesn't mean it isn't/hasn't/doesn/t, just means I haven't seen it.)
 
The fault that shows up in the processor status file is rack data error check slot 3. Slot 3 is an output relay module that drives a/c solenoids only ? it also gives the hex value s:6 = 350h.
 
From the online help:
xx50 A rack data error is detected. This error is recoverable.
xx = 03 means "slot 3".
edit: I have just cleared a mistake where I thought superdave was talking about slot 5.
That it is recoverable means that it is possible to avoid the CPU going into fault by programming a fault routine. If that is a good idea is up to superdave.

Anyway, make sure that large (or even small) coils (solenoids, contactors) are always fitted with surge suppressors. This is important even if you use relay outputs.
 
Last edited:
I believe it says rack fault slot 3. My thinking is that I'm getting some inductive noise from the solenoids thru the card onto to the backplane causing the processor to fault out ? That's why I thought replacing the relay output card with a triac module might help the situation.

You are probably exactly right...I have personally seen this twice. Surge suppression did not fix it in my case. In my situation, the SLC I/O was being controlled by a PLC5. I changed to triac outputs to cure it. The relay outputs 7 and 8 on 1746-OW16 are very close to the backplane. One of these outputs was the culprit on my machine.
 

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