Concern about an AB SLC 5/03

Hi,
One of my clients has a slc 5/03 (early revision as I can't do indirect addressing) and they called about an alarm they kept getting.

This is a redundant alarm, however only one of them were occurring (and it seemed to be happening more frequently).

The first alarm compares two integers and depending upon certain conditional bits will latch high if conditions merit.

The 2nd alarm (the one that's been giving them fits) used a pid's pv and compared it to a 'scratch pad' integer. Just before the logic for this alarm there's a sub statement moving the 'alarm' value into the scratch pad integer.

This same integer is repeatedly used throughout the logic to collect analog inputs, compare them to max/min, and then go to different scl commands.


Since this logic has been like this for some time I'm perplexed as to why it's now giving alarms?
Could the processor, card, rack issue that I should look at?

A few weeks ago there were 3 data out of range alarms (analog inputs were outside the normal range of 3277 - 16383). When I came across this the plant mentioned the incoming power had over 30V between two of the three phases (when measured to ground). Some were 250's, while one was in the 280's-290's.

Since these out of range alarms occurred on 2 different analog inputs I figured the only common ground would be the 24VDC... and figured that the strange incoming power might have some effect.

But.. now... I don't know..

Depending on what hte analogue inputs are maybe they need calibrating. I would be surprised if the coltage fluctuations were causing the problem. Otherwise swap the cards/inputs used to see if the problem goes with.
I would also physically check the termiantio s on the equipment as in the past I have found poor connections that were there for years before giving a fault.
I agree that there willnot be a problem with the logic as you stated it has been there for years, I also can't see the processor causing this problem.

Cheers
Peter