AB SLC Analog updating problem

Using an ab slc 5/03... plant suffered some sort of power loss.. what we're seeing is the analog card (typical ab slc analog input card) is not being updated in the program....
When first started (and a 4-20ma generator connected to input) the 4ma signal reponds appropriately... can change to another value and also get response.. but then the input seems to 'lock up'.. and not change states anymore.
DC was checked and it's 24vdc, ab power supply was replaced with new one. Backplane replaced. Analog input card was replaced.
Any ideas on what we could try next?

could the slc need a firmware upgrade for some reason?
bad slc?

We're stumped...any help would be greatly appreciated...


Thanks....
Russ

A lot of the AB analog cards require bits set in the configuration table to work as required. The usual practise is to write to these bits on first scan to initialise the card but some people just set the bits in the data table which works until the is a power cycle. I am not sure if this is your problem as you say you can see the raw values change. Regards Alan Case

What is the part number of the analog module? Alan is correct about some modules requiring set-up bits but the standard current and voltage input and output modules for the SLC 500 system do not require this. Knowing the module number will help with finding your problem. From what you have described, it does not sound like a problem with the module, but that will be better defined when the number is known.

Here's a quick update and resolution to the situation.... it seems that there were a couple of problems going on.
1. the replacement pressure transducer didn't have the same range as the original (instead of being -10 to +11"WC it was 0 to +20"WC). Since the unit has a set point of -1.00"WC meant that the meter was pegging out at one end of the range.
So.. when they'd tried out the new transducer the input went to one end of the range (I'm assuming for arguments sake it's the 3277 value).
Anyways... in the logic.. if the analog input ever gets to either extreme (either 3277, or 16383... if memory serves me right..these values might not be exact..but you get the idea .) then an alarm occurs (with a latching rung) and a default value is substituted.
So... when the new transducer was tested and it's return value went past a 'threshold value' for alarm, the unit put in a default value.
But... the panel view didn't have these alarms in their alarm table. So the operators weren't aware that the unit was in such a condition.
A few slight programming mods and new panelview alarms corrected the logic/alarm side of things.... but now the plant needs a properly ranged transducer to complete the repair.
Thanks for all your help and feedback guys... sorry.. I wasn't on site, didn't even see the progs... just got a few phone calls asking for some help.

I'll know better next time. Start with step one.

95% of all PLC problems are sensors, the other 105% is the math.