Compact Logix RTD Module

Good day all. I have a 1769-IR6/A RTD module for our Compact Logix control and I'm having a problem with an input temp. All channels are being used on the module and all but one are working fine. I'm pretty sure that this module can't be configured per channel. This is a system that has been in place for almost 2 years, this is a new problem. I ran the RTD straight from the module, bypassing the field wiring, and I have the same result. It is on the ladder named "Temperature Control", rung 3, tag is Local:11:I.ch2Data. I have swapped wires, tried everything I can think of and am none the wiser. Any help someone may be able to offer would be greatly appreciated.

looks like you might have yourself a bad channel on that module ... did you swap the wires from that particular RTD to another working channel? ... did the system work OK on that "trial" channel? ...

note: before swapping any wires around, it's always a good idea to DOUBLE-CHECK and make sure that the signal wires haven't been chafed or otherwise come into contact with any power wires ... you don't want to damage a working channel by connecting "juice" to it ... (maybe that juice is what damaged the problem channel in the first place) ...

the configuration is shown below – but it looks like all of your channels are set up the same – so that's probably not your problem ...

since this is an existing system which just recently started acting up, then the notes on page 31 of the link below (about the module's distance from the power supply) probably aren't going to help – but look at them any way ...

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um005_-en-p.pdf

I'm betting (pocket change only) on a bad module ... good luck with it ...

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Thanks Ron, I did swap the wires and the problem remained the same. Placing an order for a new module.

I was given this work order after another electronics tech here gave up. I did not do a very thorough investigation. It turns out all of the tanks are not reading properly below Im posting my results using a calibrated hand-held temperature probe vs. what the PLC is showing.

Tank # PLC Temp Temp Probe Temp
2 100F 161F
4 156F 200F
6 -16F 97F
8 116F 200F
10 43F 191F
12 66F 153F

Looking like the module surely is to blame now but I wanted to update this thread just in case I'm missing something here. Thank you much for the support.

are your sensors TWO-WIRE or THREE-WIRE type RTD units? ...

and if they're the three-wire type, are the "extra" (sense) wires connected properly? ...

do you have a spare (uninstalled) RTD that you could hook up right to the front of the module? ...

put the "test" probe in a container of water of a known temperature and see what you get ... then move the wires to the next channel and repeat the test ...

remember that RTD units measure temperature by measuring RESISTANCE ... ANY poor connection anywhere in the wiring will translate into a temperature offset/error in the reading ...

are any of these RTD connections located in a corrosive atmosphere? ...

any chance that someone has been substituting RTD sensors and using the wrong types? ...

how far away (module count) is the RTD module located from the CompactLogix power supply? ...

put the "test" probe in a container of water of a known temperature and see what you get ... then move the wires to the next channel and repeat the test ... I will try this now.

according to everything you've posted so far, this test should come up with temperatures which are "scatter shot – all over the place" – and indicate that the RTD module is truly defective ...

on the other hand, IF (big IF) the temperatures are correct throughout this test using a "known good" probe and wiring, then we've really got some SERIOUS thinking to do ...

let us know what you find ...

Is there another rtd card in the same chasis or another chasis you can swap with for a quick test?

Sounds like your module is bad.

I just received my new module. Because I already have a module in place it should be a simple matter of pulling the old and insertin the new, yes?