Micrologix1400 and IF4 getting an odd error condition

[jay mason]

I have a an issue with a micrologix 1400 control system with a 1762 if4 analog card.
I have 3 devices connected to the analog card one 0 to 10 vdc. and 2, 4-20ma transducers
For some reason the 0-10 volt signal which is a strain gauge amplifier is showing saturation on my HMI and shuts down the system but not the other two signals are fine.
If I power down and back up this clears the fault and all is fine for a day or so then I get the same fault the analog card shows 32768 as the counts which would be saturation.
Is there a reason the micrologix would retain the saturated condition?
Thanks
Jay

 

[James Mcquade]

jay,

Several things come to mind.

1. has the program changed in regards to the analog input and math?
check your math statements.
2. load cell amplifier is going bad.
3. load cell is going bad. Happens more often than you think. we replace 10-20 a month. 10k to 200k in size.
4. have you checked the wiring? is the wiring shielded and grounded in only one location?

you may want to consider unlatching the math overflow / underflow bit in the last rung of your program to prevent the plc from faulting out.

regards,
james

 

[jay mason]

Thank you
seems to be field collapse from the over head crane is causing the issue.
again thank you
Jay