CompactLogix 35E I/O drop, no Fault

[KKleinstick]

Hello all,


I have a CompactLogix 35E that has been in operation for ,,, much longer then I have worked here!


The problem is, the I/O will drop out intermittently. Output cards go dark, the Analog and RTD card's power lights shut off, Input cards still show the inputs, and if I'm fast/lucky enough and online I can see warning symbols pop up on all of the I/O like they are inhibited.

Then, everything kicks in and the machine takes off again like nothing happened. It isn't a major fault, just a disruption, but it happens a lot.


(the rest is more for flavor, but it might help)
Originally, the machine was alarming and stopping due to a temperature not being in the right range of the set point. On a HMI trend a spike into negative was found and (suspecting a flapping wire) I put in a bounce timer to get us by until we had down time to make the repair.
Now, without the operator needing to walk over and reset the alarm, we noticed a "hiccup" ... and that brought us to the above problem.


Thanks in advance

 

[pturmel]

Are you sure there's no fault? If the processor has a fault handler, it can reset its own faults. (Most of them.)

 

[Picklemon]

My initial thoughts:
1) One of the bus levers on the top of the I/O cards is not fully engaged, possibly disconnecting intermittently due to temperature or vibration.
2) The End Cap on the right hand side of the I/O cards is not installed properly.
3) You have power supply problems. The input cards only need a 0V common to show the lights and will function at a much lower voltage, but the output cards and analog cards require external power.
The cards I use most commonly will not function properly below 20.4VDC. It could be an overloaded, component failure, or a loose wire.

The negative temperature spike might be a symptom of any of these.

It has been a while but I don't think any of these manifest as controller faults on this controller, unless the card is set to stop the PLC on communication loss.
I had to program my own diagnostics to capture I/O card failures.

 

[JTCat]

Those cards are supplied with external power sources correct? I would check power supply issues. If the input cards aren't having any issues then the power going to them isn't a problem. The output cards need adequate power in order to indicate.