Micrologix 1500 Steady Fault Light Processor

[EVargas]

We have on site 7 equal Micrologix PLC, controlling 7 equal HVAC system for 7 room. The room have redundant HVAC units. All of them have 2 recirculation fans and some of them show the same fault sometimes.

The PLC's have two analog card and the first one who has the Recirculation Fan#1 have been change (the second card have installed the recirculation fan #2), because it's showing a condition that don't allow the fan run property, and having a redundant HVAC system, I shut down the recirculation Fan 1 and the recirculation fan 2 is able to take the 100% load, normally they work 50% each.

Why the problem is happening in all the stand alone PLC with the same card?

I want to try to do a verification of the grounding, any other suggestion or idea?

 

[Ken Roach]

Welcome to the Forum !

Can you describe the fault in more detail ? You said that "some of them show the same fault sometimes" and that the Fault LED is on steady.

How do the controllers recover ?

Does replacing the analog module allow the controller to recover ?

Does cycling power allow the controller to recover ?

Does replacing the CPU allow the controller to recover ?

Has anyone been able to go online with the controller to retrieve a fault code ?

Grounding problems are certainly one reason for a controller to fault, but sudden disconnection of the I/O backplane or induced noise is another.

Do you have a lot of vibration of the control enclosure ?

 

[EVargas]

Ken,

Thanks for your replay.

Can you describe the fault in more detail ? You said that "some of them show the same fault sometimes" and that the Fault LED is on steady. Yes the fault LED is on steady on.

How do the controllers recover ? The fault don't allow the return fan #1 to run properly, but anything else still running fine.

Does replacing the analog module allow the controller to recover ? No, we change 3 same card on 3 different unit and the fault continue.

Does cycling power allow the controller to recover ? Yes, but then again the fault came on after sometime, not in medially.

Does replacing the CPU allow the controller to recover ? Never try this

Has anyone been able to go online with the controller to retrieve a fault code ? I try yesterday to establish communication but I was not able, still working on that.

Grounding problems are certainly one reason for a controller to fault, but sudden disconnection of the I/O backplane or induced noise is another. Thanks, I will going to see this in more details.

Do you have a lot of vibration of the control enclosure ? Just a small vibration, because the enclosure is close to the HVAC units, but is not much.