Analog output fail A1S

[arnoldzw]

Hi all,

 

Have an question about Mitsubishi analog output card. A1S68DAI. 

 

This module does have 8x  4-20mA output signals.

We use the first 5 channels and connect these to the analog input of frequency drives. These drives are in the same cabinet. (No external cables)

 

 

The machine is now about 10 years old, and the analog module fails. 

 

We assumed that it was probably the age in combination with the enviroment.

So we checked wiring,  measured the input resistance of the drives (350ohm), and replaced the module. 

Also replaced the backplane of the plc.

 

All good again. 

But after some days same problem again. 

 

 

Thinking about an grounding issue, but don’t know where to begin to search for this kind of issues and how to measure faults like this and which maybe not always be present.

 

 

Analog output cards are expensive, to I can place five analog isolators between  PLC and frequency drives.

But that’s an workaround and no solution in my opinion.

 

Does anyone has an idea?

[Theuns]

It could also be noise from one of the VSD's causing your module to fail. What type of VSD's in panel ?

[d4rkm4n]

Not really familiar with VFD but is whole module fail or just a point?

Anything abnormal from 5 of those VFD? 

I think isolator is also a solution, your system been running fine for 10 years then not even with new module. Probably something on your VFD.

Btw, I always wonder, what is the resistance reading indicate when we measure on intput/output terminal? 

[Gambit]

The AnS series is eol. You should consider replacing it with a newer series (system Q or the current iQ-R) it's quite simple.

 

Edited February 16, 2024 by Gambit

[arnoldzw]

We are using Emotron VFX drives. 
 

think its because of an fault in one of the inversters, or some grounding issues. 

[Goghie]

First is to notice that, the machine has to have much more than 10 years, because of A1S. 

Second, is from my experience - when I had similar problems in past it was almost always grounding or/and  sometimes overvoltage. My advice is put IT transformer with slightly reduced secondary voltage in front of  24VDC  power supply, change PLC power supply from 230VAC to 24VDC, provide separate paths to PLCs LG and FG (Logic Ground and Fault Ground).