Created Date: May 20,2016

Created by: FishFacs

Hello everyone.

I have a bunch of VFD drives. They are sending 0-10VDC feedback to an AD P2-16AD2. I have a problem with the reading on one drive specifically.

The feedback is a linear voltage reading that is scaled from 0-100%. 0V=0%; 5V=50%; 10V=100%. Etc

The problem is, the PLC is updating this one particular VFD very slowly (if at all). It will jump from 0V to 2V to 5V very erratically (usually a full 30 seconds between jumps). Sometimes it will just stay at 0V (reporting as "UNDER " on the module display). Most of the time the reading is incorrect.

Troubleshooting steps I 've performed:

I have tested the polarity and the reading on the wires with two independent handheld meters and the voltage is increasing as I would expect. The multimeters are reading the correct voltage and it is scaling nicely.

I 've moved the troublesome VFD feedback connection to a different PLC point. Same problem. The PLC points appear to be working fine when connected to other devices.

I 've connected the troublesome VFD signal to a nearby DDC panel, and the DDC reads it fine.

I 've replaced the wire. The pair is independently shielded and grounded off on one end.

I 've tested it with only the troublesome point connect to the PLC (everything else disconnected) and the same problem ensues.

The total distance is about 25ft through EMT pipe. I 've also draped a temporary wire across the floor with the same results.

I'm at a loss. I don't know why the PLC would be having issues reading the voltage from this particular VFD, considering it is reading the exactly same feedback from 3 other identical VFDs just fine. All unused points are jumped to common as per the manual. Also, the hand meter reads the voltage just as I would expect from the wires (the voltage is scaling accurately with the drive speed). I don't have access to an oscilloscope to test for noise, but I can't see why this one point would be more noisy than the other VFDs. All the drives are equipped with load/line reactors.

Any electricians here have any ideas?

Created Date: May 23,2016

Created by: mwdkmpr

I have tested the polarity and the reading on the wires with two independent handheld meters and the voltage is increasing as I would expect. The multimeters are reading the correct voltage and it is scaling nicely.

Did you check the voltage while it was still connected to the PLC? Maybe try to put a capacitor in parallel with the PLC input to try and remove any AC noise.

What size is the VFD that is causing the problem?