Control Logix/Powerflex analog input problems

[wintek]

I have a control logix plc and two powerflex drives with speed and current feedback to the PLC (4-20ma). 24V is supplied from a common powersupply.

When I have any combination of 3 or more of the analog input signals connected all signals go crazy. Signals work fine if less than 2 are connected.

Any ideas?

 

[ScottyUK]

The drive's 0-10V analogue output -ve terminal is connected to chassis ground. Where is your 24v ground connected to? Are you creating unintended current paths through the ground connections when you connect multiple inputs?


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[NWBeaver]

Just to add to what Scotty said, the cable shielding should only be grounded at one end, so as to prevent ground loops.

What about the size of 24v power supply?

 

[djs]

Hello;
Sounds like you may have a grounding issue between the two drives. One way to fix this is to use loop powered signal isolators.