Connecting digital outputs to VFD.

[Merle]

Hello,

I'm using a US5-x10-TA30 PLC (pnp digital outputs) to control the input lines on a Lenze VFD.  The digital input lines on the VFD are 24V.  In a situation like this, since both interfaces are 24v, is it normal/acceptable to connect the digital outputs of the PLC directly to the inputs of the VFD?  Or should I be using relays on the PLC outputs to drive the VFD inputs?  For reference, the Lenze VFD is a "I55AP222D00301K00S" (manual attached).

lenze-i550-protec-Operating Instructions-21.pdf

[kratmel]

In my opinion, such a connection is possible.

After considering the scheme of the input circuits of the VFD, we can come to the conclusion that the output current of the PNP is sufficient to turn on the IF inputs. However, you should understand that the VFD is a source of interference. Therefore, you must pay attention to grounding the VFD and minimizing the length of conductors that can cause interference.

If the distance from the PLC to the VFD is significant, then you should use the relay circuit and isolate the PLC from interference that can come through the long cable to the VFD.

[Joe Tauser]

We drive the inputs of Invertek drives directly from the PLC transistor outputs all the time.  All you need to do is connect the drive common to the 0V reference of the PLC.

In these applications the VFD is in the same panel as the PLC, so distance isn't an issue.

Joe T.

[Merle]

In my application the VFD and PLC are essentially in the same enclosure so conductor length is fairly short (< 2ft) .  Like you @Joe Tauser, I was hoping to connect the VFD common to the 0V on the PLC as well since I want to use the VFD 10V output to power a potentiometer that is connected to the PLC analog inputs.

Thanks for your replies.