VFD · FEEDBACK
Why a VFD Needs Fault, Ready and Running Feedback — Not Just a RUN Command
A PLC output saying RUN and a motor actually running are different facts. Feedback closes the state loop.
VFDFaultReadyRunningFeedback
A command is only the intention
The PLC output may be ON while the VFD is faulted, disabled or missing a permissive. For the same reason, an HMI running lamp should normally come from verified drive state rather than the command bit alone.
Closed-loop state
PLC RUN CMD→VFD→READY / RUN / FAULT→PLC decision
Think in at least three feedback states
| Feedback | Meaning | PLC use |
|---|---|---|
| Ready | Drive available to run | Run permissive |
| Running | Actual running state | Status / next sequence step |
| Fault | Drive abnormal condition | Block run / alarm |
Add a feedback timeout after the command
If Running does not arrive within a defined time after RUN is commanded, the PLC can identify a “commanded but not running” condition. This timeout is process logic, not a replacement for safety functions.
Treat fault reset as a separate action
Repeated automatic reset can hide the underlying cause. Separate the reset request and only allow it when the process and restart conditions are understood.