Why VFD Run Command and Speed Reference Are Separate
The common wiring mistake is assuming that “run” and “how fast” are the same signal. They are two different questions to the drive.
Run and speed answer different questions
A Run Command tells the VFD to start or stop. A Speed Reference tells it what frequency or speed to target while running. One digital output does not automatically define the speed.
There are multiple reference paths
The speed reference may arrive through 0–10 V, 4–20 mA or an industrial network. Whatever path you choose, the VFD parameters for command source and frequency-reference source must match the physical wiring and PLC logic.
Continuous dosing example
A PLC can energize a digital RUN output while its analog output sends the feeder speed. If measured flow is below target, the analog reference can rise; if flow is high, it can fall. A drive fault input should still block RUN independently of that reference.
Commissioning checks
- Confirm terminal or network Run source
- Confirm the configured frequency-reference source
- Check expected frequency at 0 V, 5 V and 10 V
- Use Fault/Ready feedback instead of open-loop RUN only
- Verify restart behavior if the analog reference remains present after stop