PLC Simulator
F-23 · vendor-neutral function

VFD Speed Reference Sources

The speed reference is the requested output frequency or process demand. It can come from the keypad, 0–10 V, 4–20 mA, preset speeds, a motorized potentiometer, PID output or a fieldbus word.

Test this function in the lab Open the full VFD guide

Why it matters

The behavior behind the parameter.

Command and reference are independent. A drive with a valid RUN command can remain at zero speed because the selected reference is missing, incorrectly scaled or clamped by minimum, maximum or skip-frequency limits.

  • Analog references need signal type, scaling and loss detection.
  • Preset and motor-pot references are internal drive functions.
  • PID turns process error into the speed reference.

Interactive proof

Test vfd speed reference sources in three passes.

Keep the motor, load and starting condition constant. Change one function at a time, then use the electrical and mechanical evidence to explain the result.

  1. 01

    Run with keypad reference and record commanded versus actual hertz.

  2. 02

    Switch to preset speeds, then motor-pot raise/lower and compare the active source.

  3. 03

    Select PID and move the process setpoint while watching process value and output frequency.

Load F-code F-23 in the function lab

Evidence to watch

The function is proved by changed behavior, not by a parameter value alone.

  • Raw analog or fieldbus value
  • Scaled and limited reference
  • Commanded frequency versus actual frequency

Common commissioning mistakes

These errors can make a healthy drive appear faulty or create a misleading test.

  • Troubleshooting run logic while the reference remains zero.
  • Confusing 0–10 V with 4–20 mA scaling.
  • Ignoring minimum, maximum and skip-frequency limits.

Primary technical references

Transfer the concept; verify the exact drive.

This guide uses vendor-neutral terminology. For real equipment, use the manual for the installed model, option cards and firmware, plus the machine risk assessment and approved commissioning procedure.

Rockwell PowerFlex 520-series user manualSiemens SINAMICS G120 function manualDanfoss VLT AutomationDrive programming guideABB ACS580 manual directory

Related VFD functions

F-61–F-63

VFD Preset Speeds

Preset speeds are stored frequency references selected by digital inputs or control bits. They provide repeatable operating points without an analog signal.

Read and test F-71–F-72

VFD PID Control for Pumps and Fans

A drive PID function compares a process setpoint with transmitter feedback and continuously changes motor frequency to reduce the error.

Read and test F-20

VFD Run Command Sources

A VFD run command can come from the local keypad, hardwired terminals or a fieldbus control word. The selected source must match the signal the PLC or operator is actually sending.

Read and test

From explanation to evidence

Change the function and watch the motor respond.

Open the VFD function lab