# Understanding VFD speed control input using a potentiometer

I am working on hooking up a potentionmeter as a speed control input to a variable frequency drive.

Here is are the diagrams from the VFD manual:

(Its a Lenze AC Tech SMVector ESV112N01SXB; full manual)

The potentionmeter I have does have 3 terminals and appears to go up to 10 kOhm.

Based on the definitions of terminals 2,5,6 I find it confusing to understand what is required. Especially #2 "analog common" (common what?)

Since a potentiometer is basically just a resistor, I had the impression that it would only need the pot center and one of the other two, not both.

If I do not actually need to wire all three, which of 2, 5, 6 actually should be used?

Possibly I could just try it various ways and experiment ... but I'd prefer not to risk damaging the device (assuming that's possible with these connections).

I hope to come out of this actually understanding how it should work, not just wiring tips. Thanks!

• "Since a potentiometer is basically just a resistor, ..." No, a potentiometer is a pair of resistors whose total resistance is equal to the resistance of the whole track. The ratio is set by the wiper position. Commented Feb 19 at 14:04

A potentiometer is not just a resistor it is an adjustable voltage divider. Connect it exactly the way the diagram shows. The CCW end connects to COM.

Common is the negative of the power supply, zero volts. The potentiometer voltage represents the desired speed, zero to 100 percent.

• Is the VFD doing a comparison of the divided voltages? Commented Sep 14, 2020 at 1:07
• it is checking the voltage at Ain ... it is unknown if it is comparing that input voltage to another voltage Commented Sep 14, 2020 at 2:08
• You can safely assume that the potentiometer voltage is given to an analog to digital converter. If there is a closed-loop speed control it will be implemented digitally. Setting the potentiometer is a remote means of setting the desired speed as an alternative to setting the speed using the keypad.
– user80875
Commented Sep 14, 2020 at 3:05

When connected as shown in the operating instructions, as the potentiometer (recommended to have a value between 2 kΩ to 10 kΩ) is turned from fully anti-clockwise towards fully clockwise, the wiper will provide an incremental voltage ranging from 0 V to 10 V DC to terminal 3 which the VFD will interpret as a set speed reference, (typically) equating from minimum speed (a few hertz) to 50 Hz. As the potentiometer is rotated from fully anti-clockwise to fully clockwise, the connected motor will speed up fairly linearly from its pre-set minimum to its scaled maximum.

All three potentiometer connections are required for satisfactory operation. As indicated, the impedance of the VFD input circuit (at terminal 3) is greater than 50 kΩ so if the zero volts (analog common) was removed from the bottom / anti-clockwise end of the potentiometer, most of the 10 V would still be present at terminal 3 and this would not change much as the potentiometer shaft was rotated.