Application Note

4 Fluke Corporation Multimeter measurements on variable frequency drives using the new Fluke 289 DMM

Output voltage and motor speed

(Output frequency using voltage as a reference)

An important new feature on the 289 multimeter is its’ ability

to simultaneously display both the filtered output voltage and

frequency (motor speed) at the same time without having to push

additional buttons or change functions.

To measure the ac output voltage and motor speed, either at the

drive or at the motor disconnect:

1. Plug the black test lead into the common jack and the red test

lead into the V/Ω jack.

2. Select the 289’s ac voltage function.

3. Select MENU then (LPF+Hz)

to enable the low pass filter

and the Hz function.

4. Connect the black probe to one of the three phase output voltage

or motor terminals. This will be the reference phase.

5. Connect the red probe to one of the other two phase output

voltage or motor terminals and record the reading or save to the

289’s internal memory.

6. Leaving the black probe on the reference phase now move the

red probe to the third phase output voltage or motor terminal and

record or save this reading.

7. Check to make sure that there is no more than a 2 % difference

between these two readings. These readings should also agree

within these limits with the controller display panel if available.

8. If the low pass filter is not enabled the output voltage readings

may be between 10-30 % higher than what is expected and the

frequency readings will be inaccurate and unstable.

Output voltage and motor speed using the low pass filter

Output voltage reading with low pass filter enabled

Output voltage and frequency (motor speed)

without the low pass filter (incorrect readings)

Output voltage and frequency (motor speed)

using the low pass filter (correct readings)