Amprobe ACD-330T Clamp-On-Multimeter - Manual (Page 27)

ADJUSTABLE SPEED MOTOR CONTROLLERS
You can measure input current, output current and frequency of adjustable speed motor
controllers. The output current frequency is used to calculate the rotating speed of the
motor, while input current frequency is used to measure the frequency of the power line.
The frequency of the output current is important because the voltage frequency is often
meaningless for the calculations of motor controller speed.
1) Set the rotary switch to " A ".
2) Clamp around an input or output phase (as required), and run motor at desired speed.
Be sure the clamp jaws are securely closed, or measurements will not be accurate.
3) Observe the display for true RMS current.
4) Measure an output phase of the motor controller and press Hz button momentarily to
enter dual display mode. Then you will see the frequency reading be shown on small dig-
its. Nominal motor speed is calculated formula is shown below:
RPM = 120 F/P
F: measured frequency.
P: number of pairs of motor poles
5) Press the MAX • MIN button for more than 1 second to record readings. To view read-
ings, momentarily press MAX • MIN button.
6) Press the MAX • MIN button for more than 1 second to exit recording.
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