Measurement of main circuit voltages, currents and powers Precautions for maintenance and inspection
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7.2.2 Measurement of voltages and use of PT
Inverter input side
As the input side voltage has a sine wave and it is extremely small in distortion, accurate measurement
can be made with an ordinary AC meter.
Inverter output side
Since the output side voltage has a PWM-controlled rectangular wave, always use a rectifier type volt-
meter.
A needle type tester cannot be used to measure the output side voltage as it indicates a value much
greater than the actual value.
A moving-iron type meter indicates an effective value which includes harmonics and therefore the
value is larger than that of the fundamental wave.
The value monitored on the operation panel is the inverter-controlled voltage itself. Hence, that value
is accurate and it is recommended to monitor values (analog output) using the operation panel.
PT
No PT can be used in the output side of the inverter. Use a direct-reading meter. (A PT can be used in
the input side of the inverter.)
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