Measuring the motor voltage and the motor current by means of a digital multimeters

Question:

Can the motor voltage and the motor current (at the output of the drive controller) be measured correctly by means of a digital multimeter?

Answer:

a) Motor voltage:
No, the motor voltage cannot be measured correctly by means of a digital multimeter, as the drive controller presents a pulse-width modulating voltage of the DC bus. Due to technical reasons the digital multimeter is not able to detect the effective value. For measuring the effective value only a moving iron instrument is suitable. The drive controller also presents at code C0052 the effective value of the voltage between the motor phases.

b) Motor current:
Yes, the effective value of the motor current can be measured by means of a digital multimeter (True-RMS), as the frequency inverter shows a sinusoidal current.  The frequency inverter also presents at code C0054 the effective value of the motor current.

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