How to Measure PWM Inverter Output Accurately

+ Portable Multimeter

Measure PWM Outputs Correctly

VFDs generate PWM output waveforms to control the speed and torque of three-phase AC induction motors. Unlike sinusoidal AC power, PWM signals contain high-frequency switching components that can affect voltage and frequency measurements when using standard measurement techniques. Engineers performing maintenance or commissioning must verify that inverter output values match the intended operating conditions while accounting for the characteristics of PWM signals.

Accurate verification requires measuring the inverter's output voltage and frequency while minimizing the influence of high-frequency switching components. Comparing measured values with the drive's displayed operating values helps confirm normal inverter operation and identify measurement discrepancies that could otherwise be mistaken for equipment.

Accurate PWM Measurement Solution

Accurate measurement of pulse width modulated inverter outputs requires filtering unwanted switching-frequency components before calculating the True RMS voltage and output frequency. Conventional handheld digital multimeters often measure both the fundamental waveform and high-frequency switching signals, resulting in readings that may exceed the values displayed by the variable frequency drive. Keysight Handheld Digital Multimeters incorporate a switchable 1 kHz low-pass filter designed for pulse width modulated motor-drive applications. These instruments enable accurate voltage and frequency measurements on inverter outputs while maintaining the safety ratings required for industrial electrical measurements. This allows maintenance technicians to compare measured values with the drive to display more confidently during commissioning, preventive maintenance, and troubleshooting activities.

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