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What is the difference between "THD" and "thd" measurements for PowerLogic and ION Meters

Users may notice that there are two different Total Harmonic Distortion measurements when looking at the Modbus map for various PowerLogic and ION Meters

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PowerLogic and ION Meters

Harmonic Calculations


THD. Total Harmonic Distortion (THD) is a quick measure of the total distortion present in a waveform and is the ratio of harmonic content to the fundamental. It provides a general indication of the “quality” of a waveform. THD is calculated for both voltage and current. The power meter uses the following equation to calculate THD, where H is the harmonic distortion:


thd. An alternate method for calculating Total Harmonic Distortion is used widely in Europe. It considers the total harmonic current and the total RMS content rather than fundamental content in the calculation. The power meter calculates thd for both voltage and current. The power meter uses the following equation to calculate THD, where H is the harmonic distortion:


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