THD and TDD computation

The TOTAL HARMONIC DISTORTION (THD) factor is used as a measurement indication of the signal deviation from the pure sine wave.

THD of voltage is computed by the instrument on expression:



where Un and U1 is RMS (or amplitude) values of  the n-th and fundamental harmonics of the measured voltage, correspondingly.

For current I it is the same:


For current TDD:


Here I Max Demand - Current Maximum Demand.

 Voltage and current THD, current TDD calculation is based on up to 40-th order harmonics