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