PSM1700 PsimetriQ user manual
16-11
16.9 Harmonics and distortion
Harmonic distortion introduced by a signal transformer
may be measured either at a single spot harmonic or as
the thd computed from a series of harmonics.
The primary of the transformer is energised either by the
output of PsimetriQ or by external means and CH2 is
connected across the secondary. It is usual to measure
harmonic distortion with the secondary loaded.
Specify the single harmonic, or the maximum series
harmonic via the SETUP menu.
PsimetriQ analyses for up to 50 harmonics in real time,
using multiple DFTs (refer to the chapter on gain/phase
analysis for the formulae for DFT analysis). Each harmonic
is individually phase referenced to the fundamental so that
the in-phase and quadrature components can be
separately filtered. As the harmonics are usually very
small, this technique is important to give adequate noise
rejection.
The series harmonic data is combined to give the thd
(refer to the chapter on harmonic analysis for the thd
formula).
The single harmonic and the thd are expressed as dB
relative to the fundamental.
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