Arbiter Systems 931A, Operation Manual

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3.3.1.5 Harmonics
Setup 5
HARMONICS
Press the HARMONICS key to view a graphic display of the
magnitude of individual harmonics for the signals routed to
Channels 1 or 2. The input multiplexing circuitry determines
which input signals are connected to the measurement chan-
nels, according to selections made by the operator (refer to
Sections 3.5.1.2 and 3.5.2.2).
Harmonics up to the 50th are shown for fundamentals of 50 or 60
Hz. At 400 Hz, only harmonics up to the 7th are displayed, due to the
instrument bandwidth limitation of 3.05 kHz.
Harmonics are measured by first determining the AC fundamental and
the DC components of the signal, and removing them algebraically from
the digitized waveform. For the spectral display, K-factor, and individual
harmonic measurements, Fast Fourier Transform analysis determines the
residual. Dividing the rms of the residual by the wide-band rms amplitude
determines the Total Harmonic Distortion (THD). With these techniques,
harmonic measurement accuracy is not dependent upon fundamental
frequency.
Select any harmonic with the movable cursor found in the graphic
display using the arrow keys. The display also shows corresponding
numerical values of the amplitude and the phase angle of the harmonic
relative to fundamental. Press CHANNEL 1 SELECT or CHANNEL 2
SELECT to toggle the display between the signals applied to Channels 1
or 2.
Numerical display of THD and K-factor are always available. THD is
the rms of the residual, including noise and spurious signals, as a percent
of the wide-band rms. K-factor is the rms sum of the fundamental plus
the individual harmonics (each weighted by the square of the harmonic
number) expressed as a ratio to the fundamental. It is an estimate of the
heating effect of harmonic energy in magnetic materials. K-factor is used
to determine transformer de-rating. K-factor is 1.0 for a perfect sine wave
and greater than 1.0 with distortion.
3.3.1.6 Waveform
Setup 6
WAVEFORM
ENTER
Press the WAVEFORM key to view a graphic display of the
waveforms for the signals, which are routed to Channels 1 and
2.
The input multiplexing circuitry determines which input
signals are connected to the measurement channels, according
to selections made by the operator.
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