Arbiter Systems 931A, Operation Manual

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The DSP computes wide-band (i.e. to 3.05 kHz) active power in
Watts by taking the average of instantaneous values of voltage and current
multiplied by each other. Wide-band reactive power (VARS) is determined
by taking the vector difference of the product of the wide-band rms
voltage and current (wide-band apparent power) less the active power.
The formula is shown in 3.4 below:
(3.4) ReactiveP ower =
p
( V A )
2 −
( ActiveP ower )
2
The polarity of the wide-band reactive power is determined by the
narrow-band result. Press SHIFT then NARROW-BAND to switch the
measurement mode from wide-band to narrow-band. Narrow-band mode
measures the fundamental magnitude of the voltage and current only,
using proprietary DSP algorithms. Harmonics are ignored. Dashes will
appear in the display if insufficient signals are present during measurements
performed in narrow-band mode. Narrow band results are computed in 3.5
and 3.6.
(3.5) ActiveP ower = V
f und
×
I
f und
×
cos ( θ )
(3.6) ReactiveP ower = V
f und
×
I
f und
×
sin (
−
θ )
3.6.3 Apparent Power – Power Factor
The Model 931A can measure the apparent power (volt-amps, or VA) and
power factor from the combination of an AC voltage routed to Channel 1
and an AC current routed to Channel 2.
NOTE: See Section 3.6 for input connection description
3.6.3.1 Configuring the Channels
Configure the chosen measurement channels after connecting the voltage
and current to the appropriate input terminals (see Figure 2.1 for instru-
ment locations).
Press CHANNEL 1 SELECT to configure measurement channel 1 and
to view the following menu:
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