Arbiter Systems 931A, Operation Manual

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Display phase angle as 0
◦
C to 360
◦
C or as
±
180
◦
C, and a lagging phase
angle may also be chosen to be positive or negative by convention. Select
your preferred phase convention as described in Section 3.3.1.13, under
Menu. See Figure 3.1 for Phase Angle definitions.
3.3.1.3 Power/Vars
Setup 3
POWER
VARS
Press the POWER/VARS key to display active and reactive
power for the combination of signals 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. (see Section 3.5.1.2).
To use the POWER/VARS function, Channel 1 must be set
to measure AC voltage, and Channel 2 must be set to measure AC current.
In wide-band mode, active power (watts) is measured by taking the
average of the products of the instantaneous values of voltage and current,
including the effects of harmonics.
Reactive power (Vars) is measured by taking the vector difference of the
wide-band apparent power less the active power (active power is described
above). The wide-band apparent power is the product of the wide-band
rms voltage and the wide-band rms current.
(3.2) W ide
−
band V ARs =
p
V A
2
+ W
2
Mathematically, reactive power is defined as the square root of the
quantity apparent power squared minus active power squared. The sign of
the wide-band reactive power is determined from the sign of the narrow-
band reactive power.
In narrow-band mode, active power (Watts) is measured by multiplying
the fundamental voltage and current magnitude and the cosine of their
phase angle, all determined accurately by DSP. Harmonics are ignored.
Narrow-band reactive power (Vars) is measured by multiplying the funda-
mental voltage and current by the sine of negative of the fundamental phase
angle, all determined accurately by DSP. Again, harmonics are ignored.
(3.3) N arrow
−
band V ars = V
f und
×
I
f und
×
Sin (
−
Θ)
Press the POWER/VARS key a second time to toggle the display
from Power to Energy. Both Watt-hours and VAR-hours are continuously
accumulated. Use the RESTART key to zero the Energy readings. Power
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