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9.6 POWER FACTOR
(Extended main board).
Power factor
of an AC power system is the ratio of real power in watts (W) divided by apparent
power in volt-amperes (VA). For sinusoidal signals, power factor is calculated from phase angle
θ
as cos(
θ
)
.
Power factor readings can range from 1.000 to 0.000 with three decimal places
and an accuracy of 0.1% for sinusoidal signals at 50/60 Hz. While power factor is always
positive, a minus sign is artificially assigned for negative phase angles, and power factor is set
to 0 for phase angles greater than 90°.
Example of power factor measurement to 0.001 resolution
Application:
Measure power factor with 0.001 resolution for two sinusoidal AC signals
centered around 0º.
Solution:
•
As for phase angle, jumper signal conditioner for maximum sensitivity to catch zero voltage
crossings and minimize effects of amplitude jitter. Apply one AC signal to Channel A and
one to Channel B.
•
Under Input+Display tab, select Extended (an extended main board is required). Set Mode
to Phase, Function to “A to B (+
–
180)”, and Gate time 0.25 sec (if four transmittals per
second are desired).
•
Under Scaling tab, set decimal point to 3 places. Make both trigger slopes the same. Set
Custom Curve to “Power Factor”. A Multiplier is not needed with power factor.