Introduction and Specifications
Specifications
1
1-23
1-17. Calculating Power Uncertainty
Overall uncertainty for power output in watts (or VARs) is based on the root sum square (rss) of
the individual uncertainties in percent for the selected voltage, current, and power factor
parameters:
Watts uncertainty
UUUU
2
power voltage current PFadder
=++
22
VARs uncertainty UUUU
2
VARs voltage current VARsadder
=++
22
Because there are an infinite number of combinations, you should calculate the actual ac power
uncertainty for your selected parameters. The method of calculation is best shown in the
following examples (using 90-day specifications):
Example 1
Output: 100 V, 1 A, 60 Hz, Power Factor = 1.0 (Φ=0)
Voltage Uncertainty Uncertainty for 100 V at 60 Hz is 0.04% + 6.6 mV, totaling:
100 V x .0004 = 40 mV added to 6.6 mV = 46.6 mV. Expressed in percent:
46.6 mV/100 V x 100 = 0.047% (see “AC Voltage (Sinewave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.08% + 300 µA, totaling:
1 A x .0008 = 800 µA added to 300 µA = 1.1 mA. Expressed in percent:
1.1 mA/1 A x 100 = 0.11% (see “AC Current (Sinewaves) Specifications”).
PF Adder Watts Adder for PF = 1 (Φ=0) at 60 Hz is 0% (see “Phase Specifications”).
Total Watts Output Uncertainty = U
2
power
=++=0047 011 0 012%
22
.. .
Example 2 Output: 100 V, 1 A, 400 Hz, Power Factor = 0.5 (Φ=60)
Voltage Uncertainty Uncertainty for 100 V at 400 Hz is 0.04% + 6.6 mV, totaling:
100 V x .0004 = 40 mV added to 6.6 mV = 46.6 mV. Expressed in percent:
46.6 mV/100 V x 100 = 0.047% (see “AC Voltage (Sinewave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.08% + 300 µA, totaling:
1 A x .0008 = 800 µA added to 300 µA = 1.1 mA. Expressed in percent:
1.1 mA/1 A x 100 = 0.11% (see “AC Current (Sinewave) Specifications”).
PF Adder Watts Adder for PF = 0.5 (Φ=60) at 400 Hz is 2.73% (see “Phase Specifications”).
Total Watts Output Uncertainty = U
2
power
=++=0047 011 273 273%
22
....
VARs When the Power Factor approaches 0.0, the watts output uncertainty becomes unrealistic
because the dominant characteristic is the VARs (volts-amps-reactive) output. In these cases,
calculate the Total VARs Output Uncertainty, as shown in example 3:
Example 3 Output: 100 V, 1 A, 60 Hz, Power Factor = 0.0872 (Φ=85)
Voltage Uncertainty Uncertainty for 100 V at 60 Hz is 0.04% + 6.6 mV, totaling:
100 V x .0004 = 40 mV added to 6.6 mV = 46.6 mV. Expressed in percent:
46.6 mV/100 V x 100 = 0.047% (see “AC Voltage (Sinewave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.08% + 300 µA, totaling:
1 A x .0008 = 800 µA added to 300 µA = 1.1 mA. Expressed in percent:
1.1 mA/1 A x 100 = 0.11% (see “AC Current (Sinewave) Specifications”).
VARs Adder VARs Adder for Φ=85 at 60 Hz is 0.02% (see “Phase Specifications”).
Total VARS Output Uncertainty = U
2
VARs
= 0 047 011 0 02 012%
22
....++ =
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