Introduction and Specifications
General Specifications 1
1-25
1-28. 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
PFadder
2
current
2
voltage
2
power UUUU ++=
VARs uncertainty
VARsadder
2
current
2
voltage
2
VARs UUUU ++=
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 (Sine Wave) 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 (Sine Waves) Specifications”).
PF Adder Watts Adder for PF = 1 (Φ=0) at 60 Hz is 0 % (see “Phase Specifications”).
Total Watts Output Uncertainty
= %12.0011.0047.0U
222
power
=++=
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 (Sine Wave) 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 (Sine Wave) Specifications”).
PF Adder Watts Adder for PF = 0.5 (Φ=60) at 400 Hz is 2.73 % (see “Phase Specifications”).
Total Watts Output Uncertainty
= %73.273.211.0047.0U
222
power
=++=
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 (Sine Wave) 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 (Sine Wave) Specifications”).
VARs Adder VARs Adder for Φ=85 at 60 Hz is 0.02 % (see “Phase Specifications”).
Total VARS Output Uncertainty
= %12.002.011.0047.0=U
222
VARs
=++
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