Fluke 5520A - Calculating Power Uncertainty

5520A
Service Manual
1-22
1-22. 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), 1 year specifications
Voltage Uncertainty Uncertainty for 100 V at 60 Hz is 150 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
17 mV/100 V x 100 = 0.017% (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.036% + 100 µA, totaling:
1 A x 0.00036 = 360 µA added to 100 µA = 0.46 mA. Expressed in percent:
0.46 mA/1 A x 100 = 0.046% (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 = U
2
power
=++=0017 0046 0 0049%
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, 150 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
17 mV/100V x 100 = 0.017% (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.036% + 100 µA, totaling:
1 A x 0.00036 = 360 µA added to 100 µA = 0.46 mA. Expressed in percent:
0.46 mA/1A x 100 = 0.046% (see “AC Current (Sine Waves) Specifications”).
PF Adder Watts Adder for PF = 0.5 (Φ=60) at 400 Hz is 0.76% (see “Phase
Specifications”).
Total Watts Output Uncertainty =
U
2
power
=++=0017 0046 076 076%
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 = 0.174 (Φ=80)
Voltage Uncertainty Uncertainty for 100 V at 400 Hz is, 150 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
17 mV/100V x 100 = 0.017% (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.036% + 100 µA, totaling:
1 A x 0.00036 = 360 µA added to 100 µA = 0.46 mA. Expressed in percent:
0.46 mA/1 A x 100 = 0.046% (see “AC Current (Sine Waves) Specifications”).
VARs Adder VARs Adder for Φ = 80 at 60 Hz is 0.02% (see “Phase Specifications”).
Total VARS Output Uncertainty = U
2
VARs =0
017
0046 0 03 0058%
2
2
....++=