Calculating Power Uncertainty - Fluke 5520A Service Manual

5520A
Service Manual

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
VARs uncertainty
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 ( =0), 1 year specifications
Voltage Uncertainty Uncertainty for 100 V at 60 Hz is 150 ppm
100 V x 190 x 10
17 mV/100 V x 100 = 0.017% (see "AC Voltage (Sine Wave) Specifications").
Current Uncertainty Uncertainty for 1 A is 0.036%
1 A x 0.00036 = 360 A added to 100 A = 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 ( =0) at 60 Hz is 0% (see "Phase Specifications").
Total Watts Output Uncertainty =
Example 2 Output: 100 V, 1 A, 400 Hz, Power Factor = 0.5 ( =60)
Voltage Uncertainty Uncertainty for 100 V at 400 Hz is, 150 ppm
100 V x 190 x 10
17 mV/100V x 100 = 0.017% (see "AC Voltage (Sine Wave) Specifications").
Current Uncertainty Uncertainty for 1 A is 0.036%
1 A x 0.00036 = 360 A added to 100 A = 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 ( =60) at 400 Hz is 0.76% (see "Phase
Specifications").
Total Watts Output Uncertainty =
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 ( =80)
Voltage Uncertainty Uncertainty for 100 V at 400 Hz is, 150 ppm
100 V x 190 x 10
17 mV/100V x 100 = 0.017% (see "AC Voltage (Sine Wave) Specifications").
Current Uncertainty Uncertainty for 1 A is 0.036%
1 A x 0.00036 = 360 A added to 100 A = 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
Total VARS Output Uncertainty =
1-22
2
U U
power voltage
2
U U
VARs voltage
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
U
power
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
U
power
-6
= 15 mV added to 2 mV = 17 mV. Expressed in percent:
= 80 at 60 Hz is 0.02% (see "Phase Specifications").
U
VARs
2 2
U U
current PFadder
2 2
U U
current VARsadder
100 A, totaling:
2 2
0 017 . 0 046 . 0
100 A, totaling:
2 2
0 017 . 0 046 . 0 76
100 A, totaling:
2 2
= 0 017 . 0 046 . 0 03
2 mV, totaling:
2
0 049% .
2 mV, totaling:
2
. 0 76% .
2 mV, totaling:
2
. 0 058% .