Fluke 5520A - Page 17

Manual Supplement 5520A Operator
16 7/11
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 1 year 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 190 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 19 mV added to 2 mV = 21 mV. Expressed in percent:
21 mV/100 V x 100 = 0.021 % (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.05 % + 100 μA, totaling:
1 A x 0.0005 = 500 μA added to 100 μA = 0.6 mA. Expressed in percent:
0. 6 mA/1 A x 100 = 0.06 % (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 =
%064.0006.0021.0
22
power
=++=
2
U
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, 190 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 19 mV added to 2 mV = 21 mV. Expressed in percent:
21 mV/100V x 100 = 0.021 % (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.05 % + 100 μA, totaling:
1 A x 0.0005 = 500 μA added to 100 μA = 0.6 mA. Expressed in percent:
0.6 mA/1A x 100 = 0.06 % (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 =
%76.076.006.0021.0U
22
power
=++=
2
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 60 Hz is, 190 ppm + 2 mV, totaling:
100 V x 190 x 10
-6
= 19 mV added to 2 mV = 21 mV. Expressed in percent:
21 mV/100V x 100 = 0.021 % (see “AC Voltage (Sine Wave) Specifications”).
Current Uncertainty Uncertainty for 1 A is 0.05 % + 100 μA, totaling:
1 A x 0.0005 = 500 μA added to 100 μA = 0.6 mA. Expressed in percent:
0.6 mA/1 A x 100 = 0.06 % (see “AC Current (Sine Waves) Specifications”).
VARs Adder VARs Adder for Φ = 80 at 60 Hz is 0.03 % (see “Phase Specifications”).
Total VARS Output Uncertainty =
%070.003.006.0021.0=U
22
VARs
=++
2