Calculating power uncertainty – Atec Fluke-5500A User Manual
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Fluke Corporation
5500A Black and White Extended Specifications
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
U
U
U
U
+
+
=
VARs uncertainty
VARsadder
2
current
2
voltage
2
VARs
U
U
U
U
+
+
=
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
.
0
0
11
.
0
047
.
0
U
2
2
2
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
.
2
73
.
2
11
.
0
047
.
0
U
2
2
2
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
.
0
02
.
0
11
.
0
047
.
0
=
U
2
2
2
VARs
=
+
+