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Output Voltage Measurement Using a Fluke Calibration 5790B
The typical input impedance of a 5790B (input 1 or 2) is a 10 MΩ in parallel with
100 pF. For lower-value shunts, the loading error is comparable with or exceeds
the shunt error when used to measure current directly.
Table 4 shows the loading effects of the 5790B on Current Shunts in the range of
the 1 mA to 200 mA.
Table 4. Typical Loading Effect of a 5790B, 2.2 V Range
DC
Current
Loading
Loading
(mA)
Error
Error
(ppm)
(ppm)
1
0
0
10
-8
-8
20
-4
-4
50
-2
-2
100
-1
-1
200
0
0
The 5790B is optimized for use with the A40B shunts. For convenience,
these loading values are preprogrammed into the Loading Error tables
located in the shunt properties. Refer to the 5790B Operators Manual for
more information.
Output Voltage Measurement – Loading Effect
The published specifications for a Current Shunt represent its performance under
ideal conditions. In practical use, placing the input of the voltage measurement
device in parallel with the Current Shunt introduces an additional impedance
(loading effect) which will result in a measurement error. See Figure 3. The 1 mA
boxed Current Shunt has less than 8 mΩ output resistance, so resistive loading
effects are negligible. The capacitive loading effect is less than 15 ppm per
100 pF at 100 kHz. For the non-active Current Shunts, the loading effect
becomes more significant as the resistance value of the Current Shunt increases,
that is, as the nominal current value decreases. For the most accurate
measurements, the error due to this loading effect must be calculated and used
as a measurement correction.
1 kHz
10 kHz
AC-DC
Loading
Diff.
Error
(ppm)
(ppm)
0
-1
0
-8
0
-4
0
-2
0
-1
0
0
Note
30 kHz
AC-DC
Loading
AC-DC
Diff.
Error
Diff.
(ppm)
(ppm)
(ppm)
+1
-4
+3
+2
-9
+10
+1
-4
+5
0
-2
+2
0
-1
+1
0
0
0
Precision AC Current Shunt Set
Operating Information
100 kHz
Loading
AC-DC
Error
Diff.
(ppm)
(ppm)
-16
+11
-21
+49
-7
+23
-2
+9
-1
+4
0
+2
15
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