Precision AC Current Shunt Set
15
Output Voltage Measurement Using a Fluke 8508A
The input impedance of an 8508A on its DC function is >10 G
Ω
and the loading effect
for measuring DC current with any Current Shunt is negligible. The typical AC function
(DC coupled) low frequency input impedance of an 8508A is 1 M
Ω
in parallel with
135 pF. The impedance reduces with frequency to typically 550 k
Ω
|| 135 pF at 100 kHz.
For the lower-current Current Shunts, the loading error is comparable with or exceeds the
shunt error when used to measure current directly.
Table 5 shows the loading effect of the 8508A on Current Shunts in the range of 1 mA to
1000 mA.
Table 5. Typical Loading Effect of an 8508A 2 V ACV Range
DC
1 kHz
10 kHz
30 kHz
100 kHz
Current
(mA)
Loading
Error
(ppm)
Loading
Error
(ppm)
AC-DC
Diff.
(ppm)
Loading
Error
(ppm)
AC-DC
Diff.
(ppm)
Loading
Error
(ppm)
AC-DC
Diff.
(ppm)
Loading
Error
(ppm)
AC-DC
Diff.
(ppm)
1
0 0 0 -2
+2 -6
+6
-20
+20
10
-80 -80 0 -82 +2 -92 +12 -172 +92
20
-40 -40 0 -41 +1 -45 +5 -80 +40
50
-16 -16 0 -16 0 -18 +2 -31 +15
100
-8 -8 0 -8 0 -9 +1 -15 +7
200
-4 -4 0 -4 0 -4 0 -8 +4
500
-2 -2 0 -2 0 -2 0 -3 +1
1000
-1 -1 0 -1 0 -1 0 -1 0
Use the following formula correct for the loading effect:
Where: AC-DC
calibrated
and Loading error are expressed in ppm.
⎟
⎠
⎞
⎜
⎝
⎛
−
×
⎟
⎠
⎞
⎜
⎝
⎛
+
×
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
=
1,000,000
error
Loading
1
1,000,000
DC
-
AC
1
R
calibrated
calibrated
V
I
Summary of Contents for A40B
Page 6: ...A40B Instruction Manual iv...
Page 8: ...A40B Instruction Manual vi...
