4.Measurement Tutorial
Loading Errors (AC Voltage)
In the AC voltage function, the input impedance
of the multimeter appears as a 1 MΩ
resistance in parallel with 100 pF of capacitance. The cabling that you use to connect
signals to the multimeter also adds capacitance and loading. The table below shows the
multimeter's approximate input resistance at various frequencies.
Input Frequency
Input Resistance
100 Hz
1
MΩ
1 kHz
850 k
Ω
10 kHz
160 k
Ω
100 kHz
16 k
Ω
For low frequencies, the loading error is:
Error
s
s
100 R
(%
1
)
R
M
−
×
=
+
Ω
At high frequencies, the additional loading error is:
Error
(
)
2
S
in
1
(%)
100
2
1
1
F R
C
=
×
−
+
π × ×
×
R
s
= source resistance
F = input frequency
C
in
= input capacitance (100 pF) plus cable capacitance
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