Keysight 34972A - Page 299

Tutorial 7
Keysight 34970A/34972A User’s Guide 299
AC Loading Errors
In the AC voltage function, the input of the internal DMM appears as a 1 MΩ
resistance in parallel with 150 pF of capacitance. The cabling that you use to
connect signals to the instrument will also add additional capacitance and
loading. The table below shows the approximate input resistance at various
frequencies.
For low frequencies:
Error (%) =
Additional error for high frequencies:
Error (%) = 100 x
F = Input frequency
R
s
= Source resistance
C
in
= Input capacitance (150 pF) + Cable capacitance
Use low-capacitance cable when measuring high-frequency AC signals (see page
269).
Input Frequency Input Resistance
100 Hz
1 kHz
10 kHz
100 kHz
700 kΩ
600 kΩ
100 kΩ
10 kΩ
100– R
s
×
R
s
1 MΩ+
----------------------------
1
12π FR
s
C
in
×××()
2
+
------------------------------------------------------------------
1–