Keysight 34972A - Page 292

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292 Keysight 34970A/34972A User’s Guide
Loading Errors Due to Input Resistance
Measurement loading errors occur when the resistance of the device-under-test
(DUT) is an appreciable percentage of the instrument’s own input resistance. The
diagram below shows this error source.
Where:
V
s
= Ideal DUT voltage
R
s
= DUT source resistance
R
i
= Input resistance (10 MΩ or > 10 GΩ)
Error (%) =
To minimize loading errors, set the DMM’s DC input resistance to greater than 10
GΩ when needed (for more information on DC input resistance, see page 142).
Loading Errors Due to Input Bias Current
The semiconductor devices used in the input circuits of the internal DMM have
slight leakage currents called bias currents. The effect of the input bias current is
a loading error at the internal DMM’s input terminals. The leakage current will
approximately double for every 10 °C temperature rise, thus making the problem
much more apparent at higher temperatures.
R
s
DMM
R
i
HI
LO
V
s
100– R
s
×
R
s
R
i
+
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