Agilent Technologies 34972A User Manual page 279

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.
R
s
HI
V
s
LO
Where:
V = Ideal DUT voltage
s
R = DUT source resistance
s
R = Input resistance (10 M or > 10 G)
i
– 100  R s
-------------------------- -
Error (%) =
R s + R i
To minimize loading errors, set the DMM's DC input resistance to
greater than 10 G when needed (for more information on DC input
resistance, see page 130).
Measurement Fundamentals
R
DMM
i
Chapter 7 Tutorial
4
7
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