User`s guide

279
Chapter 7 Tutorial
Measurement Fundamentals
4
7
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 M or > 10 G)
Error (%) =
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).
R
s
DMM
R
i
HI
LO
V
s
100– R
s

R
s
R
i
+
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34970A Refresh UG.book Page 279 Wednesday, February 17, 2010 12:34 PM