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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 (%) =
−100 x R
s
R
s
+ R
i
To minimize loading errors, set the DMM’s dc input resistance to
greater than 10 G
Ω when needed (for more information on dc input
resistance, see page 113).
V
S
R
S
HI
LO
R
i
DMM
8
Chapter 8 Tutorial
Measurement Fundamentals
357