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Errors in High Resistance Measurements
When you are measuring large resistances, significant errors can occur
due to insulation resistance and surface cleanliness. You should take
the necessary precautions to maintain a “clean” high-resistance system.
Test leads and fixtures are susceptible to leakage due to moisture
absorption in insulating materials and “dirty” surface films. Nylon and
PVC are relatively poor insulators (10
9
ohms) when compared to PTFE
Teflon
â
insulators (10
13
ohms). Leakage from nylon or PVC insulators
can easily contribute a 0.1% error when measuring a 1 M
Ω resistance in
humid conditions.
DC Current Measurement Errors
When you connect the multimeter in series with a test circuit to
measure current, a measurement error is introduced. The error is
caused by the multimeter’s series burden voltage. A voltage is developed
across the wiring resistance and current shunt resistance of the
multimeter as shown below.
Teflon is a registered trademark of E.I. duPont deNemours and Co.
Ideal
Meter
V
s
I
LO
R
s
RV
b
V
s
= source voltage
R
s
= DUT source resistance
V
b
= multimeter burden voltage
R = multimeter current shunt
Error ( % ) =
−100% x V
b
V
s
7
Chapter 7 Measurement Tutorial
Errors in High Resistance Measurements
205