HP 34401A, User Manual

Page: 204 / 236

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

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
R V
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