User`s guide

Measurement Tutorial 3
34450A User’s Guide 85
Errors in High Resistance Measurements
When you are measuring large resistances, significant errors
can occur due to resistance insulation 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
Ω) when
compared to PTFE insulators (10
13
Ω).
Leakage from nylon or PVC insulators can easily contribute
a 0.1% error when measuring a 1 MΩ resistance in humid
conditions.
Offset Compensation
A resistance measurement involves measuring a voltage (E)
induced across the resistance by a known current source.
10 MΩ 100 nA 100 nW
100 MΩ 100 nA / 10 MΩ 1
µW
Tab le 3-2 Examples of measurement ranges (continued)
Range Test Current DUT Power at Full Scale
Ideal
Meter
E
R
I