User`s guide

54 U2741A User’s Guide
3 Measurement Tutorial
If power dissipation is a problem, you should select the
digital multimeter's next higher measurement range to
reduce the errors to acceptable levels. The following table
shows several examples:
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
Ω) when
compared to Polytetrafluoroethylene (Teflon/PTFE) insulators
(10
13
Ω). Leakage from nylon or PVC insulators can easily
contribute a 0.1% error when measuring a 1 M
Ω resistance
in humid conditions.
Ta bl e 3 - 2 Power dissipation for various resistance ranges
Range Test current DUT
power at full scale
100 Ω 1 mA 100 mW
1 kΩ 0.83 mA 689 mW
10 kΩ 100 mA 100 mW
100 kΩ 10 mA 10 mW
1 MΩ 900nA 810 nW
10 MΩ 205 nA 420 nW
100 MΩ 205 nA ||10 MΩ 35 nW
User's Guide.book Page 54 Friday, August 8, 2008 9:11 AM