Removing Test Lead Resistance Errors
To eliminate offset errors associated with the test lead resistance in
2-wire ohms measurements, follow the steps below.
1. Short the ends of the test leads together. The multimeter displays the
test lead resistance.
2. Press Null from the front panel. The multimeter displays “0”
ohms with the leads shorted together.
Power Dissipation Effects
When measuring resistors designed for temperature measurements
(or other resistive devices wit h large temperature coefficients), be awar e
that the multimeter will dissipate some power in the device-under-test.
If power dissipation is a problem, you should select the multimeter’s
next higher measurement range t o reduce the errors to acceptable
levels. The following table shows several examples.
Settling Time Effects
The 34401A has the ability to insert automatic measureme nt settling
delays. These delays are adequate for resistance measurements with less
than 200 pF of combined cable and device capacitance. This is p articularly
important if you are measuring resistances abov e 100 kΩ. Settling due to
RC time constant effects ca n be qu ite lon g. Som e pr eci sion resi sto r s and
multi-function calibrators use large parallel capacit ors (1000 pF to 0.1 µF)
with high resistor values to filter out noise currents injected by their
internal circuitry. Non-ideal capacitances in cables and other devices may
have much longer settling times than expected just by RC time constants
due to dielectric absorption (soak) effects. Errors will be measured when
settling after the initial connection and after a range chan ge.
Range
100 Ω
1 kΩ
10 kΩ
100 kΩ
1 MΩ
10 MΩ
Test Current
1 mA
1 mA
100 µA
10 µA
5 µA
500 nA
DUT
Power at Full Scale
100 µW
1 mW
100
µW
10
µW
30
µW
3
µW
Chapter 7 Measurement Tutorial
Removing Test Lead Resistance Errors
204