Resistance Measurement Considerations
The multimeter offers two resistance measurements: 2-wire and 4-wire ohms. For both methods, the test
current flows from the input HI terminal, through the resistor being measured. For 2-wire ohms, the
voltage drop across the resistor being measured is sensed internal to the multimeter. Therefore, test lead
resistance is also measured. For 4-wire ohms, separate "sense" connections are required. Because no cur-
rent flows in the sense leads, the resistance in these leads does not give a measurement error.
The errors mentioned earlier in this chapter for DC voltage measurements also apply to resistance meas-
urements. Additional error sources unique to resistance measurements are discussed below.
The 4-wire ohms method provides the most accurate way to measure small resistances because it reduces
test lead and contact resistances. This is often used in automated test applications where resistive and/or
long cable, numerous connections, or switches exist between the multimeter and the DUT. The recom-
mended connections for 4-wire ohms measurements are shown below.
For the 34465A and 34470A, you can also enable offset compensated resistance measurements using
[SENSe:]{RESistance|FRESistance}:OCOMpensated {OFF|ON}. Offset compensation removes the effects of
small dc voltages in the circuit being measured. The technique involves taking the difference between two
resistance measurements, one with the current source set to the normal value, and one with the current
source set to a lower value.
Removing Test Lead Resistance Errors
To eliminate offset errors associated with test lead resistance in 2-wire ohms measurements, follow these
steps:
Short the test lead ends together and read the displayed test lead resistance.
Press Null. The multimeter will store the test lead resistance as the 2-wire ohms null value, and subtract
that value from subsequent measurements.
See also "Null Measurements."
Keysight Truevolt Series Operating and Service Guide
165
Measurement Tutorial
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