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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 res-

istive and/or long cable, numerous connections, or switches exist between the multimeter and the DUT.

The recommended 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

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 cur-

rent 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

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.