4 Wire Resistance Measurement

This document explains how ohmmeters measure resistance how 2 wire resistance measurements work how 4 wire resistance measurements work and the special considerations for each measurement type.

4 wire resistance measurement. In 4 wire resistance measurements current is forced through the source terminals hi lo. Four terminal sensing 4t sensing 4 wire sensing or 4 point probes method is an electrical impedance measuring technique that uses separate pairs of current carrying and voltage sensing electrodes to make more accurate measurements than the simpler and more usual two terminal 2t sensing four terminal sensing is used in some ohmmeters and impedance analyzers and in wiring for strain. Usually wire resistance is very small only a few ohms. The 4 wire mode requires 4 wire switching and more cabling but it is more accurate than the 2 wire mode for precision measurements with resistances below 100 kω.

Specifications such as input range accuracy and stability for 4 wire resistance measurements using the ni 9219 can be found in the device datasheet. By knowing the sheet resistance 4 53 reading in ohms square and the resistivity 2 pi probe pin spacing reading in ohm cm you can calcul. Four wire resistance measurement configuration. The following figure shows a 4 wire resistance measurement including lead resistance.

Because 4 wire measurements typically employ test currents well above those needed for two wire testing a secondary advantage comes through the use of a high current stress test. Watch this video above and or read below to learn more. The ni 9219 is a cdaq module capable of doing 4 wire resistance measurements. One solution is called the kelvin or 4 wire resistance measurement method.

For this kind of connection 4 wires are needed leading to the name. A current is passed through the unknown resistance and measured. I use this 4 wire method with a four point probe to measure the sheet resistance of thin metal shields. With the 4 wire connection the idea is to have separate wires to deliver the measurement current and to measure the voltage drop over the resistance.

It involves the use of an ammeter and voltmeter determining specimen resistance by ohm s law calculation. Suppose we wished to measure the resistance of some component located a significant distance away from our ohmmeter such a scenario would be problematic because an ohmmeter measures all resistance in the circuit loop which includes the resistance of the wires r wire connecting the ohmmeter to the component being measured r subject. Keithley s 5 digit model 2110 dmm supports both two wire and four wire configurations for resistance measurement ranges of 100ω 1kω 10kω 100kω 1mω 10mω and 100mω. Greater precision resistance testing allows resistance measurements down into the milli ohm.