Bench DMMs have an extra set of banana jacks called “sense.” Known as a Kelvin or 4-wire resistance measurements, these inputs accurately measure small resistors. Like, milliohms small. This video shows how to make a 4-wire measurement, prove when it is accurate, and alternatives to 4-wire. See below for an explanation of the alternative method shown.
Behind the scenes
Doing yet another DMM episode was a tough call for me. However, I am working on a project that requires me to characterize both a 1 ohm and a 100 milliohm resistor. The element14 community was kind enough to send me an MP720028 bench DMM. As shown in the picture, it has an extra set of banana jacks called “4-wire sense.” These connections make 4-wire resistance measurements. In this video, I show the same resistor measured with the traditional 2-wire and advanced 4-wire configuration. (Spoiler Alert! The 2-wire measurement was almost twice as big as the 4-wire!)
Alternative 4-Wire Resistance Measurement
In the video, I show one optional method of using a multimeter with 4-wire resistance capability. The trade-off is that it requires at least two multimeters. Since the 4-wire measurement is making two measurements at the same time: voltage and current, the alternative method does the same thing. A bench power supply, ideally with current limiting, applies a voltage to the resistor under test (RUT). One multimeter is used to measure the current through the resistor and, another measure the voltage across it.
In a pinch, you could use the bench supply’s ammeter for the current, however, its precision is probably much less than the average DMM. Once the voltage and current are known, a little bit of ohm’s law determines the RUT’s resistance!