4 Wire Measurement for Small Value Resistors

When measuring resistance most of us set our phasers for OHMS and start prodding, but for very low value resistors this can become problematic. The resistance of your leads, their connection to the meter and their connection to the conductive object in question may be if equal or greater than the resistance of the object itself. You could always short out your leads, record that resistance and then subtract it from your final measurement but chances are you will be using the least significant digit of your meter which means your readings are already going to be suspect.

Four wire measurement works by passing a known current though your mystery object via 2 wires and measuring the resultant voltage drop across the object with an additional 2 wires. With only the incredibly low current required to measure voltage passing through the "voltage leads" there will be only an immeasurably small voltage dropped in the leads themselves and their connections. This high accuracy voltage measurement can be used, along with your known current to calculate the resistance of your mystery object with a high degree of accuracy. E/I = R