Why measure resistance with four wires?
Managing two leads can be challenging enough, especially when you are measuring tiny components in tight spaces. But trying to check a small solder joint, flex connector or chip resistor with four leads can be a real trial. Switching lead configurations can lead to swapped banana plugs and measurement mistakes. And changing from voltage probes to Kelvin leads and back takes time. So why measure resistance with four wires? Using two wires to measure voltage does not seriously impact measurement accuracy. The voltage input on a multimeter generally has a 10 Megohm input impedance, so very little current flows in the leads, and the resulting voltage drop in the leads is negligible. Current measurements are also not significantly affected by series lead resistance. However, resistance measurements are subject to inaccuracies because of lead resistance. When performing a resistance measurement the multimeter switches a current source into the measurement loop. The current is driven through
