Tektronix - Using The DMM Series To Make Simple And Accurate Resistance Measurements

Our thanks to Tektronix for allowing us to reprint the following article.

Using two wires to measure resistance is convenient, but causes measurement error. You can virtually eliminate this error by using four leads and a multimeter with separate source and measure terminals. Unfortunately, adding additional leads and connections makes the measurement more complicated. You have additional leads to connect and you may have to swap clips and probes as you change from voltage to resistance. Now a new concept enables you to take four-wire resistance measurements with just two leads.

Why Measure Resistance With Four Wires?

Managing two leads can be challenging enough, especially when you are measuring small 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 an input impedance of 10 Megohm, 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. Unfortunately, in the case of resistance measurements, lead resistance can be a source of significant inaccuracies...

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