All,

Hi everyone, I just joined the forum but I've been visiting this site for a while now. It helped solidify some of the concepts learned in school. There is something that I am not able to grasp when talking about 4-wire resistance measurements. With 2-wire measurements, the DMM acts as a constant current source then measures the voltage drop, thus calculating the resistance. With 4-wire measurement why isn't the resistance of the sense lines an issue.

 

Our Ebook has material on the subject - http://www.allaboutcircuits.com/vol_1/chpt_8/9.html.

 

The two methods are fundimentally identical, but the 4 wire measures the voltage from the current regulator at the resistor, thus eliminating a potential error source, the resistance of the leads themselves. If you have 6 digits or more of accuracy it matters quite a bit. Industry does actually have such meters, and uses them in a routine basis.

 

All,

Hi everyone, I just joined the forum but I've been visiting this site for a while now. It helped solidify some of the concepts learned in school. There is something that I am not able to grasp when talking about 4-wire resistance measurements. With 2-wire measurements, the DMM acts as a constant current source then measures the voltage drop, thus calculating the resistance. With 4-wire measurement why isn't the resistance of the sense lines an issue.

Because the current is zero (or close to it) through the sense lines.
0 * Rsense = 0V drop

(* jcl *)