Four-probe Conductivity Measurement

why in four probe method for finding conductivity a constant current is used?
- Yash (age 18)
India

People use the 4-probe method rather than the simpler 2-probe method because the contribution of the contacts to the two-probe resistance can be large and hard to control. So long as the voltage sensor has high enough impedance, negligible current flows through the voltage contacts in a 4-probe measurement, so they don't contribute to the measured voltage. The voltages generated at the current contacts are not directly sensed. So one can infer the conductivity of the material so long as one knows the geometry and the current through the current contacts. In practice, it's usually easiest to use a fixed constant-current source, so that the only measurement needed is of the voltage. If some other current source is used, you have to also measure the current.

Mike W.

(published on 09/02/2013)