The four probe method effectively eliminates contact and spreading resistance when measuring resistivity, unlike the two probe technique. In an ideal scenario with a perfect current source and a voltmeter with infinite input impedance, the current remains constant throughout the circuit, allowing for accurate resistance calculations using Ohm's law. Non-ideal effects may arise when measuring samples with very high or low resistance, necessitating a deeper understanding of the technique. The discussion also touches on the potential for varying probe distances and the distinction between the four probe method and the Wenner array for resistivity measurements.
PREREQUISITESResearchers, electrical engineers, and materials scientists interested in accurate resistivity measurements and the nuances of different measurement techniques.
f95toli said:It should be fairly obvious if you draw a circuit diagram.
In the ideal case (perfect current source and voltmeter with inifinite input impedance) the series/contact resistance is eliminated simply because the current is the same in the whole circui (no current flows into the voltmeter) and the voltmeter is only measuring across the sample.
Since you know the current and the voltage you then calculate the resistance from Ohms law
Note that there are of course instances where non-ideal effects come into playl; e.g..when measuring samples with very high (several megaohms) or low resistance (milliohms); so it is important to understand how the technique actually works.
Edit: I just realized that I assumed you were referring to "through" measurements (e.g. a resistor), but since you are referring to resistivity you might actually be asking about van der Paw measurements (of e.g. thin films)?