Register to reply

Advantages of four probe method

by ruchika
Tags: advantages, method, probe
Share this thread:
ruchika
#1
Feb6-09, 06:30 AM
P: 3
how does contact resistance and sprearding resistance gets in eliminated in four probe technique for measuring resistivity in comparison to two probe technique where we encounter these resistances?
Phys.Org News Partner Physics news on Phys.org
Technique simplifies the creation of high-tech crystals
Working group explores the 'frustration' of spin glasses
New analysis of oxide glass structures could guide the forecasting of melt formation in planetary interiors
f95toli
#2
Feb6-09, 07:05 AM
Sci Advisor
PF Gold
f95toli's Avatar
P: 2,241
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)?
sp105
#3
Feb10-09, 02:48 AM
P: 18
May I come to know that how the current remains constant throughout the resistance.
Quote Quote by f95toli View Post
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)?

f95toli
#4
Feb10-09, 06:01 AM
Sci Advisor
PF Gold
f95toli's Avatar
P: 2,241
Advantages of four probe method

Well, the current MUST be the same as long as all the components are connected in series, right? That's one of the basic laws of circuit theory; current in=current out.
Hooking up the voltmeter won't change the way the current flows in the circuit, since we can assume that its input impedance is infinite (i.e no current is flowing in the leads going to the voltmeter).
sp105
#5
Feb16-09, 02:57 AM
P: 18
thanks for such a kind reply
goku1991
#6
Mar22-11, 06:53 AM
P: 2
In four probe method, do we 'have' to mearure the potential drop between the center 2 terminals, or, could we swap the functions of the probes...
Also, can we, (theoreticaly), alter the distances between the probes which measure voltage, instead of all the probes being equidistant, that is...?
Studiot
#7
Mar22-11, 08:17 AM
P: 5,462
Don't know if you are referring to the Wenner array for resistivity measurement in layered materials

http://www.google.co.uk/#sclient=psy...b0f135803d42c7

or the series method described by others?
goku1991
#8
Mar24-11, 01:31 AM
P: 2
@ Studiot:
I would be referring to the series method... thanks!


Register to reply

Related Discussions
Measuring pH probe potential and interfacing probe with uC Electrical Engineering 1
Advantages of a trailer General Physics 3
Photocells advantages & disadvantages Introductory Physics Homework 2
Advantages of using an immersion heater General Physics 0
Disadvantageous Advantages. Biology 7