Tech Talk 4: Four Point Probe: Measuring and Calculating Resistivity

[@ErikMrazBR]

I've read 3 articles and one lecture about it. I was thinking about how complicated it could be, but then I found your video. Clean explanation, thanks!

[@nagenderch6298]

Very beautiful video

[@bahtiyarcerit8878]

Hi.! Firstly Thank for this learnly video. I have a two question. Please answer to my questions. Which Did you used material for measurement of conductivity? Doesn't the material you use affect the conductivity measurement?

[@dr.arpitgoyal963]

For passing Current can we use a DC source like a constant current power supply. Or can we simply use LCR meter and measure Rp. Please guide. Thanks

[@mgchemicals]

Ours is an AC and DC source but I've come across papers that used strictly a DC source so a power supply can work

[@aygenahsenerdogan2620]

Hi thank you very much for this video , it was really helpful. I would like to measure the resistivity of the weld in thin welded sheets. Can you please advise how to measure it with 4 probes method ?

[@mgchemicals]

If you want to measure a certain area, it can become a bit tricky as the 4-point probe method is useful for thin strips as we showed in the video. You would have to know the cross-sectional area across the weld (this is the thickness of the weld strip multiplied by the distance between the probes that measure resistance, we suggest 2.5cm). You would need also the thickness of the weld area and then you can calculate the resistivity using the formula we show in the video.

[@LonelyBird100]

From where did you buy these probs?

[@mgchemicals]

We cut a sheet of acrylic then drilled holes where the pins fit through. The probes are pogo pins and we used an epoxy to fix them into the holes in the acrylic. You can then attach your wires from the multimeter and current source into the end of the pogo pin and crimp for a good connection

[@dr.arpitgoyal963]

Can you give details of pogo pins such as diameter, length etc... also if any supplier or link

[@besherorabi7227]

Can we apply a voltage and measure the current instead, because I find it quite confusing, because to apply a current I am applying a voltage and allowing my circuit to withdraw Amperes till a certain value.

[@besherorabi7227]

Also, can I measure the electrical conductivity of a hydrogel with this set-up?

[@mgchemicals]

Besher, what you're describing is likely a 2-point probe set up where you take 2 probes and measure the resistance across a trace (like in the video) which is actually measuring current flow between the probes with the voltage fixed (although you can adjust the sensitivity of the multimeter). This will work as well, you just have to fix the distance between the probes to 1 inch and you can use the formula for resistivity which is rho = R*A/l where R is the resistance measured, A is the distance between the probes time the trace width and l is the thickness of the coating

[@karhukivi]

The outer electrodes are used to pass a small current and ideally a constant-current source is used. You don't need to know what voltage it is putting out as it is the voltage across the inner pair of electrodes that is used in the calculation.

[@mashrishi]

Can this method be used in determining the resistivity of a silicon semiconductor ?

[@mgchemicals]

I don't think so, the semiconductor would probably not be sufficiently conductive to register readings

[@karhukivi]

Yes it can and there are several articles on it online. The formula is a bit more complicated and depends on the diameter of a circular disk of the semiconductor and its thickness.

[@rundrish8740]

That was interesting. I have always found the difference between resistance and resistivity quite confusing.

[@mgchemicals]

A lot of people get confused over the 2 terms. I'm glad this video helped clarify this for you

[@volkanyanardag464]

First of all I have to admit I am very excited about your product. I used this for my master's thesis for my research. But I unfortunately correct something briefly. The surface resistance, which you determined in the video, is not entirely correct. The measurement is not entirely correct. The surface resistance can be determined using the 4-point measurement method by dividing the measured voltage by the current fed in. But this is not an infinitely large area. The correction factor changes accordingly. The determined surface resistance is to be provided with pi/ln(2) for infinitely large areas with thin layers and for finitely large areas the correction factor approaches pi/ln(2). In addition, the distances of the four-point measuring method must be equidistant for a correct measurement. So the distances between contact tips must have the same distance.