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4 point probe measurement help

  1. Jun 26, 2003 #1
    4 point probe measurement help!!

    I will really appreciate if somebody can help me:

    I was trying to measure the electrical conductivity of some conductive polymer films using the 4 point probe technique. Altough is widely described and seems easy to arrange, I have been unable to measure my samples due to the following problems:

    1.- As soon as I turn on the power source the films burns out (like a fuse)due to the joule effect, I guess, even when I set the power source in the "constant current" mode, fixed to the minimum.
    2.- When I tried to measure the electrical conductivity of the semiconducting samples, (or at least I thought so...), no voltage drop is detected between the inner probes, and no current flows at all. It seems to be "too insulating" to close the circuit
    3.- The digital multimetter is always changing the voltage drop measurement, whether the current source is on or off. Could it be due to the connections?... some bi-metalic joint effect?

    I hope some of you have done this kind of measurements before, I really need to know the conductivity of my samples. If you need further information feel free to contact me...
     
  2. jcsd
  3. Jun 27, 2003 #2
    For the first problem you could put a shunt resistor in the cicuit to limit the current through the sample.

    If the sample is insulating then you wont read a votlage across the inner leads.

    A perferred method is to use a lockin-amp and measure the AC-resistance. It will give you a better S/N ratio. Otherwise you might need a nanovolt meter you get decent results.

    How are you attaching your leads to the sample? This was a major problem that I ran into while making these type measurements.


    JMD
     
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