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Help: Measuring Resistance of Microelectrode ?

Discussion in 'General Electronics Discussion' started by jeremealmore, Aug 25, 2010.

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  1. jeremealmore

    jeremealmore

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    Aug 25, 2010
    Dear All ,

    I was trying to measure the resistance of an Epoxy coated Tungsten Microelectrode using a HP Multimeter.

    The electrode length is 135mm and diameter is 200 micrometer.

    Both tips are stripped of epoxy insulation.

    When I tried to measure the resistance directly (by touching the multimeter leads on both ends ) , the multimeter showed "0L"

    Then I tried putting the electrode to some depths of saline and placing another needle along with it and then touching the multimeter leads on electrode and needle. Again the reading was "0L"

    I tested the multimeter with known resistances and needles/wires higher diameters and its working well !

    I googled a lot to find any theoretical problems associated with measuring the resistance of such fine microelectrods with multimeter . I couldnt find any definite answer .


    [The ideal resistance of the microelectrode is 10 mega ohms as per the company catalouge, but i need to test it atleast for some]


    Can anyone help me in this issue ? Is there any theoretical problems associated with this measurement ? If so what can be an alternative method ?

    Please help !!!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    place it in series with a load drawing a known current and measure the voltage drop across it. Best if you can measure voltage and current simultaneously.

    Oh, do it with DC to avoid inductive load issues.
     
  3. jeremealmore

    jeremealmore

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    Aug 25, 2010
    Thanks Steve, for your help ! :)

    I will try that method .
     
  4. trobbins

    trobbins

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    Jun 15, 2010
    You may want to recheck the use of the multimeter - but try to scrape clean the area used to make contact - the W surface may be contaminated, although I would have thought you would have got a reading. You could also try putting the multimeter probes next to each other on the W. Sometimes certain sections of multimeter probe tips can also be troublesome and contaminated - so perhaps try different probes and try to scratch/wipe the surfaces.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
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    Jan 21, 2010
    Hang on. 10 Meg -- I read it as 10 milliohms

    My method won't work.

    Check that your meter can actually read > 10 Mohm.

    The resistance may also depend on the electrode being in a solution, so contact with multimeter probes may not measure the right thing.
     
  6. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    Yes I thought it was a typo, but quickly checking on its use by others, the resistance may well be 20Meg for such a long length. So best to try the multimeter again but just check a much smaller length of wire - eg. 5-10mm - but not sure if the epoxy coating can be stripped back that far without ruining your application.
     
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