How to test a thermistor

john March 21, 2011 9 Comments

Thermistors are of two types, NTC (negative temperature coefficient) and PTC (positive temperature coefficient types). As their name indicates the resistance of an NTC thermistor will decrease with temperature and the resistance of a PTC thermistor will increase with temperature. Both PTC as well as NTC thermistors can be roughly checked by using an analogue multimeter.

Keep the analogue multimeter in resistance mode. Connect the multimeter terminals to the thermistor leads. Polarity is not an issue here. Now heat the thermistor by moving your heated soldering iron tip to it. Now you can see the multimeter reading smoothly increases or decreases depending on whether the thermistor under test is PTC or NTC. This will happen only for a healthy thermistor.

For a faulty thermistor, following observations are possible.

  • The change in reading will not be smooth or there will not be any change.
  • For a short thermistor the meter reading will be always zero.
  • For an open thermistor the meter reading will be always infinity.

This is only a rough test. For a perfect check up; you need some way to measure the temperature and the corresponding resistance reading must be according to the thermistor’s temperature-resistance characteristics provided by the manufacturer.

Comments
  • March 31, 2014

    Please let me know the procedure for testing Thermister NTC by voltage method.

    • Seetharaman
      March 31, 2014

      Feed constant DC current of 1mA andd measure the DC voltage drop across the thermistor By now heating the thermister measure the chane in voltage if it falls it is NTC and if it raises it is PTC.

  • zeeshan
    February 13, 2014

    very useful information thank you so much

  • Martin Mala
    September 8, 2012

    The NTC and PTC seem to have the same descriptions on this article. According to this article defination, the NTC becomes a PTC when temp rises and the PTC becomes an NTC when temp lowers.Please clarify i cud be wrong. Thank you.

    • leandro v
      February 6, 2014

      The article states that for ntc the resistance will decrease when the temperature increase, while for ptc the resistance will increase when the temperature increase.

  • fube niba
    August 21, 2012

    please i will like to know more about testing thermistor and ordre componet on an A/c/chiller circut if you help i will be greatful
    thanks in advance

  • August 8, 2012

    Plz how to test IC and to read their pin accordinly

    • fube niba
      August 21, 2012

      yes it importan if i can know test for IC and read their pin accordinly

  • waky
    November 29, 2010

    thanks 4 th blog, i find it technical inspiring, as of yet i had probls in trouble shooting of th PTC, thnx alot,

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