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How to measure NTC Thermistors?



The following general precautions have to be taken when measuring NTC thermistors:

1.Never measure thermistor in air; this is quite inaccurate and can give deviations of more than 1K.For measurements at room temperature or below, use low viscosity silicone oil or some other non-conductive and non-aggressive fluid. For higher temperature use oil, preferably silicone oil.

2.Use a thermostatic liquid bath with an accuracy and repeatability of better than 0.1c.Even if the fluid is well stirred, there is still a temperature gradient in the fluid. Measure the temperature as close as possible to the NTC

3.After placing the NTC in the thermostatic bath, wait until temperature equilibrium between the NTC and the fluid is obtained. For some types this may take more than 1min. Make sure that the NTC sensor is at an adequate depth below the fluid level, as ambient temperature can be conducted though wires or clamps to the sensing element.

4.Keep the measuring power as low as possible, otherwise the NTC will be heated by the measuring current. Miniature NTC thermistors are especially sensitive in this respect. Measuring power of less than 5% of the dissipation factor in the used medium is recommended, which gives self-heating of less than 0.05c.

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