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In this article we will describe how to test a ptc heating resistor - to check if it is good.

PTC heating resistorA resistor whose resistance value changes depending on the temperature it is exposed to.

There are 2 main types of PTC heating resistors: negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors.

PTC thermistors are thermally sensitive resistors whose resistance increases as the temperature they are exposed to increases. Therefore, if heat is applied to a PTC thermistor, its resistance will increase accordingly.

Since a thermistor is a component that changes its resistance based on the heat applied, we can use this property to test it.

All you need to test a thermistor is an ohmmeter or a multimeter that includes an ohmmeter. We then use the ohmmeter to check the resistance after various stages of testing to see if the thermistor is behaving as the thermistor should. If it does, it's good. If it doesn't, it's a fault.

Equipment Needed to Test Thermistors

Thermistor (to be tested)
Heaters, dry blowers or any type of heating device


How to Test NTC Thermistors
Likewise, an NTC thermistor is a thermally sensitive resistor whose resistance decreases as the temperature it is exposed to increases.

We will check this feature to see if it behaves accordingly.

First, before applying any heat to the thermistor, check its rating. For example, the thermistor might be 100Ω, 1KΩ, 10KΩ, 100KΩ, etc.

Before any heat is applied to the thermistor, its resistance value should be very close to its rated resistance value.

So, for example, if we are testing a 10KΩ thermistor, before we heat it up, its resistance value should be very close to 10KΩ. If you are in a relatively warm room, it will probably be around 9.3KΩ. If you are in a cooler area, it will have a higher value.

This is the first preliminary test to check if the thermistor is good. If it is close to its rated resistance value, then it is good so far. If it is far or very far from the rated value, then the thermistor is faulty and should be discarded.

The next test is to apply heat to the thermistor. This can be done with a heater, a dry hair dryer, or any type of heating device.

When you apply heat to the body of a thermistor, its resistance should begin to steadily decrease within a few seconds of the heat being applied. If the NTC thermistor follows this behavior, it is good. If not, it is faulty and should be discarded.



How to test a ptc thermistor Testing a PTC thermistor follows all the same steps as an NTC thermistor.

First check the thermistor with an ohmmeter without heating. When using a PTC thermistor at room temperature or lower, the thermistor should measure a very low resistance.

Now heat the body of the thermistor as before. The resistance of the PTC thermistor should rise gradually and steadily within a few seconds of the heat being applied.

If the resistance increases steadily, thenPTC Thermistorsis good. If not, it is faulty and should be discarded.