A thermistor is an extremely useful type of resistor. If you need a current limiter, a temperature sensor or an overcurrent protector, they can be perfect for the job. Read on to find everything you need to know about thermistors. 

What is a thermistor?

A thermistor is a resistor that is capable of sensing temperature and changing its resistance proportionally to the change in heat. Usually, for thermistors, the resistance decreases as the temperature rises. They tend to be made from a mixture of metals and metal oxides.

Two types of thermistor

There are two different types of thermistors depending on your requirements. NTC thermistors (Negative temperature coefficient thermistors) decrease their electrical resistance as the temperature rises. This is particularly useful for measuring temperatures: from heating systems to limiting currents within power supply limits, NTC thermistors are important in a range of appliances.

PTC thermistors (positive temperature coefficient thermistors) increase in resistance as the temperature rises. This is useful for self-regulating heaters: once the temperature falls, more current gets through to the heating element resulting in the heater raising the temperature. What’s more, they can also operate as a fuse to protect against over-currents in appliances.

Both are different from the resistance temperature detector (RTD). RTDs are made from metal meaning that they can cope with higher temperatures. This also means they’re bigger and more expensive. Plus, while they can measure a higher temperature range, this comes at the cost of reacting to minute temperature changes less effectively. 

Advantages of thermistors

One of the main benefits of thermistors is that they’re inexpensive – it doesn’t cost much to add one to your appliance or project. To add to this, as they’re small in size they can measure temperature in a precise way. They sensitively react to temperature changes and quickly adjust the level of resistance. As such, they provide a high resolution of control over temperature – minute changes are quickly detected. 

Disadvantages of thermistors

On the flipside, while the thermistor offers precise reactions to small temperature changes, this is only possible because of its limited range. The maximum temperature that it can be exposed to is 662F. Another issue is that the thermistor’s resistance to temperature is non-linear: hot and cold temperatures – at their extremes – can disproportionately affect the device. Sometimes, thermistors can offer inaccurate readings too. This usually occurs when the current passing through the thermistor causes the device itself to heat up, resulting in inaccurate readings. 

Thermistors are the perfect tool if you want an appliance to react to small temperature changes. By following the guide above, you should be all set to purchase one today and benefit from this nimble tool.


Sumit is a Tech and Gadget freak and loves writing about Android and iOS, his favourite past time is playing video games.

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