A thermistor, also known as a thermal resistor, is a semiconductor and is used in specific applications to compensate for temperature variation. Thermistors are often chosen because of their simple structure and are used as a lower cost alternative to thermocouples. Using a thermistor is a good option for limiting a temperature range within a system and aren’t as useful in high temperature scenarios.

How Thermistors Work

There are two types of thermistors, which differ because of their relationship between temperature and resistance.

●     NTC: negative temperature coefficient

  • Resistance decreases as temperature increases, and vice versa

●     PTC: positive temperature coefficient

  • Resistance increases as temperature increases, and vice versa

The resistance of a thermistor changes depending on the material used to form the thermistor. Thermistors are non-linear, meaning the connection between resistance and temperature is reflected in a curve or graph, not a straight line.

Putting all the details together, a thermistor is basically a temperature sensor, where a current allows the system to convert the thermistor’s resistance into a voltage. As the voltage changes the temperature controller reads this change and the system adjusts as needed.

What Thermistors Measure

A thermistor is used to measure temperature. Operating as a temperature sensor, a thermistor reflects the temperature within the system or in the surrounding area, relaying information to the temperature controller.

These sensors work best when measuring a single temperature of a system, as they usually connect to a controller that allows the user to change the temperature as needed, such as with an air conditioner or refrigeration unit. While there are two types of thermistors, only NTC thermistors are used in temperature measurement.

Using a thermistor with a setpoint in the middle of the desired range is ideal, as this provides the most accurate measurements and gives the system time to adjust its function depending on the temperature. Having a setpoint in the middle of the range also ensures the device, such as a cooler, doesn’t reach the upper or lower limit before the controller has time to reflect the current temperature reading.

Applications for Thermistors

Thermistors are present in many systems used in daily life and can be found in household items, almost anything with the option to set a specific temperature probably uses a thermistor of some kind. The application of a thermistor in these settings is to either directly measure a temperature or to protect the heating or cooling circuits within the system itself.

A few of the most common applications for thermistors include:

●     Digital thermometers

●     Automotive settings

  • Measure oil temperature
  • Measure coolant

●     Household appliances

  • Ovens
  • Refrigerators

●     Heaters

●     Coolers

  • Home units
  • Commercial air conditioning
  • Display cases
  • Refrigeration

A thermistor is an integral part of many systems, as it is the temperature sensor of the system. Using a thermistor has many practical applications, all with the goal of providing the temperature controller with necessary information about the temperature of the environment. Choosing a thermistor is a cost-effective, simple, and functional option that works best as a sensitive sensor monitoring a specific range of temperatures.

Probes designs and manufactures a wide range of custom thermistors. Regardless of where your company is in the development process, we can assist in the planning, design and manufacture of the thermistor you need for a specific application. Please contact us today!