# Thermistor Definition Construction and Applications

Published on 24/2/2012 and last updated on 24/8/2018
The word Thermistor stands for Thermal Resistor. The resistance of a thermistor gets changed with the change in temperature. The resistance of a thermistor has high sensitivity to temperature. Because of that we widely use it for measurements of temperature. The base material of a thermistor are mixtures of metallic oxides such as manganese, nickel, cobalt, copper etc. Semiconductor-based thermistors are also available in the market. It has Negative Temperature Coefficient of Resistance that means resistance of the thermistor gets decreased with increase in temperature. A thermistor may be more sensitive than a Resistance Temperature Detector (RTD) and Thermocouples Temperature Detector. The resistance of a thermistor lies between 0.5Ω to 75 MΩ. We can apply a thermistor temperature sensor for measuring temperature from - 20°C to 120°C.

## Construction of Thermistor

There are different shapes and sizes of thermistors available in the market. Smaller thermistors are in the form of beads of diameter from 0.15 millimeters to 1.5 millimeters. Thermistors may be in the form of disks and washers made by pressing thermistor material under high pressure into flat cylindrical shapes with diameter from 3 millimeters to 25 millimeters.

## Characteristics of Thermistors

The relationship governing the characteristics of thermistors is given below as: R1 = resistance of thermistor at absolute temperature; T1oK. R2 = resistance of thermistor at temperature T2oK. β = constant depending upon material of transducer. From the above equation, we can conclude that the relationship between temperature and resistance is highly nonlinear. A thermistor usually exhibits a negative thermal resistance temperature coefficient of about 0.05 / oC.

## Applications of Thermistors

Thermistors are used for the measurement of temperature as a change of temperature produces a large change in their resistance. They are used for the control of the temperature in any circuit.

Thermal Compensation - They can be used for the temperature compensation in any circuit. For example in any circuit a simple carbon resistor is connected which has a positive thermal coefficient. So, if the resistance of carbon resistor is to be made unaffected by the temperature so a thermistor having same negative thermal coefficient is connected in series with it. So, as due to rising in temperature resistance of resistor increases and resistance of the thermistor decreases by the same amount as the magnitude of there thermal coefficients is same. So, as the resistor and thermistor are in series, thus the net resistance of resistance remains the same. We use thermistor also for measurement of thermal conductivity of electrical materials.

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Thermistor Definition Construction and Applications
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