A thermistor is a type of temperature sensor that relies on the principle of resistance change with temperature. It is a semiconductor device whose electrical resistance changes significantly with temperature variations. There are two main types of thermistors: Negative Temperature Coefficient (NTC) and Positive Temperature Coefficient (PTC) thermistors.
Here's how a basic NTC thermistor works to measure temperature:
Resistance-Temperature Relationship: NTC thermistors are designed with materials that exhibit a strong and predictable change in resistance with temperature. Typically, as the temperature increases, the resistance of the thermistor decreases. This relationship can be described using a specific mathematical formula or a resistance-temperature table provided by the thermistor manufacturer.
Circuit Connection: The thermistor is connected within an electrical circuit. A common configuration is to connect the thermistor in series with a known resistor (usually a fixed-value resistor) to create a voltage divider circuit. This forms a simple resistive network.
Voltage Measurement: A voltage is applied across the voltage divider circuit. As the temperature changes, the resistance of the thermistor changes accordingly, which alters the voltage distribution across the circuit.
Voltage Output: The voltage at the junction between the thermistor and the fixed resistor changes with temperature due to the changing resistance of the thermistor. This voltage can be measured using an analog-to-digital converter (ADC) if digital output is required, or it can be directly measured using an appropriate voltmeter or microcontroller.
Temperature Calculation: Using the resistance-temperature relationship of the thermistor, the measured voltage can be converted into an equivalent temperature value. This conversion typically requires knowledge of the specific thermistor's resistance-temperature characteristics and the properties of the voltage divider circuit.
Calibration and Compensation: To ensure accurate temperature measurements, the thermistor circuit may require calibration to account for any nonlinearities in the resistance-temperature relationship. Compensation techniques can also be applied to correct for inaccuracies caused by factors such as self-heating of the thermistor during operation.
NTC thermistors are widely used in various applications, including temperature monitoring and control, automotive systems, medical devices, and industrial equipment.
It's important to note that the exact implementation and circuit design can vary based on the specific requirements of the application and the characteristics of the thermistor being used.