A basic temperature sensor, also known as a thermistor, measures temperature through changes in its electrical resistance in response to temperature variations. The word "thermistor" is a combination of "thermal" and "resistor," indicating its operation based on temperature-dependent resistance.
Thermistors are made of semiconductor materials, usually metal oxides like nickel, cobalt, manganese, or iron, that exhibit a significant and predictable change in resistance as the temperature changes. There are two main types of thermistors:
Negative Temperature Coefficient (NTC) thermistor: In this type, the resistance decreases as the temperature rises. NTC thermistors are the most common and widely used type in temperature sensing applications.
Positive Temperature Coefficient (PTC) thermistor: In this type, the resistance increases as the temperature rises.
Here's how a basic NTC thermistor measures temperature:
Resistance-Temperature Relationship: NTC thermistors have a characteristic resistance-temperature relationship, which means their resistance decreases as the temperature increases (and vice versa). This relationship is often nonlinear, and the specific relationship depends on the type and material of the thermistor.
Circuit Connection: The NTC thermistor is connected within an electrical circuit. It can be part of a voltage divider circuit or a Wheatstone bridge circuit, depending on the application and the accuracy required.
Voltage Measurement: When the NTC thermistor is subjected to a temperature change, its resistance alters accordingly. As a result, the voltage across the thermistor changes in response to the temperature variation.
Analog-to-Digital Conversion: The voltage changes detected across the thermistor are then converted into a digital signal through an analog-to-digital converter (ADC) if a digital temperature reading is desired. This digital value can then be processed by a microcontroller or a computer.
Calibration: To convert the digital value into a temperature reading, the system requires calibration, which involves establishing a relationship between the resistance of the thermistor and the corresponding temperature.
The microcontroller or the processing unit uses this calibration data to determine the temperature based on the resistance reading from the thermistor. By continuously measuring the resistance and converting it to temperature using the calibration data, the thermistor-based temperature sensor provides accurate temperature measurements in various applications, such as weather stations, thermostats, and industrial control systems.