A basic temperature sensor, such as a thermistor, measures temperature by exploiting the property of materials to change their electrical resistance in response to temperature variations. A thermistor is a type of resistor whose resistance value changes with temperature.
There are two common types of thermistors: NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient).
NTC Thermistor (Negative Temperature Coefficient): In an NTC thermistor, the resistance decreases as the temperature increases. This means that as the temperature goes up, the electrical resistance of the NTC thermistor drops, and as the temperature goes down, the resistance increases.
PTC Thermistor (Positive Temperature Coefficient): In a PTC thermistor, the resistance increases as the temperature increases. This means that as the temperature rises, the electrical resistance of the PTC thermistor also increases.
The basic principle behind the operation of a thermistor is as follows:
NTC Thermistor: As the temperature changes, the movement and behavior of charge carriers within the thermistor's semiconductor material change. At higher temperatures, more charge carriers are available for conduction, leading to a lower resistance. Conversely, at lower temperatures, fewer charge carriers are available, resulting in a higher resistance.
PTC Thermistor: In this case, the behavior is opposite. As the temperature increases, the movement of charge carriers becomes more restricted, leading to an increase in resistance. At lower temperatures, charge carriers have more mobility, resulting in a lower resistance.
To measure temperature using a thermistor, you can create a simple electrical circuit that incorporates the thermistor as one of the components. By measuring the electrical resistance of the thermistor, you can indirectly determine the temperature based on the known resistance-temperature relationship of the thermistor.
This relationship is often characterized using a Steinhart-Hart equation or another similar mathematical model. Calibration is necessary to correlate the resistance of the thermistor to actual temperature values. Depending on the precision required, additional components like a microcontroller, analog-to-digital converter (ADC), and temperature lookup tables might be used to accurately convert resistance readings into temperature values.
In summary, a basic temperature sensor (thermistor) measures temperature by monitoring the change in its electrical resistance in response to temperature fluctuations, based on the type of thermistor being used (NTC or PTC).