A basic temperature sensor, such as a thermistor, measures temperature by responding to changes in temperature with corresponding changes in its electrical resistance. A thermistor is a type of temperature-sensitive resistor made from semiconductor materials, typically ceramics or polymers, that exhibit a significant change in resistance in response to variations in temperature.
The basic principle behind a thermistor's operation is as follows:
Resistance-Temperature Relationship: Thermistors are designed with a specific resistance-temperature relationship, which means their resistance changes predictably with temperature. There are two main types of thermistors: positive temperature coefficient (PTC) and negative temperature coefficient (NTC). In PTC thermistors, resistance increases with temperature, whereas in NTC thermistors, resistance decreases with temperature.
Measuring the Resistance: To measure the temperature, a known current (usually a small constant current) is passed through the thermistor, and the voltage across the thermistor is measured. Using Ohm's law (V = I * R), where V is the voltage, I is the current, and R is the resistance, the resistance of the thermistor can be calculated.
Temperature Calculation: By knowing the resistance-temperature relationship of the thermistor, the temperature can be calculated based on its resistance value. This is often done using a lookup table or a mathematical equation provided by the thermistor manufacturer.
Output: The temperature value is then converted into a readable form (analog or digital) and may be displayed on a screen, logged in a data logger, or used for various control and monitoring purposes in electronic systems.
It's essential to calibrate the thermistor's resistance-temperature relationship accurately to ensure accurate temperature readings. Different thermistors may have different sensitivity ranges and accuracies, so it's essential to choose the appropriate thermistor for the specific application and temperature range needed. Additionally, environmental factors, such as self-heating from the current passing through the thermistor, should be considered to obtain precise temperature measurements.