A basic temperature sensor, such as a thermistor, measures temperature by utilizing the change in its electrical resistance with temperature variations. A thermistor is a type of resistor whose resistance changes significantly with temperature.
The most common types of thermistors are NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient). NTC thermistors are designed to have a decreasing resistance as the temperature increases, while PTC thermistors have an increasing resistance with temperature rise.
Here's how a basic NTC thermistor measures temperature:
Resistance-Temperature Relationship: Thermistors have a known resistance-temperature relationship, which is typically provided by the manufacturer in the form of a resistance-temperature curve or table. This curve shows how the resistance of the thermistor changes at different temperatures.
Circuit Connection: The thermistor is connected in a simple electrical circuit. For instance, it can be connected in series or parallel with a known reference resistor.
Voltage Measurement: A known current or voltage is applied to the circuit, which causes a current to flow through the thermistor. As the thermistor temperature changes, its resistance changes accordingly.
Voltage Divider Principle: The circuit setup creates a voltage divider network, where the voltage across the thermistor and the reference resistor depends on their respective resistances. The changing resistance of the thermistor alters the voltage across it.
Voltage Output: The output voltage from the voltage divider is measured using an analog-to-digital converter (ADC) or an analog amplifier circuit. This voltage can be proportional to the temperature of the thermistor.
Calibration and Conversion: To obtain an accurate temperature reading, the output voltage needs to be calibrated using the resistance-temperature curve provided by the manufacturer or derived from calibration experiments. Once the calibration is done, the measured voltage can be converted into temperature using appropriate mathematical equations or lookup tables.
It's important to note that the accuracy and precision of the temperature measurement depend on the quality of the thermistor, the calibration process, and the electronic components used in the circuit. Additionally, factors like self-heating and thermal inertia can also affect the sensor's performance, especially in rapid temperature changes or high-frequency applications. Proper consideration of these factors is crucial to ensure accurate temperature measurements.