A basic temperature sensor, such as a thermocouple, measures temperature based on the principle of the Seebeck effect. The Seebeck effect is a phenomenon in which a voltage is generated at the junction of two dissimilar metals when there is a temperature gradient across the junction.
Here's how a basic thermocouple works to measure temperature:
Thermocouple construction: A thermocouple consists of two different metal wires or conductors joined together at one end to form a measuring junction. The other ends of the wires are connected to a temperature measuring instrument or controller.
Temperature gradient: When there is a temperature difference between the measuring junction and the free ends of the thermocouple wires, a voltage is generated across the junction due to the Seebeck effect.
Measurement of voltage: The voltage generated at the junction is measured by the temperature measuring instrument. The magnitude of this voltage is directly related to the temperature difference between the junction and the free ends of the thermocouple.
Reference temperature: To determine the actual temperature at the measuring junction, you need to know the temperature of the free ends of the thermocouple. This reference temperature is typically provided by a separate temperature sensor or a cold junction compensation circuit.
Temperature calculation: The temperature measuring instrument or controller uses the measured voltage and the reference temperature to calculate the temperature at the measuring junction. The relationship between the voltage and temperature is characterized by the thermoelectric properties of the specific metal combination used in the thermocouple.
Calibration: Thermocouples require calibration to ensure accurate temperature measurements. Calibration involves determining the relationship between the voltage output and the corresponding temperature for the specific thermocouple being used.
Thermocouples are widely used temperature sensors due to their simplicity, reliability, and broad temperature range capabilities. Different types of thermocouples are available, each with specific metal combinations tailored for various temperature ranges and applications. The most common types include Type K, Type J, Type T, Type E, and Type N thermocouples, among others.