A basic temperature sensor, such as a thermocouple, measures temperature by exploiting the principle of the Seebeck effect. The Seebeck effect states that when two dissimilar metals are joined together at two junctions, and there is a temperature gradient along the length of the metals, a voltage is generated at the junctions.
Here's how a basic thermocouple works:
Thermocouple materials: A thermocouple consists of two different metal wires or alloys, typically made of different combinations of materials like iron, copper, constantan, or chromel. The two wires are connected to form two junctions.
Temperature gradient: When one end of the thermocouple is exposed to a temperature different from the other end, a temperature gradient is established along the length of the thermocouple.
Generation of EMF: Due to the Seebeck effect, a small voltage (electromotive force or EMF) is generated at the two junctions. The magnitude of this voltage depends on the temperature difference between the two junctions and the specific characteristics of the thermocouple material.
Measuring the voltage: The generated voltage can be measured using a voltmeter or a specialized electronic circuit. The voltage is proportional to the temperature difference between the two junctions, and the relationship between the voltage and temperature is unique for each type of thermocouple.
Reference junction: To determine the absolute temperature at one of the junctions, a reference temperature (usually the temperature at the other end of the thermocouple) needs to be known. This reference junction is typically maintained at a constant known temperature, and its contribution to the voltage measurement is taken into account during temperature calculations.
Temperature calculation: By comparing the measured voltage with a known temperature-voltage calibration table or equation specific to the thermocouple type, the temperature at the measuring junction can be determined.
Thermocouples are widely used in various industrial and scientific applications due to their simplicity, durability, and wide temperature measurement range. However, it's important to note that thermocouples may introduce some measurement errors due to issues such as non-linear response, cold junction compensation, and signal interference. To achieve higher accuracy, more sophisticated temperature sensors like resistance temperature detectors (RTDs) and thermistors are often used.