A basic temperature sensor, such as a thermocouple, measures temperature based on the principle of the Seebeck effect. The Seebeck effect is a phenomenon where a voltage is generated at the junction of two dissimilar metals when there is a temperature difference between the two junctions.
Here's how a basic thermocouple temperature sensor works:
Principle: A thermocouple consists of two wires made of different metals or metal alloys. When one end of the thermocouple (known as the hot junction) is exposed to the temperature being measured, and the other end (known as the cold junction) is at a reference temperature (usually ambient temperature), a temperature gradient is created along the length of the thermocouple.
Seebeck effect: The temperature gradient causes an electric potential difference (voltage) to be generated between the hot and cold junctions of the thermocouple. The magnitude of this voltage depends on the temperature difference and the specific characteristics of the metal or alloy used in the thermocouple.
Measurement: The generated voltage is directly proportional to the temperature difference between the hot and cold junctions. To measure the temperature accurately, you need a reference point (often called a reference junction or cold junction compensation) at the cold end of the thermocouple to provide the ambient temperature. This reference point ensures that the temperature difference measured is accurate, and the actual temperature can be calculated using appropriate tables, calibration curves, or thermocouple-specific equations.
Signal processing: The voltage generated by the thermocouple is typically very small, so it needs amplification and signal conditioning before it can be read by a temperature measuring device or controller. Signal conditioning includes removing any unwanted noise and compensating for any errors introduced due to the connection and extension of the thermocouple wires.
Output: The temperature measurement is then presented as an electrical signal (usually in millivolts) corresponding to the temperature being measured. The reading can be displayed on a digital temperature indicator, data logger, or sent to a temperature control system for further processing.
Thermocouples are widely used temperature sensors due to their simplicity, durability, and wide temperature measurement range. However, it's important to note that they may have some limitations in terms of accuracy and sensitivity, especially when measuring very low temperatures or requiring high precision. Other temperature sensors, such as RTDs (resistance temperature detectors) and thermistors, are also commonly used depending on the specific application requirements.