A basic temperature sensor, such as a thermocouple, measures temperature through the principle of the Seebeck effect. The Seebeck effect is a phenomenon where a voltage is generated in a circuit consisting of two dissimilar conductive materials when there is a temperature difference between the two junctions of the materials.
Here's how a basic thermocouple works to measure temperature:
Thermocouple Materials: A thermocouple consists of two different metal wires joined at one end to form a junction. The metals used are typically chosen based on their thermoelectric properties, which means they produce a measurable voltage when subjected to a temperature gradient. Common thermocouple materials include types like Type K (Chromel-Alumel), Type J (Iron-Constantan), Type T (Copper-Constantan), and others.
Temperature Gradient: The thermocouple is placed in an environment where temperature needs to be measured. When the junction (the measurement point) experiences a temperature difference from the other end (the reference point), a voltage is generated across the thermocouple.
Measurement of Voltage: The generated voltage is a function of the temperature difference between the two junctions. This voltage can be measured using a voltmeter or other electrical measurement equipment. Since the voltage output is directly related to the temperature difference, it can be used to calculate the temperature at the measurement point.
Reference Junction Compensation: The Seebeck effect generates a voltage proportional to the temperature difference between the two junctions of the thermocouple. However, to determine the absolute temperature at the measurement point accurately, you need to know the temperature at the reference junction (where the thermocouple wires are connected to the measurement circuit). This reference junction temperature is typically measured using a separate temperature sensor (e.g., a thermistor or another thermocouple) and then used for compensation.
Temperature Conversion: Once the voltage is measured and the reference junction temperature is known, the thermocouple's output voltage is converted to a temperature reading using calibration tables or mathematical equations specific to the thermocouple type. These conversion tables or equations provide the relationship between voltage and temperature for that particular thermocouple material.
Thermocouples are widely used in various applications due to their simplicity, ruggedness, and wide temperature range capabilities. However, it's essential to note that thermocouples may have inherent errors, especially when used over extended periods or extreme temperature ranges. To improve accuracy, calibration and compensation techniques are applied based on the specific application requirements.