What is the Seebeck effect, and how is it utilized in thermocouples for temperature measurement within a power plant?

The Seebeck effect is a thermoelectric phenomenon where a temperature difference between two dissimilar electrical conductors or semiconductors creates a voltage difference between them. This voltage difference is directly proportional to the temperature difference. In thermocouples, the Seebeck effect is utilized for temperature measurement by joining two different metal wires at two points, forming two junctions. One junction, called the measurement junction (or hot junction), is placed at the location where the temperature is to be measured. The other junction, called the reference junction (or cold junction), is maintained at a known reference temperature, often 0°C (ice bath) or a temperature-compensated electronic circuit. The temperature difference between the measurement junction and the reference junction generates a voltage, according to the Seebeck effect. This voltage is measured by a voltmeter or data acquisition system. Because the voltage is directly related to the temperature difference, the temperature at the measurement junction can be determined. Different combinations of metals, such as type K (Chromel-Alumel) or type J (Iron-Constantan), are used to create thermocouples for different temperature ranges and applications within a power plant, such as measuring flue gas temperatures, steam temperatures, and bearing temperatures.