Thermocouple is a type of temperature measuring sensor or thermoelectric sensing element made of two different materials (metals) with two junctions. A junction is called a cold junction or reference junction and the temperature at this junction is constant. The other is called a hot junction or gauge junction. When these two junctions are at different temperatures, a voltage is generated and this voltage is used to interpret the temperature. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get an Original Essay The effect of temperature difference in creating a voltage is called the thermoelectric effect and is the basic principle used in the use of thermocouple. for temperature measurement. Thermocouples can be designed to measure temperatures ranging from -200? to 2000 ?. They have the widest temperature measurement range of all temperature sensors. The principle of operation is based on the discovery of the German physicist Johann Seebeck. He discovered in 1821 that when different metals are joined at the ends and there is a temperature difference between the joints, a magnetic field is observed. This is what he calls thermomagnetism. This magnetic field was later discovered to be the result of a thermoelectric current, supporting the theory that two dissimilar metals, when joined, create a voltage at their junction. It is this voltage that is useful in determining the temperature. Temperatures can be very low or very high. The voltages generated are generally very low and of the order of microvolts. The magnitude of the tension depends on the type of materials used. Seebeck Effect Seebeck's discovery is the so-called Seebeck effect which is actually an example of an electromotive force (EMF). An electromotive force leads to measurable currents or voltages. Under open circuit conditions where there is no internal current flow, the voltage gradient (?V) is directly proportional to the temperature gradient (?T): ?V = -S(T)?TOwhere S (T) is a temperature-dependent material property known as the Seebeck coefficient. The standard measurement setup shows four temperature regions and therefore four voltage contributions. The passage from Tmeter to Tref in the lower copper wireThe passage from Tref to Tsense in the alumel wireThe passage from Tsense to Tref in the chomel wireThe passage from Tref to Tmeter in the upper copper wireThe first and fourth contributions are directly cancel because these regions involve the same temperature change and the same metal. Consequently, the Tmeter does not influence the measured voltage. The second and third contributions do not cancel each other because they involve different materials. The measured voltage turns out to be: V = Where S+ and S- are the Seebeck coefficients of the conductors attached respectively to the positive and negative terminals of the voltmeter (chromel and alumel in the figure)To obtain the Tsense measurement, it is necessary to know the temperature at the reference junctions. Measuring voltage alone does not allow the determination of Tsense. There are two (2) methods for establishing the temperature at reference junctions: The first is the use of an ice bath to create a fixed temperature. The reference terminal block is immersed in a semi-frozen bath of distilled water at atmospheric pressure. The precise temperature of the melting point phase transition acts as a thermostat setting the Tref. to 0?.The second method consists of using a sensor (called “cold junction compensation”). The temperature of the reference terminal block may vary, but its temperature is,.