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Application of thermoelectric phenomena in science and engineering

E. d. with. the thermocouple is directly proportional to the temperature difference between junctions of dissimilar metals. In some cases, there are deviations from this rule, due to changes in the internal structure of the metal at certain temperatures. However, for various ranges of temperatures you can pick up such thermocouples, for which this rule is executed. Thus, measuring e. d. with. thermocouple, you can determine the temperature difference between the junctions, t. e. to measure thermocouple temperature. The temperature measurement accuracy is determined by the accuracy of the measurement is e. d. with. voltmeter.

Since there are currently accurate and sensitive voltmeters, the thermocouple can measure very small temperature difference. In addition, thermocouple can measure very low, so n high temperature, therefore, thermocouples are widely used in science and technology as an accurate thermometer. One such thermocouple is shown in figure. 18.8. Omitting one of the junctions (And) in the melting snow, determine the temperature of the other junction (In) voltmeter, a scale graduated in degrees. Sometimes to increase the sensitivity, several thermocouples connect to the battery (rice. 18.9). This allows measuring very small flows of radiant energy (for example, from the star).

In practice, often use thermocouple iron-Constantan (alloy si+Ni), copper-Constantan, chromel (alloy Cr+Ni)-alumel (alloy Al+Ni) etc. For measuring high temperature using thermocouple, made of refractory metals, for example, platinum and its alloys (rice. 18.6).

Thermocouples are widely used not only to control, but for automatic temperature regulation, since the thermocouple temperature data come in the form of an electrical signal (thermo-e. d. S.), which can be easily enhanced with the help of electron tubes and used for power control of the heater.

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