Thermocouple Thermometer—Thermoelectric Effect Temperature Measurement
definition:
A pair of conductors of different materials that produce an electromotive force in a circuit based on the Seebeck effect. A pair of conductors of different materials that are bonded together at one end and use their thermoelectric effect to achieve temperature measurement.
Overview:
A thermocouple is a temperature sensing element and an instrument. It directly measures the temperature, converts the temperature signal into a thermal electromotive force signal, and converts it into the temperature of the measured medium through an electrical instrument (secondary instrument). The basic principle of thermocouple temperature measurement is that two conductors of different compositions form a closed loop. When there is a temperature gradient at both ends, a current will pass through the loop. At this time, there is an electromotive force - thermal electromotive force - between the two ends. This It's the so-called Seebeck effect. Two homogeneous conductors with different compositions are hot electrodes. The end with a higher temperature is the working end, and the end with a lower temperature is the free end. The free end is usually at a constant temperature. According to the functional relationship between thermoelectromotive force and temperature, a thermocouple indexing table is made; the indexing table is obtained when the free end temperature is 0°C. Different thermocouples have different indexing tables.
When a third metal material is connected to the thermocouple loop, as long as the temperature of the two joints of the material is the same, the thermoelectric potential generated by the thermocouple will remain unchanged, that is, it will not be affected by the third metal being added to the loop. Therefore, when measuring the temperature of a thermocouple, the measuring instrument can be connected. After measuring the thermal electromotive force, the temperature of the measured medium can be known. When measuring temperature of a thermocouple, it is required that the temperature of its cold end (the measuring end is the hot end, and the end connected to the measuring circuit through the lead is called the cold end) remains constant, so that the thermoelectric potential is proportional to the measured temperature. If the (environmental) temperature of the cold end changes during measurement, the accuracy of the measurement will be seriously affected. Taking certain measures at the cold end to compensate for the effects caused by temperature changes at the cold end is called cold end compensation of thermocouples. Attached: Thermocouple cold end compensation calculation method: from millivolts to temperature: measure the cold end temperature, convert it to the corresponding millivolt value, add it to the millivolt value of the thermocouple, and convert the temperature. From temperature to millivolts: measure the actual temperature and cold end temperature, convert them into millivolts respectively, and subtract them to get the millivolt value, which is the temperature.
