Briefly analyze the difference between thermocouple and thermal resistance

Both thermocouples and thermal resistances belong to the touch temperature measurement in temperature measurement. Although their effects are the same as measuring the temperature of objects, their principles and characteristics are different. First of all, let's introduce thermocouples, which are temperature measurement The most widely used temperature equipment in the world, its main features are the wide size of the kiss, the relatively stable function, the simple structure, the good dynamic response, and the remote transmission of 4-20mA electrical signal, which is convenient for automatic control and centralized control. The principle of thermocouple temperature measurement is based on the thermoelectric effect. When two different conductors or semiconductors are connected into a closed loop, when the temperatures at the two junctions are different, a thermoelectric potential will occur in the loop. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect. The thermoelectric potential that occurs in a closed loop is composed of two potentials; the thermoelectric potential and the touch potential. Thermoelectric potential refers to the potential that occurs at the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so their potentials are also different, and touch potential literally refers to two different conductors. When they touch each other, a certain amount of electron diffusion occurs because their electron densities are different. When they reach a certain equilibrium, the potential formed. The magnitude of the touch potential depends on the material properties of the two different conductors and the temperature of their touch points. . The thermocouples used in the world now have a standard specification. The thermocouples are divided into eight different divisions according to the international regulations, namely B, R, S, K, N, E, J and T. The lowest measurement temperature is It can measure minus 230 degrees Celsius and up to 1600 degrees Celsius. Among them, B, R, and S belong to platinum series thermocouples. Because platinum belongs to precious metals, they are also called precious metal thermocouples and the remaining ones are called cheap metal thermocouples. I. There are two types of thermocouples, ordinary type and armored type. Ordinary thermocouples are usually composed of hot electrodes, insulating tubes, protective sleeves and junction boxes, etc., while armored thermocouples are a combination of thermocouple wires, insulating materials and metal protective sleeves. A solid assembly formed by stretching. However, the electrical signal of a thermocouple requires a special wire to transmit, which is called a compensation wire. Different thermocouples require different compensation wires, the main effect of which is to connect with the thermocouple to keep the reference end of the thermocouple away from the power supply, so that the temperature of the reference end is stable. The compensation wire is divided into compensation type and extension type. The chemical composition of the extension wire is the same as that of the compensated thermocouple, but in practice, the extension wire is not made of the same metal as the thermocouple. A wire with the same electron density is replaced. The connection between the compensation wire and the thermocouple is usually very clear, the positive pole of the thermocouple is connected to the red wire of the compensation wire, and the negative pole is connected to the remaining color. Most of the raw materials of the usual compensation wires are copper-nickel alloys. Secondly, let's introduce thermal resistance. Although thermal resistance is widely used in the industry, its use is subject to certain constraints because of its temperature measurement scale. The temperature measurement principle of thermal resistance is based on the resistance value of conductors or semiconductors. characteristics that change with changes in temperature.

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