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How to distinguish between thermocouple and thermal resistance

by:Sure     2021-08-05
First, let me introduce thermocouples. Thermocouples are the most widely used temperature devices in temperature measurement. Their main characteristics are wide measurement range, relatively stable performance, simple structure, good dynamic response, and the ability to transmit 4-20mA electrical signals remotely. , It is convenient for automatic control and centralized control. The principle of thermocouple temperature measurement is based on the thermoelectric effect. Connecting two different conductors or semiconductors First, introduce thermocouples. Thermocouples are the most widely used temperature devices in temperature measurement. Their main characteristics are wide measurement range, relatively stable performance, simple structure and good dynamic response. It can transmit 4-20mA electrical signals remotely, which is convenient for automatic control and centralized control. The principle of thermocouple temperature measurement is based on the thermoelectric effect. Two different conductors or semiconductors are connected into a closed loop. When the temperatures at the two junctions are different, thermoelectric potential will be generated in the loop. This phenomenon is called the pyroelectric effect, also known as the Seebeck effect. The thermoelectric potential generated in the closed loop is composed of two kinds of electric potential; thermoelectric potential and contact potential. Thermoelectric potential refers to the electric potential generated by the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so they generate different electric potentials. The contact potential, as the name implies, refers to when two different conductors are in contact. Because their electron densities are different, a certain amount of electron diffusion occurs. When they reach a certain equilibrium, the potential formed by the contact potential depends on the material properties of the two different conductors and the temperature of their contact points. Thermocouples currently used internationally have a standard specification. The internationally stipulated thermocouples are divided into eight different divisions, namely B, R, S, K, N, E, J, and T, and the lowest measuring temperature can be measured. The temperature is minus 270 degrees Celsius, up to 1800 degrees Celsius. Among them, B, R, and S belong to platinum series thermocouples. Because platinum is a precious metal, it is also called a precious metal thermocouple. The rest are called cheap metal thermocouples. There are two types of thermocouple structures: common type and armored type. Ordinary thermocouples are generally composed of hot electrodes, insulating tubes, protective sleeves and junction boxes. The armored thermocouple is a solid combination formed by combining and assembling the thermocouple wire, insulating material and metal protective sleeve after stretching. But the electrical signal of the thermocouple needs a special wire to transmit, this kind of wire is called compensation wire. Different thermocouples require different compensation wires, and their main function 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. Compensation wires are divided into two types: compensation type and extension type. The chemical composition of the extension wire is the same as that of the thermocouple being compensated. However, in practice, the extension wire is not made of the same material as the thermocouple. Even wires with the same electron density are replaced. The connection between the compensation wire and the thermocouple is generally 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. Generally, the material of the compensation wire is mostly copper-nickel alloy. Next, we introduce thermal resistance. Although thermal resistance is widely used in industry, its application is limited due to its temperature measurement range. The temperature measurement principle of thermal resistance is based on the resistance value of conductor or semiconductor. The characteristics that change with temperature changes. It also has many advantages. It can also transmit electrical signals remotely. It has high sensitivity, strong stability, interchangeability and accuracy. However, it requires power supply and cannot instantaneously measure temperature changes. Industrial thermal resistance generally uses Pt100, Pt10, Cu50, Cu100. The temperature measurement range of platinum thermal resistance is generally minus 200-800 degrees Celsius, and copper thermal resistance is minus 40 to 140 degrees Celsius. The thermal resistance is the same as the thermocouple, but it does not require a compensation wire, and it is cheaper than the thermocouple.
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