Thermocouples and thermal resistors are both contact-type temperature measurement in temperature measurement. Although their functions are the same to measure the temperature of objects, their principles and characteristics are not the same.
First of all, introduce the thermocouple . Thermocouple is the most widely used temperature device in temperature measurement. Its main characteristics are wide temperature measurement range, stable performance, simple structure, good dynamic response, and the ability to transmit 4-20mA electricity. Signal for easy 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 temperature at the two junctions is different, a thermoelectric potential will be generated in the loop. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect. The thermoelectric potential generated in a closed loop is composed of two potentials; the temperature difference potential and the contact potential. The temperature difference potential refers to the potential generated by the two ends of the same conductor due to different temperatures. Different conductors have different electron densities, so they generate different potentials. The contact potential, as its name implies, is when two different conductors are in contact. Because of their different electron densities, there is a certain amount of electron diffusion. When they reach a certain equilibrium, the potential formed. The size of the contact potential depends on the material properties of the two different conductors and the temperature of their contact points. At present, the thermocouples used in the world have a standard specification. The international regulations stipulate that the thermocouple is divided into eight different graduations, which are B, R, S, K, N, E, J, and T. The lowest possible measurement temperature is Measured at minus 270 degrees Celsius, up to 1800 degrees Celsius, of which B, R, and S belong to the platinum series thermocouples . Since platinum is a precious metal, they are also called noble metal thermocouples and the remaining ones are called cheap metal thermoelectrics. Even . There are two types of thermocouples, ordinary and armored. Ordinary thermocouples are generally composed of thermal electrodes, insulating tubes, protective sleeves, and junction boxes. Armored thermocouples are assembled by combining thermocouple wire, insulating material and metal protective sleeve. It is a solid combination made by drawing. However, the electrical signal of the thermocouple needs a special kind of wire to transmit. This kind of wire is called a compensation wire. Different thermocouples require different compensation wires. Their main function is to connect 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 compensation type and extension type. The chemical composition of extension wires is the same as that of the thermocouple being compensated. However, in practice, extension wires are not made of the same material as thermocouples. Replace the wires with the same electron density. The connection between the compensation wire and the thermocouple is generally clear. The positive electrode of the thermocouple is connected to the red wire of the compensation wire, while the negative electrode is connected to the remaining color. Most of the materials of general compensation wires are copper-nickel alloys.
Secondly, we introduce the thermal resistance. Although the thermal resistance is also widely used in industry, but because of its temperature measurement range, his application is limited. The temperature measurement principle of the thermal resistance is based on the resistance value of the conductor or semiconductor. A characteristic that changes with temperature. It also has many advantages. It can also transmit electric signals remotely, with high sensitivity, strong stability, interchangeability and accuracy. However, it requires power supply excitation and cannot measure temperature changes instantaneously. Industrial thermal resistance generally uses Pt100, Pt10, Cu50, Cu100. The temperature range of platinum thermal resistance is generally minus 200-800 degrees Celsius, and the copper thermal resistance is minus 40 to 140 degrees Celsius. The thermal resistance is the same type as the thermocouple, but it does not need a compensation wire and is cheaper than a hot couple .
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