The difference between thermocouple and thermal resistor

fighting

The difference between thermocouple and thermal resistor [Copy link]

The difference between thermocouple and thermal resistor

【Source: China PCB Technology Network】【Author:】【Time: 2006-1-10 8:48:32】【Click: 165】

Both thermocouples and thermal resistors belong to contact temperature measurement. Although they have the same function of measuring the temperature of an object, their principles and characteristics are not exactly the same. First, let me introduce the thermocouple. Thermocouple is the most widely used temperature device in temperature measurement. Its main features are wide measuring range, relatively stable performance, simple structure, good dynamic response, and the ability to transmit 4-20mA electrical signals remotely, which is convenient for automatic control and centralized control. The temperature measurement principle of thermocouple 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 be generated in the loop. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect. The thermoelectric potential generated in the closed loop consists of two potentials: thermoelectric potential and contact potential. Thermoelectric 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 the potential they generate is also different. As the name suggests, the contact potential refers to the potential formed when two different conductors are in contact because their electron densities are different, so a certain amount of electron diffusion is generated. 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 internationally have a standard specification. The international regulations stipulate that thermocouples are divided into eight different divisions, namely B, R, S, K, N, E, J and T. The lowest temperature can be measured at minus 270 degrees Celsius and the highest temperature can reach 1800 degrees Celsius. Among them, B, R, and S belong to the platinum series of thermocouples. Since platinum is a precious metal, they are also called precious metal thermocouples, and the remaining ones are called cheap metal thermocouples. There are two types of thermocouple structures, ordinary type and armored type. Ordinary thermocouples are generally composed of thermocouples, insulating tubes, protective sleeves and junction boxes, while armored thermocouples are a solid combination of thermocouple wires, insulating materials and metal protective sleeves after assembly and stretching. However, the electrical signal of the thermocouple requires a special wire to transmit, which we call a compensation wire. Different thermocouples require different compensation wires, whose main function is to connect with the thermocouple to keep the reference end of the thermocouple away from the power supply, so that the reference end temperature 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 compensated thermocouple. However, in practice, the extension wire is not made of the same metal as the thermocouple. It is generally replaced by a wire with the same electron density as the thermocouple. 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. Most of the general compensation wires are made of copper-nickel alloy. Next, let us introduce thermal resistors. Although thermal resistors are widely used in industry, their application is limited due to their temperature measurement range. The temperature measurement principle of thermal resistors is based on the characteristic that the resistance value of a conductor or semiconductor changes with temperature. It has many advantages. It can also transmit electrical signals remotely, has high sensitivity, strong stability, good interchangeability and accuracy, but requires power excitation and cannot measure temperature changes instantaneously. Industrial thermal resistors generally use Pt100, Pt10, Cu50, Cu100. The temperature measurement range of platinum thermal resistors is generally -200-800 degrees Celsius, and that of copper thermal resistors is -40 to 140 degrees Celsius. Thermal resistors are classified in the same way as thermocouples, but they do not require compensation wires and are cheaper than thermocouples. </

zcgzanne

Well, I have encountered many on-site repairs, but there are too many PT100 products at present.

dongin

I learned...