The difference between thermocouples and thermoresistors
Thermocouple and thermal resistance both belong to the contact temperature measurement in temperature measurement, although their role is the same to measure the temperature of the object, but their principle and characteristics are not the same.
First of all, introduce the thermocouple, thermocouple is the most widely used temperature device in temperature measurement, his main characteristics are wide kiss detection range, relatively stable performance, simple structure, good dynamic response, more able to transmit 4-20mA electrical signals, easy to 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, the thermoelectric potential will be generated in the loop when the temperature at the two contact points is different, this phenomenon is called the thermoelectric effect, also known as the Seebeck effect. The thermoelectric potential generated in the closed loop is composed of two kinds of potential; Temperature difference potential and contact potential. Thermal potential refers to the two ends of the same conductor due to different temperatures caused by the potential, different conductors have different electron densities, so the potential they produce is not the same, and the contact potential as the name suggests refers to two different conductors in contact, because their electron density is different so produce a certain electron diffusion, when they reach a certain balance of the formation of the potential The size of the shock potential depends on the material properties of the two different conductors and the temperature of their contact point.
At present, the thermocouple used internationally has a standard specification, the thermocouple is divided into eight different degrees, respectively B,R,S,K,N,E,J and T, the measurement temperature can be measured at a minimum of minus 270 degrees Celsius, up to 1800 degrees Celsius, of which B,R,S belongs to the platinum series of thermocouples, because platinum belongs to precious metals, so they also They are called precious metal thermocouples and the few that remain are called cheap metal thermocouples. There are two types of thermocouple structure, ordinary type and armored type. Ordinary thermocouples are generally composed of thermal electrodes, insulating tubes, protective bushing and junction boxes, etc., while armored thermocouples are a solid combination of thermocouple wire, insulating material and metal protective bushing after stretching. However, the electrical signal of the thermocouple needs a special wire to be transmitted, which is called the compensation wire. Different thermocouples need different compensation wires, and its main function is to connect with the thermocouple to make the reference end of the thermocouple away from the power supply, so that the reference end temperature is stable.
Compensation wire is divided into compensation type and extension type two, the chemical composition of the extension wire is the same as the compensated thermocouple, but in practice, the extension wire is not used with the same material as the thermocouple metal, generally used and thermocouple with the same electron density of the wire instead. The connection of the compensation wire to the thermocouple is generally clear, the positive end of the thermocouple connects the red line of the compensation wire, and the negative end connects the remaining color. Most of the general compensation wire materials are made of copper-nickel alloy.
Secondly, we introduce the thermal resistance, although the thermal resistance is also widely used in industry, but because of its temperature measurement range, its application is limited to a certain extent. The temperature measurement principle of thermal resistance is based on the resistance value of conductors or semiconductors with the change of temperature characteristics. Its advantages are also many, can also be far transmission of electrical signals, high sensitivity, strong stability, interchangeability and accuracy are better, but the need for power excitation, can not be instantaneous measurement of temperature changes. Industrial thermal resistance generally uses Pt100,Pt10,Cu50,Cu100, platinum thermal resistance temperature measurement range is generally minus 200-800 degrees Celsius, copper thermal resistance is minus 40 to 140 degrees Celsius.