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What is the difference between thermocouple and thermal resistance?

Release date: 2017-07-20 09:42:57 Visits: 781

Thermocouples and thermal resistors are all in the temperature measurement of the contact temperature, although the same role is to measure the temperature of the object, but their principles and characteristics are not the same.
Thermocouple is the most widely used temperature measurement device, its main feature is the measurement range is wide, the performance is relatively stable, while the structure is simple, dynamic response is better, more remote transmission 4-20mA electrical signal, easy to control and centralized control The Thermocouple temperature measurement principle is based on thermoelectric effect. Connect two different conductors or semiconductors to a closed loop. When the temperatures at the two junctions are different, the thermoelectric potential will be generated in the loop. This phenomenon is called thermoelectric effect, also known as the Seebeck effect. The thermoelectric power generated in the closed loop has two potentials: the temperature difference potential and the contact potential.
Temperature difference potential refers to the same conductor at both ends due to different temperatures generated by the potential, different conductors have different electron density, so they produce the potential is not the same, and the contact potential as the name suggests refers to two different contact with the conductor, Because of their electronic density, there is a certain amount of electron diffusion, and when they reach a certain equilibrium, the magnitude of the contact potential depends on the material properties of the two different conductors and the temperature of their contact points. At present the international application of the thermocouple has a standard specification, the international requirements of the thermocouple is divided into eight different degrees, respectively, B, R, S, K, N, E, J and T, the minimum temperature can be measured Measured at minus 270 degrees Celsius, up to 1800 degrees Celsius, where B, R, S are platinum series thermocouple, because platinum is precious metals, so they are called precious metal thermocouple and the rest of the few are called cheap metal thermoelectric I.
Thermocouple structure has two kinds, ordinary type and armored type. Ordinary thermocouple is generally composed of hot electrodes, insulated tubes, protective sleeves and junction boxes and other parts, and armored thermocouple is the thermocouple wire, insulation materials and metal protective sleeve combination of the three after assembly A solid combination of workmanship.
The thermocouple''''s electrical signal requires a special wire for transmission, which we call the compensation wire. Different thermocouples require different compensation wires, the main role is to connect with the thermocouple, so that the thermocouple reference side away from the power supply, so that the reference end temperature stability. Compensation wire is divided into two types of compensation and extension, extending the chemical composition of the wire and the compensated thermocouple the same, but in practice, the extension of the wire is not the same material and thermocouple metal, the general use and thermal Even with the same electronic density of the wire instead. The connection of the compensating conductor to the thermocouple is generally clear, and the positive pole of the thermocouple connects the red wire of the compensating conductor, while the negative pole connects the remaining color. Most of the material of the compensation wire is copper nickel alloy.
Although the thermal resistance in the industrial application is also more extensive, but because of his temperature range so that his application has been a certain limit, the thermal resistance of the temperature measurement principle is based on the conductor or semiconductor resistance with the temperature changes characteristic. Its advantages are many, but also remote signal, high sensitivity, stability, interchangeability and accuracy are better, but the need for power excitation, can not instantaneous measurement of temperature changes.
Industrial thermal resistance generally use Pt100, Pt10, Cu50, Cu100, platinum thermal resistance of the temperature range is generally minus 200-800 degrees Celsius, copper thermal resistance of minus 40 to 140 degrees Celsius. Thermal resistance and thermocouple the same type of distinction, but he does not need to compensate for the wire, and cheaper than the hot even.
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