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technical article
Principle of thermal resistance
2011-5-26 17:00:46

                                                                                                                                               Principle of thermal resistance

Thermal resistance is the most commonly used type of temperature detector in low and medium temperature areas. Its main features are high measurement accuracy and stable performance. The measurement accuracy of platinum thermal resistance is the highest. It is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
1. Thermal resistance temperature measurement principle and material
Thermal resistance temperature measurement is based on the characteristic that the resistance value of a metal conductor increases with temperature.
Most of the thermal resistances are made of pure metal materials, and platinum and copper are currently the most widely used. In addition, materials such as copper, nickel, manganese and rhodium have been used to make thermal resistances.
2. Composition of thermal resistance temperature measurement system
Thermal resistance temperature measurement system generally consists of thermal resistance, connecting wires and display instruments. You must pay attention to the following two points:
① The graduation number of the thermal resistance and the display instrument must be the same
② In order to eliminate the influence of the resistance change of the connecting wire, a three-wire connection method must be used.
(2) Armored thermal resistance Armored thermal resistance is a solid body composed of a combination of temperature sensing elements (resistors), leads, insulation materials, and stainless steel sleeves. Its outer diameter is generally φ2 ~ φ8mm, and the minimum can reach φmm. .
Compared with ordinary thermal resistance, it has the following advantages: ① small size, no air gap inside, small measurement hysteresis in thermal inertia; ② good mechanical properties, vibration resistance, impact resistance; ③ can bend, easy to install ④ long life .
(3) End-face thermal resistance The end-face thermal resistance temperature-sensing element is wound by a specially treated resistance wire and is closely attached to the end surface of the thermometer. Compared with the general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of the bearing pad and other parts.
(4) Explosion-proof thermal resistance Explosion-proof thermal resistance uses a junction box with a special structure to expose the explosive mixed gas inside its casing due to sparks or arcs.
The repair of the resistor body must change the length of the resistance wire and affect the resistance value. For this reason, it is better to replace the new resistor body. If welding repair is used, it can only be used after verification after welding.

3. Structure of thermal resistance
(1) Proficient thermal resistance Structure and characteristics of thermal resistance temperature sensing element (resistance body) commonly used in industry. From the temperature measurement principle of the thermal resistance, it can be known that the change of the measured temperature is directly measured by the change of the resistance value of the thermal resistance. Therefore, changes in the resistance of various wires such as the lead of the thermal resistance body will affect the temperature measurement. In order to eliminate the influence of the lead resistance, a three-wire system or a four-wire system is generally used.
(2) Armored thermal resistance Armored thermal resistance is a solid body composed of a combination of temperature sensing elements (resistors), leads, insulation materials, and stainless steel sleeves. Its outer diameter is generally φ2 ~ φ8mm, and the minimum can reach φmm .
Compared with ordinary thermal resistance, it has the following advantages: ① small size, no air gap inside, small measurement hysteresis in thermal inertia; ② good mechanical properties, vibration resistance, impact resistance; ③ can bend, easy to install ④ long life .
(3) End-face thermal resistance The end-face thermal resistance temperature-sensing element is wound by a specially-treated resistance wire and is closely attached to the end surface of the thermometer. Compared with the general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the measured end face, and is suitable for measuring the end face temperature of the bearing pad and other parts.
(4) Explosion-proof thermal resistance Explosion-proof thermal resistance uses a special structure of the junction box to limit the explosion of the explosive mixed gas inside the casing due to the impact of sparks or arcs, etc., within the junction box. explosion. Explosion-proof thermal resistance can be used for temperature measurement in explosion-hazardous areas in the Bla ~ B3c class area.