Thermal resistance application principle

We all know that the thermal resistance is the most commonly used temperature detector in the low-temperature region. Platinum thermal resistance is the highest measurement accuracy. It is widely used not only in industrial temperature measurement but also as a standard reference instrument. Its main features are high measurement accuracy and stable performance.

1. Thermistor temperature measurement principle and material Thermistor temperature measurement is based on the characteristic that the resistance value of the metal conductor increases with the increase of the temperature to measure the temperature.

Most of the thermal resistance is made of pure metal materials. At present, platinum and copper are the most widely used materials. In addition, the use of dian, nickel, manganese, and tantalum has been used to manufacture thermal resistors.

2. The composition of the thermal resistance temperature measurement system The thermal resistance temperature measurement system is generally composed of thermal resistance, connecting wires and display instruments. Must pay attention to the following two points:

1 The index number of the thermal resistance and the display instrument must be the same. 2 In order to eliminate the influence of the change in the resistance of the connecting wire, a three-wire connection must be used.

(4) Flameproof thermal resistance flameproof type thermal resistance through the special structure of the junction box, the explosion of the inner shell of the mixture of gas due to spark or arc and other shadow resistor body repair must inevitably 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 soldering is used, it must be verified after passing the soldering. 3. The structure of the thermal resistance (1) The structure of the common thermal resistance temperature sensing element (resistor body) The characteristics are shown in Table 2-1-11. From the temperature measurement principle of the thermal resistance, it can be seen that the change in the measured temperature is directly measured by the change in the resistance of the thermal resistor. Therefore, various lead resistances, such as lead wires of the thermal resistor, are obtained. The changes will affect the temperature measurement. In order to eliminate the influence of lead resistance, the three-wire or four-wire system is adopted in the same way. For details, see the first section of Chapter III of this paper.

(2) Armored thermal resistors Armored thermal resistors are solid bodies composed of a temperature sensing element (resistor), lead wire, insulating material, and stainless steel bushing, as shown in Figure 2-1-7. Generally φ2 ~ φ8mm, the minimum up to φmm.

Compared with common thermal resistance, it has the following advantages: 1 small size, no internal air gap, thermal inertia, small measurement lag; 2 good mechanical properties, vibration resistance, impact resistance; 3 can bend, easy to install 4 long service life .

(3) End face thermal resistance The face end thermal resistance temperature sensing element is wound by a specially treated resistance wire and is attached to the face of the thermometer. The structure is shown in Figure 2-1-8. Compared with general axial thermal resistance, it can more accurately and quickly reflect the actual temperature of the tested end face, and is suitable for measuring the end face temperature of the bearing pad and other parts.

(4) Flameproof RTD flameproof RTDs are limited to the junction box by the junction box with a special structure, and the explosion of the explosive gas mixture inside the casing due to sparks or arcs will not be induced in the production site. . Flameproof RTDs can be used for temperature measurement in explosion-hazardous areas in Bla-B3c zones.