First, the application principle of thermocouple The advantages are: Here you can find the related products in Wireless Measurement, we are professional manufacturer of Wireless Measurement,Wifi Measurement,Wireless Pt100 Temperature Sensor,. We focused on international export product development, production and sales. We have improved quality control processes of Wireless Measurement to ensure each export qualified product. Wireless Measurement,Wifi Measurement,Wireless Pt100 Temperature Sensor Xi'an Gavin Electronic Technology Co., Ltd , https://www.gaimcmeas.com
Thermocouples are one of the most commonly used temperature sensing components in the industry.
1 Measurement accuracy is high. Because the thermocouple is in direct contact with the object to be tested, it is not affected by the intermediate medium.
2 Wide measurement range. Commonly used thermocouples can be continuously measured from -50 to +1600 °C. Some special thermocouples can measure -269 °C (such as gold-iron nickel-chromium), up to +2800 °C (such as tungsten-bismuth).
3 simple structure, easy to use. Thermocouples are usually made up of two different wires and are not limited by size and opening. They have a protective sleeve and are very convenient to use.
1. The basic principle of thermocouple Temperature Measurement solders two conductors or semiconductors A and B to form a closed loop, as shown in Figure 2-1-1. When there is a temperature difference between the two attachment points 1 and 2 of the conductors A and B, an electromotive force is generated between the two, and thus a current of a magnitude is formed in the loop. This phenomenon is called a thermoelectric effect. Thermocouples use this effect to work.
2. Types and Structures of Thermocouples (1) Types of Thermocouples Thermocouples can be divided into standard thermocouples and non-standard thermocouples. The standard thermocouple that is called refers to the thermocouple that the national standard specifies the relationship between the thermoelectric potential and the temperature, the allowable error, and the uniform standard index table. It has a display instrument that is compatible with it. Non-standardized thermocouples are not as good as standardized thermocouples in terms of use or order of magnitude. Generally, there is no uniform indexing table, which is mainly used for measurement in some special occasions. Standardized Thermocouples Since January 1, 1988, thermocouples and thermal resistors have all been produced in accordance with IEC international standards, and seven standardized thermocouples, S, B, E, K, R, J, and T, have been designated as China's unified design. Thermocouple.
(2) Structure of thermocouple In order to ensure reliable and stable operation of the thermocouple, its structural requirements are as follows:
1 The welding of the two hot electrodes constituting the thermocouple must be firm;
2 The two hot electrodes should be well insulated from each other to prevent short circuits;
3 The connection between the compensation wire and the free end of the thermocouple should be convenient and reliable;
4 The protective sleeve should ensure that the hot electrode is sufficiently isolated from harmful media.
3. The temperature compensation of the cold junction of the thermocouple is generally expensive due to the thermocouple material (especially when using precious metals), and the distance between the temperature measurement point and the meter is very long. In order to save the thermocouple material and reduce the cost, the compensation wire is usually used to heat the electricity. The even cold end (free end) extends into a relatively stable temperature control chamber and is connected to the meter terminals. It must be pointed out that the function of the thermocouple compensation wire only extends the hot electrode, so that the cold end of the thermocouple moves to the instrument terminal of the control room, which itself does not eliminate the influence of the temperature change of the cold end on the temperature measurement, and does not compensate. Therefore, other correction methods are needed to compensate for the influence of the cold junction temperature t0 ≠0 ° C on the temperature measurement.
When using the thermocouple compensation wire, it must be noted that the model is matched, the polarity cannot be connected incorrectly, and the temperature between the compensation wire and the thermocouple connection terminal cannot exceed 100 °C.
Second, the application principle of thermal resistance
Thermal resistance is the most commonly used temperature detector in the mid-low temperature zone.
Its main features are high measurement accuracy and stable performance. Among them, platinum heat is the highest measurement accuracy, it is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.
1. Thermistor temperature measurement principle and material Thermistor temperature measurement is based on the fact that the resistance value of a metal conductor increases as the temperature increases. Most of the thermal resistance is made of pure metal materials. At present, platinum and copper are the most widely used. In addition, thermal resistances have been fabricated using materials such as dian, nickel, manganese and tantalum.
2. Structure of thermistor (1) Well-known thermal resistance industry commonly used thermal resistance temperature sensing element (resistor). From the temperature measurement principle of the thermal resistance, it is known that the change in the measured temperature is directly measured by the change in the resistance of the thermal resistance. Therefore, changes in the resistance of various wires such as the lead wires of the thermal resistor body may affect the temperature measurement. To eliminate the influence of lead resistance, a three-wire or four-wire system is used.
(2) armored thermal resistance armored thermal resistance is a solid body composed of temperature sensing element (resistor), lead wire, insulating material and stainless steel casing, as shown in Figure 2-1-7, its outer diameter Generally, it is φ2~φ8mm, and the minimum is φmm.
Compared with ordinary type thermal resistance, it has the following advantages: 1 small volume, no air gap inside, 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 end face thermal resistance The temperature sensing element is wound by a specially treated resistance wire and is closely attached to the end face of the thermometer. Compared with the general axial thermal resistance, it can reflect the actual temperature of the tested end face more correctly and quickly, and is suitable for measuring the end face temperature of the bearing bush and other parts.
(4) Flameproof thermal resistance flameproof thermal resistance through a special structure junction box, the explosion of the explosive mixture inside the shell due to the impact of spark or arc is limited to the junction box, the production site will not lead to explosion . Explosion-proof thermal resistance can be used for temperature measurement in explosion-prone areas in the Bla~B3c class.
  3. The composition of the thermal resistance temperature measurement system The thermal resistance temperature measurement system generally consists of a thermal resistance, a connecting wire and a display instrument. The following two points must be noted:
1 The thermal resistance and the index number of the display instrument must be the same. 2 In order to eliminate the influence of the change of the resistance of the connecting wire, the three-wire connection method must be adopted.
(2) armored thermal resistance armored thermal resistance is a solid body composed of temperature sensing element (resistor), lead wire, insulating material and stainless steel casing, as shown in Figure 2-1-7, its outer diameter Generally, it is φ2~φ8mm, and the minimum is φmm. Compared with ordinary type thermal resistance, it has the following advantages: 1 small volume, no air gap inside, thermal inertia, small measurement lag; 2 good mechanical properties, vibration resistance, impact resistance, 3 bending, easy installation 4 long service life .
(3) End face thermal resistance end face thermal resistance The temperature sensing element is wound by a specially treated resistance wire and is closely attached to the end face of the thermometer. Compared with the general axial thermal resistance, it can reflect the actual temperature of the tested end face more correctly and quickly, and is suitable for measuring the end face temperature of the bearing bush and other parts.
(4) Explosion-proof type thermal resistance flameproof type thermal resistance through the special structure of the junction box, the explosive mixture inside the casing is damaged by the spark or arc and other shadow resistors must change the length of the resistance wire and affect the resistance value. It is better to replace the new resistor body for this purpose. If welding repair is used, it must be verified after welding to be used.
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Thermocouple and RTD applications