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Introduction of the Difference between EK Thermocouple and PT100 Thermal Resistance

Key words: thermocouple, PT100 thermal resistance, working principle of thermocouple, working principle of PT100 thermal resistance, types of thermocouple, structure of thermocouple
EK Thermocouple and PT100 Thermal Resistance

  EK thermocouple
Thermocouples are one of the most commonly used temperature sensing components in the industry. The working principle of thermocouples is based on the Seeback effect.
That is, the two ends of the conductors of different compositions are connected into a loop, and if the temperatures of the two terminals are different, a physical phenomenon of thermal current is generated in the loop. The advantages are:
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

Two kinds of conductors or semiconductors A and B are welded together to form a closed circuit, as shown in Figure 2-1-1.

When there is a temperature difference between the two attachment points 1 and 2 of conductors A and B.
An electromotive force is generated between the two, thus forming a current of a magnitude in the loop. This phenomenon is called a thermoelectric effect.
Thermocouples use this effect to work.

2. Types and structure formation of thermocouples
(1) Types of thermocouples
Commonly used thermocouples can be divided into two categories: standard thermocouples and non-standard thermocouples. The called standard thermocouple refers to a thermocouple whose national standard specifies the relationship between its thermoelectric potential and temperature, the allowable error, and a uniform standard index table. It has a display instrument that is compatible with it. Non-standardized thermocouples are inferior to standardized thermocouples in terms of application range or magnitude, and generally do not have a 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 designated seven standardized thermocouples S, B, E, K, R, J, T are 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. Temperature compensation of the cold junction of the thermocouple
Because thermocouple materials are generally more expensive (especially when using precious metals), and the temperature measurement point is far away from the meter. In order to save the thermocouple material and reduce the cost, the compensation wire is usually used to extend the cold end (free end) of the thermocouple to a relatively stable temperature control room and connected to the meter terminal. It must be pointed out that the role of the thermocouple compensation wire only extends the hot electrode, moving the cold end of the thermocouple to the meter terminal of the control room. It does not eliminate the effect of cold junction temperature changes on 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 thermocouple compensating conductor, attention must be paid to the type matching, the polarity can not be misconnected, and the temperature of compensating conductor and thermocouple connecting end can not exceed 100 °C.

 PT100 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 thermal resistance has the highest measurement temperature, and it is not only widely used in industrial temperature measurement, but also made into a standard reference instrument.

1. Principle and material of thermal resistance temperature measurement
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 resistances are made of pure metal materials, and the most widely used ones are platinum and copper. In addition, thermal resistance has been produced using materials such as nickel, manganese and tantalum.

2, the type of thermal resistance
1) Ordinary type thermal resistance
From the temperature measurement principle of the thermal resistance, the change of the measured temperature is directly measured by the change of the resistance of the thermal resistance. Therefore, variations in the resistance of various wires such as the lead wires of the thermal resistor body may affect the temperature measurement.
2) Armored thermal resistance
The armored thermal resistor is a solid body composed of a temperature sensing element (resistor), a lead wire, an insulating material, and a stainless steel bushing. Its outer diameter is generally 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 be bent for easy installation
4> long service life.

3) End face thermal resistance
The end face thermal resistance temperature sensing element is wound by a specially treated resistance wire and is placed close 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 confines the explosive mixture gas in its shell to the junction box due to the influence of spark or arc through a special junction box. The production site will not lead to over explosion. Explosion-proof thermal resistance can be used for temperature measurement in explosive areas where the Bla--B3c level is explosive.

Pt100: Used for thermal resistance, thermocouple, series temperature instrument, temperature transmitter, pressure differential pressure transmitter, hot runner heater, compensation cable, control cable, etc.
Cu50: For thermal resistance, thermal resistance thermometer, thermal resistance calibrator, thermal resistance simulator - copper thermal resistance simulator, copper thermal resistance, armored thermal resistance.
The pt100 and cu50 measure temperatures are different, the PT100 measures the high temperature point, and the CU50 measures the temperature low point.
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