Introduction: Thermocouple is a temperature sensing element. What is the working principle of thermocouple ? How does it complete the function of temperature sensing? This article will answer you~~
First, the working principle of thermocouple - - Introduction
Thermocouple is a commonly used temperature measuring component, which can be directly used for temperature measurement, and converts the temperature signal into a thermoelectromotive force signal, which is then converted into the temperature of the measured medium by the secondary instrument. Thermocouples have many advantages such as simple structure, convenient manufacturing, wide measuring range, high precision, small inertia, and easy transmission of output signals. Therefore, they are widely used in temperature measurement.
In addition, the thermocouple is also an active sensor. It does not require an external power supply for measurement. It is extremely convenient to use. It is commonly used to measure the temperature of the gas or liquid in the furnace and the pipeline and the surface temperature of the solid.
Second, the working principle of thermocouple - - classification
Commonly used thermocouples can be divided into standard thermocouples and non-standard thermocouples. The standard thermocouple 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. The standard thermocouple has the display instrument that is compatible with it. Non-standard thermocouples refer to thermocouples that do not meet the requirements of standard thermocouples. They are often expressed as inferior to standard thermocouples in the order of magnitude of use, and there is no uniform indexing table, which is mainly used for measurement in special occasions.
Thermocouples can be classified into six types: non-fixed type, threaded type, fixed flange type, movable flange type, movable flange angle type, and tapered protection tube type according to the type of fixing device.
Thermocouples can be classified into four types of special-purpose thermocouples, such as detachable thermocouples, flameproof thermocouples, armored thermocouples, and spring-loaded thermocouples.
Third, the working principle of thermocouple - - structure
The shape of the thermocouple has considerable differences due to different needs, but its basic structure is almost the same. It consists of a hot electrode, an insulating sleeve protection tube, a junction box, etc., usually with display instruments, recording instruments, electronic regulators, etc. The instrument is used together.
Fourth, the working principle of thermocouple
The thermocouple uses the thermoelectric effect to measure the temperature. The thermoelectric effect means that the two ends of the conductors of different compositions are joined into a loop. When the temperature of the two junctions is different, an electromotive force is generated in the loop, and the generated electromotive force is generated. It is called thermoelectric potential. The end that we use directly to measure the temperature of the medium is called the working end or the measuring end. The end that is not directly used to measure the temperature of the medium is called the cold end or the compensating end, and the cold end is connected to the display instrument or other supporting instruments. The thermoelectric potential generated by the thermocouple is shown above.
The thermodynamic force generated by the thermocouple consists of two parts, one is the contact electromotive force of the two conductors, and the other is the temperature difference electromotive force of the single conductor. Therefore, the magnitude of the thermoelectric potential is only related to the temperature of the conductor material constituting the thermocouple and the two joints, and is independent of parameters such as the shape size of the thermocouple. When the thermocouple two electrode materials are fixed, the thermoelectromotive force is a function difference between the two junction temperatures.
Thermocouple working principle
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