1.Basic principle of single-head tube temperature measurement
According to the functional relationship between thermal electromotive force and temperature, the single-head tube index table is made; the index table is achieved under the condition that the temperature of the free end is at 0°C, and different single-head tubes have different index tables.
The single-head tube is a temperature-sensing element and a primary instrument. It directly detects the temperature and converts the temperature signal into a thermal electromotive force signal, and then converts it into the temperature of the measured medium through an electrical instrument (secondary instrument).
The basic principle of single-head tube temperature measurement is that two material conductors with different components form a closed circuit. When there is a temperature gradient at both ends, there will be an overvoltage in the circuit. At this time, there is an electromotive force between the two ends - thermal electromotive force , which is the so-called Seebeck effect.
When the third metal material is connected to the single-head tube circuit, as long as the temperature of the two junctions of the material is the same, the thermoelectric potential generated by the single-head tube will remain unchanged, that is, it will not be affected by the third metal connected to the circuit. influences. Therefore, when measuring the temperature of the single-head tube, the survey instrument can be connected, and after the thermal electromotive force is measured, the temperature of the measured medium can be known. Two homogeneous conductors of different composition are thermodes, the end with higher temperature is the office end, and the end with lower temperature is the free end, and the free end is usually at a constant temperature.
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, thus forming a large and small current in the circuit. This phenomenon is called the thermoelectric effect. Single head tubes use this effect to work.
Two conductors with different components (called single-head tube wire or thermode) are joined at both ends to form a loop. When the temperature of the junction is different, an electromotive force will be generated in the loop. This phenomenon is called the thermoelectric effect, and this This kind of electromotive force is called thermoelectric potential. The single-head tube uses this principle to measure temperature. Among them, the end directly used to measure the temperature of the medium is called the working end (also called the measuring end), and the other end is called the cold end (also called the compensation end); the cold end and the Connect the display instrument or supporting instrument, and the display instrument will point out the thermoelectric potential generated by the single-head tube.
The single-head tube is actually a kind of energy converter, which converts heat energy into electric energy, and uses the generated thermoelectric potential to measure the temperature. For the thermoelectric potential of the single-head tube, the following issues should be paid attention to:
1. The volume of the thermoelectric potential generated by the single-head tube, when the material of the single-head tube is average, has nothing to do with the length and diameter of the single-head tube, but only related to the composition of the single-head tube material and the temperature difference between the two ends.
2. The thermoelectric potential of the single-head tube is the difference of the temperature function at both ends of the single-head tube, not the function of the temperature difference between the two ends of the single-head tube.
3. When the material composition of the two single-head tube wires of the single-head tube is confirmed, the volume of the thermoelectric potential of the single-head tube is only related to the temperature difference of the single-head tube; if the temperature of the cold end of the single-head tube is kept constant, the The thermoelectric potential of the tube is only a single-valued function of the temperature at the office end.
