Classification and principle of temperature probe
2024-11-30 00:00:01
There are two types of temperature probes: thermocouple and thermal resistance.
1. What is the measuring principle of thermocouple?
The working principle of the thermocouple is based on the Seeback effect, that is, two ends of conductors with different compositions are connected into a loop. If the temperature of the two connection ends is different, a physical phenomenon of thermal current is generated in the loop.
The thermocouple is composed of two different wires (hot electrodes), and their ends are welded to each other to form the measuring end (also called working end) of the thermocouple. Insert it into the medium of the temperature to be measured; and the other end of the thermocouple (reference end or free end) is connected to the display instrument. If there is a temperature difference between the measuring end and the reference end of the thermocouple, the display instrument will indicate the thermoelectromotive force generated by the thermocouple.
2. What is the measuring principle of thermal resistance?
The thermal resistance is measured by the characteristic that the resistance of the metal conductor or semiconductor changes with temperature when the temperature changes. The heated part of the thermal resistance (temperature-sensitive element) is a skeleton made of thin metal wire evenly wound around the insulating material It is formed on the substrate by laser sputtering process. When the measured medium has a temperature gradient, the measured temperature is the average temperature of the dielectric layer within the range of the temperature sensing element.
3. How to choose thermocouple and thermal resistance?
Choose according to the temperature measurement range: generally choose thermocouple above 500 ℃, and choose thermal resistance below 500 ℃;
Choose according to the measurement accuracy: choose a thermal resistance for high accuracy, and choose a thermocouple for low accuracy;
Choose according to the measurement range: the thermocouple generally refers to the "point" temperature, the thermal resistance generally refers to the space average temperature;
4. What is an armored thermocouple and what are the advantages?
The name in the IEC1515 standard is "mineral insulatedthermocouplecable", that is, inorganic mineral insulated thermocouple cable. The hot electrode, insulator and sheath are formed by integral drawing, and the outer surface seems to be covered with a layer of "armor", so it is called an armored thermocouple. Compared with general assembled thermocouples, it has the advantages of high pressure resistance, good bendability, good oxidation resistance and long service life.
5. What are the index numbers of thermocouples? What are their characteristics?
The thermocouple indexing numbers are mainly S, R, B, N, K, E, J, T and so on. Among them, S, R, B belong to precious metal thermocouples, N, K, E, J, T belong to cheap metal thermocouples.
The characteristic of S indexing number is that it has strong anti-oxidation performance. It is suitable for continuous use in oxidizing and inert atmosphere. The long-term use temperature is 1400 ℃ and the short-term temperature is 1600 ℃. Among all thermocouples, the accuracy grade of the S index number is the highest, and it is usually used as a standard thermocouple;
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