The difference between armored thermocouple and hot air furnace thermocouple
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The thermoelectric potential of the armored thermocouple will increase as the temperature of the measuring end increases. The size of the thermoelectric potential is only related to the material of the thermocouple conductor and the temperature difference between the two ends, and has nothing to do with the length and diameter of the thermoelectrode.
The two ends of the conductors of two different components are welded to form a loop. The direct temperature measuring end is called the working end, and the terminal end is called the cold end, also known as the reference end. When there is a temperature difference between the working end and the reference end, a thermal current will be generated in the loop. When the display instrument is connected, the corresponding temperature value of the thermoelectric potential generated by the thermocouple will be indicated on the instrument.
Scope of application and operating temperature:
In the case of coal gas containing phosphide, the outer casing adopts a new type of silicon carbide protective casing produced by introducing German technology. The porosity of this product is close to zero. It has high air tightness, excellent oxidation resistance and corrosion resistance; extremely high hardness, excellent wear resistance; high strength, and the strength increases with the increase of temperature. It isolates the corrosion and erosion of various high-temperature harmful gases to the casing, and can be used for a long time under working conditions of about 1420℃.
When the gas does not contain phosphides, the outer casing substrate is made of heat-resistant alloy steel. By using internationally advanced surface treatment technology, a 0.5~1.2mm thick metal-ceramic coating material is formed on the surface of the metal casing. The coating material has the characteristics of high hardness (up to HV1450), high density (≥99.5%), low porosity (<0.5%), strong bonding with the substrate (≥75MPa), and good high-temperature wear resistance and corrosion resistance. The thermal barrier effect of the coating allows the protective casing to be used for a long time under working conditions of about 1300℃. The difference between armored thermocouples and hot air furnace thermocouples
The inner sleeve adopts corundum protection tube to provide a clean measurement environment for the platinum germanium wire. The inner and outer sleeves are filled with ceramic micropowder with high thermal conductivity to reduce vibration during use.
Thermocouples for hot blast furnaces in steel plants (WR□一) The hot blast furnaces in the steel industry are mainly used to provide hot air for the smelting process. The dome temperature thermocouples operate at a high temperature of 1200~1250℃ for a long time, and the highest use temperature can reach 1280℃, and there is strong vibration during the air supply process. Due to the different coal quality used by various enterprises, the cleanliness of the coal gas produced is also different. During the combustion process of the hot blast furnace, there are often sulfur, phosphorus and other compounds. Thermocouple protection sleeves are required to be resistant to high-temperature airflow erosion, particle wear and high-temperature gas corrosion. Traditional thermocouple protection sleeves such as corundum, molybdenum disilicide, ordinary silicon carbide, etc. are prone to brittle breakage, wire contamination and corrosion due to their porosity, high-temperature strength and high-temperature brittleness. The service life of the thermocouple is short and there is no reliable operation cycle. When nickel-based high-temperature alloy protection sleeves are used in coal gas with phosphides, the high-temperature corrosion failure time is about 20 to 30 hours. In the long-term practice of temperature measurement of various hot blast furnace domes, our company has continuously summarized experience, applied new achievements in the field of materials, and adopted special SiC Or heat-resistant alloy as the outer protective tube, corundum as the inner protective tube, and the measuring end is processed. This special thermocouple has been successfully developed and used on the hot air furnace arch of the relevant users for more than half a year.
Structural principle of armored thermocouple
It is made of conductor, high-insulation magnesium oxide, and outer jacket 1Cr18Ni9Ti stainless steel protective tube, which are drawn in one piece many times. The armored thermocouple product mainly consists of a junction box, a terminal block and an armored thermocouple as the basic structure, and is equipped with various installation and fixing devices.
Thermocouple temperature measurement principle
It is based on the thermoelectric effect. When two different conductors or semiconductors are connected into a closed loop, when the temperatures at the two junctions are different, a thermoelectric potential will be generated in the loop. This phenomenon is called the thermoelectric effect, also known as the Seebeck effect.
As a temperature measurement sensor, armored thermocouples are usually used in conjunction with temperature transmitters, regulators and display instruments to form a process control system to directly measure or control the temperature of fluids, steam and gas media and solid surfaces in the range of 0-1800℃ in various production processes.
Armored thermocouples have many advantages such as bendability, high pressure resistance, fast thermal response time and durability. Like industrial assembled thermocouples, they are used as sensors for measuring temperature and are usually used in conjunction with display instruments, recording instruments and electronic regulators.
Calibration method of armored thermocouples
Calibration method and device for metal melt rapid armored thermocouples.
The device mainly consists of a flat heating coil that can accommodate two quartz tubes at the ends of the measured couples, two armored thermocouples with the same shape as the measured couples and corresponding temperature control display output devices.
Calibration method:
First, use two calibration thermocouples to find the points in the flat heating coil that make the thermoelectric potential of the two calibration couples the same, replace one of the calibration couples with the measured couple, and when other conditions remain unchanged, wait for the reading of the measured couple to stabilize and compare it with the reading of the calibration couple to know whether the value of the measured couple is accurate.
Features:
a. The device consists of a flat heating coil, a pair of calibration armored thermocouples and a temperature control display output device.
b. The verification method is to insert two calibration thermocouples from both ends of the heating coil to make the hot ends of the armored thermocouples contact. By changing the position of the calibration thermocouple in the heating coil, the thermoelectric potential of the two calibration thermocouples is the same. Replace one of the calibration thermocouples with the measured fast thermocouple, read its thermoelectric potential value in the stable state and compare it with the thermoelectric potential of the calibration thermocouple to know the accuracy of the measured fast armored thermocouple.
Armored thermocouples are divided into two types: insulated type and shell type.
It has many advantages such as bendability, high pressure resistance, fast thermal response time and durability. It is the same as industrial use. As a sensor for measuring temperature, it is usually used with digital display, recording instrument and electronic regulator. At the same time, it can also be used as a temperature sensing element. It can directly measure the temperature of liquid, steam and its gas medium and solid surface in the range of 0℃~800℃ in various production processes. Compared with, armored thermocouples have the advantages of bendability, high pressure resistance, short thermal response time and durability.
