The thermoelectromotive force of the sheathed thermocouple will increase with the increase of the temperature of the measuring terminal. The thermoelectromotive force is only related to the thermocouple conductor material 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 with different components are welded to form a loop. The direct temperature measurement end is called the working end, and the wiring terminal end is called the cold end, also called the reference end. When there is a temperature difference between the working end and the reference end, thermal current will be generated in the loop. Connect the display instrument, and the instrument will indicate the corresponding temperature value of the thermoelectromotive force generated by the thermocouple.
Hot blast stove thermocouple in iron and steel plant The hot blast stove in the steel industry is mainly used to provide hot blast to the smelting process. The vault temperature measuring thermocouple operates at a high temperature of 1200~1250℃ for a long time, and the high temperature can reach 1280℃, and it is in the process of air supply. There is strong vibration. Due to the different quality of coal used by various enterprises, the cleanliness of the gas produced is also different. There are often compounds such as sulfur and phosphorus in the combustion process of hot blast stoves. The thermocouple protection sleeve is required to be able to withstand high-temperature air erosion, particle wear and high-temperature gas. corrosion. Traditional thermocouple protection sleeves such as corundum, molybdenum disilicide, ordinary silicon carbide, etc., due to porosity, high temperature strength, high temperature brittleness, etc., can easily lead to brittle breakage, coupling wire contamination, corrosion, and short thermocouple service life. , There is no reliable operating cycle. The high-temperature corrosion failure time of nickel-based superalloy protection sleeves is about 20-30 hours when used in coal gas with phosphide. In the long-term practice of temperature measurement on the vaults of various hot blast stoves, our company has constantly summed up experience and applied the results in the field of materials, using special SiC or heat-resistant alloys as the outer protection tube, corundum as the inner protection tube, and measuring the end After processing, the special thermocouple was successfully developed and used on the vault of the hot blast stove of the relevant user for more than half a year. What is the difference between an armored thermocouple and a hot stove thermocouple? Scope and operating temperature
When the coal gas contains phosphides, the outer casing adopts a new type of silicon carbide protective casing produced by the introduction of German technology, and the porosity of this product is approximately 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. Insulate the casing from corrosion and erosion caused by various high temperature and harmful gases, and it can be used for a long time at about 1420℃.
In the case that the gas does not contain phosphide, the outer casing is made of heat-resistant alloy steel, and through the use of 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 force with the substrate (≥75MPa), etc., and has good high temperature wear resistance and resistance Corrosion performance. The thermal barrier effect of the coating enables the protective sleeve to be used for a long time at about 1300°C.
The inner casing adopts corundum protection tube to provide a clean measurement environment for platinum germanium couple wires. The inner and outer tubes of the hot blast stove thermocouple are filled with high thermal conductivity ceramic powder to reduce vibration during use.
The hot blast stove thermocouple is specially developed for the steel industry. It has the advantages of high temperature resistance, corrosion resistance, air erosion resistance and long life. It is suitable for the temperature measurement of the vault hot vent or hot blast pipe of blast furnace and hot blast stove, and can also be used for temperature measurement of natural gas, coal, cement and other kilns.
The structure principle of armored thermocouple
It is made of a conductor, high-insulation magnesium oxide, a 1Cr18Ni9Ti stainless steel protective tube with a jacket, which is drawn into one body for many times. Armored thermocouple products are mainly composed of junction box, terminal block and armored thermocouple, and are equipped with various installation fixtures.
Armoured thermocouples are divided into two types: insulated type and shell-connected type.
It has many advantages such as flexibility, high pressure resistance, fast thermal response time and durability. It is the same as industrial use. As a temperature sensor, it is usually used with display instruments, recording instruments and electronic regulators. At the same time, it can also be used as a temperature sensor. Temperature sensing element. It can directly measure the temperature of liquid, steam and its gaseous medium and solid surface in the range of 0℃~800℃ in various production processes. In contrast, armored thermocouples have the advantages of flexibility, high pressure resistance, short thermal response time, sturdiness and durability.
The principle of thermocouple temperature measurement
It is based on the thermoelectric effect. Connecting two different conductors or semiconductors 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 fluids, Temperatures such as steam and gaseous media and solid surfaces.
