What are the advantages and disadvantages of N-type thermocouples compared to K-type thermocouples?
相比有哪些优缺点？ What are the advantages and disadvantages of N- type thermocouples compared to K-type thermocouples ? Advantages of N-type thermocouple:-High temperature oxidation resistance, long-term stability. K-type thermocouple nickel-chromium positive electrode caused by preferential oxidation of Cr and Si elements
Inhomogeneity and thermo-electromotive force drift, increase the Cr and Si content in the N-type thermocouple, so that the oxidation mode of the nickel-chromium alloy is changed from internal oxidation to external oxidation, so that the oxidation reaction only occurs on the surface;-Low temperature short-term thermal cycle stability is good ,
And suppress the magnetic transition;-strong resistance to nuclear radiation. The N-type thermocouple eliminates the Mn and Co, which are easily degenerate elements in the K-type, and further strengthens the resistance to neutron radiation.-In the range of 400 ~ 1300 ℃, the thermoelectric characteristics of the N-type thermocouple
The linearity is better than that of the K type. Disadvantages of N-type thermocouples:-N-type thermocouples are harder than K-type materials and more difficult to process;-Relatively expensive. The thermal expansion coefficient of N-type thermocouple is 15% lower than that of stainless steel.
The outer sleeve should be made of NiCrSi / NiSi alloy; the non-linear error is large in the range of -200 ~ 400 ℃.
K-type thermocouple replaces S-type thermocouple for temperature measurement
The platinum-rhodium 10-platinum thermocouple with s graduation number is commonly known as single platinum rhodium thermocouple or s-type thermocouple. It was made of a precious metal more expensive than gold. At that time, a 1.65m long s-type thermocouple cost about 1800. Yuan, annual consumption of four temperature measurement points
About 30 sticks, with a total value of more than 60,000 yuan; long-term use temperature is in the range of 0 ~ 1400 ℃, short-term 1600 ℃. Its reliable performance and long service life are characterized by strong oxidation resistance. It should be continuously used in an oxidizing and inert atmosphere.
use. Among all thermocouples, s-type thermocouples have the highest accuracy level and are usually used as standard thermocouples; the national standard for the diameter of thermocouple wires is Ф0.5mm, and the weight and service life of precious metals that are lower than the standard will be doubled.
The k-division nickel-chromium-nickel-silicon thermocouple is commonly known as the k-type thermocouple, and its price was only 1/5 of that of the s-type thermocouple at that time. The long-term use temperature is -200 to 1300 ° C and the short-term 1400 ° C. Its reliable performance and long service life are characterized by anti-oxidation
It has strong chemical properties and is suitable for continuous use in an oxidizing and inert atmosphere. It has good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity. 使用最广泛，k型热电 K-type thermocouple is the most widely used of all thermocouples, and k-type thermocouples
The accuracy grade of the couple is divided into grade I and grade II. Generally, grade I is required to increase the price, which needs to be ordered by agreement. It is the cheapest metal thermocouple with the largest amount at present, and its amount is the sum of other thermocouples. The k-type thermocouple generally uses Ф2 .5mm even wire
For assembly, there is also a diameter of 3.2mm for the material, and the diameter of the filament is higher than the national standard (Ф2.0mm), and the service life of the product is significantly increased.
The Ф25mm double-layer tube protective sleeve material used in s-type thermocouples is double-layer high-aluminum or corundum ceramics; corundum is a ceramic tube suitable for high temperature and corrosion resistance at a temperature of 0 ~ 1600 ° C. Disadvantages: fragile; high aluminum
0 ～ 1800 ℃, high temperature and corrosion resistant ceramic tube. Cons: Fragile.
The most common metal protection tube material for k-type thermocouples produced according to national standards is 1Cr18Ni9Ti, which is a stainless steel tube protection tube with a wall thickness of not less than 2mm; the diameter of the k-type thermocouple material is 3.2mm.
The diameter of the tube is Ф20mm; all the thermocouple test ends are automatically welded by automatic argon arc welding equipment. The weld seam is smooth, firm and free of pits, which can effectively extend the service life of the sensor. Use of k-type thermocouples with different protection tubes
The temperature is as follows:
Description of the use temperature when using different protection tubes 1Cr18Ni9Ti
0 ～ 1000 ℃
Most commonly used thermocouple protection tube Corundum 0 ～ 1300 ℃
High temperature and corrosion resistant ceramic tube. Disadvantages: fragile high aluminum 0 ～ 1300 ℃
High temperature and corrosion resistant ceramic tube. Disadvantages: fragile-1400 ℃, K type thermocouples can be used instead of S type thermocouples for temperature measurement_ldjaw_ 上海 博客 316L
0 ～ 1000 ℃
Corrosion-resistant metal protective tube 904L better than 1Cr18Ni9Ti
0 ～ 1000 ℃
Most of the strong corrosion-resistant metal protective tube junction boxes that can resist the chemical production process are generally stainless steel junction boxes, which are divided into two types: waterproof and flameproof.
The compensation cable connected to the k-type thermocouple can be used as a shield structure with high temperature resistance, low temperature, acid resistance, alkali resistance, oil resistance, abrasion resistance, aging resistance, waterproof and non-flammability. It has excellent anti-interference performance and low capacitance. ,
Inductive performance extended precision grade heat-resistant compensation wire——KCB nickel-chromium-nickel-silicon thermocouple compensation wire; it has excellent electrical insulation performance, and the cable with wire-pair shielding and general shielding can effectively prevent external interference and improve measurement
Accuracy; KCB conductor is a combination of multiple strands of alloy wire. The positive electrode is copper, the negative electrode is nickel-plated copper, the positive electrode is red, and the negative electrode is blue. PVC insulation, the positive electrode of the insulation layer is red, and the negative electrode is blue. PVC sheath.
After collecting and consulting the relevant information mentioned above, according to the actual situation at the site, I redesigned and selected the thermocouples for the temperature measurement of the furnace temperature of the two mixed iron furnaces in our factory:
1. The thermocouple wire adopts k-type nickel-chromium-nickel-silicon k-type thermocouple with k division number, and the accuracy grade is Ⅱ. Based on the principle that the diameter of the wire is higher than the national standard (Ф2.0mm) and the service life of the product is significantly increased, I chose the diameter of the wire
2. The protective sleeve of the thermocouple is made of Ф25mm double-layer pipe material with a temperature of 0 ～ 1600 ℃, high temperature resistance and corrosion resistance, and a double-layer high-aluminum or corundum ceramic pipe.
3． The junction box is made of general waterproof stainless steel junction box;
4． Compensation cables use heat-resistant KCB nickel-chromium-nickel-silicon thermocouple compensation wires with a shield structure that is resistant to high temperature, aging, waterproof and non-flammable;
5． The secondary instrument was also re-selected, and a paperless recorder with a temperature measurement range of 1000 to 1400 ° C and an accuracy level of 0.5 was selected, which can manually receive signals from s-type thermocouples and k-type thermocouples.
After the above modification, after many years of practical application, it has been proved that the k-type nickel-chromium-nickel-silicon thermocouple WRNT-130 can fully meet the process requirements for the normal use of the mixed iron furnace (the temperature of the furnace of the mixed iron furnace usually reaches 1300 ° C). When the maximum temperature reaches
1500 ° C, so it is not used), thus achieving the economic effect of saving more than 50,000 yuan in annual production costs; because the thermocouple used is a cheap metal, naturally there is no management problem of recycling, which plays a once and for all role. in
At that time, it had attracted the attention of the company leaders. For this reason, we also gave our company a small change award.
Nowadays, as the value of gold increases, the raw material used in industrial s-type thermocouples, platinum, is currently priced at more than 610 yuan per gram, and the recycling price of waste platinum-rhodium 10-platinum wire has also increased to 420 yuan / Grams;
A small project years ago, the use of k-type thermocouples instead of s-type thermocouples. At this stage, the price of k-type thermocouples is only 1/10 of that of s-type thermocouples. For this reason, the accumulated production costs saved for the company should reach Hundreds of thousands of yuan! And
Recycling of platinum-rhodium-platinum 10-platinum wires with complicated management processes is also omitted.
Nowadays, the current leader of our factory arranges for me to manage the instruments and meters of the hot-rolled sheet line with a higher degree of automation. There are two thin-plate soaking furnaces in the hot-rolling line under my jurisdiction. Maximum temperature
It is only 1300 ° C. Now, s-type thermocouples are used in the high-temperature measurement area. The model WRPG-1340TsL = 457mm (rated temperature range 0-1300 ° C, class II), with a total of 76 installation points. High
The unit price of the segment is 3300 yuan, and only those with a diameter lower than the national standard can be purchased, limited to Ф0.45mm, and the service life is doubled.) Its annual consumption is about 30 pieces, with a total value of more than 100,000 yuan; The zone uses a k-type thermocouple.
The high temperature area of the soaking furnace is very similar to the process environment of the furnace of the mixed iron furnace. The environment of the high temperature area of the soaking furnace without hot metal splashing is better than that of the mixed iron furnace. Therefore, according to the successful application of k-type thermocouples in the past,
，使用寿命与s型热电偶相当)来替代现用的s型热电偶，用具有高温刚玉管双重保护套管的铠装 Based on experience, the “Measurement Plan for the Transformation of the Hot-melt Soaking Furnace for Thin Plates” was made. It is planned to use a class I k-type thermocouple with a service life equivalent to that of the s-type thermocouple.) Armoring of protective sleeves
K-type thermocouples and compensation cables use heat-resistant KCB nickel-chromium-nickel-silicon thermocouple compensation conductors with a shield structure that has high temperature resistance, aging resistance, water resistance, and non-flammability, and is used to receive k-type thermocouple thermoelectric signals PLC module
Measurement of sheet soaking furnace temperature. In order to ensure the convenience of replacement, the k-type thermocouple core can be made according to the size of the current s-type thermocouple core, which can be directly installed, and the original protective sleeve can also be partially used.
Replace the compensation wire and PLC module, and modify the PLC program. It can meet the requirements of the process and save production costs.