How to distinguish between positive and negative of K type thermocouple
What is the positive and negative of K-type thermocouples? In the case of
Thermocouple in the use of the process often encounter will encounter an embarrassing thing, that is, the positive and negative distinction between the thermocouple, do not look at this small problem can get you blushing, a few days ago in a field operation, To the company under the leadership of the inspection work, just a friend connected thermocouple, but because of positive and negative problems stumped. The boss asked him which root is positive and negative ah? He thought for a long time, can not tell. Finally, he always use the way to detect the positive and negative thermocouple, he still can not answer, because some manufacturers do not specify the product at the factory caused a number of on-site operators can not figure out which is the cathode, which is the negative , Today to a friend to say something, so as not to encounter when rush, the following first talk about: nickel-chromium - nickel silicon thermocouple
Let me talk about the relevant parameters of nickel-chromium-nickel silicon thermocouple
Nickel-chromium-nickel-silicon thermocouple (K-type thermocouple) is currently in the 500 ℃ above the temperature of the largest amount of cheap metal thermocouple, the amount of other metal thermocouple is the sum.
The nominal chemical composition of the positive electrode (KP) is Ni: Cr ≈ 90: 10, the chemical composition of the negative electrode (KN) is Ni: Si≈97: its use temperature range is -20 to 1100 (1300) ℃.
K-type thermocouple with good linearity, high thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, cheap, etc., can be used for oxidizing, inert atmosphere. K-type thermocouples can not be used directly at high temperatures for sulfur, reducing or reducing, oxidizing alternating atmospheres and in vacuum, and are not recommended for use in weakly oxidized atmospheres.
Say the chemical composition of nickel-chromium-nickel-silicon thermocouple: nickel-chromium-nickel-silicon (nickel-aluminum) thermocouple (sub-number K) of the positive electrode is chromium 10% nickel-chromium alloy (KP) 3% nickel-silicon alloy (KN). , According to this feature, with the magnet can be easily identified thermocouple positive and negative. It is characterized by the use of wide temperature range, stable performance at high temperatures, thermoelectromotive force and temperature of the relationship between the approximate linear, cheap, therefore, it is currently the largest amount of a thermocouple, nickel chromium - nickel silicon thermocouple, K type Thermocouples are suitable for continuous use in oxidizing and inert atmospheres. Short-term use temperature of 1300 ℃, long-term use temperature of 1100 ℃. After the selection of high-quality K-type thermocouple can be used as a standard for the sub-working with nickel-chromium-nickel and other base metal thermocouple, in this thermocouple add the metal yttrium and magnesium and other elements, antioxidant properties can be further improved , The maximum use of temperature can reach 1300 ℃. In order to give full play to the advantages of cheap cheap metal, in the same temperature measurement site, you can install a few thermocouples, the use of its high sensitivity and thermoelectric properties of the characteristics of the approximate linearity to achieve the purpose of accurate measurement, K-type thermocouple is antioxidant A strong base metal thermocouple. Not suitable for vacuum, carbon, sulfur atmosphere and oxidation and reduction of alternating atmosphere of the use of bare silk. When the oxygen partial pressure is low, the nickel chrome in the chromium will be excellent oxidation (also known as green erosion), so that the thermoelectromotive force has changed greatly. But the impact of metal gas on the more so Therefore, the use of metal thermocouple protection tube.
Now I want to tell you how to thermocouple positive and negative: First, nickel-chromium-nickel silicon thermocouple two lines have obvious color distinction, there is a green, one is gray, green for the positive, if Is the armored thermocouple wire, you can use a small magnetic material, on the negative surface, that is, where the gray wire above the wire, if there is a negative This is now the use of nickel-chromium - nickel silicon thermocouple scene a lot, but much better The user replaced the nickel-chromium-nickel-aluminum thermocouple with a nickel-chromium-nickel silicon thermocouple. But there are still some old users or foreign use of nickel-chromium-nickel aluminum thermocouple. Although the chemical composition of the two thermocouples are different, but the thermoelectric properties of the same, using the same index table.
