——镍铬-镍硅热电偶 K-type thermocouple ——Nichrome-NiSi thermocouple
Nickel-chromium-nickel-silicon thermocouples (K-type thermocouples) are the cheapest metal thermocouples currently in use, and their usage is the sum of other thermocouples. The nominal chemical composition of the positive electrode (KP) is: Ni: Cr = 90: 10, the nominal chemical composition of the negative electrode (KN) is: Ni: Si = 97: 3, and its operating temperature is -200 ~ 1300 ° C. K-type thermocouples have the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, and low price. They can be used in oxidizing inert atmosphere. Widely used by users. K-type thermocouples cannot be directly used in sulfur, reducing or reducing, oxidizing atmosphere and vacuum at high temperature, nor are they recommended for welding two different metal conductors together in a weakly oxidizing atmosphere to form a closed circuit. If a temperature difference is generated by heating at the welding end (that is, the measurement end), a thermal electromotive force will be generated in the circuit. This phenomenon is called Seebeck-effect. If the temperature at the other end (ie the reference end) is kept constant (generally 0 ° C), then the thermoelectromotive force of the loop becomes a single-valued function of the temperature at the measurement end. This kind of element that measures the temperature by measuring the thermoelectromotive force, that is, two pairs of metal conductors, is called a thermocouple.
作为一种温度传感器，K型热电偶通常和显现仪表，记载仪表和电子调理器配套运用。 K-type thermocouple is a kind of temperature sensor. K-type thermocouple is usually used together with display instrument, record instrument and electronic conditioner. K-type thermocouples can directly measure the external temperature of liquid vapor and gaseous media and solids ranging from 0 ° C to 1300 ° C in various consumptions. K-type thermocouples are usually composed of the main components such as temperature sensing elements, fixed installation of the device and junction boxes. K-type thermocouple is the cheapest metal thermocouple with the largest amount, and its amount is the sum of other thermocouples. K-type thermocouple wire diameter is generally 1.2 ~ 4.0mm. The nominal chemical composition of the positive electrode (KP) is: Ni: Cr = 92: 12, the nominal chemical composition of the negative electrode (KN) is: Ni: Si = 99: 3, and its operating temperature is -200 ~ 1300 ° C. K-type thermocouple has the advantages of good linearity, large thermoelectromotive force, high flexibility, good stability and averaging, strong oxidation resistance, and low price. It can be widely used by users in oxidizing inert atmosphere. K-type thermocouples cannot be used directly at high temperatures for sulfur, restorative or restorative, oxidizing alternate atmospheres and vacuum, and are not recommended for use in weakly oxidizing atmospheres.
Thermocouple temperature measurement principle Thermocouple temperature measurement must be composed of three parts: thermocouple, connecting wire and display instrument.
According to the thermocouple core and thermocouple wire composed as shown on the right, if the hot end of the thermocouple is heated so that the temperature at the cold and hot ends is different, a thermoelectric potential will be generated in the thermocouple circuit. This physical phenomenon It is called a thermoelectric phenomenon (ie, a thermoelectric effect). The potential generated in the thermocouple circuit is composed of two parts: the temperature difference potential and the phase contact potential. Contact potential: It is a thermoelectric potential generated when two conductors with different electron densities contact each other. When two different conductors A and B are in contact, assuming that the electron densities of conductors A and B are Na and Nb and Na> Nb, respectively, the diffusivity of the electrons in the two directions on the contact surface of the two conductors is not the same. Similarly, the number of electrons diffused from conductor A to conductor B is greater than the number of electrons diffused from B to A. Conductor A loses electrons and appears positive, while conductor B gains very electrons and appears negative. Therefore, an electrostatic field from A to B is formed on the contact surfaces of the A and B conductors. This electric field will stop the barrier diffusion movement and accelerate the electrons to move in opposite directions, increasing the number of electrons from B to 4. And finally reach the state of dynamic equilibrium. At this time, a potential difference is also formed between A and B, and this potential difference is called a contact potential. This potential is only related to the temperature of the contact point between the properties of the two conductors. When the information of the two conductors is constant, the contact potential is only related to the temperature of the contact point. The higher the temperature, the more active the electrons in the conductor, and the more electrons diffused from the A conductor to the B conductor, resulting in a higher electric field strength at the contact surface, and therefore a higher contact potential. In this way, the thermoelectric potential of the temperature difference generated by 1 is displayed in the display instrument 3 through the connecting wire 2.
特性检出(测温)元件热电偶是工业上最常用的温度检测元件之一。 K-type thermocouple characteristic detection (temperature measurement) element Thermocouple is one of the most commonly used temperature detection elements in the industry. It must be equipped with a secondary meter, and its advantages are: ① High measurement accuracy. Because the thermocouple is in direct contact with the measured object, it is not affected by the intermediate medium. ② Wide measurement range. Commonly used thermocouples can be continuously measured from -50 to + 1600 ° C. Some special thermocouples can be measured as low as -269 ° C (such as gold-iron-nickel-chromium) and as high as + 2800 ° C (such as tungsten-rhenium). ③ The structure is simple and easy to use. Thermocouples are usually composed of two different metal wires, and are not limited by size and opening. They have maintenance sleeves and are very convenient to use. According to the temperature measurement range and accuracy, the thermocouple with the corresponding graduation number is used at the temperature of 1300 ~ 1800 ° C. When the requested accuracy is higher, the B-type thermocouple is generally used; the requested accuracy is not high, and the atmosphere allows the application of tungsten-rhenium thermoelectric Couplings, tungsten rhenium thermocouples are generally used above 1800 ° C; S-type thermocouples and N-type thermocouples are available when the application temperature is 1000 ~ 1300 ° C and the accuracy is higher than the requirements; K-type thermocouples and N-type thermocouples are generally used below 1000 ℃ Coupling, common E-type thermocouple below 400 ℃; T-type common thermocouple at 250 ℃ and negative temperature measurement, T-type thermocouple is stable and accurate at low temperature.