In industrial production, temperature sensors are the core part of temperature measurement, with a wide variety. According to the measurement method, it is divided into contact type and non-contact type. According to the temperature measurement material and signal type, it is divided into resistance type and thermoelectric EMF type, that is, what we usually call thermal resistance and thermocouple. Among them, thermocouple is one of the widely used temperature measuring elements. It has been widely used in industrial production because of its low price, wide temperature measuring range, stable output signal, resistance to harsh environment and other factors. So do you know the unstable factors of thermocouples?

The Thermoelectrode volatilizes at high temperature. Most of the couple wire materials of the thermocouple are alloy materials. Due to the different vapor pressure of each component material, the degree of volatilization is also different. After being used at high temperature for a certain time, the proportion of alloy components will change, which will lead to significant changes in thermoelectric potential. In redox, the instability of many thermocouples is caused by the oxidation of thermocouple wires. Copper constantan, iron constantan and nickel chromium nickel silicon thermocouples can undergo oxidation reaction. If the Thermoelectrode is uniformly oxidized, the influence may be smaller; If it has preferential oxidation, the effect is very serious. In the case of low oxygen partial pressure (i.e. hypoxia), the chromium in the nickel chromium electrode will produce preferential oxidation and change the combined composition of the couple wire. Embrittlement, embrittlement is the most common factor for thermocouple scrapping. Contamination, grain growth, redox reaction and long-term Recrystallization at high temperature are the reasons for the embrittlement of the Thermoelectrode of the thermocouple. Thermoelectric electrodes are used in atomic reactors. When they are bombarded by neutrons, some elements are transformed into other elements, which changes the composition of thermoelectric electrodes. For example, the rhodium of the armored platinum rhodium thermocouple will be transformed into palladium, and a small amount of platinum will first become gold and then mercury, so as to change the thermoelectric characteristics and reduce the thermoelectric potential. Some low-cost metal thermocouples, such as iron, nickel chromium and nickel aluminum (silicon), have no obvious effect on the evolution of neutron radiation. However, the transmutation of copper under radiation causes great changes in composition. Therefore, in the case of neutron radiation, nickel chromium nickel aluminum thermocouple is more suitable, and nickel chromium silicon nickel silicon (n-type) thermocouple is better. The above is the relevant content introduced by Xiaobian. If you still don't understand, you're welcome to call and we'll solve it for you in detail!