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Factors Determining the Degradation and Service Life of Thermal Resistors http://yunrun.com.cn/tech/2521.html The degradation and service life of thermal resistors depend mainly on the following two factors: one is the change in the resistance-temperature characteristics caused by the degradation of the wire material used in the thermal resistor； Secondly, the strength of the thermal resistance protection tube deteriorates due to mechanical action or chemical corrosion, resulting in peeling and damage. 1. Degradation of thermal resistance wires: The wires used for thermal resistors include platinum, nickel, copper, and others. To ensure the stability of its properties, not only must the physical properties of the material itself be stable, but its chemical composition must also be of high purity, typically at 99.99%-99.999% or ultra-high purity. If the purity decreases, the resistance temperature coefficient will change, resulting in an increased deviation. Generally, the lower the purity of the wire, the smaller its resistance temperature coefficient. Thermistors made from high-purity platinum wires suffer degradation of the wire material due to the influence of the surrounding atmosphere, which leads to a decrease in the temperature coefficient of resistance; moreover, this rate of degradation increases exponentially as the temperature rises, so caution is necessary when using them. The impact of the atmosphere is particularly severe for hydrogen, hydrocarbons, metal vapors, etc. Therefore, for thermoresistors used in high temperatures, their wire, frame, and protective tube must all be thoroughly cleaned and heat-treated before use. 2. Degradation of the thermal resistance protection tube: The most important factors determining the lifespan of a thermal resistor are its mechanical strength and resistance to chemical corrosion. Additionally, the quality of the temperature-sensing elements used by the manufacturers of thermal resistors also affects their lifespan; this issue is discussed in detail in the article “Choosing the right platinum resistance elements to improve their quality and service life”. Therefore, the protective tube must be carefully selected based on the medium being measured, the atmosphere, etc.; otherwise, continuous temperature measurement cannot be achieved. The method for selecting a thermal resistance protection tube is the same as that for selecting a thermocouple protection tube; refer to the article titled \"Materials and Application Scenarios of Thermocouple Protection Tubes\" for details.