A fixed flange thermocouple is a widely used industrial temperature sensor. It operates based on the thermoelectric effect, using two different metal conductors in a closed circuit to directly convert temperature changes into a thermoelectromotive force signal. Its most distinctive feature is flange mounting, which connects tightly to pipes or vessels via a flange plate. This mounting style provides excellent sealing and pressure resistance, making it suitable for harsh industrial environments involving high pressure, high temperature, and corrosive media. With a robust structure, convenient installation and removal, and low maintenance costs, it is typically used with a protective sleeve to extend its lifespan. It is widely applied in temperature measurement and control systems across industries such as petroleum, chemicals, power generation, metallurgy, and industrial furnaces.