Thermal fuses (also called thermal fuses) use the characteristics of temperature-sensitive materials to sense temperature and melt, detect abnormal temperature and cut off the circuit. It can detect the abnormal temperature rise of household or industrial electrical products and cut off the circuit quickly and timely, so as to prevent the fire before it happens. The temperature sensitive materials used in thermal fuses are divided into two types: organic compounds and low melting point alloys. Below we discuss organic compound type thermal fuses.

　　Second, the thermal fuse structure principle

　　The organic compound type thermal fuse adopts a metal shell, and the temperature-sensitive organic compound-temperature sensing body is placed in the shell. Under normal circumstances, the current passes through the lead, the movable electrode, the movable disc, the casing and the fixed lead, and the current does not flow through the temperature sensing body (the temperature sensing body is an insulator). Therefore, the internal resistance of the thermal fuse is very small, and the allowable current carrying can reach AC15A.

　　The metal casing of the thermal fuse is equipped with a movable electrode, a spring and a temperature sensing body. The spring B is installed in a compressed state, and its elastic force can hold the movable electrode in contact with the lead A by means of the circular plate. In the normal state, the current is conducted through the lead A, the movable electrode, the metal casing and the lead B.

　　When the ambient temperature exceeds the operating temperature, the heat transmitted through the lead wire and the metal shell melts the temperature sensing body into a liquid state. At this time, the spring A and the spring B pop up and expand, and the elastic force of the spring A presses the movable electrode toward the spring B side, thereby breaking the circuit.

NTC thermistor resistance ratio test method

Learn about thermistors

PIR Lens 8605-3

PIR Lens 8140

PIR Lens 8308-3