reed relay
A reed relay is a magnetic field sensor that operates with spring contacts that are actuated by a magnetic field. In order to reduce sparking between the reed contacts as far as possible, they are located in a glass tube that is empty of air or filled with inert gas. The two switching contacts are spring-loaded and made of ferromagnetic nickel and iron.
In the resting state, the two switching tongues are only a short distance apart. The switching principle is based on the reluctance principle. The two switching tongues are closed by the magnetic flux which is applied from outside and which passes through the switching tongues. A magnetic flux density of at least 50 Gauss( Gs) is required to override the restoring force of the spring tongues.
This closing process can be controlled by permanent magnets passing the reed contacts or by an electromagnet placed around the glass tube. When switching the reed contacts, the position of the magnetic field relative to the soft magnet switchings is crucial.
Both methods are used in practice. Reed relays with permanent magnets are used, among other things, in magnetic contacts and are used for position detection, for example, to indicate the opening or closing status of containers.
In contrast to normal relays, reed relays have a much longer service life, which is 1,000 million switching cycles and even more. In addition, reed relays can be switched at a high switching frequency of several hundred hertz. The mean time between failures( MTBF) is well over 100,000 hours.
Reed relays have very small dimensions and can be used in SMT technology or through-hole technology( THT) on printed circuit boards. They are robust, extremely reliable and shock-resistant. There are versions for very low currents and voltages, but also for high- voltage applications with voltages of several kilovolts (kV) and currents of several amperes (A).