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Reed relays are electro-magnetic switches, which use an armature (metal strip) inside a reed capsule (enclosed glass tube). The armature is held in place by a permanent magnet and is sealed in the capsule containing an inert atmosphere, such as nitrogen, which prevents electrical flux shorting. As a result the relay can operate against high voltages or act as a voltage isolator.

When an electrical current is applied to the two metal contacts of the reed relay (also known as an actuating current), it causes the presence of a strong electro-magnetic field which attracts the movable contact of the armature known as the “pick-up point”. This can be at a preset current level or with a single entry of a signal voltage. The pick-up point is “energised” and the contacts change position opening or closing according to the design nature, providing the ability to switch large electrical loads, e.g. AC/DC, and allowing for low level voltage detection.

Reed relays provide a range of advantages such as leading, repeatability, reliability and long electrical service life. There are extremely durable, as the design of the reed capsule prevents of the relay from being exposed to outside contaminants that can damage the moving contact and its spring potential lifetime is much longer than mechanical switches of the same size. Importantly, due to the low pick-up and drop-off voltage, even at close to zero voltage the device is able to reliably switch off.

They are often used in applications such as telecommunications, high voltage detection, AC/DC switching, safety shut down systems and power automation. Due to their low operational cost, compact size and advantage over mechanical switching systems in repeatability, relays are often used in industrial processes where small current and low voltage must be monitored and switched regularly. Reed relays are ideally suited to process industry and automation, computers and electronic control systems, medical instrumentation, high-end audio systems and security, building and fire alarm systems.

Typically, reed relays are used as components and need to be mounted on the designed PCB or assembly board through the threaded end of the coil holder. The contact design consists of normally open (NO) contacts and normally closed (NC) contacts. The LC circuit ensures that high speed current flow can occur without the risk of open circuits, and it also produces a low drop-off voltage to ensure reliable and low-voltage switching. The use of a single coil in the LC circuit helps further reduce the power consumption. These features make LC circuits suitable for applications such as safety systems shut-down, AC/DC switching, computer memory banks and general low-voltage switching.

Finally, it is important to note that reed relays are highly reliable due to the sealed chamber in which the armature is held, and the permanent magnet which blocks the movement of the armature to prevent oxidation resulting in intermittent signals. Furthermore, the internal inert atmosphere provides a far higher level of protection against electro-static discharge (ESD) than with a normal open contact circuit. As a result, reed relays can be used for high voltage and safety applications such as high voltage transformers, DC power supply wiring, and safety systems shut-down.