When it is necessary to control a circuit load by using a separate low-power signal, or where the states of several circuits must be controlled by a single signal, such types of Reed Switch applications can be classified are Relay Applications.
Reed Switches are used in Reed Relays that help switch a wide range of circuits and loads. Areas of application are primarily in automatic test equipment and in electronic instrumentation applications as the embedded reed switches have a fast operate time compared to mechanical relays, and run for up to a billion operations with consistent contact performance. Reed Relays are also particularly useful in switching extremely low current loads due to their low leakage current and are also useful for switching microwave and radio-frequency circuits.
Apart from straightforward single circuit loads, Reed Relays can be used to simultaneously switch multiple circuits and are available in a variety of configurations from simple single pole switching to multi-pole switching, in various contact forms such as normally open, normally closed, change-over, make before break, and latching, and also in custom Reed Relays capable of switching multi-pole circuits with custom mixed contact forms and more. Specific circuits can be turned off or on before switching other circuits and this feature is especially useful in safety applications.
On the high voltage and current switching side, specially designed reed relays using a thicker Copper winding are used to switch the loads at a specific current range, and these are used in critical current sensing applications such as food processors to stop motors at the slightest increase in motor load. Reed Relays find applications in overload protection and multi-pole multi-form reed relays are used in complex switching circuits in Automatic test equipments, signal switching, and encryption.
The basic construction of a simple single pole reed relay consists of a bobbin with four terminal pins, two of which are attached to the ends of the Copper winding, a reed switch centrally inserted into the bobbin and welded to two of the other terminal pins. This assembly is then placed within a relay cover which is then encapsulated. This simple reed relays works helps switch a higher circuit load with an operate voltage as per design, in most cases 5 or 12 volts. A diode is also added sometimes to help handle the back EMF from the winding. Some examples of Reed Relay type applications are listed below.