Relays and Switches

Relays and switches are among the most important components in the general area of electromechanical devices. Both of these have been in use for many years and continue, in modem form, to be essential elements in many modem switching applications including electronic systems. Early forms of relays were simple and controlled a single contact. Telephony created the need for more complex forms of relays and switches early in its history, and has continued ever since to require advances. Switching functions such as counting, registration, translation, etc., are accomplished by relays and switches. The most difficult and complex switching functions arise from centralized or common control types of automatic control systems including telephone central offices and computers. These are often referred to as the "brains" of the system. Modem trends in relays and switches are in miniaturization, hermetic sealing, improved reliability in the presence of shock and vibration and in higher operating speeds. Glass-enclosed contacts of the "dry reed" and mercury types have had an important part in achieving better performance. Another important trend is for them to become competitive, compatible and combinational with solidstate switching devices and systems as illustrated by the ferreed. Research is continuing actively with miniaturized relays, piezoelectric relays, glass-enclosed contact relays, higher-speed relays, transistor-operated relays and combinational devices such as the ferreed. One form of ferreed will operate from a 5 μsec pulse and remain operated until released by a similar pulse.