Core Materials for Magnetic Latching Wire Spring Relays

Iii telephone switching circuits it is often necessary to hold a relay operated for a long period of time. An example of such a case is a relay which remains operated during a telephone conversation. In order to hold a conventional relay operated for a long period of time, it is usually locked electrically through one of its own make contacts. This method of latching requires that a continuous current be supplied to the relay coil. In the past, relays with mechanical locking features or auxiliary permanent magnets also have been used. These relays, however, frequently require two electromagnets, one to operate the relay and activate the locking mechanism and the other to deactivate the locking mechanism and allow the relay to release. A relay which requires a mechanical locking mechanism, since it needs two electromagnets, is equivalent to two relays and is therefore uneconomical. The latching force, winch holds the magnetic latching relay operated, depends upon the residual magnetic induction and coercive force of the magnetic materials used in the structure of the electromagnet. The magnetic latching relay is operated by a short current pulse. After the removal of the pulse the relay remains operated. A current pulse of 999