Patent GB-198776-A (GB)
Abstract: 198,776. Relay Automatic Telephone Co., Ltd., and Rousseau, E. J. C. March 8, 1922. Automatic and semiautomatic exchange systems.-A subscriber on an automatic private branch exchange who has been connected by the P.B.X. operator to a manual exchange line, can by a manual operation, such as the momentary depression of his switch-hook disconnect himself from the P.B.X. operator's board and at the same time cause the manual connection to be held. The automatic subscriber is then free to call another automatic subscriber and after releasing this connection he can restore the original connection with the manual subscriber, all the operations being carried out without giving any signal to the P.B.X. operator. The invention is described as applied to an automatic private branch exchange of known type in which all the connections are made by relays. A P.B.X. subscriber A on removing his receiver is connected in known manner over a link L and trunk OT to an idle recorder R, whereupon the cut-off relay CO and a slow-release relay Fare energized in series over the holding circuit H, deenergizing the line relay LE. If connection is required to another P.B.X. subscriber, the recorder R, in response to dialling impulses, picks out a marking wire Mn individual to the wanted line and the connection is completed in the usual manner, but if a public exchange connection is desired, a digit assigned to the P.B.X. operator is dialled, and the recorder picks out a marking wire MO over which a marking relay OM is energized. A circuit MC is thereby completed for a relay OTR associated with the engaged trunk OT, this relay breaking the holding circuit H. The cut-off relay CO relapses before the slow-release relay F, which remains energized over the calling loop, and closes a circuit 2 for a line lamp SL at the P.B.X. switchboard. The P.B.X. operator plugs into the calling party's line jack LJ, closing a series circuit 3 for the cut-off relay CO and the relay F, and extinguishing the lamp SL. The insertion of the answering plug AP, Fig. 3, also completes a circuit 4 for a relay XRS which closes a circuit 5 for a guard relay G1. The operator now ascertains the wanted number and completes the connection in any known manner. If the subscriber A wishes to confer with another P.B.X. subscriber and then return to the original manual subscriber, he momentarily breaks his loop, for example, by depressing the switch-hook, thereby de-energizing the relay XRS and completing a circuit 6 for an auxiliary guard relay G2, which energizes a high resistance holding relay EH in circuit 7. Relay EH locks up over its upper armature and places a holding loop 8 across the manual subscriber's line. The high resistance of the relay EH prevents the lamp SL from glowing in the circuit 7. The P.B.X. subscriber A is now at libertv to establish connection with another party in known manner, and after completion of this conversation he may reconnect himself with the public subscriber either by again dialling the digit assigned to the P.B.X. operator or by again breaking loop by depressing the switch-hook. This causes the relays CO and F to relapse, but since the latter relay is slow to release, a momentary circuit 9 will be completed which short-circuits the holding relay EH. The relay EH then relapses, removes the holding loop 8, extends the subscriber A to the manual line and restores the circuit 3 of the relays CO and F.