Patent GB-267608-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/42
Filed: 1925-12-17
Abstract: 267,608. Automatic Telephone Manufacturing Co., Ltd., Saville, W., and Passmore, W. O. Dec. 17, 1925. Automatic eachange systems. - A relay bridged across the outgoing end of a trunk at the point at which talking battery is fed to a calling party responds to the alternate connection of battery and earth to the lower conductor of the trunk indicating that a busy condition has been encountered, and in responding causes the switches which have been seized over the trunk to be released and a busy signal to be transmitted to the calling party. The arrangements may include a two-step relay which only operates fully after the bridged relay has first de-energized and then re-energized. Figs. 1 and 2 show, respectively, circuit arrangements in which the bridged relay is at a repeater and at a first code selector. Repeater, Fig. 1. The line and release relays A, B operate as usual and impulses are repeated to succeeding switches at contact 5. During the repetition of a digit, relay CE energizes and completes a circuit for relay J which locks up. When the called subscriber replies, relays I, D and reversing relay DR operate, the latter connecting up booster metering battery and unlocking relay J which by its slow release determines the duration of the metering impulse. If a busy condition is encountered, battery and earth are alternately connected to the lower trunk conductor. At the first battery connection, relay I releases and energizes relay 00 which in turn partially operates two-step relay G. At the next earth connection, relay OC releases and relay G operates fully, opening the outgoing loop to release the succeeding switches and connecting up a busy tone and busy flash lead BF over the lower winding of the line relay A to the lower incoming talking conductor. If the call is extended to an operator, relay OC remains energized and, by completing an alternative circuit for relay B, puts release under the control of the operator. In a slightly-modified repeater, the relay G is not of two-step type but operates fully upon the release of relay I, and the lower winding of relay A is connected to earth, at first over a back contact of relay CE and then over a front contact of relay B. First code selector, Fig. 2. Relay I<1> operating over the loop causes the partial operation of two. step relay ST which, when relay I<1> releases in response to a busy condition, operates fully. The next operation of relav I' causes the energization of relay BR which locks over the calling loop, releases relay A to release the connection and connects up a busy tone at armature 34. The circuits of relays ST, BR include a back contact of relay D<1> to prevent busy release taking place in response to the battery reversals which are employed in connection with the transmission of digits from the register-controller. When the call is extended to an operator, relay OH operates when the calling subscriber hangs up and closes an alternative circuit for the usual release relay (not shown). The remaining operations of the first code selector are similar to those described in Specification 233,007.