Patent GB-729031-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: ROSENFELDER ROBERT ISAAC
IPC: H04Q3/62
Filed: 1950-11-06
Abstract: 729,031. Automatic exchange systems. AUTOPHONE, Ltd. Nov. 6, 1950, No. 27017/50. Class 40 (4). In an exchange, relays which respond to an impulsing relay operated by the dialled digits to control the selection of a uniselector or of a wiper set of a uniselector are also operated at some other stage in the setting up of a connection to serve other functions. A P.A.B.X. has a number of links each terminating in a uniselector-type call finder having two banks and two wiper sets spaced at 180 degrees and in a pair of uniselector-type connectors LS1, LS2 each having two wiper sets, and each wiper set of each of the pair of connectors gives access to one of the four groups into which the subscribers' lines are divided. The wiper set and connector are selected by a first digit 1 . . . 4, the selection being controlled by relays P, A, X which as described below also operate at some other stage in the setting-up of the connection. Privileged subscribers and calls from tie-lines may break in on an engaged line. When a receiver is lifted the caller's line relay L is placed in series with a chain start circuit and should all the links be in use with a busy tone relay GI. Otherwise a relay A in a free link is energized in series with L which partially operates for its contact l1 to mark the call finder CF. The test relay J connects C in series with the finder driving magnet DF, whereupon C operates L fully to release A and switches the line loop through to the windings of J. The hold relay B completes a circuit over the normal contacts of the banks d1, d2 of the connectors LSI, LSII for F to earth the start lead ST of the tone generator, dialling tone being then sent over lead DT and a winding of J. The first digit 1 . . . 4 selects the connector and wiper set serving the wanted line group 1 . . . 4 respectively; relay O selects the wiper set and N the driving magnet DSI or DSII to be used. Thus after the first impulse relay P prepared by the dialling relay E locks up, during the second impulse the wiper switching relay O locks over its early contact o2 and A follows, in response to the third impulse a circuit is completed over a make contact of A for N and the fourth impulse temporarily brings up X to release O. At the end of the digit M, H pull up. In response to a second digit 1 . . . 8, the chosen connector LSI or LSII is rotated to a subscriber's line. If the second digit is 9, P is held when E releases over a circuit including the wiper c of the connecter, and the third digit positions the connecter on to one of the lines connected to contacts 10 ... 19. If the second digit is 0 a circuit is completed over contacts 10 . . . 19 for the driving magnet to step the wipers to contact 20 to await a third digit 1 ... 4. At the end of the second digit F, M release. After the last digit T tests the called line during the release period of P and, if free, operates in series with the line relay L of the called line. When the called party answers Y switches through, T releases and E disconnects the ringing current. Release. This is under the control of the calling subscriber. If the called party hangs up first Y, E fall back to revert busy tone. If the caller holds up his receiver after the called party releases a calling condition exists on his line. Breaking in to busy connection. A privileged subscriber by operating a key causes X to operate followed by P which disconnects the busy tone lead ET. X completes a talking connection so that a triangular conversation can now take place or the wanted subscriber may release whereupon his line tests free and is rung, T operating to release X, P. Discriminatory ringing. Privileged subscribers' lines are provided with a resistance 10 which together with a break contact l2 is in shunt across a winding of L. So when C operates a relay D is connected in series with the resistance 10 whereupon D changes over from the normal ringing current lead RS to a lead DS. Similarly a different ringing tone may be sent back to the caller. Tie lines. Calls from tie lines are treated in the same way as calls from privileged subscribers. When a call is connected to a tie line, relay R operates, short-circuits T, holds J and shunts the bridge in the line. X switches through and P disconnects the busy tone lead ET. Since R would also operate in a call to a privileged subscriber's line and relay M shortcircuits R until after the second digit, privileged subscribers and tie lines are respectively given two and three digit numbers.