Patent GB-368285-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/00
Filed: 1930-12-02
Abstract: 368,285. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, and TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool. Dec. 2, 1930, No. 36320. [Class 40 (iv).] In a bi-directional selector arranged to hunt over successive levels, a relay which operates over a circuit independent of the wipers to control rotary release is also used on the completion of a connection to control metering, the relay co-operating with the change-over relay for this latter purpose. Booster battery metering is provided, the booster battery being connected during the release period of these two relays. Setting of selector. When a call originates relay A operates followed by B, and the first digit train is repeated by A to VM to step the wipers. C holds during the train and, when C releases, E pulls up and locks, changing over to the rotary magnet RM. The second digit train is repeated to RM, C holding in a parallel circuit. The initial circuit of E is broken at rotary off-normal contacts NR but C enables E to hold during the train. As shown in Fig. 2, the wiring of the terminals wiped by 4W is such that first lines of P.B.X. groups are connected to battery, intermediate lines are wired to corresponding terminals wiped by 3W whilst final lines and single subscribers lines are left disconnected. If the connection is to the first line of a P.B.X. group then, during the interval between the releases of C and E, a circuit is completed from 3W to G. If the line is busy G energizes and completes a circuit for HS (over 4W) which in turn re-energizes C. C re-completes the circuit of E which is sufficiently slow-to-release to hold during the period taken for the above cycle. HS also completes a circuit for RM to move the wipers to the next terminal set, HS releasing when RM operates. If this line is busy, 3W again finds earth and G remains up. This earth is also connected to 4W and, as C is up, HS re-operates over its lower winding. HS and RM thus interact until a free line, the last line of the group, or the last bank terminal is reached. All lines in level busy. If the group spreads over more than one level and all the lines in the first level are busy, the wipers are stepped past the 10th bank terminals and cam springs S operate. HS restores as 4W fails to find earth and HC pulls up, completing a circuit for the rotary release magnet RZM which enables the wipers to move back clear of the bank. C remains energized over hc1 and, when the rotary off-normal springs remake, HS and G re-operate. HS enables the vertical magnet VM to step the wipers one step. The vertical magnet springs V open, HC de-energizes, RZM releases and the rotary magnet circuit is again completed to move the wipers into engagement with the first bank terminals. Hunting over this level takes place as previously described. All lines busy. If all the lines of the group are busy the wipers are moved to the last terminals and wiper 4W does not find earth. HS does not re-operate, C releases, G remains locked up and busy tone is connected from BTT to the calling party. Line free, ringing, metering, release. When a free line is found, battery is connected over 3W and earth will not exist on 4W. Consequently G releases and HS does not reoperate. C and E restore and H pulls up and locks. Ringing is connected over F to the called party and E and HC operate to prepare the metering circuit. When the called party replies F energizes and D pulls up, reversing the battery connection at A to the calling party for supervision purposes. E releases slowly followed by HC and during the slow period of these two relays booster battery from BB is connected to the private wire to meter the call. Calling party release is provided but if the called party should release first, D falls away and the called subscriber held lamp CSH is lighted. This lamp may be connected in series with a common supervisory relay to give an alarm if the condition exists for more than a predetermined time. When the calling party clears A releases, B falls back, F and H restore and the release magnet ZM pulls up to restore the switch. When B and H release earth is removed from the private wire, to enable preceding switches to restore, but earth is replaced shortly afterwards, by the release magnet springs Z, to prevent re-seizure before the switch is fully restored. Night service arrangements. Any line in a P.B.X. group, other than the first, may be used for night service. When connection is made to such a line, C releases and, if the circuit is busy, earth is found over 3W and 4W. G pulls up and locks but, as C is back, HS cannot operate and busy tone is returned to the calling party.