Patent GB-322242-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-09-05
Abstract: 322,242. Automatic Telephone Manufacturing Co., Ltd., Paulett, W. H., and Gillings, C. Sept. 5, 1928. Automatic exchange systems. - During the hunting motion of a switch, the switching relay, which is operated over the test wiper, is connected to and disconnected from the wiper at each step. The invention is described as adapted to group selectors, group selectors with two sets of wipers, incoming selectors accessible over twowire trunks and first selectors with transmission bridges arranged for fourth wire metering on reply and for metering at the ends of a call by booster battery and fourth wire methods. The switch (Fig. 1) operates so far as its vertical movement is concerned in the usual wav and hunting takes place due to the interaction of G and R. Each time G operates, earth at 18 is connected through H to the test wiper 27 and when a free terminal, marked by battery, is reached, H operates breaking the circuit of R at 7. H is held by earth returned over 27. The battery potential which marks the switch as free may be applied over a normal contact or (as in Fig. 2, not shown) over a back contact of the change-over relay which is energized in series with the release magnet. Fig. 4 shows a switch accessible over a two wire trunk. The switch cannot feed back potential to indicate its idle condition so the bank of the switch having access to the outgoing end of the trunk is connected permanently to battery which condition is rendered ineffective on an engaged circuit by earth on the test wiper of an engaging switch. The switch is operated in the usual way, earth at 171 being connected to the test wiper in series with relay H at each operation of relay G. Relays D and are bridged across the speaking conductors when the line is switched through, the relays being shorted by a contact 166 of C when further impulses are repeated to switches ahead, C then operating in series with battery from 176 instead of the vertical magnet V. Relay I is held saturated by C whilst impulses are repeated to prevent false impulses when I and D are subsequently re-inserted. If the switch moves to its eleventh rotary position, cam springs S operate relay BF intermittently from 191 connecting busy tone and flash over the calling loop from 191<1>, relay AB being held from 180 during the release periods of A. If busy signal is received from a subsequent switch relay I de-energizes on the first battery pulse allowing BP to operate its' light armature 179 and to energize fully when I re-operates. Relay BF energizes on the next deenergization of I and repeats the busy signal, in synchronism with I, to the calling party. Relay B provides operator hold facilities over the calling loop, being held energized by I at 168 when A and AB release if the circuit has been extended to an operator and extending battery over the line from 164<1> to the preceding switch. Fig. 6 illustrates the invention as applied to a first selector arranged for booster metering at the end of a call. The switch operates as before described and when the call is released relays A and AB de-energize. Relay B is slow to release and during its release period booster battery is connected over the test wiper. If the circuit is unsuccessful or has been extended to an operator relay MD will be energized and will not commence to de-energize until relay B has fully released, thus preventing the completion of the metering circuit.