Patent GB-618807-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1946-11-08
Abstract: 618,807. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and IRGIN, C. R. Nov. 8, 1946, No. 33189. [Class 40 (iv)] In a system in which the calling subscriber's meter is operated over a fourth wire from the battery feeding selector, the operating current of the guard relay of this selector passes over the metering wire to ensure its continuity. As described, the battery feed for the calling party is provided at the first selector which gives access to 2-wire or 3-wire trunks and metering occurs at the end of conversation or, in the case of time metering, at intervals during conversation. Non-numerical switching, Figs. 1, 2. The operation of line relay R starts an idle finder LF1 to extend the calling line to a link circuit CC, whereupon the switch SH hunts for an idle first selector marked by earth on the c wire. When this is found, test relay TA pulls up, switches through, operates cut-off relay T in series with R and connects up VA to extend the common start wire 10 to the next finder of the group to deal with subsequent calls. If a selector is not seized within a certain time, thermal relay TH operates and transfers the starting condition to another idle finder. Relay VA may also operate to busy the link in the case of the individual fuse blowing or during maintenance. First group selector, Figs. 3, 4. Line relay A energizes first over the c wire and then over the loop and connects up dialling relay VAA which completes an operating circuit for guard relay C and the vertical magnet VM. During impulsing, C is short-circuited at each break, allowing the magnet VM to operate, and VAA is short-circuited at each make, so that it falls back at the end of the train and closes the circuit of the rotary magnet RM. Test relay PA operates when an idle outlet is found, locks over its low resistance winding and switches through. Subsequent trains of impulses are repeated by A over the a wire as earth impulses, and VAA is operative during each train. If no idle outlet is found, the selector stops in the 11th position and a busy signal is given. If no impulses are received within a given time, thermal relay THA operates and brings about release of the selector and link circuit, and cut-off relay T, Fig. 1, remains held over the loop to which an alarm tone is applied from lead 16. Metering. When the calling party hangs up, the release of A short-circuits C and permits VAA to energize. Relay Z is thereby connected to the b wire and operates to battery in the final selector, connecting metering battery to wire Z. Relay VAA falls back again after C and shortcircuits PA to initiate release of the selector and of the preceding and succeeding switches. In the case of time metering, relay Z is operated at predetermined intervals by booster metering impulses from time zone metering equipment associated with the outgoing junction, PA being held in series. Second or incoming selector, Fig. 5. When the selector is reached over a three-wire trunk, the neon tube NT is not required. Upon seizure, relay CA energizes over the c wire and resistance YT which may be short-circuited if the junction is a long one, connects up PB and sends back dialling tone if required. Impulses received over the a wire are repeated by AA to vertical magnet AVM, while PB is shortcircuited between impulses and finally releases at the end of the train, closing the circuit of rotary magnet ARM. When an idle outlet is found, PB re-operates and switches through. Release is initiated by the removal of earth from the c wire at the preceding selector. If the selector terminates a two-wire junction, relay B is normally energized over AA (upper winding) and the a wire to an earth at an outgoing relay set which is removed when the junction is seized. Relay B then falls back and connects up CA, the c wire being permanently earthed. Upon release, a high voltage pulse is applied to the b wire to reoperate B. Final selector, Figs. 6, 7. Relay CB operates over the c wire upon seizure and the first train of impulses received over the a wire are repeated by AB to vertical magnet BVM in series with VAB which falls back at the end of the train and connects up change-over relay UA. The final impulse train therefore goes to rotary magnet BRM and on the release of series relay VAB the wanted line is tested by PC. If it is busy, PC is inoperative, UA falls back and a busy signal is returned. If it is idle, however, PC energizes, UA being held temporarily, and places VAB under the control of ringing leads 55, 54 to ring the wanted subscriber. Ring cut-off relay ZA operates upon reply followed by feed relays AB, Y, battery being connected to the a wire for supervision if required and to the b wire for subsequent metering. Breaking in. A toll operator finding the wanted line is busy may apply battery to the b wire to operate Y which completes a speaking circuit and prepares a fresh circuit for PC to seize the line as soon as it becomes idle. P.B.X. hunting. All the lines of a P.B.X. group except the last are earthed in the d bank to provide a stepping circuit for rotary magnet BRM by interaction with UA, this circuit being opened when an idle line is found by the temporary holding of VA in series with PC. Specification 617,267 is referred to.