Patent GB-518438-A (GB)
Title: Improvements in or relating to private automatic telephone exchange systems
IPC: G07C1/20
Filed: 1938-08-26
Abstract: 518,438. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., (Pouliart, W.). Aug. 26, 1938, No. 25157. [Class 40 (iv)] In an automatic private or private branch exchange with checking arrangements for a watchman's round, equipment accessible from a number of sub-stations gives an indication when a predetermined sequence or time schedule of calls from such sub-stations is broken. Key WSK at the indicating equipment, depressed when the watchman starts a round, operates relays Ws and Bt and magnet CRM of timing apparatus energizes. On reaching the 1st substation, he makes a call and dials 7, the impulses being repeated by As to slow relay Lm and magnet SM of a local link market, Lm operating Sd during the train. On the relapse of Sd, N pulls up over the marker in series with bridge relay Cs, which remains inert, whereupon T pulls up over the market, 4th wire circuit and wiper a of sequence control switch MS the back stroke magnet of the switch and relay H being energized by T. Relay H connects ringing current over condenser CN to the a wire to inform the watchman and opens the circuit of magnet CRM of the timing equipment which restores to normal. When the watchman replaces his receiver, the link circuit and relays other than Ws and Bt release, MS takes a step to 4th wire of the next sub-station, and the equipment awaits the next call. If the calls are made according to the schedule, 20 substations being provided for, MS reaches contacts 21 and L pulls up so that when the watchman restores key WSK on his return, meter RM is operated during the release period of L. If the watchman is late at the first sub-station, timing contacts TC operate A over the 1st contacts of MS (b) and Al pulls up to light the individual sub-station lamp AL1, operate an alarm AB, and restore the timing equipment. Relay Sm also pulls up. If the watchman subsequently makes the call, the operation of T and H releases A and Al and magnet FM of another meter is energized during the release period of Sm. MS takes a step as before. If a double time interval is to be allowed for the 1st sub-station, the 1st contact in MS (b) is not connected so that when A operates after the first time interval, Al does not energize and the timing equipment is maintained in operation by B. When timing contacts close after the next interval, Al pulls up and gives the alarm as previously described. For succeeding substations, single intervals are allowed for by stoppings to terminal BW which is connected up when Ws is operated whereas double intervals. are allowed for by strappings to AW which is not connected up by Ws. Lateness on return from the last sub-station is indicated by lamp WL. While the watchman is on the round, depression of key CK will light the lamp of the last sub-station he called from. Three time intervals may be allowed for by using another pair of relays similar to A and B, operated after the second time interval, Al being then operated after the third interval over an additional strapping terminal for MS (b). A time stamp operated by contacts of H may be provided and the sequence switch may be replaced by a hunting switch. Contact 7 of the marker is normally connected to busy tone lead BTL.