Patent GB-542039-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1940-06-22
Abstract: 542,039. Exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and PEARCE, O. A. June 22, 1940, No. 10748. [Class 40 (iv)] In a party-line system of the kind described in Specification 476,813 in which two switches at each sub-station are stepped alternatively by impulses from the exchange to connect up the instruments on outgoing and incoming calls, the exchange equipment individual to the line is provided with means for (1) denying service to any subscriber, (2) isolating a sub-station at which a permanent calling condition arises, and (3) preventing the use of the line if it becomes faulty. Outgoing call.-The closure of switchhook contacts SH1 completes a starting loop through rectifier MRE for relay ST which connects up ON and starts the transmission of impulses over wires 14, 15. The first impulse operates PG which reverses the battery connections to the line, and subsequent impulses control PR which sends high voltage negative impulses over the + wire to step the switches F and advances the switch S in synchronism. After an appropriate number of steps, contacts F1, F2 close a loop through the set at the calling substation and stop relay SZ energizes. The usual line switch operates, and switching relay CT energizes in parallel with the cut-off relay. When the called party replies, booster battery on wire M actuates the calling subscriber's meter MTR which is connected up over S3. Upon release, CT falls back and impulsing to restore the switches P is resumed until S reaches a normal position, when ON is disconnected. Incoming call.-When a party line subscriber is selected at the final selector, relay IC energizes, connecting up start relay ST and the cut-off relay. Relay CR energizes as well as ON, so that high voltage positive impulses are sent over the + wire to step the switches C. After the appropriate number of impulses, wiper S4 encounters ringing return battery in the final selector and stop relay SZ operates, whereupon CT switches the line through to the ringing circuit, the loop at the wanted substation being closed at contacts C1, C2. Upon release, IC, SZ, CT fall back and impulsing is resumed to restore the switches C. Revertive call.-The call is extended to a revertive call switch, which, after the calling party has hung up, sends impulses to step the switches C to select the wanted party, and both parties are rung in parallel. The resistances 10 are adjusted so that each party receives the same feed current. Upon release, the switches C are first restored, after which CT falls back and the switches F are restored. Barred service.-The circuit of stop relay SZ includes wiper S6 and individual jack links OL, so that any subscriber may be denied outgoing service by removal of the corresponding link. Similarly the subscribers have individual outlets in the final selector banks including jack links IL which permit the barring of incoming service. Permanent loop at a sub-station.-The omission to dial operates an alarm in the first selector. To isolate the sub-station, key KPR is actuated to energize SR momentarily, thus releasing CT. During the relapse of SR, high voltage current is fed over the line in a direction. to operate PGR, which opens the starting loop and locks mechanically, and when SR is back, impulses are sent to restore the switches F. Relay PGR may be unlatched by the replacing of the receiver. Line faults.-When a call is initiated by a loop on the line, stop relay SZ energizes after the first impulse since the starting loop is not broken by the off-normal movement of the switches F. The latter remain in their first position in which contacts F1, F2 remain open at all sub-stations, and RF energizes and locks under the control of key KR, opening the incoming call circuit and setting up an alarm condition. A ground fault on either wire operates RF at once or when a call is initiated.