Patent GB-516741-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M15/10
Filed: 1938-07-06
Abstract: 516,741. Automatic exchange metering systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., and BEALE, C. E. July 6, 1938, No. 20022. [Class 40 (iv)] In a system in which timing equipment associated with a repeater at a particular office controls repeated metering at that and other offices, the repeater is seized over different routes for locally originated and incoming calls, and in the former case the timing apparatus controls the application of booster impulses to the c-wire. In the case of incoming calls it causes an alternating current signal to be sent to the originating office at the end - of each conversational period to control metering as described in Specification 475,419. The repeater described comprises a speech amplifier and repeats selecting and other signals as impulses of alternating current. Adjustable resistances are included in the A.C. transmitting circuits to enable the repeaters to be adapted for use with junctions of different lengths. Repetition of selecting impulses. The outgoing repeater, Figs. 1 and 2, is reached from 'local switches over the wires -1, +1, P1 and from incoming switches over -2, +2, P2, relay CM operatirig in the latter case in series with the line relay A. Relay A is followed by release relay B and relay CC which starts a seizing pulse by connecting commercial frequency A.C. to the outgoing junction and energizes CR which pulls up sluggishly to terminate the pulse by releasing CC and locks up. It also holds CM if receiving and shortcircuits its line winding. In the incoming repeater, Fig. 3, relay 2AC responds to the seizing impulse and is followed by 2C, R, 2B. Relays R, 2C fall in succession at the end of the impulse but 2B remains locked in series with RP which now pulls up. On the relapse of R, the talking wires are bridged to prepare the associated switch and on the relapse of C, supervisory relay D and relay I are cut into the bridge. Relay A repeats selecting impulses to CC, C, the former repeating them in A.C. form and the latter disconnecting the rest of the junction circuit throughout each digit. At the incoming repeater, 2AC and R repeat the impulses and 2C shunts relays I, D throughout each digit. Reply signal; metering. Supervisory relay D energises E and starts an A.C. impulse back over the junction, relay DR terminating it shortly afterwards and locking up. AC at the outgoing end responds to the pulse and energizes SA which locks up, disconnects CC and connects magnet TSM of the timing switch to six-second pulses on wire 15. It also reverses the connections of the line relay to initiate metering in the case of incoming calls. In the case of locally-originated calls on which CM is not operated, it also initiates the operation of S and Z relays DA, DB which cause relay J to repeat impulses received from lead 19 in accordance with the zone as booster impulses over the c-wire. Twelve seconds before the end of a conversational period the timing- switch connects J to   a pulse wire 16 to cause warning pips to be sent from an 800-cycle source over line relay A acting as'a transformer. At the end of the period TS energises RM which is followed by RN, the timing switch is sent home and RM, RN fall back. RM in tandem calls connects commercial frequency A.C. to the incoming junction to control the meter as described in Specification 475,419 and disconnects the outgoing side of the junction circuit. In locally originated calls it shunts out DB and DA, DB are operated in due course to cause a further impulse or series of impulses over the c-wire. Release. When the calling party hangs up, the relapse of A energises C and on the relapse of B, CB pulls up and CC starts a long A.C. releasing pulse. C, CB, CC then fall back in succession to terminate the pulse. RN is operated to home the timing switch while CB is operated and these relays keep the repeater guarded. At the incoming office, 2AC responds to the releasing pulse and is followed by 2C, R. The latter releases the switches and shunts out 2B which releases DR. At the end of the pulse 2AC, 2C, R and finally RP fall back. Marking the outgoing end of the junction busy from the incoming end. If the incoming repeater or associated selector is being tested or if the selector sticks off-normal, relay E is operated from the c-wire over its right-hand winding and connects the AC source to the junction. AC responds at the outgoing end and marks the repeater busy. Speech amplifier. The repeater comprises a voice current repeater TVR, the input of which is normally shunted by a resistance and condenser in series to prevent howling. This shunt is removed by CR shortly after the repeater is seized. During A.C. signalling, when the junction is disconnected from the voicecurrent repeater, the circuits of the latter are modified by relays C, CC to prevent howling. Applications of rectifier. Ground connected via rectifier MR guards the circuit while armature j1 is between its contacts without short circuiting the booster battery when J is fully operated.