Patent GB-197646-A (GB)
Abstract: 197,646. Siemens & Halske Akt.-Ges. May 9, 1922, [Convention date]. Automatic exchange systems.-Different grades of lines to which different connections are permitted have distinctive potentials associated with their incoming and outgoing terminals, and when a connection has been set up a polarized relay BR compares the distinctive potentials of the calling and called lines and releases the connection if the latter is higher than the former. In the bye-path arrangement shown in Fig. 1, the relay BR is in the setting-path VLI, AS, LW, which is replaced, if the connection is permitted, by a speaking path established by the called subscriber's line switch, such as IVWN2. It will be seen that the distinctive potentials BPI, BPII are so connected that lines of the group NL have unrestricted access to all lines, lines HL have access to all lines except main-exchange lines AL, inter-branch lines QL are only permitted connection to lines NL or HL, and lines AL are onlv permitted connection to lines NL. In a modification, the distinctive potential on the lefthand side of the relay BR is not derived from the calling line, but is determined by the position to which the switch AS is set. In a second modification, the invention is applied to a large bye-path system of the kind described in Specification 16538/13, the relay BR being connected in the speaking path. The arrangement shown in Fig. 1 will first be described with reference to Figs. 2 and 3. Operation of calling subscriber's preliminary selector IVWNI. The closing of the subscriber's loop completes a circuit D1, 3, TN1, b, a, 6, 7, 8. The relay TN1 is of too high resistance to permit energization of the stepping magnet D1, but it closes a circuit for this magnet through its own low-resistance winding. After the switch has taken its second step the relay TN1 relapses and closes a circuit D1, 15, 16. When an idle trunk VL1 is reached, the relav TN1 is energized in a circuit 17, 18, 19, 3, TN1, b, a, 6, 7, 8 and switches the line through to the relay A1. Operation of the setting-path switches AS1, LW1. The relay A1 energizes relay V1 and closes a starting circuit for the stepping magnets such as D2 of idle call finders. When the finder AS1 reaches the trunk VL1 a circuit 36, P, 37, 39, R, 40, T1, 41 is closed to energize relays P, R, T1. Relay P stops the switch AS1 and relay T1 opens the common starting circuit. The first digit dialled by the subscriber is repeated by relay A1 over a circuit 48, 50, U, 51, H to raise the connector LW1. At the termination of the digit the series relay U relapses and energizes relay E, which locks itself and closes the contact 56. so that the second digit is repeated to the rotary magnet D3. Discriminating test. At the termination of the second digit the relapse of relay U completes the left-hand circuit of the discriminating relay BR to the distinctive potential BPI associated with the calling line, the right-hand side of this relay being connected over wiper 63 to the distinctive potential BPII of the called line. If the connection is a forbidden one the relay BR becomes energized, closing the circuit of the connector release magnet M at contact 66 and a busy-tone circuit at contact 67. In the present case the connection is assumed to be between two lines of the unrestricted group NL, so that relay BR is not energized. Operation of called subscriber's preliminary selector IVWN2 to complete the speaking path. The relapse of relay Q a moment after relay U completes the circuit 57,69, P1, 70, 72, 74 of the test relay PI, which becomes energized if the wanted line is idle and energizes relay F1, which locks itself and energizes relay B1 and closes a circuit 86, 87, 89, TN2, 90, 92, D4 to energize relay TN2, which closes a low-resistance circuit 93, 90, 92 for the stepping magnet D4. After the second step the relay TN2 is de-energized and the circuit of magnet D4 is maintained over 92, 97, 110. Since the relay Bl has disconnected the normal battery feed of the c-wires of all disengaged speaking trunks, the only trunk that is selectable at this moment by the switch IVWN2 is the trunk VL1, of which the c-wire is connected to battery through the low-resistance upper winding of relay S1 and contact 80. When the switch reaches this trunk a circuit 86, 87, 89, TN2, 90, c, S1, 81, 80 is completed to energize relay TN2, which stops the switch and switches the called line to the trunk VL1. (It should be noted that during the operation of the switch IVWN2 the relay F1 by opening its contact 7 prevents the starting of any calling subscriber's preliminary selector, and by energizing relay U1 holds up the testing operation of a second setting- path connector.) Release of the setting-path switches. When the switch IVWN2 left its normal position the relay PI was de-energized and energized a relay G, which locked itself up, but now the relay P1 is energized again in a circuit 74, 110, 108, 109 72, 70, this being possible because the contact 69 is now open and both windings of the relay are in circuit. The magnet M is thus energized to release the connector LW1 and to open the circuit 36, P, 37, 84, R, 85, 41, so that the setting-path AS1, LW1 is restored to common service. The relay R relapses, but relay Sl remains locked and marks the trunk VL1 non-selectable to the setting- path switches by keeping the contact 39 open. Supply of ringing current. The calling subscriber now again operates his impulse sender, and at each impulse the potential across the called line rises owing to the opening of the shunt circuit through the calling line. Thus the condenser at the called substation is intermittently charged and the bell rung. , Release. When the subscribers disconnect themselves the relapse of relay V1 disconnects battery from the c-wire of the trunk VL1 so as to de-energize relays TN1, TN2, which close circuits for restoring the switches IVWN1, IVWN2 to normal. Second system, Fg. 4. In this modification the trunk VL1 has separate test wires cn1 ch1, cq1, ca1 for the four grades of lines, so that a relay LN1, LH1, LQ1, or LA1 is energized and sets the switch AS1 to one of four positions all belonging to the trunk VL1, and a discriminating potential BPI appropriate to the calling line is connected to relay BR over the wiper 204 of the switch AS1. Third system, Fig. 5, representing a modification of the system described in Specification 16538/13. The relay BR is included in the speaking-path AS1, VW1, RW, VW2, AS2 and distinctive potentials are connected to it over wipers 301, 302, 303, 304 of the switches AS1, AS2. On the calling side the potential is that found by the wiper 301, but on the called side a relay U2 connects the discriminating circuit to the wiper 304.