Patent GB-364532-A (GB)
Title: Improvements in systems for controlling switching operations in telephone exchanges by means of alternating current impulses
IPC: H04Q1/442
Filed: 1930-07-26
Abstract: 364,532. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. July 26, 1930, No. 22604. Convention date, July 27, 1929. [Class 40 (iv).] Switching operations are controlled by alternating current impulses which are converted into direct current impulses by a relay which is connected to the line wires through rectifiers. The Figure shows a system for setting up a connection from an operator's position EP through an automatic exchange over a long distance line IL. Initiation of call. After the operator has connected herself to the long distance line IL, key AK is momentarily depressed. to apply A.C. from source IS to the line IL and operate line relay R<1>. This relay is connected to the line through rectifiers K<1> .. K4 and impedarces R<0> and when operated causes energization of relays R2, R<3>, R<4> in sequence. Relay R<3> de-energizes relay R<2> but itself remains held until cessation of the impulse, when both R<1>, R<3> are released and relay R<5> is energized over a circuit prepared by R<4> which remains locked up. Relay R<5> closes a circuit over relays R<6>, RI<1>, relay RI<1> operating to energize relay DR which initiates operation of call senders such as SS in known manner to connect the line to a group selector GV. As soon as the circuit to the selector is established relay RI<3> is operated to short-circuit one winding of RI<1> and thereby cause operation of relay R<6> which connects a source SU of buzzer current to winding 18 of coil R‹ and thereby indicates to the operator that the register RE is ready to receive numerical impulses. Relay RI<3> also associates the register RE with the junction by operation of relays RI<2>, RT<2>. As soon as the register is taken into use contact 13 is opened and relay RG<1> is operated in the circuit of RI<3> which releases and causes the release of relay R<6>. Registration of digits. Numerical impulses are now transmitted by the dial switch FS which during operation energizes relay FR to connect the line IL to the A.C. supply IS and intermittently operates relays IR, ER to transmit impulses. The relays R<1>, R<2>, R3 are impulsed in the manner previously described and the impulses are repeated over the leads 17, 29 and recorded on the register RE. The group selector GV is then set under the control of the register in known manner and relay RT<4> is operated to disconnect the register and operate relay R<8> which extends the talking circuit. When the selector GV finds an idle connector LV test circuit over relays RG<3>, RV<1> is completed and as soon as connector (operated in known manner) moves, relay RV<1> is energized. If the called line is idle, sequence switch SOJ moves directly into the talking position (position 11) to short-circuit one winding of relay RV<1>, and thereby cause operation of relay RG<3> and the consequent sequential operation of relays RI<3>, R<6>, which latter applies buzzer current to the line to signify that the connection is complete. If the called subscriber is engaged in a long distance conversation relay RV<1> is intermittently shortcircuited by interrupter PS to transmit an intermittent buzzer signal to the operator. If engaged in a local call, however, the sequence switch is stopped in position 9 to connect the operator directly to the subscriber, and the operator may break the local connection by transmitting a series of impulses from the dial FS to operate relay RV<6> which operates clutch magnet VR of the sequence switch, thereby causing the switch to move into its talking position and connect battery at contact 55 to the test wire to terminate the local connection. Ringing called subscriber. The ringing signal is transmitted by operation of the dial switch FS to transmit a series of impulses. The first impulse energizes relay R' which causes operation of relays RV<6>, RV<7> which connect the source of ringing current CS to the called line. Signalling termination of conversation. When the called subscriber replies, the transmitter circuit is closed through a relay RV<5> which causes the release of relay R<6> to disconnect the buzzer signal and operate a time relay TL which after a predetermined time operates relay R<9> to prepare circuit of clearing signal relay R<10>. At the end of conversation, replacement of the receiver de-energizes relay RV<5> and consequently relay R<6> operates to energize relay R<10> which transmits a clearing signal from the source BS to the indicator KR. The relay R<10> also operates clutch magnet OR of switch SOJ which is driven one revolution and in passing through position 11, 12 operates relay R<13> to release relay R<10>. Release. The connection may be released at any time during setting up or during or after conversation by depression of key AK to transmit an impulse of long duration. This impulse operates relays R<1>, R<2>, R<3>, relay R<3> remaining operated sufficiently long to cause release of relay R<4>, which effects de-energization of relay R<5> upon release of the key AK. Restoration of relay R<5> causes sequential release of relays RI<1>, RG<1>, RV<1> which effects restoration of the selectors. Correcting impulses upon retransmission. The relay R<2> is short-circuited by a resistance r which determines the time period of de-energization at each impulse in order that the repeated impulses may be of invariable length independent of the length of the A.C. impulse transmitted over the line.