Patent GB-525004-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1939-02-11
Abstract: 525,004. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., and SCOWCROFT, J. Feb. 11, 1939, No. 4510. [Class 40 (iv)] In a party-line arrangement in which each station has a line relay for controlling a selecting switch, the line relays at all the stations are disconnected after a selecting operation has taken place and are reconnected after the call has finished, so that the ordinary release signal may be given by breaking the loop. The party-line 11, 12, which may be a waystation line for railway signalling, terminates in a small automatic exchange in a repeater which includes a mechanical impulse regenerator 27, 28 and a discriminating switch DS. The latter determines in accordance with the first two digits received from the partyline whether the exchange switches are to be taken into use or whether the call is a revertive one. Revertive call. An idle condition of the line is indicated by the absence of any tone or speech when the receiver is lifted. Dial key DK connects the local battery to the line to operate relay LC, which connects up A, B, BR, TC, the last relay supplying dial tone. Dialled impulses are repeated to the switch DS and to the setting magnet S of the impulse regenerator, the marking magnet M being controlled by dialling relay C. Sequence switch SS advances one step after each digit is received. If the first two digits indicate a revertive call, P energizes after the first, making a fresh impulsing circuit for DS, and WS energizes after the second, opening the outgoing loop and preparing for the absorption of those digits. DS is not affected by the third and fourth digits. Relay E operates in position 5 of SS and connects up I, LH, IP, IS, and P falls back. On the return of dial key DK, relays LC, A, B, BR fall back and SS advances to position 6, in which S energizes in place of E, releasing IP, IS and connecting impulsing battery to the line to operate high resistance polarised relay L at each station, which connects up BA. SS goes to position 7 and magnet T operates to start impulse transmission by the impulse regenerator which controls I at springs 63, SS advancing one step at the end of each train. Since WS is up, impulse relay I is held over wiper SS5 in positions 7 and 8, and therefore the first two digits are suppressed, but for subsequent digits, relay I sends reversal impulses over the line. The third or tens digit steps the switch SA at each station, but the units digit steps SA only at the stations denoted by the tens digit, the discrimination being effected by the operation of D or R when dialling relay CA falls back. When CA falls back after the units digit, relay BS energizes at the wanted station and operates the bell BL, ringing tone being fed inductively to the line. At all stations CA by its second operation and release connects up AA, AB to disconnect line relay L, whereupon BA falls back and restores SA. Relay AB is biassed so that it remains operated until it is restored by current in an appropriate direction through its left-hand winding. Relay BS is disconnected at the called station when the receiver is lifted. After the impulse regenerator has completed its operation, SS moves to position 11 in which S falls back and connects the line to feed relay LA, which connects up BD and HL is held. Upon release, HL completes homing circuits for DS, SS, and during the restoration of SS, RR pulls up and reverses the battery over the line to restore AB at all stations. Call set up over exchange switches. Dialled impulses are received in the manner described above, and in this case WS is not operated. There are only three dialled digits, however, and on the return of dial. key DK, since E is not yet up, the successive release of A, BR causes an extra digit 1 to be recorded in the impulse regenerator, after which SS advances to position 5 and E operates, connecting up I, HL, IP, IS as before, but the circuit of I being independent of spring 63. Relay HL closes the outgoing loop, whereupon a selector is taken into use and KA energizes over the test wire. In position 6 of SS, S energizes in place of E, connecting impulsing battery to the line and releasing IP, IS, provided KA has operated. Impulse transmission begins in position 7 of SS, springs 63 now being bridged across the outgoing loop. The first impulse of the first and second digits is sent over the line by relay RC under the control of springs 49, this relay being then disconnected by RE, which is held at its second operation until impulsing is ended. This results in the operation of AB at each station, the number 11 being unallotted. Completion of the connection and release take place as described above. A call to a manual board by dialling the single digit O is set up in a similar manner, the extra digit 1 referred to above being sent over the line as the second digit. This extra digit is in all cases absorbed in the selector. Incoming calls to party line. The line is selected by the first two digits of the four-digit number. Relay KY energizes over the test wire and connects up WS, which A energizes over the calling loop and connects up B, BR, TC, the latter applying a tone to indicate that the party line is in use. The last two digits are repeated by A to the impulse regenerator, the switch DS being unaffected since WS is up. SS than advances to position 5, in which E operates, connecting up I, HL, IP, IS. Relay KC energizes, and since A is still up, connects up BK and releases B, BR. In position 6 of SS, S energizes in place of E, releasing IP, IS and connecting impulsing battery to the line, so that in subsequent positions impulses are repeated thereto by I, which is controlled by springs 63 of the impulse regenerator. When impulsing is finished, SS advances to position 11 in which S falls back and connects the line to feed relay LA, which responds to the called party's reply and connects up BD, HL being held. Upon release by the calling party, A, BK fall back, opening the test wire and disconnecting KY. Release from the party line takes place as described above.