Patent GB-288547-A (GB)
Title: Improvements relating to automatic circuit selectors for telephony
IPC: H04Q3/00
Filed: 1928-03-30
Abstract: 288,547. Tchoubritch, Derval, & Co. April 11, 1927, [Convention date]. Automatic exchange systems.-A calling line is connected over front contacts of its line relay A and over an idle link such as II<2> to the calling side of an associated feed-group E - - O, and a wanted line, selected say by a two-digit marker, is connected over back contacts of its line relay and over the same link to the called side of the feed-group. On a calling line the line relay A is disconnected but locked by the cut-off relay B; en a wanted line it is not energized at all. The marking operation energizes a relay ab which connects battery to the upper side of the C-relays of the wanted line and connects the lower side of these relays over wires 85 to the corresponding feed-groups, where the circuit is completed to ground only in the feed-group seized by the calling line; the wanted line is therefore connected to the same link and feed-group as the calling line, and the feed-group at once disconnects ground from its wire 85 to prevent other wanted lines from being connected to it. The marker comprises a set of control relays R - - Y, two counting-chains a - - j, k - -y of single-relay type, and 10 tens-relays Z. In the following description it is assumed that subscriber 17 is calling 90. Connection of calling line to link and feedgroup. The line relay A connects battery to the upper side of associated C-relays, which are connected in the lower side over wires 9 to ground in idle feed-groups. The C-relay of the first idle link, say II<2>, is energized and locks itself in circuit 13, 14 in series with the cut-off relay B, which disconnects A from line but keeps it locked. The C-relays of other idle links may be energized but only momentarily, as each relay opens the locking-circuit of the next. The calling line is switched over 11, 12 to the feed relay E, which marks the link busy to other calling lines by opening circuit 9. Relays K, L and M become energized. Seizure of idle marker. Circuit 20 is closed for marker-connecting relays P, P<1>, which both become energized if both markers are free, but P opens the locking-circuit of P<1> so that only P remains looked. The locking-circuit includes relays O (which opens circuit 20) and R. If both markers are busy relay A is energized, with the result that the busy relay F becomes energized and sends back tone. Operation of marker by two digits. Relay S is energized by E and therefore responds to the digits. Relays V and X are energized throughout each digit. The first energization of S energizes T, which locks itself. The first impulse therefore energizes V, which locks itself. At the termination of the first impulse T is shortcircuited and falls back, so that the second impulse short-circuits V, which falls back. At the termination of the second impulse T is again energized, and the cycle starts again. At every odd impulse (T and U both energized) ground is connected over 26, 40, 41, 42, and at every even impulse (T and U both de-energized) ground is connected over 26, 40, 61, 62, 63, 64. This results in a building-up of the chain a - - j, a being first energized over 42, locking itself at 26 and preparing a circuit for b, which is then energized over 64, locks itself to 26, unlocks a and prepares a circuit for c, and so on. The relapse of V at the end of the first digit closes a momentary circuit for W, which locks up and transfers the control circuits to the second chain k - - y. During the second digit Y is energized as well as V and X, so that at the end of the digit ground is connected to circuits 30, 73 and battery to 76. Circuit 30 energizes N, which unlocks M, so that ground is momentarily connected through J to wire 85 of the link II<2> ; circuit 73 energizes Z<9> under control of the first counting-chain; and circuit 76 is extended through contacts of the second counting-chain and Z<9> to relay ab of the wanted line. Connection of wanted line to calling feedgroup. Supply of ringing current. Relay ab energizes the corresponding C-relay of link II<2> over wire 85 in series with J. The C relay locks itself in circuit 13 in series with the cut-off relay B and switches the wanted line over 88, 89, 90, 91 to relay H and a ringing wire 98. When the subscriber replies, relay H extends the called line to the back-bridge relay G which completes the connection. Release. Relays K, L relapse successively when the calling subscriber hangs up, and in the interval battery is disconnected from circuit 13 to unlock the C-relays. Busy signal. If the wanted line is busy its abrelay is disconnected by B, J is not energized, and when M ialls back F is energized and sends back busy-tone.