Patent GB-412591-A (GB)
Title: Improvements in automatic telephone systems
IPC: H04Q3/42
Filed: 1932-12-29
Abstract: 412,591. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. Dec. 29, 1932, No. 36811. Convention date, Dec. 29, 1931. [Class 40 (iv).] In a system employing group selectors of the type in which a numerical switch marks a group of backwardly-hunting switches, the first one or more group selectors is or are set directly by the subscriber and the remaining switches under control of a register controller which may be set while the hunting operation of the selector with which it is associated is proceeding. The invention is described with reference to a system in which the calling line is extended non-numerically as described in Specification 412,590 to a feed circuit comprising a numerical switch GV which picks out a group of finders GS1 in accordance with the first digit, and associated permanently or temporarily with a register controller which receives the remaining digits and transmits their complements (with respect to 11), to a 2nd group selector stage and to a directly operated final selector LV, each register acting, in response to a signal from the switch it has controlled, to initiate the transmission of the next digit. The hunting switches are of the power-driven no-normal type. On release by the calling party the sequence switch at the final selector connects the impulse relay to the called line to prevent release of the final selector and cause the transmission of a tone signal if the called party has not hung up. Register-controller. When the non-numerical link switches through, R1 .. R4 pull up. R1 repeats the 1st digit to the magnet GVM1 of the numerical switch GV1 and the remaining digits to the magnets ReM1 .. ReM3 of the registers Re1 .. Re3. The magnet SORM which is slow acting is energized in parallel with the registers in turn and at the end of each digit allows the sequence switch SOR to take a step. When the 1st selector switches through, R5 releases R4 and (provided SOR has reached its 3rd position) the magnet ReM1 is energized in circuit 21. ReM1 energizes R7 which short circuits ReM1. Interaction continues until the register reaches position 12, impulses being sent over the trunk by the stepping relay R7 which also holds R5 during impulsing over a 2nd winding of which the inductive effect helps the rise and fall of current in the impulse circuit. At the end of the digit R5 is released by a signal from the group selector and R4 pulls up again, energizing ReM1 R5 is again energized when the final selector is ready and releases R4 to allow Re1 to take a step and so initiate the transmission of the next digit. Re2 in a similar manner is moved to position 13 by a signal from the final selector to initiate the transmission of the last digit. At the end of this digit, R5 is released by the final selector and on the relapse of R4, Re3 moves to 13 releasing R3, which completes the line circuit and releases R4. 1st and 2nd selectors. As soon as the register Re1 moves off-normal, circuit 18 is made for driving the idle finders GS1 1 of the wanted group. In the successful one, GR1 switches through energizing R5, R6 in series. R6 moves the sequence switch S01 off-normal and repeats the digit from the register controller to the numerical switch magnet GVM2. The sluggish magnet SOM1 of the sequence switch is energized in parallel and at the end of the digit allows the switch to move to position 3 in which R5, R6 are released, the latter advancing the sequence switch to 4 in which the magnets GSM2 of the idle finders in the selected group are started. In the successful one GR2 switches through energizing R6 which drives the sequence switch to its last position. Final selector. GR2 drives the sequence switch 2 steps off-normal to provide a circuit for R8, R5 in series and so signal the readiness of the switch to receive impulses to the register controller. R8 gives the sequence switch a further step and repeats the tens digit to LVM1. Dialling relay R9 energizes magnet SOM2 and at the end of the digit the sequence switch moves from 4 to 7 releasing and reenergizing R5, R8 to signal the register controller, and to 8 when R8 pulls up. The final digit is thus repeated to LVM2. At the end of the digit R9 falls and the sequence switch moves to 10 releasing R8, R5 to release the register controller. Busy test, ringing, reply and release. If the line is busy LVR cannot pull up and the sequence switch is stepped in position 10 and sends a busy signal. If it is idle, LVR pulls up in series with the cut-off relay in position 9, locks and drives the sequence switch to 11 in which ringing current is sent out over R10. When the subscriber replies, R10 moves the sequence switch to 12 in which R8, R10 are cut off. Back-bridge relay R11 in the feed circuit drives SOR to its 6th position. When the calling party hangs up, R1, R2 fall back releasing R11 if necessary and SOR and the registers Re1 . Re3 and GV1 are restored in turn. R2 releases GR1 which restores the sequence switch S01 after which GS2 is restored. GR2 is released by GR1 and, provided the called party has hung up, homes the sequence switch S02 after which the final selector is driven with the aid of springs 57, 58 by magnet LVM2 to the next group and then by LVM1 to normal. If the called party fails to hang up, S02 is stopped in position 13 by R8 which pulls up over the called loop and a tone is connected to the line.