Patent GB-357607-A (GB)
Title: Improved call finding arrangements in automatic and semiautomatic telephone systems
IPC: H04Q3/00
Filed: 1930-05-26
Abstract: 357,607. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. May 26, 1930, No. 16186. [Class 40 (iv).] A call finder comprises four single-motion switches with wipers permanently connected together, but not joined to an outlet, the outlet being wired to terminals in the banks of two of the switches. The finders have no individual relays, the switches being controlled by a relay group common to a plurality of finders. On release the switches remain on the contacts used and when a call originates these switches are homed, that finder having access to the calling line is set in motion to find the calling circuit and then one of the switches having access to the outgoing route is moved to connect the wipers with that route. When the subscriber's line is looped L energizes connecting earth to the start wire s which energizes the relay A, B, C, or D corresponding to the bank to which the calling line is wired. Assuming A energizes, this relay shorts its winding (I) reducing the potential at ts4 to prevent B, C or D from becoming energized. R operates and T energizes followed by P, Q. Either switch AM or switch BM is on its second contacts and, if this is AM, then one of the switches BM, CM or DM is connected to the commoning in bank BH, CH or DH. It is assumed that BM is in this condition. As R, T, P are up, earth is connected over P (II) and wiper X to AM over contact 2 of AH and this switch steps to position 3. R now releases due to T having energized and, before P falls away, earth over P (II) is connected over wiper Y and BH to home switch BM (CM or DM is similarly homed if either of these had been the last switch used). P now falls away and before Q de-energizes AM is stepped from earth over wiper Z to its fourth terminals and then over wiper Y and P (II) to its home position, P re-energizing in this circuit to hold Q. When AM reaches home P and Q fall away and S pulls up. As the calling line is in the banks of AM, the combined effect of A and S steps AM over wiper A to its second contact (BM, CM or DM would have operated if the relay B, C or D had been energized instead of A). In position 2 of AH, as A is energized, AM again operates over wiper X to move its wipers into position 3 when a circuit is completed over wiper Z to move AM to position 4 where its wiper AH is connected over wiper Y to energize relay A. (A similar action for BM occurs if B had energized whilst if C or D had pulled up relay X is operated over position 2 of the switch). Relay X energizes relay Y, connecting AM over wipers Y and T to wiper AC, AM moves the wipers AA, AB, AC, AH until AC encounters battery from K over wire c of the calling line. TS then pulls up over its winding (I), holding over (II), breaking the stepping circuit and energizing K which releases L and removes earth from s to release A. TS connects earth over a6 to wiper B to step BM to its second contacts, connecting the call finder wipers over BA, BB, BC to the trunk to the next switch in the train, from which earth is received over c to hold K. TS releases T and before the start relay A has fallen away R re-operates releasing S and TS,Rde-energizing shortly afterwards. The earth returned from the seized switch passes over wipers BC and T to ADM and this magnet steps the wipers T, Y, Z, X, A, B, C, D to another free finder marked by absence of earth over T. Had the calling line been in the banks of BM, CM or DM, switch AM would have been moved to its second terminals to connect with the outgoing citcuit. If the caller clears before connection to it has been established, T is held over p1 until AM (or BM) is on its 3rd contacts and the other used switch has been homed when I' falls away and T releases. When another call originates RT, P and Q pull up but as no circuit exists for P over wiper X, it falls away, closing a circuit, over wiper Z, for the switch left on its third contacts when the operation proceeds as described above.