Patent GB-418995-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M11/02
Filed: 1933-05-03
Abstract: 418,995. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, and COMYN, F. E., 12, Rawlins Street, Fairfield, both in Liverpool. May 3, 1933, No. 12920. [Class 40 (iv).] A numerical selector controlled by a group marking switch is driven in a self-interrupting circuit independent of the wipers of either switch until the magnet is held energized by the marker over the penultimate contact of the group preceding the wanted one. On release of a slow relay consequent on the relapse of the dialling relay, the circuits of the magnets are opened and the selector steps on to the last contact of the preceding group. The invention is described in connection with a P.A.X. comprising 25 point finder-connector links, but by using off-set doubleended wipers the capacity may be increased to 50 lines. The connectors are marker controlled by the first digit and directly impulsed by the second. Normal call. Two-step line relay LK makes marking and starting circuits at its light armatures lk1, lk2. The circuit for the start relay ST passes to battery over stepping relay G and, in parallel, over magnet RSM of the marker, Fig. 3, if the allotter is standing on an idle link, and ST operates under these circumstances. If the allotter has not preselected a link, the circuit to RSM is open, ST remains inert, and G interacts with DSM until an idle link is found whereupon battery over RSM short-circuits G and ST pulls up. Relay G now interacts with the finder magnet FDM until marking battery over LK holds the right hand winding of G in series with FH which holds over its left hand winding. ST and FH fall back slowly in turn, G remaining held over its left hand winding until FH is back, so that the allotter takes a step. Meanwhile, ground over DSS (4a) operates B, Fig. 3, which switches the line through to relay A and line relay LK has fully operated to perform its cut-off function. A holds B and dialling relay C pulls up over the first contact of the marker to connect up dialling tone lead 13. The first digit (2, 3 or 4) is repeated by A to marker magnet RSM, C remaining held in series with RSM since CR is also operated. If the digit is 3 or 4, magnet CNM of the connector receives an impulse when RSS passes contact 3, closes CON to complete a self-stepping circuit for itself, and chases the marker. When the marked contact is reached, CNM holds over CNS (4c), RSS until MC operates consequent to the release of C and CR whereupon CNM falls back and the connector takes one more step. If the digit is 2, CNM only takes one step. Relay MC holds, re-operates C over the marker followed by CR, and transfers the impulsing circuit to the connector magnet CNM which takes the units digit, C remaining held during the train. When C falls back, and during the slow release period of CR, H tests the line and if it is idle, pulls up, cuts out its high resistance winding and completes the ringing circuit from lead 16 over F, the return circuit passing over A (lower) to provide tone for the calling party. When the called party replies, F pulls up and locks over its right hand winding. Busy signal and release. If H does not operate, F pulls up over its right hand winding on the relapse of CR and connects the busy tone lead to the lower speaking wire. When the calling party replaces his receiver (and also the called party in case of a successful call) A releases followed by B and MC, whereupon CNM and RSM go home in turn. Privileged subscriber breaks in. Such subscribers have grounded contacts in bank 3b of the finder, so that CR pulls up again when a line is found busy (F and M operated and H unoperated) and a speaking connection is completed over condensers QA, QB. When the prior connection has been released, H pulls up, short-circuits the right hand winding of F to release it, and releases CR, whereupon the wanted line is rung and the call proceeds as normally. Conference facilities. The various desired parties are called up and requested to dial 0. The marker steps to last contacts and short circuits B which relapses to remove a short circuit on the right hand winding of CF, Fig. 1, whereupon this relay connects the conference line CL to the line circuit and disconnects the link circuit. Each party thus becomes connected to the conference line and is fed over the corresponding relay CF. Unobtainable numbers. The numbering scheme is 21-20, 31-30, 41-45, and if 1 or 5-9 is dialled for the first digit, there is no holding circuit for the magnet of the connector which therefore rotates to normal. When C relapses, F pulls up over the marker and connects up busy tone from 14. If digits 46-40 are dialled, C is maintained operated after the units digit over wiper 4c and the marker to prevent the switch through, but no busy signal is sent. Ringing and tone equipment. When FH in the allotter operates consequent on the finding of the calling line, ground on wire 11 operates MS which makes the heater circuit of a vacuum thermostat VLT1. After a time, VLT1 operates MT which holds in series with MS, disconnects the heater of VLT1 and connects up the heater of VLT2 so that after a further period MS, MT are shunted down. The ringing and tone equipment are in operative condition during the time MS is operated, the vibrator VIB and vibrating relay BR being energized by MS. The pendulum armature VIB1 of the vibrator alternately makes circuits for the two halves of a primary winding of transformer XFR, the halves being connected to a relay P and balancing retard R so that P interacts with VIB to sustain the oscillation of VIB1. The current induced in the secondary of XFR supplies ringing current to leads 15, 16 while current from one of the primaries supplies dialling tone to lead 13. The vibrating relay BR releases itself intermittently by introducing resistance YH into its energizing circuit and induced currents in a second winding supply busy tone to lead 14. The periods of the ringing current and tones are determined by a relay chain IA-ID. Ringing leads 15, 16 each supply half the connecting circuits. Calling absent parties. Access to a code calling equipment is obtained by setting the connector on its last contacts by dialling 43. The impulsing circuit is extended over wiper 4c and wire 12 to the code calling equipment and the appropriate code calling digit is dialled. The equipment causes the code to be audibly signalled and the wanted party, by dialling an answering number at the nearest substation, connects himself to the equipment over which a conversational circuit is completed.