Patent GB-321216-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-08-02
Abstract: 321,216. Automatic Telephone Manufacturing Co., Ltd., Burns, G. A., and Deyes, H. S. Aug. 2, 1928. Automatic exchange systems. - A two-digit connector, having rotary movement only, hunts in response to the first digit to the last line of the group preceding the wanted group, and is directly stepped by the second digit to the wanted line. The first digit is stored by a group of relays which operate in turn and re-operate in turn if the digit dialled is greater than the number of relays in the group. Hunt. ing commences immediately the second pulse is received. In the 50-line system illustrated, calls are made over a pre-selected finder-connector link, the finders and connectors being 8-bank 25- point switches acting as 4-bank 50-point switches. Speaking current is fed to both subscribers in parallel from the same relay. Call finder.-The two-step line relay LK and common start relay ST operate in series, LK operating only its light armature 14. The distributor switch DS has pre-selected the link to be used and earth at 17 operates G which connects earth to DM2. Relay G and magnet DM2 interact to step FS until wiper 24 encounters the line marked by earth at 15, when G is shortcircuited and A operates (15, 24, 25. 26, 27, 29, 21). Relays A and B pull up and LK operates fully, disconnecting ST and itself from the calling loop. In addition to connecting relay to the loop, relay B disconnects the finder drive magnet at 20, returns dial tone to the subscriber from 45 and extends earth at 23 to step the distributor switch DS which preselects another free link, the switch being stopped on the last contact if all the links are engaged by the multipling to contacts 31 of relay B. Connector. The subscriber dials the two-digit number required. The first pulse is repeated by A to pull up C and DA in parallel (50, 49, 48, 31) and C allows RZ to operate its light armature 58. Relay DA throws the circuit for the next pulse to DB which in turn connects the next pulse to DC. If digit 1 is dialled DA pulls up and locks up (54, 55, 56) to 23 and no hunting takes place. If two pulses are sent, DB operates breaking the .circuit of DA and locking itself up (59, 56) to 23. At 61 earth is placed on the last contact of the ,connector switch and removed from the 10th contact and the switch steps by self interruption to the 10th contact (63, 64, 65), If three pulses are received DC operates releasing DB and stepping the switch to the 20th contact. The fourth and fifth impulses re-operate respectively DA and DB and earth at 85 and 86 respectively control the switch setting. At the end of the train the switch is resting on the last contact of the preceding tens group (e.g. if digit 3 is dialled the switch stands on the contact of line 20) but relays DB, DC control contacts' such as 87, 88 in the private bank of these circuits to prevent the call being switched through when RZ operates. At the end of the train C falls back and RZ operates fully (58, 23) disconnecting dial tone at 45, connecting the test circuit at 68, breaking the self drive circuit of DM1 at 64 and connecting the repeated impulse circuit to DM1 at 51. The next series of impulses are repeated to DM1 and the switch is stepped directly to the terminals of the required line. Testing and ringing. Relay C operates with the first pulse and, before it releases, earth on a busy circuit will operate G (71, 68, 70) disconnecting the impulsing circuit from DM1 at 49, locking itself up to 23 at 72 and connecting busy tone from 73 to the calling subscriber. If the circuit is free when C releases H pulls up from battery via the called subscriber's line relay (70, 68, 71, H, 72, 73) locking up at 75. Relay H connects ringing from 78 to the called line (ringing tone leaking back via 47), opens the holding circuit of the counting relay chain, and disconnects the impulsing circuit from DM1. Relay F operates when the called subscriber replies' and locks up to 23 switching the circuit through, speaking current being fed from relay A. Release. When both subscribers have hung up, relay A falls back followed by B, releasing H, F, LK and RZ and DM1 drives the connector switch to its home position. Relay C operates in parallel to DM1 guarding the switch at 84 from seizure before the home position is reached.