Patent GB-261817-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1925-07-27
Abstract: 261,817. Automatic Telephone Manufacturing Co., Ltd., (Automatic Electric Co.). July 27, 1925. Automatic exchange systems.-In an impulse sender, particularly useful in systems employing two-motion callfinders, the first motion of which is controlled numerically, a rotary control switch for determining the number of impulses sent is adapted to occupy any position when not in use, the impulses being sent when the switch is moving from a marked position to a, definite position. Means are also provided for keeping the callfinder in step with the rotary control switch during the sending of the controlling impulses, Common stepping relays, which interact with the stepping magnets of the finder, are located in common apparatus comprising an allotting switch and the impulse sender. In the system described, each group of 100 subscribers' lines is served by a number of two-coordinate line-finders F associated with which are a common impulse sending switch 110, 111 and a finder allotting switch 151 - - 156. In moving to a predetermined position after having engaged a pick-up contact marked by a calling line, the switch 110, 111 sends the necessary number of impulses to a finder F preselected by the allotting switch, to raise it to the level containing the calling line, after which it hunts in this level under the control of its test wiper 22. If all the finders of a group are busy, the allotting switch does not continue hunting but comes to rest in a final position until one falls idle. The impulse sending switch 110, 111 is of the no-normal backstroke type. the two halves of its bank being multipled together to provide four cycles of operation per complete revolution. Assuming that the subscriber's line 2. 3 terminates in the fourth level of the finders, when the line relay 5 energizes, a stop conductor 102 extending to the eighth and twentieth contacts 103, 103<1>. in the lower bank of the impulse sending switch is earthed : the twelfth and twenty-fourth contacts 104, 104<1> are permanently connected to battery. The start conductor 101 is earthed also, energizing the stepping relay 120, and a slow-release relay 26 of the preselected finder F. The stepping relay 120 closes a circuit over earthed common conductor 150 for stepping magnet 127 which advances the switch a step and de-energizes the relay 120 ; if all the finders are busy, the conductor 150 is not earthed and the impulse sending switch is not advanced. The relay 120 and magnet 127 interact in the usual manner until one of the earthed pick-up contacts 103, 103<1> is engaged, when a pick-up relay 121 energizes, locks to the starting wire 101. energizes slow relay 122. and prepares the impulsing circuit to the vertical magnet 28 of the finder F. The next time. the stepping relay 120 energizes, it closes the circuit of the vertical magnet 28 and locks over the interrupter contacts 42 of this magnet and conductors 173, 171. As the interrupter contacts 42 do not open until the magnet 28 has almost completed its stroke, the de-energization of the stepping magnet 127 is correspondingly delayed so that the stepping speed of the impulse switch is governed by the speed of operation of the vertical magnet 28. When a contact 104, 104' is engaged by the impulse switch and four impulses have been sent, the pick-up relay 121 is short-circuited, and circuits are completed for relays 124. 123. Relay 123 locks over its lower winding, opens the circuit of the stepping magnet 127, and closes a rocking circuit for the common rotary stepping relay 124 over conductors 171, 173 and the interrupter contacts 41 of the finder rotary magnet 27. The stepping relay 124 energizes the rotary magnet 27 over wire 174, and thereafter the usual interaction occurs until the unearthed test contact of the calling line is engaged, when a short-circuit is removed from switching relay 25 which energizes in series with stepping relay 124. Relay 124 does not respond, but relay 25 locks up and grounds the test wiper 22, causing the response of cut-off relay 4 and holding the line relay 5 over its lower winding. Earth is now removed from the start and stop wires 101, 102, but before relay 26 falls away, earth is applied to the holding wire from the associated group selector S. Relay 25 earths wire 172, thereby energizing a guard relay 125 and the stepping magnet 126 of the allotting switch, which is stepped round until an idle finder is engaged. The wiper 152 touches the next contact before leaving a preceding one to hold up the guard relay 125 during hunting. This relay holds open the starting circuit to prevent the impulse sending switch from being started by another line calling at this time. If all the finders are busy, when the wiper 152 arrives on an extra last contact 167, no earth is found thereon fed over common wire 150, and the stepping magnet 126 is not energized. As soon as a finder falls idle, its switching relay 25 relapses, the wire 150 is earthed and the allotting switch again hunts. No restoring means are necessary for the control switch 110, 111, since irrespective of its resting position, its stepping magnet 127 is energized immediately the start conductor 101 is earthed, but no impulses are sent until a marked position is reached and the pick-up relay 121 is energized.