Patent GB-291045-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1928-01-09
Abstract: 291,045. Associated Telephone & Telegraph Co., (Assignees of Stehlik, R. F.). May 25, 1927, [Convention date]. Automatic exchange systems. - Two-motion call-finders are provided with an additional testbank for controlling the vertical motion, each contact being connected over an individual resistance to a common starting relay, so that marking potential connected to a contact energizes the relay. A finder is preselected by one or other of two allotters which are used alternately in the case of simultaneous calls. The allotters FA1, FA2 are 25-point switches having access to a group of 20 finders connected to the banks of the allotters in the regular and reverse order respectively, the first and last terminals of the respective banks being resting terminals and the remaining four sets of terminals being marked permanently busy. The system described is identioal with that described in Specification 299,814, which claims different features. Line relay 2 of calling subscriber A numbered 85 removes ground from private terminal 29 in the banks of the finder F and at 27 grounds the eighth terminal in the vertical test bank VB and completes a circuit for relay 101 over one of a series of resistances 82 individual to the terminals of VB. Relay 101 at 128 completes parallel circuits for relays 102 and 103 of FA1 and FA2 in series with corresponding magnets 105, 106, and whichever relay pulls up first open the circuit of the other. The magnets do not operate in these circuits. Assuming that 102 pulls up first, start relay 4 of finder F energizes, over 71, 112, 120 and at 40 completes a circuit of stepping relay 5 which at 43 completes a circuit for itself independent of 48 and at 42 energizes vertical magnet 12. Relay 5 and magnet 12 interact in the usual manner until vertical test wiper 53 reaches the marked level, when change-over relay 6 operates over its lower winding in series with 5. Relay 6 does not operate when the winding is placed in series with relay 101 on relapse magnet 12 during the hunting movement. Relay 6 locks Itself over its upper winding, temporarily holds relay 5 while changing over its circuit so that it interacts with rotary magnet 13, and grounds the release, wire 61 at 44 to prepare a circuit for switching relay 3. Rotary movement continues until the short-circuit of relay 3 by grouiacl over wiper 32 on non-calling lines is removed and relay 3 operates in a circuit in series with 5, which remains de-energized. At 37, relay 3 closes a circuit for itself independent of the contacts of other relays, at 38 grounds conductor 72 to energize magnet 105 of FA1 over 111, 138, 119, 136, 132. and at 36 feeds back ground from the release wire 61 to the relays 2 (lower) and 1 in series. Relay 1 clears the line and at 24 removes ground from the marked terminal of VB so that. if no other call is pending, 101 relapses followed by 102 which breaks the circuit of 105 to advance allotter FA1 one step and prepare a further circuit for 105 over 131, 132, 116 and wiper 110 so that FA1 steps on until wiper 110 fails to find ground over conductors such as 69 and off-normal contacts 52. If, however, another call has been initiated during the operations resulting from a call from A, relay 101 remains energized when relay 3 switches through, but relay 102 still falls back to operate allotter FA1 since it is short-circuited over 130 to 128 and over 119, 111 and 72 to 38. Relapse of 102 completes the circuit of 103 of FA2 which starts its preselected finder to hunt for the second calling line. All finders busy; statistical metering. Busy common conductor 70 loses ground at 52 and the wipers of FA1, FA2 are stepped on to their last and first terminals respectively. If a call is now attempted, relays 101, 102 energize as before but ground from 120 is extended over 137, 112 to conductor 141 to operate an overflow meter. A common relay energized in series with the release magnets may operate a meter recording the total number of calls dealt with by a group of finders.