Patent GB-249958-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1925-01-22
Abstract: 249,958. Coventry Automatic Telephones, Ltd., and Wilman, C. W. Jan. 22,1925. Automatic exchange systems; metering.- In a multi-exchange system, calls for example from an exchange A to an exchange F may be set up over alternative routes, such as AEF, ABDF, ABCF, and an unsuccessful attempt over one route is followed automatically by a fresh attempt over another. For this purpose the code-translating registercontrollers are arranged to respond to an alltrunks-busy signal to release the connection so far as it has been set up and to recommence their transmitting operations on a different code. In the system illustrated the register-controllers are of the type described in Specification 235,824. the code being determined by the setting of a hunting switch MS, the terminals of which are connected through a distributing frame to ten wires from an impulse-delivering machine. The different codes giving access to a particular exchange are allotted successive positions in the switch MS, which steps automatically from one of these positions to the next when a route is found to be unavailable. Instead of taking a step forward the switch MS may bring into play a different set of wipers. The last code of a group may be one which routes the call to an operator. The code-changing circuit is also completed if a faulty trunk or faulty battery conditions are encountered. If the subscriber delays unduly before or during dialling the switch MS is driven to the last set of terminals shown in Fig. 3, and sends a code for routing the call to an operator. Whenever connection is extended to an operator the release of the connection may be transferred to the operator. According to the Provisional Specification, different register-controllers may give different preference to the alternative routes, and only part of the connection set up may be released when a route is found to be unavailable. The operations in the normal setting-up of a. call will be described first. Seizure of register-controller. Relay 14 (energized in series with the ineffective upper winding of relay 27) energizes relay 19 which closes a circuit for driving the switch 9 - - 13, and when the wiper 10 reaches the ungrounded terminal of an idle register-controller, relay 29 and the lower winding of relay 27 are no longer short-circuited and receive current through the magnet 8. Relay 29 locks itself and disconnects relay 19. Relay 27 energizes relay 101, Fig. 3, which energizes relay 102, which grounds the wire 38 to hold relay 27, and dial tone from a coil 106 is sent to the calling line bv induction between the two windings of relay 27. Operation of register-controller. Impulses are repeated by relay 14 to relav 101 which repeats them to exchange and number registers. The exchange registers control the setting of the code switch MS. During each digit relay 108 is energized, and at its first energization energizes relay 110, which locks itself and cuts out the tone coil 106. Outgoing exchange digits are delivered by an impulse machine through the switch MS and circuit 36 to relay 40, a switch TS being advanced between each digit and the next bv an impulse in wire 144 to bring into play a different wiper of the switch MS. First selector, Fig. 2. The first digit is repeated by relay 40 to vertical magnet 1. a relay 45 also being energized. At the first step a relay 46 is energized in circuit 51, 4, 50, 49, 48, 47, and locks itself at 52 independently of contacts 50, 49. At the termination of the digit, relay 45 relapses and energizes the rotary magnet 2 in circuit 53. 50, 49. 48, 47. Magnet 2 opens the circuit of relay 46 which opens the circuit of magnet 2, and if the first trunk in the selector level is busy relay 46 is energized again in circuit 7, 55, 4, 51 and again energizes magnet 2, and in this way the rotary movement is continued until a free trunk is found, whereupon relay 56 being no longer short-circuited becomes energized and completes an outgoing loop through both windings of relay 61 and lower winding of relay 62. Relay 62 is electropolarized and does not respond. Succeeding digits are repeated by relay 40 at contact 60, relay 45 being energized during each digit to provide a clean dialling circuit. Release of register-controller. After the last numerical digit has been sent, wiper 104 of the switch TS opens the circuit of relay 102 which unlocks relay 27 to complete the talking connection and disconnect the register-controller. Metering. When the called subscriber answers, the reversal of current in the lower winding of electropolarized relay 62 energizes this relay, which closes a metering circuit 31, 42, 79, 78. If the calling subscriber is at a satellite exchange, this circuit may energize a relay to reverse the .current in the calling trunk. All trunks busy; change of route. The 11th a terminals of all rows of the selectors, for example 81, are supplied with alternate ground and battery potentials, so that when a selector fails to find an idle trunk the relay 61 is de-energized and energizes relays 67, 119 in circuit 64, 65, 66, 67, 39, 119, 115, 116. Relay 67 unlocks relay 56 and energizes the first-selector release magnet 3 in circuit 4, 68, 48, 47. Relay 56 then opens the circuit of relays 67, 119 at contact 64. Meanwhile relay 119 at contact 120 energizes magnet 121 to release the switch TS and locks up over its lower winding until switch TS regains normal. Relay 119 also at contact 123 energizes magnet 124 so as to step the code switch MS to its next position, and at the next closure of the starting- circuit 144 sending-operations appropriate to a second route commence. The last code of the group has no battery potential on its terminal in the top row of switch MS, so that, when the switch has reached that position, the relays 67, 119 cannot be energized again. The relay 61 is also de-energized, and with the same result, if a faulty trunk or faulty battery conditions are encountered. Connection to operator if calling subscriber delays before or during dialling. An interrupter 126 energizes the lower winding of a two-step relay 127 which is energized only sufficiently to attract armature 130 to connect its two windings in series. When the interrupter opens its circuit again, relay 127 becomes fully energized, its upper winding being no longer short-circuited, and unless the arrival of an impulse has meanwhile unlocked relay 127 at contact 132, the next closure of the interrupter circuit energizes relays 119, 133. Relay 119 energizes magnet 121 to release the switch TS and relay 133 grounds the wire 39 to energize relay 67 to release the connection so far as it may have been set up. Relay 133 also closes a self-interrupting circuit 141, 140, 139, 131 for magnet 124, which drives the code switch until it reaches the last set of terminals shown in Fig. 3, whereupon relay 138 is energized to open the driving circuit. In this position the code switch causes the call to be routed to an operator. Relay 133 disconnects the two parts of the bank of wiper 104 corresponding respectively to code and number digits, so that the register-controller is released as soon as the code digits have been sent. Transfer of release to operator. The manual board circuit is arranged to feed back battery on both line wires when the operator answers, thus releasing relay 61 which energizes relay 67 in circuit 64, 65, 66, 67, 33, 32. Relay 67 connects to line the two grounded windings of relay 75 (which may be of the shunt-field type to have high impedance) which holds the relay 29 independently of relay 14 in circuit 31, 42, 77, 30. If reversed battery is found on a trunk during the setting up of a connection, relay 62 closes a circuit 31, 42, 41, 37 to suspend the transmission of further digits as described in Specification 235,824. Statistical metering. The occasions when all of a group of trunks are found busy may be recorded on a meter 82 connected to an 11th test terminal and operated by a rotary 11th step contact 54.