Patent GB-459803-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/60
Filed: 1935-07-24
Abstract: 459,803. Semi-automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, BEALE, C. E., 59, Towers Road, Wavertree, and RICHARDS, I. T., 50, Meadway, Wavertree, both in Liverpool. July 24, 1935, No. 21084. [Class 40 (iv)] In a " demand trunking system long-distance calls are extended over link circuits reached over two co-ordinate hunting switches and terminating in trunk selectors, a link circuit being associable with the operator's key set and with a register-sender for the purpose of setting the trunk selectors. A calling subscriber may be recalled by the operator over a first code selector accessible from the incoming end of the link circuit with the assistance of a register-sender and a translator, the arrangement being such that a translator is connected up or not according as the sender is seized by a first code selector or by a first trunk selector. The incoming operators are equipped for assisting the demand operators when necessary, and means are provided for extending waiting calls to an operator's position in the order of their arrival. Extension of call to demand position. A demand operator prepares to receive calls by actuating position key KCA, Fig. 12, and speaking relay KS, Fig. 5, of a connecting circuit. Relay SK energizes, connecting up SL and shunting the common resistance YI to prevent operation of the SK relays of other connecting circuits. The connecting circuit is now marked in the banks of the demand selectors. A subscriber obtains access to a demand selector, Figs. 2, 3, at the trunk exchange, by dialling a particular digit. The selector hunts vertically until wiper AW encounters battery, whereupon PA energizes and connects up change-over relay C, and then hunts over the marked level until one or other of wipers P1, P2 encounters battery, whereupon PA or PB energizes and connects up the corresponding switching relay HA or HB. Relays 1B, Fig. 4, and CG, Fig. 12 energize in the test circuit, lighting the engaged lamp, Fig. 6, and extending the operator's set, Fig. 14, to the demand selector. If the call is from a regular subscriber, CO, Fig. 2, immediately operates over the negative wire, completing the talking circuit, cutting off ringing tone (applied when the selector is seized) and connecting up reversing relay RB. If the call is from a call office, CB is operated over the incoming test wire, CO is disconnected and the operator receives NU tone. The operator therefore throws key KRA to operate CO over the positive wire. Waiting calls. If no demand operator is free, the demand selector cuts in on the 10th level, of which the P1 terminals are connected as shown in Figs. 10, 11 to relays 3A-3J, the circuit of each being prepared by the next preceding. Thus the first selector to move to this level stops in position 11, the second in position 10, and so on. When 10 calls have accumulated, further selectors remain in position 1. Each relay lights a corresponding lamp on all the demand positions, and when there are 10 waiting calls, 3RP lights a similar set of lamps on the incoming positions. 3RP remains locked until the number of waiting calls has been reduced to any suitable number, e.g. 4 as shown. An ammeter may be arranged to indicate the number of waiting calls in excess of 10. When an operator prepares to receive calls by throwing keys KCA, KS, relay MN energizes and connects up 3ST over wire X, whereupon CN, Fig. 12, operates over wire Y. These relays lock locally. The holding circuit of the first waiting selector is opened, so that it restores and hunts for the marked connecting circuit. Relay 3A on falling back disconnects 3ST so that the remaining waiting selectors are released in turn and form a fresh queue. A routining relay 3RT when operated over jack springs T connects up 3RR to simulate 10 waiting calls. Establishment of wanted call. The operator records the particulars on a docket, and if the call can be completed on demand throws call key KKC, Fig. 12, whereupon DC connects the keyset, Fig. 15, to the calling side of the connecting circuit which is extended by HC to the first trunk selector, Figs. 7-9, which is also accessible from jacks at the incoming positions. Relay ICS energizes over wire S in series with CS (inoperative), connecting up SS, which holds HC over wire P. ST and GR. The switch SH hunts for and seizes an idle register-sender, Figs. 16-23 (not shown), whereupon TR pulls up. Relays K, KA energize, feeding earth over wires FR, D to operate a guard relay, and a relay which prevents seizure of a translator. Relay LF energizes in place of ST, K, KA remaining held from the sender, and shunts the high resistance winding of ICS, so that CS energizes and lights the calling lamp, Fig. 6. The operator keys the number of the trunk group required and presses the start key, whereupon combinations of light and heavy negative pulses and positive pulses are directed through rectifiers to groups of storage relays in the sender, as described in Specification 398,812. The first trunk selector moves vertically in response to the first train of impulses delivered by the sender, and change-over relay IC then falls back to connect in the rotary magnet. Hunting takes place over two sets of wipers and test relay 1PA or 1PB operates and connects up switching relay 1HA or 1HB. Battery is connected over wire S, but is only effective when the selector is seized from an incoming position. In the event of a busy condition, the selector switches through to busy tone on the lower set of wipers in the eleventh position. After all the digits have been delivered by the sender, K, KA are released, and wire FR is opened to free the sender. Having obtained a trunk to the required exchange, the operator restores call key KKC and actuates ringing key KRC, Fig. 5, connecting battery to the positive wire to ring the distant operator, who sets up the desired connection. Time checking and release. The demand operator presses key TCS to start timing apparatus, Fig. 6, of the kind described in Specification 413,000 and speaking key KS which unlocks SK, SL and frees the position circuit. The timing apparatus controls lamp TCH and warns the subscriber just before the expiry of each 3 minute period. After the third period, the continuance of the call is dependent on the operator, who may reset the timing apparatus. Upon release by the calling party, L connects earth to wire S1 to operate AS, which lights the answering lamp, Fig. 6. Actuation of release key KR opens wires P1, S to release the switch trains. Recalling the calling subscriber. If he has hung up before the call is established, he may be re-rung by means of key KRA which controls ringing relay RR of the demand selector. If the operator has cleared down the switch train, she sets up a fresh connection over the local switch train, first throwing key KKA, Fig. 13 to energize DA, which connects the keyset to the answering side of the connecting circuit and causes the switch FCH to seize an idle first code selector, which takes into use a register-sender and a translator, no earth being fed over wire D in this case. The digits representing the exchange designation are delivered to the translator which retransmits them to the switches in translated form. If the subscriber is now found to be.busy, the operator sets up a fresh connection over a train of trunk-offering switches, reached over plug TOP, Fig. 15, which is connected up by keys KTO, KKT. Specification 444,256 also is referred to.