Patent GB-461082-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1935-08-09
Abstract: 461,082. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., BAKER, G. T., and McCLEW, J. W. Aug. 9, 1935, No. 22564. [Class 40 (iv)] Calling lines are connected to first selectors by an auxiliary impulsing circuit while a finder is hunting for the calling line, and to prevent incorrect connections on simultaneous calls, the marking of a finder by a calling line is characteristic of the finder employed. The invention is described with reference to a bi-directional finder having subscribers' lines in some levels and incoming junctions in others, the auxiliary impulsing circuit being used only on calling junctions since the inter-digital pause might be shorter than the hunting time of the finder. Each junction is connected to corresponcling contacts in a number of levels equal to the number of finders (two as described) which may be hunting simultaneously for different calls. Each simultaneously hunting finder is selected by a different allotter, the level marked depending on the allotter used and the auxiliary impulsing circuit passing over wipers of the allotter. Figs. 1 and 2 show a subscriber's line circuit, a finder constructed as described in Specification 391,151, and one allotter and control circuit CS in full, the second all otter and circuit being shown in outline at ICS. Incoming junction circuits, Fig. 3, appear in levels 1 and 2, and subscribers' line circuits in levels 3 to 6, levels 7 and 8 being connected in multiple to line circuits which may be used alternatively for subscribers or call boxes according to the level in which they are marked. Both allotters serve levels 1 and 2 with preference to alternate junctions, while remaining levels are divided between the allotters, rectifiers being used in the marking and starting circuits to prevent undesired markings. Connection to subscribers' lines. On initiation of a call, L connects marking battery over resistance YA to the vertical bank VB, this battery also operating ST over the upper half of rectifier MRA. Relay LK in the control circuit pulls up over its right-hand winding to idle battery in the selector associated with the preselected finder, and locks up over its lefthand winding in series with VR which temporarily operates switching relay H over its lower winding. VM thereupon operates in a self-interrupting circuit until marking battery over VB operates fast relay VT which opens the circuit of VM, operates RS and releases H which makes a self-interrupting circuit for RM over lead 10 to common alarm apparatus. When the calling line is reached, RM is held over a circuit VB, wiper P, H (upper) and allotter wiper AS6 in which H pulls up, switches through, opens the magnet circuit and holds over its lower winding. Relay H also operates the allotter magnet AM and shunts down LK and VR to release the control circuit. Ground returned over the metering wire M operates cut-off relay K and P pulls up to connect the meter. L and ST fall back. Operation of allotter. Magnet AM operates as described in the preceding paragraph and if there is no other call, interacts with G until this relay ceases to be operated by busy ground on AS 3. If another call originates before a finder is preselected, ST makes a self-interrupting circuit for AM to save time, this circuit being opened by LK when an idle finder is reached. Connection to junctions over levels 1 and 2. Incoming junctions terminate in relay sets, Fig. 3, and have access to both control circuits, the odd and even numbered junctions having preference for the first and second control circuits respectively. When a call comes in, 1L prepares circuits for both HA, HB, and assuming an odd junction, HA operates over leads T, TA and both windings in series if control circuit CS is idle, short circuits its upper winding to guard against operation of another HA relay, disconnects HB, operates start relay ST, and marks the finder bank over RM1. Relay HA also connects the junction to the outgoing side of the finder over wipers AS1, 2 of the allotter, VR having meanwhile been operated by ST. The finder operates as described for a subscriber's line but the vertical bank is marked over wiper AS7 and the rotary movement is stopped by holding the magnet over VB, leads RM1 and P. If the first control circuit is busy, there is no circuit over T for HA but VR in the first circuit completes a circuit over vr1 for HB in the second circuit which marks the second level and stops the rotary movement over lead RM2. The marking arrangements ensure that in the case of simultaneous calls, a finder connected over a bye-path to one junction cannot be set on another junction. When the junction has been found, the release of the control circuit opens the bye-path and when cut off relay 1K operates, relay HA (or HB) is released. The junction set, Fig. 3, may be arranged to return busy tone if both control circuits are busy . Coin-box lines. It is arranged that 10 line circuits may be used alternatively for coin boxes or ordinary subscribers, and these appear in levels 7 and 8 corresponding contacts of which are multipled together. If the circuit is used for an ordinary line, the line relay contacts 211, 2l2 are connected by straps REG to mark the 7th level and a contact therein but if it is used for a coin box line, straps CB are used to mark the 8th level and a contact therein, so that the finders hunt over different levels according to the class of calling line. Post springs NP1 operate on the 8th level to send a battery signal from YF to the operator. Release of finder, normal and premature. When the calling party replaces his receiver after conversation, the consequent relapse of H makes a self interrupting circuit for RM and the finder steps to the 12th position from which it restores to normal. If the calling party restores before vertical hunting is completed, ST, LK and VR fall back, the circuit of VM is opened and H is released so that the finder cuts in on the level at which it happens to be stopped and rotates to the 12th position and releases. If the rotary movement has commenced, LK, VR, RS remain operated and the switch proceeds to the 11th position where the switch is stopped and H (upper) operated in a manner not shown. LK and VR are shunted down as in an ordinary call and release RS followed by H so that RM steps the switch to the 12th position for release. All finders busy. Absence of idle battery on common relay OFB releases this relay which operates OFR to open the driving circuits of both alloters to prevent useless hunting and to prepare overflow metering circuits OFM. Faulty working. In the case of permanent loop conditions, the selector is forcibly released after a delay and H, K relapse but P being sluggish remains held by the loop, guards the line and may operate an alarm. If a finder fails to find a vertical marking, VT is operated at the 9th level which is not used for line circuits, the finder cuts in on this level, rotates to 12th contacts and releases. If a control circuit is removed during maintenance, it is arranged that the start relay of the other circuit is made effective over jack points u11, u12 for all calls.