Patent GB-435313-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1934-03-15
Abstract: 435,313. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool, and BAKER, G. T., Blackbrook, Caerphilly, Glamorgan. March 15, 1934, No. 8219. [Class 40 (iv)] A bi-directional selector which is moved in the primary direction by impulses, in the secondary direction partially or wholly by a selfinterrupting magnet, and is released by continuing the secondary movement has the following features : (1) the release movement is also by a self-interrupting magnet; (2) the operation of the switching relay follows that of the quick-acting test relay either by being operated in response thereto (Figs. 1 and 2) or in series therewith (Figs. 5 and 6); and (3) the changeover relay is operated to connect up a busy signal (Figs. 1 and 2). The Specification describes numerical selectors for use at a satellite exchange in conjunction with the non-numerical and discriminating arrangements described in Specifications 429,767 and 432,281, the selectors being of the type described in Specification 391,123 preferably provided with interrupter springs as described in Specification 433,877. The selectors described comprise a battery-feed first selector, Figs. 1 and 2, for local calls ; a first selector, Figs. 3 and 4 (not shown), of the Provisional Specification, for incoming automatic calls ; a first selector, Fig. 3 and 4, for incoming calls from toll and manual; and a P.B.X. final selector, Figs. 5 and 6. Group selector, Figs. 1 and 2. This switch is intended to function with the discriminator described in Specification 432,281 and is connected over the bracketted leads T ... P to the hunting switch JB thereof. Relay A is operated over the calling loop through the discriminator, B and C follow, and ground from the discriminator over DM operates magnet GFM in a self-interrupting circuit until the group finder GF finds the line-finder (not shown) which is marked in GF1 by the discriminator. When this occurs, the discriminator removes ground from DM and operates SK which locks up, switches back to the call finder, and grounds T to release the discriminator. The next digit, which may come in to A over the discriminator before SK has switched through, is repeated to VM and C in series and the original circuit for C is opened. At the end of the train, C relapses to make a self-interrupting circuit for RM which rotates the switch until idle battery operates LK, over both windings in series, which energizes H to switch straight through cutting out the feed bridge, releasing A, holding B and re-operating C. It will be seen that H reverses the current flow over the lefthand winding of LK so that the resultant flux is just sufficient to hold LK. If two group selectors test simultaneously, both LK relays start to release and the first to do so restores holding current to the other. When the connection has been completed and the wanted line found idle, battery is sent back from the connector over the fourth wire to operate SD so that LK falls back followed by H which re-connects the feed bridge, and relay A re-operates. The wanted party is rung and tone is reverted, F pulling up when the party replies and locking over its lower winding to complete the speaking path in which D pulls up. Relays C and B fall back, B more slowly than C and meanwhile battery over the rotary magnet RM meters the call in the case of an ordinary subscriber. On relapse of B, this battery is replaced by ground for metering in the case of coin box lines which have battery on their meters. Release. The calling party releases A which is followed by SD, SK and F, whereupon RM steps the switch forward out of the bank, ground for RM being supplied over common wire 13 leading to apparatus for giving an alarm on faulty release. The switch shaft then drops and restores to normal where the circuit of RM is opened. If the called party clears and the calling party delays, a lamp LP lights in series with common supervisory apparatus. Busy signalling. If the group selector meets an all outlets busy condision, LK pulls up on 11th contacts followed by H and C, whereupon LK and H fall back and busy tone BT is connected to the calling line. Overflow metering occurs over bank SW. Owing to the operation of 11th step springs S1, LK does not cut out is high resistance winding so that the common battery on the 11th contacts is available for other switches. The group selector is also liable to be seized by the discriminator if all its associated tone sets are engaged (see Specification 432,281), and in this event, SK prematurely operates D to a ground on SW in the discriminator. Busy tone is thus connected to the discriminator and the condition is metered over common wire 15, prolonged holding of the switch being indicated by lamp LP. If the connector finds the wanted line busy, it reverts ground over the third wire to release LK and H, whereby the busy signal is given. Group selector, Figs. 3 and 4 (not shown), of the Provisional Specification. This selector is used for ordinary incoming automatic calls from the main exchange and its circuits are substantially similar to the group selector previously described except that it is not associated with the discriminator. Minor differences are (1) relay B is not released by D when the called party replies, and is used to hold the ring tripping relay F over its lower winding, metering being effected, if required, by current reversal, and (2) an all outlets busy condition or a busy wanted line resulting in the operation and release of LK as previously described, now brings about the operation of F over its lower winding to connect up busy tone and flash to relay A, busy hold being provided for B. Group selector, Figs. 3 and 4, for incoming toll calls and calls from the manual board at the main exchange. This selector is generally similar to those previously described, but is provided with arrangements for withholding the normal automatic ringing and for breaking in on a busy line when the selector is used by a toll operator, but not when seized from the manual board. When the selector is taken for a toll call, ground connected to the negative wire operates A and OC in series, B and C pull up, and TO locks up for the remainder of the call. The speaking wires are then looped at the distant end so that A remains operated, but OC, being differentially wound, falls back. The setting and hunting operations are performed substantially as previously described and when an idle outlet is found, LK and H operate, A falls back, C re-operates and B is held. In addition to switching out the feed bridge, H operates the ring-tripping relay F. When the connector has been set on an idle line, ground sent back over the 4th wire operates SD whereupon LK and H fall back A reoperates, and CN pulls up to prepare the ringing circuit. The operator on throwing her ringing key unbalances the lines to operate differential relay OC which releases F by shortcircuiting its lower winding so that ringing is applied, and tripped when the called party replies. The short-circuit on F is maintained, after the ringing key is restored, until F reoperates over its upper winding. On incoming calls from a manual board, differential relay OC is not operated and as TO does not pull up, ringing is applied in normal manner. Release. Restoration by the called party releases D which restores normal current flow to signal the operator who, on withdrawing, releases A, B and other operated relays and the selector releases as described in a preceding paragraph. Busy signalling ; toll break-in. If all outlets of the group selector are busy, LK operates over 11th contacts and H pulls up to operate F and C and LK and H fall back in turn. Relay F connects up toneless flash from BF and C operates a meter over SW. If the wanted line is busy, the connector returns ground over the third wire to release LK and H, and as F is operated and CN not, tone and flash from BT are connected up, B being held over a second winding during the flash. In the case of a toll call (TO operated) ground is connected over bank SW to operate the switching relay at the connector. The operator again unbalances the line to operate OC whereupon CN pulls up, locks and extends the speaking circuit to the busy line. Relay D pulls up, and ground is connected over SD to the test wiper. If the call is accepted, the engaged subscribers replace their receivers, and idle battery from the wanted subscriber's cut-off relay operates SD which holds over its lower winding in series with the switching relay in the connector and releases D to signal the operator who then re-calls the subscriber by unbalancing OC to release F as previously described. P.B.X. connector, Figs. 5 and 6. On seizure, A. B and C pull up and the tens digit is repeated to magnet VM and C in series. When C falls back, change-over relay E pulls up, re-operates C and operates LK, the units digit being repeated to RM and C, E holding dependent on C and LK (left-hand) holding itself dependent on E. At the end of the digit, C and E fall back in turn and in the meantime H (upper) tests the wanted line and if idle operates, locks over its lower winding in series with SD in the group selector and holds the cut-off relay over the third wire from the group selector. Relays A and B fall back and the line is rung from the group selector as previoully described. If the wanted line is an individual one and is busy, E on its relapse grounds the third wire to release LK in the group selector to give the busy signal. C (upper) is re-operated and in the case of a toll call, the previously described ground on SW at the group selector operates H, relays A, Band C then falling back and the call being offered as described before. P.B.X. markings are made in an additional bank P1, first lines being grounded, intermediate lines unmarked and last lines connected to battery. If the first line