Patent GB-381995-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1931-08-07
Abstract: 381,995. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, GRINSTED, W. H., Under the Plane, London Lane, Bromley, Kent, and PATTERSON, W. G., 68, Eltham Road, Lee, London. Aug. 7, 1931, No. 22403. [Class 40 (iv).] In systems using booster battery metering, the subscriber's meter and cut-off relay are controlled over different wires from a circuit available in common to a number of subscribers (e.g. a call finder) and a rectifier is inserted in the metering wire of the commonly available circuit to prevent the holding relays locking up over the meter. The meter is normally short-circuited by ground on the holding wire thereby ensuring correct operation on repeated metering. The two wires may branch from the holding wire in the call finder, or, as described below, an entirely separate wire for the cut-off relay is grounded by the switching relay of the call finder, this arrangement preventing false operation of a final selector testing the line at the moment of metering. In the call-finder system described, the switches are similar constructionally to the selectors described in Specification 378,585. The switches have two wiper-sets each accessible to two groups W, Y and X, Z respectively of calling lines, calls in groups W, X being normally dealt with by one allotter and in groups Y, Z by another allotter. If an allotter is busy, a call which it would normally deal with may be switched over to the other allotter or to an auxiliary allotter. Operation of call finder ; metering. It is assumed that the allotter shown in Fig. 3 normally deals with calls in groups W and X, its circuit being provided with two corresponding start relays P, Q. The calling line relay L makes marking and starting circuits and a start relay, say P, group W, pulls up followed by PA and R (i) which holds over R (ii). If the allotter is standing on an engaged finder, its test relay G fails to operate and DM steps the allotter until G pulls up to battery over the holding conductor of the associated group selector, whereupon the magnet is held and GG pulls up, locks and replaces G by direct ground over test key TK. Relay GG also holds PA over winding (ii), connects up the common test relay T of the finder and also its spray magnet SM. The finder is stepped by magnets DM1, DM2 until T operates to battery over the cut-off relay CO whereupon the spray magnet is disconnected, TT pulls up and operates switching relay HA, relays R, GG, TT fall back in turn and HA holds to ground which has, by this time, been returned from the associated group selector. Relay PA also falls back to release the allotter magnet DM which thereupon steps the allotter on to the next idle finder. The cut-off relay CO, on operation, is held by the switching relay in a circuit local to the finder, and the meter M is connected over a rectifier RF to the holding conductor of the switch train. Metering occurs when one or more booster battery impulses are connected to the holding conductor in known manner. All finders busy ; statistical metering. Relay U pulls up over last (25th) contacts of the allotter, and temporarily stops the allotter until it locks over winding (ii) and short-circuits its high resistance winding (i). Relay U grounds a starting wire SP for timed pulses over EP. The allotter makes another hunt and stops on reaching 24th contacts to operate meter CM. If V is operated by a ground pulse at this time, it maintains the pulse start circuit and, at the end of the pulse, relapses to connect up the magnet which steps the allotter to contacts 25 where U (released by V) pulls up again and short-circuits winding (i) to allow the allotter to start again. If V is not operated the switch remains on contacts 24 until it is. Control by Y, Z allotter of a call in groups W, X. The starting arrangements are shown in Fig. 4 which connects up to corresponding leads at the left of Fig. 3. If the W, X allotter. Fig. 3, is engaged in a call from W (P, PA operated) and a call comes in from X to operate start relay Q, QQA in the other allotter pulls up, starts the allotter and holds over ppa1, qqal, ggg<5> to q<2> in the W, X all otter. Similarly, PPA is operated by a call from W when the normal allotter is engaged in a, call from X. Modified arrangements using an auxiliary allotter. The two normal allotters are crossconnected as shown in dotted lines in Fig. 4, the start relays of the auxiliary allotter being connected to the points of intersection of these lines. Testing ; dealing with faults. Contact hb6 of one of the switching relays connects a buzzer to the test-jack to indicate the wiperset in use. If an allotter fails to step, or a finder does not seize the calling line, thermal relay TH operates W which switches over the start wires to the other (or auxiliary) allotter, busies the finder over key TK, and operates an alarm when TH has restored. The allotter is restored to service by operating key RK to release W.