Patent GB-413810-A (GB)
Title: Improvements relating to circuit arrangements for electric relays
IPC: H04Q3/42
Filed: 1933-03-14
Abstract: 413,810. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and HUMPHRIES, H. E., 61, Rochester Way, Blackheath, both in London. March 14, 1933, No. 7744. [Class 40 (iv).] A relay normally connected between two equipotential points and operated by creating a potential difference between these points, has a break contact which, on opening, maintains a potential difference across the relay independent of the conditions which effected its operation. Such a relay is applicable where circuit conditions necessitate a winding occupying the whole of the available space (no holding winding), the maximum load being one changeover contact, or the operating potential being so momentary that it ceases before the armature completes its stroke. The described application relates to the final selector of Specification 378,585 modified by replacing the double-arc marking bank (52 contacts in each arc) and double-ended staggered wiper by a single-arc bank 3 and ordinary double-ended wiper. Thus, if the wanted line is in the second 50- group, the test relay must be prevented from operating until the switch has rotated through 180‹. The test circuit is closed by a relay S according to the invention (1) immediately after the tens digit has been received if this indicates a line in the first 50 or (2) as the switch passes the first contact of the second arc in the double-arc test banks 1, 2. The arrangement shown in Fig. 1 comprises only the relevant portions of the final selector described in Specification 378,585 certain of the relays being represented by contacts only. The relay S is connected between normally equipotential points of a resistance bridge L-O, the dotted connections being neglected for the present. The first digit is taken by switch DS and one or more relays such as X, V are operated in accordance therewith to select a bank such as ds1 for marking the final selector. On the relapse of the dialling relay and if the digit is 1-4 or 0, ground from b1 is momentarily passed over make-before-break contacts C2, bank ds1 to the junction of resistances L, M. This unbalances the bridge and as soon as S opens its contacts S1, the bridge is broken and S holds over N, L, b1, and connects up test relay T. The relapse of the dialling relay C also causes DS to advance to a position for receiving the units digit, whereupon C pulls up again together with E. On relapse of the dialling relay at the end of the digit, magnet LM unlatches the motor DM and the final selector rotates until T operates over the marking and test circuits, followed by TA. Relay E now falls back and switching relay H operates. The rectifier R prevents TA and T operating in series when S pulls up and also, when these relays are operated, prevents T being short circuited by ground over ta1. If the tens digit is 5-9, there is no circuit over ds1 for S when C relapses at the end of the tens digit, but the final selector when rotated at the end of the units digit, connects up a momentary ground from the first contact of the marking bank 3 over test bank 1 or 2, after the switch has rotated 180‹, to operate S so that the final selector tests the dotted arcs. Wanted line busy. The final selector rotates to last contacts where T is operated over wipers 1 or 2, and 3. TA pulls up and E falls back as before ; but H does not now energize since it is shunted by T. Under these circumstances, busy tone is given to the calling party in a manner not shown. Modifications. Resistance L may be directly grounded, the connection indicated by a cross removed, and a contact of a relay such as B, which is operated during use of the common control circuit, applies ground to the junction of N, 0 over a back contact, a rectifier R1 being included in the circuit of S to prevent its operation under normal conditions of the circuit. When the circuit is taken into use, the ground connection between N, 0 is removed so that when ground is connected to the junction of L, M as previously described, relay S pulls up. When the circuit is released, the grounding of the junction of N, 0 releases S. Instead of grounding this junction by a contact of B, a fleeting ground signal could be applied for example by a wiper of DS during homing or by an arrangement of relay contacts. Further modifications are shown in Fig. 2. In the full line circuits, there is a circuit for S over R1, R2 but S is shunted by its own contact. When, however, the switch 1, 2 moves off normal and encounters a battery connected contact C3, S pulls up and remains operated over R1, R2 after the switch has left the contact. Release of S occurs when the switch passes a grounded contact C2. Resistance R2 may be replaced by a rectifier R offering a high resistance in circuit C3, S1 but a low resistance in the holding circuit R1, S. The dotted connection C1 over wiper 1 and the inclusion of resistance R3 constitute an alternative circuit for releasing S.