Patent GB-592989-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/42
Filed: 1945-05-04
Abstract: 592,989. Automatic exchange systems. SIEMENS BROS & CO., Ltd., and LONG, D. P. May 4,1945, No. 11442. [Class 40 (iv)] In a final selector, each marking wire between the marking switch and the marking arc of the selector is common to four outgoing lines, the lines appropriate to any particular marking being differentiated by wiper switching and by division of the contact bank into two parts. In the case of a final selector having access to two hundred lines, the marking arc is common to two lines in each hundreds group, differentiation between lines in different hundreds groups being by receipt or non-receipt of a signal at the time the selector is seized and differentiation between the two lines in the same hundreds group being determined by the value of the tens digit received. The differentiating signal used in the embodiment described is an earth potential connected to the positive speaking wire at the preceding selector. On seizure of the selector, low impedance relay A operates over the preceding loop, followed by release relay B and dialling relay C. Auxiliary relays BA, BB and coupling relay K are operated by B to connect the common control circuit to the seized selector while disconnecting it from other associated selectors. Discriminating relay P operates in series with A and locks, unless it is short circuited by an earth on the positive wire at the preceding selector. The tens digit is now registered on switch MA over the righthand winding of C. On the release of C at the end of this digit a circuit is completed for drive magnet MU and if P is energized the switch drives to the preliminary contact at the cornmencement of the dotted arcs where test relay T operates over arcs M and P in series with PA and TA (II), and connects TA (I) in series with the magnet, TA being inoperative as its windings are opposed. If P is not energized, however, T and PA operate immediately C falls back in a circuit over the marking switch banks and p2, and the selector does not move. Under either condition PA connects the impulsing circuit to MB for receipt of the units digit and arcs MB3 to MB7 then mark the appropriate contact in arc M. Differentiation between the two sets of fifty contacts is done by MA4, which operates wiper switching relay WS for tens digits 5 to 9. At the end of the units digit the drive circuit is again completed until T operates over arcs M and P and the outgoing test wire. In this case only winding (I) of TA is energized ; the relay consequently operates and operates switching relay H which locks on to the incoming P wire. H switches the speaking wires through and releases the common control circuit by releasing A followed by 13, BA, B13 and K, whereupon the digit switches self-drive to normal. On the termination of the call H is released by removal of the earth from wire P, WS is released by H and the selector homes. The contacts in arcs X1, X2 corresponding to all lines of a PBX group are commoned and connected to the contact in arc M corresponding to the first line of the group. In this way, if the first line is marked by the incoming digits all the lines of the group will be tested over X1 or X2. If the outlet tested is busy the selector is stopped, on the last contact of the arc in which search has been made, the test circuit including relay LC, which connects high impedance relay AA to the loop in place of A and induces busy tone in it over its right-hand winding. Contact lc4 connects the +wire to a busy call meter and ineffective calls to a particular line or group are recorded by connecting the appropriate contact in are M to the last contact in the corresponding + wire arc. When a busy condition is encountered earth over relay T is connected over these arcs to the meter. If it is further desired to meter ineffective calls to particular lines or groups when they lie in different arcs of the selector or when up to four different lines or groups are to be dealt with, additional arcs MA5, MA6, Fig. 3, are connected through changeover contact p 3 below contact lc4 and a separate meter is connected to each group of five contacts corresponding tu each of the four arcs of the selector. Specification 378,585 is referred to.