Patent GB-917017-A (GB)
Title: Improvements relating to automatic telecommunication switching systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1960-09-01
Abstract: 917,017. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Aug. 24, 1961 [Sept. 1, 1960], No. 30167/60. Class 40 (4). In a multi-stage relay cross-point system wherein a relay for each cross-point has an operating winding and a make-contact connected in series with each other between control conductors included in the multiples defining the cross-point, e.g. +, -, P, and control wires, a marking connection including a rectifier extends from the junction of the winding and contact of each cross-point relay to a control circuit, the arrangement being such that the control circuit applies an operating potential to one end of a control connection (which includes the control conductors in each switching stage and control conductors in the links between stages) and applies to the marking connections, sequentially from said end, a marking potential of such polarity with respect to the operating potential that operating current for the relays will flow. A trunking arrangement for two switching stages each comprising n 10 x 10 matrices is depicted in Fig. 1 (not shown) and one communication path between a line circuit LC and a supervisory circuit XBP using two such stages is shown in Fig. 2. Each vertical multiple in an array in stage 1, e.g. array 1Sn and multiple tsn0, is connected to a subscriber's line circuit LC, the vertical multiples in stage 2 going to registers REG or supervisory and transmission bridge circuits XBP, e.g. in array 2S1, multiples tr and tt respectively. Each array in the first stage has access to all arrays in the second stage, in the usual manner, by way of links such as ll. Operation.-It is assumed that a particular supervisory circuit XBP has been allocated (by means not shown) for connection to subscriber circuit LC and that a register is not needed (the use of a register in a call will be clear from the following description). In the control circuit the contact OM (encircled) will make, thus applying positive potential to the marking lead om which extends to the H (holding or control) conductor of the allotted trunk, i.e. tt. Then the contact M<SP>1</SP> (encircled) will make, which thus applies a marking (earth) to the junction of the coil and contact of the relays R<SP>1</SP> associated with the horizontal multiple H10 in all the arrays of stage 2 since the multiple H10 in array 2S1 is connected over a free link to array 1Sn. The relay R1 which receives both markings will operate thus completing a communication path between the particular line circuit and the, particular supervisory circuit. The application of this earth causes R<SP>1</SP> to energize and hence to mark the chosen link. Now the contact M (encircled) makes (M<SP>1</SP> opening very shortly afterwards) and so extends a marking condition to the relays R associated with the vertical multiple V1 in each of the arrays of stage 1. Hence R associated with the H1 multiple in array 1Sn comes up and completes the control connection (and also the communication path) between LC and XBP. The supervisory circuit now applies a holding earth via contact h to the control conductor and releases the control circuit, the relays R, R<SP>1</SP> holding in series to this earth and negative battery in the line circuit. If a register is required, as on an originating call, a path to it is set up in a similar manner using, for example, relay R<SP>11</SP>, a supervisory circuit then being connected to the already set-up path or a new one being selected depending upon the circumstances. The availability of a link can be signalled to the control circuit over a wire b, the presence of negative potential (in the above-described example) showing that the link is busy. In place of relay contacts for M, M<SP>1</SP> and OM, switching transistors (Fig. 3, not shown) may be used. It is possible that relay R<SP>1</SP> (Fig. 2), say, will release when relay R starts to operate since R will offer a very high impedance to the holding circuit when contact M<SP>1</SP> releases. This is prevented by placing a resistor Rx<SP>1</SP> or inductor Lx in the control circuit where shown. Thus for Rx<SP>1</SP> there will be a small current flow in R as soon as M makes and for Lx a higher operating potential for the holding circuit will tend to be maintained when M<SP>1</SP> opens. A three-stage network having out-going junctions connected to certain second-stage switches to which access is had via cross-links between third-stage switches is described with reference to Fig. 4 (not shown), in which negative battery is applied from the junction circuit via the second- and third-stage switches' cross-link, which relay applies a holding ground via the third-, second- and first-stage switches to negative battery in the calling line circuit. Release of the connection is thus under control of the junction circuit.