GB1504701A - Preselector circuit arrangement - Google Patents

Abstract

1504701 Automatic exchange systems POST OFFICE 23 May 1975 [31 May 1974] 24258/74 Heading H4K In an arrangement for preselecting for use one from a number of free items, the preselection is effected by enabling a thyristor associated with the item. In specific embodiments the items are the bridge magnets of a cross-bar switch used as a non numerical switching arrangement for use in either a concentrator or a register connector. General arrangement (Fig. 1).-When the battery B of the circuit is connected up relay GB operates over its left hand coil GB/1 to close contact GB I and to supply a pulse generated in the right hand winding of relay GB to the gate of thyristor TH1 via diode Dl and contact GB1. Thyristor TH1 then conducts as a current path to earth exists via contact X 1 I and resistor Rl, thereby preselecting item X,. To seize the preselected item contact L is closed to operate relay S and thereby close contacts S1 and S2. A current path then exists from battery B via thyristor TH 1 to the item X1 and thence via diode Dl and contact S1 to earth. Item X1 is therefore operated and by means not shown causes the closure of contact H1 and the release of contact L, the contacts X 1 1 and X 1 2 also being opened and closed respectively. Item X 1 is therefore provided with a holding path via contact H1 and the next free item X2 is preselected by a pulse produced in the right hand winding of relay S when this relay starts to release due to the opening of contact L, the pulse being supplied via contact S2 (not yet open) and contact X 1 2 (now closed), to turn on thyristor TH 2 . If all the items have been seized contacts X 1 3-X n 3 are open and relay GB is released thereby giving an all items busy indication. Subsequently, when any of the items X n is released due to the opening of its contact H n , the corresponding contact X n 3 closes to operate relay GB, thereby causing the preselection of the item X n in an analogous manner to the preselection of item X, when the battery B was first connected. Fig. 2 shows a modification wherein the current though the thyristor TH in the preselection state also flows though the item X, the current being limited to below the operating current of the item by the resistor R. Figs. 7-12 (not shown) illustrate how the above arrangement can be applied to a 26Î10 non numerical cross-bar switch wherein the 10 bridge magnets correspond to the items X1-Xn. Details of cross-bar switches are given with respect to Figs. 3-6 (not shown).