Patent GB-1355816-A (GB)
Title: Apparatus for the location and selection of an available elec trical or electromechanical unit within a set of such units
Inventor: PEYROT A
IPC: H04Q3/00
Filed: 1971-04-19
Abstract: 1355816 Automatic exchange systems COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 19 April 1971 [16 April 1970] 27195/71 Heading H4K An arrangement for selecting an available unit from a set of units comprises a plurality of subassemblies each arranged to preselect one of the units and which can be individually taken into use when a selection is required and a control circuit which sequentially tests the sub-assemblies and supplies enabling potentials to those sub-assemblies which on testing have been taken into use and have preselected an idle unit, the enabling potentials being each maintained by a thyristor amplifier, individual to each subassembly, until the selected unit is taken into use. The purpose of the control circuit is to remove the risk of two sub-assemblies selecting the same unit. As described the arrangement is employed for selecting a free one of a junctor circuits each of which supply a negative potential on a control wire when idle and remove that potential when taken into use. A demanding equipment such as a register of a cross-bar exchange selects a sub-assembly by enabling a relay which connects the control wires from each junctor to first windings of corresponding relays of the sub-assembly. These relays have second windings connect in series with an own relay contact between a power supply terminal and a fixed contact of a wiper switch stepped once at the end of each selection cycle and having its wiper connected to the other terminal of the supply. If this wiper is set to a position corresponding to a free junctor it completes a holding path through the corresponding relay maintaining the same while all other relays are released by a slow to operate relay. The slow to operate relay and the maintained relay together extend a path through the sub-assembly between the control wire from the pre-selected junctor and a common line to the common control circuit shown. Thus one or more of the sub-assemblies each relay the negative potential from a preselected idle junctor on one or more wires fcto to fctn. The common control circuit tests each wire in turn and on detection of a negative potential connects that wire to a positive supply. This potential marks the control wire of the junctor to be selected with positive potential, energizes a relay in the subassemble to initiate selection of a crosspoint of a cross-bar switch connected to the junctor to which the potential is applied and by virtue of the masking effect of the positive potential on the junctor control wire releases the preselected relay of any other sub-assembly that has preselected that junctor. The control circuit includes a clock driven square wave generator G and a counter comprising cascaded bi-stable BO to Bx which enable AND gates PO to PN in succession, each removing a corresponding inhibit input 2E 0 to 2 En from one amplifier AITro to AITrn at a time in succession. Each amplifier comprises a transistor such as Tro which is supplied with power from a potential divider comprising a resistor R and a Zener diode Z and which when the positive inhibit input at X is removed switches to conduction if the input 3EO from the wire fcto is negative, switching on a corresponding thyristor amplifier Tho which applies the positive potential to wire fcto. Although the transistor amplifier AITro turns off as the counter moves to its next count the thyristor amplifier remains conductive supplying positive potential to the control wire fcto until a contact in the control wire at the junctor is opened as an acknowledgement that that junctor has been adopted. Fail safe arrangement.-The circuit includes an amplifier SD coupled to the control wires fcto to fctn via diodes DBO to DBn and to 'the amplifiers AITro to AITrn via diodes dbo to dbn. In normal operation some of the control wires are at negative potential and at frequent intervals the amplifiers AITro to AITrn give positive outputs. Due to a capacitor C and resistors B8 and R10 the input bo to amplifier SD is normally maintained positive. If the counter stops the last enabled amplifier AITro to AITrn produces a positive output but when the selected junctor is adopted this output is removed and only negative potentials reach the capacitor C. The input bo of the amplifier SD thus goes negative turning that amplifier on and enabling a relay D which by closing its contacts do to dn applies enabling potentials continuously to all subassemblies. Thus selections continue to take place but there is a risk that two sub-assemblies will cause two simultaneous connections to the same junctor.