| 摘要 |
1,264,413. Automatic exchange systems. PLESSEY CO. Ltd. 26 May, 1970 [4 June, 1969], No. 28321/69. Heading H4K. In a telecommunication exchange in which a route is established through a relay switching network by the successive energization of crosspoint relays in response to the co-operation of a switching potential applied to the first relay of the succession with a succession of sources of potential applied at successive relays of the succession, the switching potential is applied via a constant current device and a voltage detector responds to changes of voltage at the output of the constant current device by replacing the switching potential by a holding potential. The arrangement allows the moment when all relays in the succession have been energized to be more reliably determined. To establish a path through the arrangement shown, transistor T2 is switched to conduction, enabling transistor T1. Transistor T1, diode wa and resistor a are connected to form a constant current arrangement which when enabled pass a constant current from the switching source S to a point D forming the let of a succession of relays R1, R2, R3, previously selected in a manner not described. Source S co-operates with a potential I1 to energize a relay R1 closing its contact r1 which in turn allows the source S to co-operate with a potential I2 energizing relay R2 &c. until at the end of the chain relay R3 closes contact r3 connecting the chain to terminating potential T. The resistance through which this is applied is distinctly different from that through which the potentials I1 to I3 are applied. Accordingly, when r3 closes the potential at D makes a sudden change which is detected by a voltage detector V. The voltage detector removes the enabling signal at the base of transistor T2, cutting off the source S and enables a transistor T3 to connect a hold potential H to the point D. In a modification (Fig. 2, not shown) the hold potential is gated through the voltage detector. |
