GB1309498A - Telephone exchange systems - Google Patents

Abstract

1309498 Automatic exchange systems SIEMENS AG 18 May 1971 [19 May 1970] 15601/71 Heading H4K In a key telephone system utilizing relays for connecting an operator to one of a plurality of exchange lines in dependence on which key she has actuated, each operator station has associated therewith a voltage sensitive testing circuit which is connected to a co-ordinate array of test wires associated in one ordinate with exchange lines and in the other with stations, which wires are subjected to an inhibit potential in the event that a time is already in use or that a single station attempts access to more than one line. In the drawing stations N1 ... Nn can access lines L1 ... Lx by the operation of L11 ... Lnx following actuation of keys 1AT11 ... ATnx. Assume N1 closes 1AT11 thereby bringing up relay N11, thereupon positive resistance battery is applied to line block line LV1 which pertains to N1. In test circuit AW1, a transistorized threshold arrangement responds to the positive battery and applies enable potential to point ST11 thereby bringing-up the selected crosspoint relay L11. The latter at its contact 4111 applies earth (positive) to station block line SV1 thereby preventing seizure of this exchange line by any other station since the threshold circuit will not respond to this potential. If station N1 was already connected to another exchange line, then the closed contact 5n12 or 6n1x pertaining to this other line (relays N hold during a connection by means not shown) would be applying positive resistance battery to line block line LV1 whereby application thereto of another similar potential would have no effect. Simultaneous actuation of keys in a same station results in neither line being seized. Simultaneous actuation of keys pertaining to a same line in different stations normally results in a race as to which test circuit will respond first, although a contact chain-selecting arrangement may be utilized to overcome this eventuality as depicted in Fig. 2 (not shown).