| 摘要 |
1. Emergency call installation comprising at least one emergency call column and an inquiry-station connected there-with through a two-branch line serving for the signal transmission as well as for the supply of the D.C. voltage to each of the emergency call columns from the inquiry-station, each of the emergency call columns including a telephone station as well as switching arrangement for establishing and interrupting the connexion with the inquiry-station, characterized in that the switching arrangement comprises a doublewound bistable relay (K) through the contact (k) of which, in the non-activated state of the emergency call column, the first branch (a) of the line is connected, through a first resistor (R1) with one electrode of a first capacitor (C1) and, in the activated state of the emergency call column, is connected with the telephone station (FE), the other electrode of the capacitor (C1) being connected with the second branch (b) of the line whereby, for activation of said emergency call column, the two electrodes of the first capacitor (C1) are adapted to be connected together through a contact (t1) which can be momentarily actuated by a key button (T), as well as through the first coil of the bistable relay (K), and that a second capacitor (C2, C3) is provided one electrode of which is connected, between the contact (k) of the bistable relay (K) and the telephone station (FE), with the first branch (a) of the line, where as its other electrode is connected with the second branch (b) of the line, and both electrodes of which are adapted to be connected together through a controllable switching element (I, Tr1) and the second coil of the bistable relay (K), whereby the controllable switching element (I, Tr1) is arranged and designed so that it closes when the feeding voltage supplied through the line (a, b), attains the zero value. |
