GB499442A - An improved return signalling device for remote control installations controlling alarm apparatus - Google Patents

Abstract

499,442. Electric signalling systems. LANDIS & GYR AKT.-GES. Feb. 16, 1938, No. 4856. Convention date, Feb. 25, 1937. [Class 40 (i)] In an alarm system comprising an alarm transmitting station and a central station connected to alarm receiving stations by a network which may be the telephone network, a return checking signal is sent by an operated alarm device over synchronously driven switches at the central and transmitting station. In the system shown, the alarm transmitter G is connected over a pilot line l1, l2 to central alarm selecting apparatus Z which disconnects a telephone subscriber's line l3, l4 from the normal line circuit l5, l6 and connects it to the pilot line as for example in the system described in Specification 498,563. When the alarm E at the substation has been operated, it closes contact e1 in the return signal circuit. The operation of transmitter G closes contact g1 so that synchronous motors S1, S2 at the transmitting and central stations drive selectors K1, K2 relays Ra, Rb being operated over off-normal contacts n1, n2 which also maintain the motor circuits. When the selectors reach contacts of the selected subscriber's line contact e1 if operated closes a simplex circuit over the subscriber's line and selector K2 to pilot wire l1, l2 whereupon the corresponding relay W and lamp M are operated over selector K1, relay W being held over contact g1 closed by the transmitter. The simplex circuit may extend also over the pilot line and the return signal may be an A.C. or D.C. signal.