GB481448A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

481,448. Fire-alarm systems. AUTOMATIC ELECTRIC CO., Ltd., (in Liquidation), and BROWN, W. J. Sept. 10, 1936, No. 24725. [Class 40 (i)] In a fire-alarm system of the type wherein a plurality of signal boxes is included in series in a loop circuit over which direct current is normally flowing, any one of the boxes may be called selectively from the central station by transmitting a numerical code of A.C. impulses. The system comprises signal boxes SS1 ... SS10 connected in loop circuit to a central station having a tape register RE and gong G for signalling the locality of a fire. A step-by-step calling magnet M is connected to each box through a condenser and is made responsive to A.C. impulses by a rectifier. The calling impulses are transmitted from a transformer TR under the control of a keyboard 1 .. 11 and finder switch S. Depression of a key to call a particular box marks a contact in the bank of wiper S2 and pulls up relay X which initiates the cyclic operation of relays X, W for driving the switch. A relay P is impulsed at alternate steps to send A.C. impulses over the loop and operate the stepping devices in the boxes simultaneously. When the marked contact is reached relay K pulls up and stepping is terminated. Under these conditions, the stepping device at the called station closes the circuit of the calling lamp L. For checking purposes a pilot lamp is operated over the wiper S3 and a stepping device M1 at the central station is operated simultaneously with the selecting devices at the boxes. The system is combined with a telephone system and when a box is called, and the box door is opened, resistance is automatically inserted in the loop circuit to cause the release of an alarm relay T. The system is then ready for the connection of the central station telephone equipment across the loop. At the conclusion of conversation, the operated selecting key is restored and the switch S hunts to its home position, the selecting devices in all the boxes being homed simultaneously. A general call to all boxes may be sent by transmitting a particular code. " Faulty conditions " working. If a break occurs in the loop a relay EW (not shown) is released and the two legs of the loop are connected in parallel to one side of the battery BA the other pole of which is earthed. If the break is not earthed the selective call system is not interfered with, but if earthed, relay LA or LB will be reoperated and the stepping magnet SM of the switch S is isolated to prevent its operation. Under these conditions impulses are transmitted over lead 11 to a fault alarm. Specifications 431,349, [Group XXXVII], and 471,759 are referred to,