GB1496481A - Security system - Google Patents

Abstract

1496481 Security system BRITISH RAILWAYS BOARD 12 Dec 1974 [12 Oct 1973] 47700/73 Heading G4H A security system for controlling access to a security zone, which access is gained through at least two sequentially opened doors, comprises a plurality of doors each provided with a lock having a keep and a respective electric control circuit comprising logic circuitry, Fig. 3, for ensuring that it is correctly shut and locked when required. The security area may be a room containing a safe (Fig. 1, not shown) to which access is obtained via a series of doors only one of which may normally be opened at a time (unless specified overriding conditions obtain), or an office corridor (Fig. 2) divided into zones made safe in turn before connecting doors, A, F, K, can be operated. The logic circuitry of each door (Figs. 4-5, not shown) checks that each door is closed and locked when it should be, receives command signals from a control unit (Figs. 8-9, not shown), and generates alarm signals if a door mechanism would not lock if required to do so, if a door has been forced open, and if a connecting cable has been cut or shorted. An alarm signal causes all doors to lock when they can do so. The first alarm signal is fed to a delay circuit (Fig. 6, not shown) incorporating a counter (50), which operates a "bleep" alarm; the other alarm signals are fed to the circuit of Fig. 7 which operate relays RLY1, RLY2 to produce police and local alarm signals. A third input to this circuit (inverters 61-63) prevents the system being fully turned on until all the doors are interlocking correctly; in this case, and if there are no alarm signals, transistor T7 conducts, to cause a relay RLY3 to operate a switch SC having contacts S1-S3. The doors may be opened (subject to the interlocking conditions) by pressing a button in the control unit; the buttons may be replaced or supplemented by time-clock operated switches. Power supply may be from a battery (Fig. 10, not shown); the supply to a door is reduced in the event of a short circuit, and also when the door has been locked. A fire alarm switch is incorporated, operation of which causes power to be disconnected from all doors, which are unlocked.