GB1498005A - Security monitoring systems for doors - Google Patents

Abstract

1498005 Security alarms BRITISH RAILWAYS BOARD 17 Jan 1975 [2 Jan 1974] 00140/74 Heading G4N [Also in Division E2] A door lock security system comprises separate detectors for detecting whether the door is closed, the bolt is thrown into its door locking position and the bolt keep is in its bolt restraining position, and monitoring means arranged to provide a door-insecure indication after a predetermined delay if all of the detectors do not detect their respective conditions when the door is required to be secure, and arranged to provide an immediate indication if the detector detects the bolt-thrown condition before the detector detects the door-closed condition. As shown in Fig. 1, the detectors are switches 1, 2, 3 operated directly by the door, bolt and keep respectively, and are shown in their doorinsecure condition. When the door is closed, the bolt is thrown and the keep restrains the bolt, the switches take their other positions and a relay RLY2 is energized to indicate a door-secure condition. If one of the switches opens, e.g. due to tampering, the relay RLY2 is de-energized to operate a delay circuit which will initiate an alarm after a preset time. If the bolt is thrown before the door is closed, a relay RLY 1 is energized and operates an alarm immediately. In a modification, Fig. 2 (not shown), the switch 2 is a double pole switch with the second switch being arranged in the circuit of relay RLY1 As shown in Fig. 3, logic circuitry is used to indicate a door-insecure condition. When the door is closed, the bolt is thrown and the keep is in position, positive signals are received on inputs 1, 2 and 3, and an AND gate A applies a signal to reset a counter J via an inverter E to indicate a door-secure condition. If one of the conditions is changed or an input lead is broken, a multivibrator formed of gates C and F and components C1, R8, R9 and VR1 applies pulses to the input of counter J which divides them by suitable ratios which can be selected by connecting outputs A, B, C or D to an input E. When the selected output changes from logic 0 to logic 1 (after the predetermined delay), this is applied, after inversion by a gate H, to gate C thus preventing further oscillations. At the same time the logic 1, applied to input E, is applied through a resistor R is to turn on a transistor T2 which controls external means directly or indirectly through relays, &c. If the bolt is thrown before the door is closed, the output of a gate B causes a transistor T1 to conduct which is used to generate external signals by direct or indirect means. The circuitry of Fig. 3 may be added to by the circuits described with reference to Figs. 4 and 5 (not shown), to indicate malfunction, deliberate or otherwise, of the keep. A construction of lock, including a bolt and keep is described with reference to Fig. 6 (not shown), in which the keep detecting means is described to be a microswitch, a photoelectric transducer or an electromagnetic transducer.