Patent GB-357389-A (GB)
Title: Improvements in electrical burglar alarm systems
IPC: G08B13/22
Filed: 1930-10-09
Abstract: 357,389. Burglar alarms. BUCHER, S., 10A, Avenue de la Gare, Fleurier, Switzerland. Oct. 9, 1930, No. 30296. Convention date, Oct. 22, 1929. [Class 118 (i).] In an electric burglar alarm installation a small central electric alarm, comprising an observation relay 17a and a normally illuminated control lamp 18a, is arranged in the caretaker's room and is connected, for example, to a safe, a window, a door and the entrance door of the caretaker's room. The safe 7 is enclosed by a grill 8 comprising metal tubes 10, along the axes of which metal wires 15 are disposed, insulated from the tubes, the current from the lead 21a passing first through the odd-numbered tubes 10 in series, then through the wires 15 within the even-numbered tubes in series, and so through lead 22a to the relay 17a. From the other terminal of the relay 17a the current passes by way of lead 25a to the wires within the odd-numbered tubes 10 in series, and from these by way of the even-numbered tubes 10 in series to the lead 24a and the source 16. Bridging of two adjacent tubes by a burglar, or sawing through a tube short-circuits the relay 17a, and the alarm is actuated. The frame 9 also comprises tubes formed of two semicircular parts secured together by screws 21 having a reduced portion 27 where they pass through holes in metal strips 22 connected in series in the alarm circuit, so that if a screw 21 is unscrewed it will bridge a tube and a strip, thus short-circuiting the relay 17a. The mass of the safe 7 is also electrically connected with one of the tubes of the grille. Movement of the safe gives the alarm by displacing one or other of two mercury switches 30, 30<1> arranged respectively parallel and at right-angles to the front face of the grille. Each lead 21a, 26a is formed by a rubber tube filled with mercury. If the two leads 21a, 22a are bridged by a resistance, electromagnetically actuated switches 35, 36 function to short-circuit the relay 17a. The lock 12 of the gate of the grille is protected by a plug 42 which must be placed in the lock to complete the circuit of the relay 17a and which contains a mercury switch adapted to break the circuit when the plug is touched lightly. Fig. 12 shows a door frame fitted with tubes and wires 57 like the safe and formed by a channel iron 49 closed by an iron flat 50, which is secured by screws 51 to an iron flat 52. Unscrewing of the screws 51 opens switches 61 and short-circuits the observation relav. The window installation comprises a rack-and-pinion device operated by a key to close the window, the mass of the rack-and-pinion device being connected to the positive side of the circuit, the negative side being connected to a pin at the base of the hole engaged by the key. Fig. 18 shows a plug 87 which is inserted in the closed lock of the door of the caretaker's room so that two contacts 90 are connected by the metal parts of the lock, a mercury switch 93 also closing the circuit. Introduction of a key into the lock from outside forces a conductor rod 91 against a contact 94 and shortcircuits the observation relay. The wiring diagram includes a current rectifier, an automatic switch for introducing an independent source of energy when necessary in place of the mains supply, testing and setting switches, a bell connected in series with a clock constructed so as to close the circuit intermittently at certain times of the day, commutation relays adapted to insert coils in the circuit of the independent source of energy to absorb overloads, and visual signals indicating to the caretaker which part of the building is being attacked.