GB223674A - Improvements in or relating to electrically-operated burglar alarm systems - Google Patents

Abstract

223,674. Draper, W., and Fairlie, T. July 31, 1923. Burglar alarms.-A burglar alarm circuit is worked by current from the lighting mains and is arraned so that when contacts arranged in the floor are trodden on, an audible alarm is sounded, a visible signal outside the building is illuminated, and part or all the lights in the building are lit up. The figure shows the arrangement of the circuit. A, A<1> are the lighting mains and in one of them, A, is an automatic switch 1. A shunt circuit B is connected across the mains on the supply side of the contact 1. This circuit contains the floor, or door or window alarm contacts B<1> in parallel, and an electromagnet B<2> the core B<3> of which is connected to the blade 1 of the switch 1. A push button switch B<4> is incorporated for arbitrarily closing the shunt circuit. A bypath C containing an auxiliary switch 2 is connected to the switch 1 so that they will open and close together is incorporated to maintain the circuit B when the contacts B<1> have been released. The shunt circuit also contains a setting-switch B<5> which, when opened, renders the shunt circuit inoperative. To set the circuits for giving an alarm the switch B<5> is closed and the switch B<4> opened. An intruder treading on contacts B<1> causes a current to flow from the positive main A through the solenoid B<2>, through the contact B<1> and through the switch B<5> to the negative main A<1>. The momentary " making " of the contact B<1> by a person treading on the floor where the contacts B<1> are arranged, and the passage of the current, results in the attraction of the core B<3> of the solenoid B<2> and the closing of the switches 1, 2. The closing of the switch 2 maintains the current flowing through the solenoid B' when the contacts B' are broken, so maintaining the core B<3> in position to keep the switch 1 closed and causing all the lights in the building to be illuminated if their individual switches are " on." Connected also to the core B<3> are switch blades 3, 4 in circuits D and E respectively, also connected to the mains A, AT. Hand switches D<1>, E<1> can put these circuits into, or out of, operation. Simultaneously with the closing of the switches 1 and 2, the switches 3 and 4 are closed, completing the circuits D and E and causing a visible signal 6 to be illuminated at some prominent place on the outside of the building, and causing an audible alarm such as a horn 7 to sound. The alarm contacts B<1> comprise recesses in the floor containing strips of metal and closed by lids having on their underside strips of metal at right angles to the strips in the recesses. The lids are held flush with the floor by springs capable of bearing the weight of a cat or dog, but not that of a man. The switch blades 1, 2, 3, 4 may be clamped at intervals on a rotary shaft 28, Fig. 4, which is rocked when the armature 29 is attracted by the magnet 23.