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US 3,947,837 AGranted
Security glazing and alarm system
AssigneePPG Industries, Inc.
InventorMichael G. Bitterice
Life of this patent
Estimating the term…
Abstract
A glazing unit having a plurality of plies is provided with a grid of fine wires electrically connected in parallel. A warning signal is activated upon a change in the resistance of the grid. The arrangement permits resetting the alarm after a partial break in the grid. A second grid may be used as the reference resistance in the alarm circuitry. Thermally induced breakage of the fine wires is avoided by providing resilient connections to the bus bars.
Claims15
A security glazing system comprising:
- a resistance grid formed by a plurality of frangible, electrically conductive wires electrically in parallel with one another and extending across an area to be protected;
- means for applying a voltage across said grid;
- and
- circuit means connected across said grid, including resistance balancing means for comparing the resistance of said grid with a reference resistance and for generating an output signal in response to an incremental change in the grid resistance corresponding to a break in one or more of said wires in the grid, said resistance balancing means being provided with adjustment means for resetting the system by re-establishing a resistance balance in the circuit while a portion of the grid wires are broken.
1 more element
A security system comprising:
- a first resistance grid and a second resistance grid, each formed by a plurality of frangible, electrically conductive wires electrically in parallel with one another, each grid extending across a respective area to be protected;
- means for applying voltages across said grids;
- and
- circuit means connected across each of said grids, including resistance balancing means for comparing the resistance of said first grid with the resistance of said second grid and for generating an output signal in response to an incremental change in the resistance of one of said grids corresponding to a break in one or more of said wires in the grid, said resistance balancing means being provided with adjustment means for resetting the system by re-establishing a resistance balance in the circuit while a portion of the grid wires are broken.
1 more element
A composite glazing unit comprising:
- at least two transparent plies, one superimposed over the other;
- bus bar means between said plies along opposite edge portions of the unit, each bus bar means including two strips, one strip overlying the other strip, at least one of said strips being electroconductive;
- a plurality of frangible, electrically conductive wires between said plies, each wire connected at each of its ends to one of said bus bar means so as to place said wires electrically in parallel to each other, each wire terminating in a bent portion lying between said strips, said bent portions being resiliently retained between said strips so as to permit movement of said wires relative to said bus bar means.
Dependencies are inferred from the claim text.