GLASS BREAKAGE DETECTOR

• US 3,863,250 A
• Filed: 01/30/1973
• Issued: 01/28/1975
• Est. Priority Date: 01/30/1973
• Status: Expired due to Term

• Current Assignee: Arthur Mccluskey Jr
• Original Assignee: Arthur Mccluskey Jr
• Inventors: McCluskey, Arthur Jr.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/328,096
• Time in Patent Office: 728 Days
• Field of Search: 340/274,273,276,261 310/8.3,8.1,8.5
• US Class Current: 340/550
• CPC Class Codes: G08B 13/04 by breaking of glass

Abstract

An alarm for sensing glass breakage having a solid state electronic shock sensor positionable on a sheet of glass and connected through a variable resistance circuit and a threshold detector SCR to a signaling device to detect the breakage of glass. The shock sensor is formed of a number of layers of materials including a piezoelectric material bonded by an electrically conductive epoxy to an electrically conductive sheet of material, such as copper, which in turn is positioned against a layer of epoxy glass, which is joined by a layer of catalyzed epoxy to a plastic case having a layer of adhesive polyurethane formed on the outside. The plastic case is mountable on a sheet of glass and when the glass is broken, the shock waves indicating breakage are transmitted through the layers of materials, which function to attenuate the signals outside the band of shock waves, to the piezoelectric material which generates an electrical signal which is transmitted via the variable resistor circuit to the threshold detector SCR to the signaling device to signal breakage of the glass.

Claims

1. In an alarm for sensing vibrations in a sheet of glass capable of breaking the glass, a vibration sensor comprising a piezoelectric element responsive to vibrations to generate an output signal, means for mounting said sensor directly on and adhered to the sheet of glass, mechanical filtration means interposed between said piezoelectric elemEnt and the sheet of glass for blocking from said piezoelectric element vibrations of a frequency and magnitude incapable of breaking the glass, and electrical circuit means coupled to said piezoelectric element for generating an alarm signal in response to an output signal from said piezoelectric element, said electrical circuit means being responsive to said output signal only when the latter reaches a voltage corresponding to mechanical vibration of the sheet of glass of a frequency and magnitude capable of breaking the glass.

2. A vibration sensor as described in claim 1 and wherein said piezoelectric element comprises a flat layer of piezoelectric ceramic bonded by a layer of electrically conductive epoxy to a sheet of copper.

3. A vibration sensor as described in claim 2 and wherein said mechanical filtration means comprises enclosing said piezoelectric element in an imperforate plastic housing, a layer of epoxy glass laminate bonded to said sheet of copper and to the interior of said housing, and a layer of polyurethane foam adhered to the exterior of said housing for bonding to the glass.

4. A vibration sensor as described in claim 1 and wherein said electrical circuit means comprises a potentiometer for adjusting the voltage of said output signal to a value low enough to preclude false alarms from vibrations of insufficient magnitude to break the glass.

5. A vibration sensor as described in claim 4 and wherein said electrical circuit further comprises an SCR having a control electrode connected to said potentiometer to thereby render said SCR conductive in response to vibrations capable of breaking the glass, and a relay circuit having a solenoid coupled to the anode of the SCR for generating an alarm signal when said SCR is in the conductive state.