SECURITY APPARATUS

Abstract: Security apparatus to generate an alarm on interference with a glass or similar panel (21). An air chamber (22) extending across the panel (21) is held at non-atmospheric pressure, preferably sub-atmospheric pressure, and an alarm (24) is responsive to change in pressure in that chamber on interference with the panel (21). The air chamber may be defined by a tubular duct (22) extending across the panel. The duct (22) may be formed by transparent tubing applied to a face of the panel (21) or it can be comprised of holes formed in the body of the panel. In an alternative construction, the panel is comprised of two parallel transparent sheets and the air chamber is defined between those sheets to extend continuously throughout a major part of the panel.

Description: SECURITY APPARATUS TECHNICAL FIELD This invention relates to security apparatus and particularly to apparatus for providing an alarm signal when glass or other panels are interfered with or broken. There are many instances where it is desirable to create an alarm signal if a glass or similar panel is broken. For example in an alarm. system for a domestic house or other building, it may be required to cause an alarm if any window is broken or cut. Existing window security apparatus can call for a conductor strip to be fixed to the inside of a window close to the surrounding framework. Such a system can readily be bypassed by cutting a suitable hole bridging the terminal points. The window can then be broken or removed without initiating the alarm. Similar problems arise in providing an effective alarm system for shop front windows, glass fronted display cases and other glazed display fronts. In these cases the application of metal conductors across the main glazed area may be expensive and unsightly. DISCLOSURE OF THE INVENTION The present invention provides security apparatus comprising a transparent panel, means defining an air chamber extending across the panel, means to hold the interior of said chamber at non-atmospheric pressure, and alarm means responsive to a change in pressure in said air chamber to produce' an alarm signal, it being understood that as used herein the term "transparent panel" includes a partially transparent and or translucent panel. The means defining the air chamber may define a tubular duct extending across the panel. - The 'duct may be formed by transparent tubing applied to a face of the panel. Alternatively it can be comprised of one or more holes formed in the body of the panel. In an alternative construction, the panel may be comprised of two parallel transparent sheets and the air chamber may be defined between those sheets to extend continuously throughout a major part of the panel. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully explained, some particular embodiments will be described in detail with reference to the accompanying drawings in which:- Figure 1 illustrates a security apparatus incorporating a double glazed panel; Figure 2 is a cross-section on the line 2-2 in Figure 1; Figure 3 is a cross-section through a control unit forming part of the apparatus shown in Figures 1 and 2; Figure 4 illustrates a modification incorporating a single glazed panel to which a vacuum tube is applied; Figure 5 illustrates a further modification in which a vacuum duct is formed within a glazed panel; and Figure 6 illustrates a modified form of control unit. BEST MODES OF CARRYING OUT THE INVENTION The apparatus illustrated in Figure 1 comprises a panel 1 formed from double glazing glass sheets 2, 3 set in a frame 4. The edges of the sheets 2 and 3 are set in the frame and sealed with an adhesive strip (not shown) so as to produce within the panel a sealed air chamber 5 which extends continuously throughout substantially the whole area of the panel. A small tube 6 is installed through the top of frame 4 to allow air to pass between the chamber* 5 and an alarm . control unit 7 fitted to the upper side of the frame. Alarm control unit 7 comprises a housing 8 which encloses a tubular chamber 9 closed by a diaphragm 10. Tube 6 connects air chamber 5 with the interior of the tubular chamber 9. A switch 13 disposed within housing 8 has an actuator 14 in engagement with the diaphragm 10 so as to be " actuated by movement of the diaphragm. This switch is wired to an alarm 15 disposed within the housing and powered from a rechargeable battery 16. Air can be pumped from the interior of the control unit via a suction fitting 17 provided with a non-return valve. The air in chamber 9 and chamber 5 can then expand by movement of diaphragm 10 so that chambers 9 and 5 are also reduced to sub-atmospheric pressure, albeit to a lesser degree than that within the casing 8 of the control unit. This causes the diaphragm to set the switch so as to turn the alarm circuit on. Any attempt to cut or break the panel will destroy the negative pressure within chambers 5 and 9 so causing movement of the diaphragm and actuation of the alarm. Similarly any disruption of the sealed casing 8 of the control unit 7 will also cause a movement of the diaphragm to activate the alarm due to loss of vacuum within the casing. The alarm mechanism is very sensitive and only a small amount of air need be removed from the casing to set the alarm. Figure 4 shows a modification in which a panel 21 formed of a single glass sheet has applied to it a small diameter tube 22 formed of glass or other transparent material. The tube is adhered to a back face of the panel and it is connected via a tube 23 to an alarm control unit 24 which may be identical to the control unit 7 of the previous embodiment. Tube 22 is extended across the panel in a zicr-zag path or formation so as to extend throughout a substantial area of the panel. In this case the interior of the tube is evacuated to sub-atmospheric pressure through the control unit. If the panel is broken or cut, the negative pressure within the tube is destroyed and the alarm will be activated. Figure 5 illustrates a further embodiment in which a glass panel 31 is formed with a series of small tubular bores 32, 33. The panel is set within a frame 34 and its outer edge engages a sealing strip (not shown) which may be formed of neoprene. The bores 32, 33 then form limbs of a continuous chamber which extends across a substantial part of the panel. This chamber is connected via a tapping 35 to a control unit 36 mounted on top of the panel frame. Control unit 36 may be similar to the control unit of the previous embodiments. Again the panel chamber is evacuated to sub-atmospheric pressure by the application of suction through the control unit and the alarm is activated when this negative pressure is destroyed on breakage or cutting of the panel. Figure 6 illustrates a modified control unit 7A which is generally similar to control unit 7 of Figure 3 and in which like components have been identified by like reference numerals but with the addition of the suffix "A". In this case however the diaphragm chamber 9A is provided by a totally sealed casing 40 disposed within the outer casing 8 of the control unit and the tube 6 connects directly with the interior of casing 8. Thus suction applied to the interior of casing 8 via the suction fitting 17A is also applied directly to the air chamber extending across the panel. This enables a significant sub-atmospheric pressure to be generated in a relatively large volume and the modified control unit is particularly suited to apparatus for protection of large windows such as shop front windows. Evacuator of casing 8 will cause diaphragm 10A to move and allow the fixed volume of air within chamber 9A to expand. This sets the switch i3A in an active or "on" condition and the alarm 15A will be activated by movement of diaphragm 10A consequent to a loss of vacuum due to interference with the panel being secured on to the casing of the control unit. The illustrated apparatus has been advanced by way of example only and many variations are possible. In particular the diaphragm and switch actuator for the alarm could be replaced by a pressure transducer or other suitable device operating in an electronic circuit. INDUSTRIAL APPLICABILITY The invention enables provision of a simple and unobtrusive means for providing an alarm signal when glass or other panels are interfixed with or broken. The invention may be applied to security for windows in domestic houses or any other buildings, shop front windows, glass fronted display cases and other glazed display fronts.

Claims: CLAIMS : 1. Security apparatus comprising a transparent panel, means defining an air chamber extending across the panel, means to hold the interior of said chamber at non-atmospheric pressure, and alarm-means responsive to a change in pressure in said air chamber to produce an alarm signal. 2. Security apparatus as claimed in Claim 1, wherein the air chamber extends continuously across and throughout a major part of the panel. 3. Security apparatus as claimed in Claim 2, wherein the panel is comprised of two parallel transparent sheets and the air chamber is defined between those sheets to extend continuously throughout substantially the whole area of the panel. 4. Security apparatus as claimed in Claim 1, wherein the means defining the air chamber defines a tubular duct extending across the panel. 5. - Security apparatus as claimed in Claim 4, wherein the duct extends across the panel in a formation which extends throughout a substantial area of the panel. 6. Security apparatus as claimed in Claim 5, wherein the formation is a zig-zag formation. 7. Security apparatus as claimed in any one of Claims 4 to 6, wherein the duct is formed by transparent tubing applied to a face of the panel. 8. Security apparatus as claimed in Claim 4 or Claim 5, wherein the duct is comprised of one or more holes formed in the body of the panel. 9. Security apparatus as claimed in Claim 7, wherein the duct is comprised of a series of said holes extending in a parallel array across the panel in one direction and a further hole extending across the panel transverse of the parallel array and interconnecting the holes of the series. 10. Security apparatus as claimed in any one of the preceding claims, wherein the means to hold the chamber at non-atmospheric pressure comprises means to evacuate the chamber to sub-atmospheric pressure and the alarm means is responsive to a loss of vacuum in said chamber.

Inventors: MILLAR FREDERICK WILLIAM, MILLAR, FREDERICK, WILLIAM
Applicants: MILLAR FREDERICK W, MILLAR, FREDERICK, WILLIAM
Application year: 1986
Main classification: G08B13
IPC codes: G08B13