IE41984B1 - Window pane - Google Patents

Abstract

1488440 Detecting breakage of window panes SAINT-GOBAIN INDUSTRIES 22 Dec 1975 [24 Dec 1974] 52339/75 Heading G4N A window pane having a tempered glass sheet 1 has an extensometric detector 6 integral with the surface thereof so that on breakage of the pane a signal is provided for operating an alarm or protection device. As shown, the detector 6 is a resistance strain gauge mounted on the bottom face of a block 4 which is bonded at 5 to the sheet 1. The block 4 also contains a second strain gauge 7 identical to gauge 6 but not in contact with the sheet 1, the two gauges being arranged in a bridge, Fig. 2 (not shown), also mounted in block 4. The bridge output is amplified and applied to a relay, Fig. 2 (not shown), via a lead 9. As shown, the pane consists also of a non-tempered glass sheet 3 and a thermoplastic adhesion layer 2.

Description

PATENT APPLICATION BY (71) SAINT-GOBAIN INDUSTRIES, A BODY CORPORATE ORGANISED UNDER THE LAWS OF THE FRENCH REPUBLIC, OF 62 BOULEVARD VICTOR HUGO, 92209 NWUILLY SUR SEINE, FRANCE. 419 8 4 This invention rnlntcs to a window pane the surface of which is provided witli a detector sensitive to breakage of the pane to emit a signal for activating an alarm or protective device.

There are known devices of this type in which the detector comprises, an electrically conducting strip which is broken when the supporting sheet is destroyed. A tempered glass sheet is preferably used as the support sheet.

Xn fact, as such a sheet has the property of breaking 10 into small fragments ovor the whole of its surface, a relatively short conducting strip may be used at any point on its surface.

It has been found that this type of pane is not satisfactory when the support sheet is solidly mounted in a frame or forms part of a laminated pane in which it is laminated to one or more other sheets: it may happen that the extension observed on breakage of the tempered sheet is not sufficient to Cause reliable breakage of the conducting strip by separation of the various pieces to trigger the alarm by.complete stoppage of the current through the detector.

There.are also known breakage detectors which comprise, on one surface of the sheet, a detector sensitive -to oscillations of a given frequency which are observed during breakage. Panes provid.ed with this type of detector have the disadvantage of also reacting to oscillations from causes other than breakage of the'.sheet.

An object of the present invention is to provide a pane which is unlikely to give a false alarm and which gives very reliable operation when the pane is broken. -241984 According to one aspect of the invention, there is provided a window pane comprising a tempered glass sheet, the .surface of which is provided with a detector capable of causing, on breakage of the pane, a signal to operate an alarm or protection device, the detector comprising an extensometrie detector integral with the surface of the •sheet.

It has been found that when the sheet is broken, because of the large cracks formed the extensometrie detector is subjected to an overall change in dimensions and this change can be used to generate a signal. Existing types of extensometrie detectors are sufficiently sensitive for this purpose.

The cost of such a pane is relatively low. The detector may have small dimensions and may be placed at any desired location. .

In an advantageous embodiment of the invention, there is used in combination with the detector integral with the surface of the sheet a second detector of identical characteristics placed adjacent the first detector in order to serve as a reference detector. The second detector may be opposed to the first in a measuring bridge to compensate for variations in the resistance of the first owing to external influences, especially variations in temperature.

Advantageously there are used two strain gauges incorporated with the other electronic elements of the measuring bridge and. an amplifier in an integrated unit fixed as a block on the sheet surface. -341884 It is advantageous for the sheet of tempered glass which receives'the detector to form part of a laminated pane in which it is laminated to one nr more lintenipcred sheets. In this case breakage will not produce a free passage. Λ preferred embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure I is a partial perspective view of a pane equipped with a detection device according to the invention, and Figure 2 is a block diagram of an electric alarm circuit.

Figure 1 shows a laminated pane equipped with a detection device, the pane comprising a tempered sheet of silicate glass X, a thermoplastic adhesion layer 2 and an untempered sheet of silicate glass 3· The detector 4 is fixed to the tempered sheet.1 by means of an adhesive layer - It takes the form of a compact block 4 on the base of which is placed an electric resistance 6 which forms an extensometric gauge sensitive to breakage. Tho adhesion renders this resistance integral with the surface of the glass sheet so that deformations of the latter are accurately transmitted. The block 4 comprises a second extensometric gauge 7, placed for example at the bottom of a space 8 formed in the base. This gauge 7 is not integral with the surface of sheet 1 but serves, on the other hand J as a reference detector in order to eliminate external perturbations which affect the electric resistance of the gauge 6; it therefore has the same characteristics as the latter. -441984 Figure 2 is a block diagram of the associated circuit. A connecting cable 9 incorporates the feed conductors and those which connect the detector to relays controlling the alarm device itself.

The measuring bridge 10 in which there are incorporated the two extensometric gauges is in the block 4, which is integral with the sheet of glass nnd of which the dimensions are similar to those of a packet of cigarettes.

Xn the case of breakage of the sheet, the measuring bridge converts the alteration in resistance of the sensitive detector to an electric signal which, after amplification, operates the relay 12. The latter is placed inside the building, away from the window at an appropriate location; it is connected to a device for sounding an alarm, for emitting a signal or for other protection devices. The rectangle 13 shows schematically the feed of current for the detector 4 and. the relay 12.

Claims (7)

1. WIIAT WE CLAIM JS:1. Λ window pane comprising a tempered glass sheet, the surface of which is provided with a detector capable of causing, on breakage of the pane, a signal to 5 operate an alarm or protection device, the detector comprising an extensometric detector integral with the surface of the sheet.

2. A pane according to Claim 1, in which the detector is a resistance strain gauge. to

3. · A pane according to Claim 1 or 2, in which a reference detector having characteristics corresponding to those of said detector is placed adjacent thereto and is not connected to the surface of the sheet.

4. A pane according to Claim 3, in which the detectors 15 are connected to a measuring bridge.

5. » A pane according to Claim 4, in which the detectors, measuring bridge and an amplifier to amplify signals from the bridge are enclosed in an integral block connected to the surface of the sheet.

6. , A pane according to any preceding claim, in which. the sheet of tempered glass forms part of a laminated pane i . comprising at least one untempered sheet.

7. A window pane, substantially as hereinbefore described with reference to the drawings. MACLACHLAN S DONALDSON - 6 ~ Agents for the Applicants .ΊΑΪΝΤ-δώθΑϊΒ iWVS&WSS TWO SHEETS 4198 4 ONE