The present invention relates to an alarm apparatus in .' indoi" st>-_ctur_ including at- ^" leasτ one glas pane.

Or the mΞri-e todav there is a number cf different methods foi providing si aiarrr function n", glas.- pan_ included in a wi-dof structure. All these methods have the disad 'antage that either a false alarm can bε ¹ triggered « or 1i is possible to get through he structure provided with the alarm in one we--' or another without triggering the. ¹ alarm. Vibration- 3 sensors often give false alarms and do not sense all _r mds of vibrations-, thus enetal .ng a brεal through. Electrical wires moidea into glass iavers can be disconnected or ovpessed • or tnere is tho possibility of mai- . ng small holes between the Wires sne using them in co— ction with small flexible tools to trap 5 desirable object, e.g. in a shop window.

Electronic sensors also often give false alarms and can be got past. These can often only be used on single panes of glass cf the float glass type, or on hardened glass. Sill- s resi, printed circuits made a ¹ the edge of a hardened glass

pane and hidden in the rebate can also be used as means for giving an alarm. In this case there are methods of getting past the alarm means without the hardened glass granulating ₅ thus not setting off the alarm since the silk screen circuit is not broken. In addition* this metho-cj does not always work o 1amin t d glass.

One object of the present invention is to achieve a.n alarm function which is not triggered without proper cause a.nd which cannot be forced by some penetration method without the a.le.rm being triggered* while at the same time the alarm also functions on laminated multilayer structures,. It is important that the alarm function is combined with a. glass structure which takes a. long time to force. When the alarm is triggered at the beginning of the break—in on the first attack attempt _? much time and work must pass before the object comes accessible. This can usually only be achieved with mul ilaminated structures, and so far there has not been any satisfactory a.larm apparatus for such structures. In accordance with the invention it is possible to create a. solution to the above mentioned problems with the aid of ultrasonics. The distinguishing features of the present inventioπ are apparen from the accompanying claims. In with the invention the risk of false ala*-m is minimum in the cases where the ultrasound is transmitted and registered in the glass pane in a multipane structure where the pane is inwards in the room or premises which is to be

pr tecteα. If £ laminated multipane structure is useα , the πsl cf false alarm is even less, since the laminations can isolate tne ultrasound to the inmost glass pane, simultaneously as each cracl , hole or the 1i 1 e in the area o glass directly triggers the alarm. Naturally, the ultrasound can be used on other glass but a deteriorated function is then obtained.

The. invention will now be described in more detail below wit reference to the accompanying drawing, which schematically illustrates the alarm configuration in accordance with the invention in a cross section and mounted in a ultiglass pan t u ture.

H window structure is illustrated on the drawing, and includes three glass panes l-S- which a.r<≡ I ept together by two laminate layers <4-,5. A transmitter _ of the ultrasonics type is mounted at a first place, preferably ax the inner glass pane 1, i.e. on the inside 10 of the window structure, and so that it is bedded into the laminate ή- contiguous with the inner glass pane 1, the transmitter _ preferably engaging directly against the actual surface of the glass pane 1 with one of its surfaces. A receiver 7 of the ultrasound sent ire the qlass pane i is mounter in an other place against th ^ glass pane 1 for registering impulses received from this pane. Ar alarm un_ 1 lustrated on the drawino is connected to

the receiver 7 via. connection cables V, and the transmitter 6 is in turn connected via. connection cables 8 to an unillustratedj suitable source of energy. The window structure is conventionally mounted in a. rebate 11. The receiver 7 can also be placed in the laminate H- contiguous to the inner glass pane 1 at a distance from the transmitter 6, and then suitably in an area of the glass pane 1 which is in the rebate 11.

The transmitter h can send an ultrasonic wave with a secret pulsation so tha.t it cannot be got past and the transmitter ca.n be of the Pico crystal type. The transmitter 6 is suitably placed such that only one pane is subjected to the ultrasonic wave? if a multipane laminated window structure is used. If a single pane is used the risk of false alarm increases. The pla.cing of the receiver 7 on the pane 1 should be made so that the best possible registration of the ultrasonic wave sent in the glass pane 1 is achieved, and thus the receiver should be at a suitable distance from the transmitter 6. The nature, size, thickness, resistance and etc of the glass enables the ultrasonic wave, which is sent from the transmitter 6, to be received in the receiver 17 in a. certain way. It is of course also possible to use two or more transmitters 6, as well as two or more receivers 7 on optional glass panes, in the cases where this is necessary.

If the glass pane is- damaged in an,- wa _r as a result of mat- ing holes in it, breal mg it etc, there is a registration in the receiver 7 that an alte ^r ation has tal en place in the received impulses, e.g. in the form of frequence increase or frequency decrease. It is possible thai the electronics controUing processes in the Transmitter a and the receive) 7 can include a time fartoi , so that changes which tal- e place in the impedance of the pane due to ei'teπor action have a longer time- than wnat intentional damage. ³ tales in time, thus red cing rhe πsl of false alarm. The descriDed system functions besl together with other pane, ana plastic, layers in a laminaτeα paclet. In such a case the transmitter _ ^• is preferablv fused tightlv against the inner pane 1 for sending the ultrasonic wave in the best way through the pane. The iaminaτp la^e ^ij - also beα_ in the transmitter crystal st> that the ultrasonic wase can penetrate into the outer panes E and _ to the minimum e ^x tent. In this wav the πsl of false alarm is limited to a minimum, since e.'tenor damaging action is not capable of affecting the impedance ir, the innermost pane 1. Analogously the system can be compared with a swimming pool where a transmitter males waves in the water. The waves are deflected against walls, tne b ttom, corners etc and create a certain wave state depending on the resistance in the water, walls etc, which can oe regarded as the impedance of the pool. I-f an ODiecL is placeα in the water, the entire- wave movement pattern 15 changed which is registered bv the

receiver or receivers. The change triggers the alarm. If the pool leaks over to an other pool, via a channel, the change can act on the inner basin so that an alarm is triggered.

With a. glass pane, it can be sufficient to lay a hand a. ainet- it for giving a false alarm. Of course, the electronics can remedy this phenomenon by adjusting the time factor upwards or downwards. In a. laminated structure, the outmost patne 3 does not actuate the alarm if a hand i laid on it, as is the ca.se when a. single glass pane is used, and thus a false alarm is practically completely excluded. Ea.ch crack, hole or the like In the glass packet does ti"igger the alarm, however.

The electronics can also be combined with other sensing patterns than ultrasonics for further improving the function of the alarm.

A transmitter 6 or a receiver 7 can also be placed on the edge or short side of the pane 1 or the panes Ξ, 3.

The ultrasonics used can of course be replaced by impulses of some other kind, which can be transmitted and received by the intermediary of at least one glass pa.ne included in a window structure, or by a similar sheet-like element.

An other conceivable placing of the transmitter 6 and

receiver 7 can be in the corner portions of the window structure, inside the rebate 11, the impulses being sent diagonally across the glass pane in question. Depending on what "thickness" the transmitter 6 and receiver 7 indicate, and if three panes are used, for example, the- corners of the outmost pane can be cut off so that the transmitter and receiver can be thicker than the laminate layer used, simultaneous! as this cut lies within the rebate width, so that transmitter and receiver are protected in the rebate 11 and 1so hidden bv it.