FR2576438A1 - Alarm detector - Google Patents

Abstract

The alarm detector according to the invention comprises a sensor C sensitive to pressure, and reacts to the pressure waves capable of being produced during a break in, for example an attempt to push in a door, break a window, remove a tile, etc. The pressure wave is advantageously converted into an electrical signal by a polarised capacitor and the signal is filtered by a filter F in order to eliminate the parasitic signals such as noise. One single sensor is sufficient for premises comprising several rooms, and it may be placed at any point at all, which does away with all cabling installations.

Description

 The present invention relates to alarm systems of the type comprising a central member to which are connected on the one hand one or more detectors, capable of providing information on a break-in or attempted break-in, and on the other hand, means alarm triggered by the central body in response to information provided by the detector.

 To effectively protect a room for use which conquelentrep8t, office, home, etc. constituting one or more rooms or the whole of any building, alarm systems of the above type are used in which the detectors are arranged at determined locations with respect to the openings, doors, windows, of the building and are connected to the central organ by electrical wiring. The number of detectors depends on the number of openings and the installation of such systems so far requires the wiring of cables, which is the source. trouble and expenses. Known detectors operate by sending and receiving a signal, electric current, microwave, infrared, ultrasound, etc.

 The present invention relates to a multi-perimeter detector, signaling the openings or attempts to open exits from a room overlooking the outside but also the openings or attempts to open occurring on intermediate exits, doors , corridors, for example, or exits from neighboring rooms. The detector according to the invention emits no signal. It therefore possibly allows it to be put into operation by leaving domestic animals inside the room to be monitored.

 In accordance with the present invention, an alarm detector is remarkable in particular in that it includes a sensor sensitive to pressure variations, capable of delivering a signal to a central organ through a filter to eliminate parasitic signals in order to avoid nuisance trips.

 The present invention takes advantage of the fact that the opening or the attempt to open a normally closed room, for example by opening a door, a window, removing a tile, even with care, causes a wave pressure which can be used as a signal to trigger an alarm. A low-pass filter eliminates parasitic signals, in particular of sound origin.

 It is understood that such a detector does not need to be installed in a predominant location, its location not being a performance criterion. It can simply be integrated into the central alarm unit.

 According to a characteristic of the present invention, the sensor comprises a transducer transforming the pressure waves into electrical signals. Advantageously, the sensor comprises a polarized capacitor delivering a voltage proportional to the pressure, and the filter is a low-pass filter.

 Other characteristics and advantages of the present invention will appear during the description which follows, given by way of nonlimiting example, with reference to the attached drawings and which will make it clear how the invention can be implemented.

On the drawings
Figure 1 is a block diagram of an alarm detector according to the present invention; and
FIG. 2 is an example of an electrical diagram of the detector of FIG. 1.

 Referring to Figure 1, the alarm detector according to the invention comprises a sensor C, advantageously constituted by a polarized capacitor of the micro-electret type, delivering a voltage proportional to the pressure. Sensor C is polarized across a resistor by a voltage of +5 volts.

 The sensor signals are transmitted to a low-pass filter F which can advantageously have a slope of 12 dB / per octave. The signals are amplified by an amplifier A, whose amplification ratio G can be for example 60. The signals are then transmitted to the output S, advantageously through a comparator with reference threshold C, the signals being compared to a reference voltage U stabilized in temperature and adjustable by a potentiometer R.

 FIG. 2 presents a detailed electrical diagram of an embodiment of the detector according to the invention.

The component values are shown in the diagram. The low-pass filter is a second-order Butterworth filter, which can advantageously be set to 10 Hz, to absolutely eliminate any untimely operation due to any noise. The schmacDmports four very low power operational amplifiers, ICIA, IC1B, IC2A, IC2B, which can be
TL O 62 from Texas. The reference threshold comparator is temperature compensated by two 1N 4148 or 1N 914 diodes (RTC). I1 delivers a square wave signal
5V. Between the sensor and the low-pass filter, and between the amplifier and the comparator, there are non-polarized head-to-tail capacitors to cut low frequencies or slow variations of the signal. Decoupling capacitors are provided conventionally.

The diagram also includes a balun which aims to create a symmetrical voltage specific to the supply of operational amplifiers. The different elements of the circuit, sensors, filters, amplifiers, etc. are conventional and shown here by way of example.

 Such a device can be adjusted very sensitively and command a trigger for the opening of a door, even in a room different from the one in which it is placed. It is understood that the detector can be placed in any place of 'a room to watch. I1 can in particular be placed in the central alarm unit, which dispenses with any wiring installation. Whatever the shape of the room, the number of exits (door, window, bays, etc.), the sensor according to the invention detects any attempt at intrusion: significant constraint at the doorframes level, attempt to break in the door, breakage and cutting glass, etc.

 The present invention is not limited to the exemplary embodiments. Which have just been described, it is on the contrary liable to modifications and variations which will appear to those skilled in the art.

Claims (7)

REVENDI CATIONS  1 - Alarm detector for a meJ type alarm device comprising a central member to which at least one detector is connected on the one hand and alarm means on the other hand, characterized in that the detector comprises a sensor sensitive to pressure variations, said sensor being capable of delivering a signal to the central organ through a filter to eliminate parasitic signals, in order to avoid nuisance tripping.  2 - Alarm detector according to claim 1, characterized in that the sensor comprises a transducer transforming the pressure waves into electrical signals.  3 - Alarm detector according to claim 2, characterized in that the sensor comprises a polarized capacitor delivering a voltage proportional to the pressure.  4 - Alarm detector according to claim 3, characterized in that it comprises an amplifier placed between the filter and the central alarm member.  5 - Alarm detector according to claim 4, characterized in that it comprises a comparator placed between the amplifier and the central organ.  6 - Alarm detector according to one of claims 3 to 5, characterized in that a non-polarized capacitor, in particular two chemical capacitors head to head, is placed at the output of the sensor, to eliminate the frequencies: low or slow variations of the signal.  7 - Alarm detector according to one of the preceding claims, characterized in that the filter is a low-pass filter, set to about 10 Hz.