CH643669A5 - Electrical device for protecting movable objects - Google Patents

Description

The invention relates to an electrical device for protecting movable objects against theft or damage, consisting of at least one sensor to be attached to the object or to a suspension of the object and the signal path connected thereto with an output stage for generating an alarm signal.

To protect moving objects against theft or damage, known room protection systems operating with ultrasound or electromagnetic waves can be used, which register every movement in the protected area and, if necessary, activate an alarm device.

In rooms where the objects are made available to the public, e.g. in museums, this method is not applicable since any movement of people would trigger the facility.

Furthermore, attempts are made to protect the objects to be protected by light or infrared barriers placed close to the objects, so that the barrier is triggered each time the barrier is penetrated. However, such devices make it necessary to construct a system which is precisely adapted to the object to be protected. Subsequent changes are therefore not possible. In addition, such devices do not allow visitors to come close enough. In addition, such a system can lead to false alarms if e.g. Insects fly through the light barrier.

For this reason, other known devices use devices which are connected directly to the object to be protected and which respond to any movement or removal of the object.

For example, it is known to use the subject e.g. to attach a metal strip on the back of a picture or picture frame or on the underside of a set up object that bridges two contacts in the idle state, but opens the circuit when the object is removed and triggers an alarm. Often, several objects are included in a loop line in this way, so that when interrupted on any

Point of the loop alarm is triggered.

In another known arrangement, the object to be protected, e.g. on the back of a picture, a magnet is attached, which closes a contact attached behind it in the idle state, but causes the contact to open when the object is removed.

In devices of this type, a change must always be made to the object to be protected, which is not always desirable in the interest of preserving value. In addition, such devices can easily be put out of operation by short-circuiting the lines or by using an external magnet. Furthermore, the device must be specially adapted to each object to be protected and special installations are required for each object.

Other known devices register every change of location of the object to be protected. For example, an arrangement is known in which a planar bridging element is attached to the back of a painting, an alarm being given when the capacitance between this bridging element and fixed sensors changes. This method also has the same disadvantage that the object to be protected has to be changed and that stationary devices have to be individually adapted for each object.

Attempts are also made to exploit the vibrations which occur when the object is stolen or damaged in order to give an alarm. A device is known in which contact is interrupted by the vibrations that occur. Such a system can be easily avoided by avoiding vibrations during theft.

Another possibility is to use electrical switches in the suspension or installation of the object, which switch an alarm circuit when the weight falls below a certain level. Such a device can of course easily be put out of operation by using an additional weight.

In addition, such devices do not register any damage without taking away the object, e.g. Cutting out parts of the canvas of a picture, knocking off parts of a sculpture, pouring acid over a picture, etc.

A device is also known in which the sensors are force transducers which, in the idle state, are loaded by the weight of the object to be protected, a signal being emitted when this force deviates from the idle state value. Known mechanical-electrical transducers are used as force transducers, e.g. to use piezoelectric sensors. This known device must be adapted to the weight of the object each time. It is very sensitive, causing false alarms. Furthermore, mounting piezoelectric transducers is a delicate problem.

The object of the invention is therefore a device for protecting movable objects against theft or damage with the following conditions:

- no changes may be made to the object to be protected,

the device must be usable for different objects with different weights and different dimensions without changes,

- the device must be tamper-proof,

the device must permit variable attachment or installation of the object without having to carry out an expensive new installation,

at the slightest damage or touching the object to be protected, an alarm must be triggered without delay

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643 669

given and the fault location can be localized,

the assembly of the device should be very simple,

- The false alarms should be practically eliminated. According to the invention, this object is achieved by a device of the type mentioned at the outset, which is characterized in that the sensor has a housing in which there is a Hall generator, a pendulum and oil consisting of a magnet, and the sensor is in motion during a movement outputs in its value changing DC voltage, and that the AC voltage component of this voltage is fed via a coupling capacitor to an AC voltage amplifier, which is followed by an amplitude discriminator, an integrator and a switching stage.

The device according to the invention is particularly suitable for protecting a painting suspended from a bar by means of a wire or a cord.

In the accompanying drawing an embodiment of the subject of the invention is shown. Specifically show: 20

1 shows a block diagram of the electrical device, FIG. 2 shows a basic diagram of the sensor,

Fig. 3 is a painting with two-point suspension and attachment of the sensor on a bar and

Fig. 4 is a side view of the hanging painting and 25 of the device.

In Fig. 1, 1 denotes a sensor, the basic scheme of which is shown in Fig. 2. This sensor has a housing in which there is a Hall generator 9, a pendulum 8 consisting of a magnet and oil. The 30 Hall generator is attached to two points on the housing. The pendulum is suspended at one point in the housing and its movement is dampened by the oil. A current of constant strength flows through the semiconductor plate of the Hall generator, on which there is a polarizing magnet, with a denoting the input and c the output terminal of the current. In the idle state of the

There is a DC voltage at the output terminal b of the sensor. During a movement of the sensor 1 and thus of the pendulum 8, a DC voltage which changes in value is produced at the output terminal b and is supplied to an AC voltage amplifier 2 (FIG. 1) via a coupling capacitor 17. The task of this coupling capacitor is to keep the DC component away from the amplifier, since this would overdrive due to its high gain. The amplifier 2 is followed by an amplitude discriminator 3, an integrator 4 and a switching stage, which consists of an amplifier 5 and a relay 6. A stabilizer, to which a positive voltage + V is applied, is connected to the input terminal of sensor a. As soon as the amplitude of the AC voltage signal appearing at the output of the amplifier 2 during a movement of the sensor 1 exceeds a certain value, the relay 6 picks up and an alarm is triggered.

3 and 4, a painting 10 is shown with two-point suspension by means of a wire 11 on a beam 13. The beam is rotatably mounted by means of an axis 16 on a plate 12 fixed to the wall. The sensor 1 is attached to the beam 13 in its center and the amplifier 2, the amplitude discriminator 3, the integrator 4 and the switching stage 5, 6 are arranged in a housing 14 on the plate 12. One end of a spring 15 is attached to the plate and the other end to the beam 13.

When an attempt is made to remove or damage the painting, the bar 13 moves and with it the sensor 1, so that an alarm is triggered. As soon as the bar returns to the rest position, the pendulum in sensor 1 also returns to its rest position. The spring 15 causes the bar to move even in the event of very careful removal of the painting.

The device described can be used wherever an unauthorized movement of material assets in connection with unlawful acts has to be detected.

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1 sheet of drawings

Claims (2)

643 669 PATENT CLAIMS Electrical device for protecting movable objects against theft or damage, consisting of at least one sensor to be attached to the object or to a suspension of the object and the associated signal path with an output stage for generating an alarm signal, characterized in that the sensor (1) has a housing in which there is a Hall generator (9), a pendulum (8) consisting of a magnet and oil that the sensor emits a DC voltage that changes in value when moving, and that the AC voltage component of this voltage an AC voltage amplifier via a coupling capacitor (17) (2) is supplied, which is followed by an amplitude discriminator (3), an integrator (4) and a switching stage (5, 6). 2. Use of the electrical device according to claim 1 for protecting a painting suspended from a bar by means of a wire or a cord, characterized in that the bar (13) is rotatably mounted (16) on a plate (12) attached to the wall, that the sensor (1) is attached to the beam and that the amplifier (2), the amplitude discriminator (3), the integrator (4) and the switching stage (5,6) are mounted in a housing (14) on the plate.