GB1563444A - Monitoring and alarm apparatus - Google Patents

Abstract

The device serves in particular for monitoring strongrooms and is actuated if a break-in attempt is made by means of drilling, explosives or welding, for example with laser beams. It has an acoustic-electrical transducer (1) in which a temperature sensor (31) is arranged. A first signal path (A) which is connected to the transducer consists of an amplifier (2), a threshold value detector (4), an integrator element (6) and an output stage (8 to 11) for generating the alarm signal and reacts to small signals which last for a relatively long period of time. A second signal path (B) which is also connected to the transducer and is of similar design to the first signal path reacts to large-amplitude signals which occur briefly and are due to an explosion caused by explosives. The temperature sensor is connected to the output stage (9) and generates an alarm signal when a threshold temperature is reached by the transducer, if for example welding takes place on the strongroom using laser beams which do not generate any solid-borne vibrations but only heat. <IMAGE>

Description

(54) MONITORING AND ALARM APPARATUS (71) We, SECURITON AG, of Alpenstrasse 20, 3052 Zollikofen Canton of Berne, Switzerland, a Swiss Body Corporate do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for monitoring safes, strong-rooms, vaults, and the like, and for producing an alarm signal in the event of an attempted burglary.

The use of such apparatus comprising socalled vibration pick-ups or contact microphones is known for protecting safes, bank vaults, and other objects. Such known apparatus essentially comprise an acoustoelectric transducer, an amplifier, and a signal detector. The mechanical or solidborne vibrations produced in the protected object by sawing, filing, drilling, or cutting during an attempted burglary are converted into electric signals, preferably by a piezoelectric transducer. These signals are amplified by the amplifier and supplied to the threshold-value detector. In order to prevent false alarms, it has also become known to connect an integrator in after the threshold-value detector so that a brief signal, such as may be produced by an unintentional blow to the protected object, will not cause the alarm to go off.A drawback of such apparatus, however, is that no alarm will be set off upon the firing of an explosive charge for opening a safe or the door of a vault by violence, or when a certain amount of heat is developed during cutting-open of the safe door by means of a blow-torch or a laser beam.

Thus there is a need for apparatus which does not possess the aforementioned drawbacks and which responds to the brief, highamplitude signals produced by an explosion, to very weak signals of longer duration, and to a maximum temperature.

According to the present invention, there is provided monitoring and alarm apparatus of the type initially described, comprising an acousto-electric transducer and a first signal path containing an amplifier, a threshold-value detector, an integrator connected in after the threshold-value detector, and an output stage for producing the alarm signal, wherein a second signal path comprising a second threshold-value detector and a delay element is connected at the output of the transducer, the first threshold-value detector responding to a transducergenerated signal which is at least one hundred times weaker than the signal to which the second threshold-value detector responds, the first integrator causing an alarm-release time-lag of at least five seconds and the relay element causing an alarmrelease time-lag of at most 50 milliseconds, and a temperature detector being disposed in the transducer and connected to the output stage for producing the alarm signal when the transducer reaches a predetermined maximum temperature.

Preferred embodiments of the invention will now be described in detail with reference to the accompanying drawing, in which: Figure 1 is a block diagram of apparatus according to the invention, and Figure 2 is a circuit diagram of an embodiment which can be produced with a minimum of circuitry.

According to Figure 1, a signal generated by an acousto-electric transducer 1 is supplied to an amplifier 2 of a first circuit path A and to an amplifier 3 of a second circuit path B. Following the amplifier 2 is a threshold-value detector 4, while a thresholdvalue detector 5 is connected in after the amplifier 3. The amplifiers 2 and 3 and the detectors 4 and 5 are so dimensioned that the detector 5 responds only to a transducer signal which is at least one hundred times greater than that to which the detector 4 responds.

When a signal is present at the output of the detector 4, the output voltage of a following integrator 6 slowly increases until the threshold voltage of a trigger circuit 8 is reached. The threshold voltage of the trigger circuit 8 and the characteristics of the integrator 6 are such that the signal must be present at the output of the detector 4 for a period of at least five seconds before the trigger circuit 8 will respond.

When a signal is present at the output of the detector 5, the output voltage of a following integrator 7 likewise increases, but the rise takes place quickly as compared with that of the integrator 6, until the threshold voltage of a trigger circuit 9 is reached. The integrator 7 and the trigger circuit 9 are so dimensioned that the signal need be present at the output of the detector 5 for at most 50 milliseconds before the trigger circuit 9 will respond.

The circuit shown in Figure 1 further comprises a gate 10 which causes an alarm relay 11 to be actuated as soon as either the triggered circuit 8 or the trigger circuit 9 is triggered.

The integrator 7 and the trigger circuit 9 may naturally be replaced by a flip-flop circuit which is triggered when the threshold value detector 5 responds and which supplies a pulse to the alarm relay 11 via the gate 10. With this arrangement, the response time of the second signal path B becomes extremely short.

The purpose of the second circuit path B is to recognize signals of great amplitude such as occur upon an explosion. Accordingly, the amplifier 3 of the second path B exhibits low amplification, possibly even attenuation. The threshold-value detector 5 responds solely to very high-amplitude signals. On the other hand, the integrator 7 connetced in after the detector 5 possesses a very low time constant.

A temperature detector 31 is disposed in the acousto-electric transducer 1 and connected to the trigger circuit 9 for producing an alarm signal when the transducer 1 reaches a certain maximum temperature.

The temperature detector 31 is preferably a dry-reed switch serving as a part of a tem- perature sensor. Two basic principles of magnetism are the basis for this temperature sensor: a dry-reed switch opens or closes when the magnetic field strength in the vicinity of the two contacts varies; and many magnetic materials change their mag- netic resistance to a considerable extent when they reach their Curie temperature. A bimetal switch may also be used as the temperator detector 31.

Tests have shown that the signal amplitudes occurring upon an explosion are from four to eight decimal powers greater than those produced by cutting with a torch. In order to achieve adequate security against false alarms and a reliable response with explosives are used, the ratio of the response thresholds of the detectors 4 and 5 should be 1:102 to 1:1or.

Tests have further shown that the signal generated in the case of an explosion dies out within 1 milliseconds. Practical trials have demonstrated that with highly-sensitive contact microphones, which are capable of responding to torch attack, the alarm release must be delayed by 5-20 seconds in order to exclude false alarms caused by disturbing noises.

Figure 2 illustrates an embodiment in which the first signal path essentially comprises an amplifier 15 and a transistor 19 serving as a threshold-value detector, and the second signal path comprises an attenuator 22, 23 and a transistor 24 serving as a threshold-value detector. The integrators of the two signal paths have a common charging capacitor 21.

The signal from the piezoelectric transducer 1 is supplied via a resistor 12 to the amplifier 15, which preferably takes the form of an integrated circuit. Diodes 13 and at the input of the amplifier 15 are intended to protect the latter from damage by signals of too high an amplitude. The output signal of the amplifier 15 is conveyed via a capacitor 16 to the base of the transistor 19, which base is biased by a resistor 17. The transistor 19 becomes conductive as soon as the signal amplitude exceeds the value of the base-to-emitter threshold voltage of the transistor 19. The charging capacitor 21 is charged by the collector current of the transistor 19. The charging of the charging capacitor 21 takes place relatively slowly since a charging resistor 18 limiting the charging current has a high value of resistance.

The signal from the transducer 1 is also supplied to the base of the transistor 24 via the attenuator consisting of the resistors 22 and 23. The attenuator 22, 23 is so dimensioned that the transistor 24 becomes conductive only at a transducer-signal amplitude which is higher by three to four decimal powers than that at which the transistor 19 becomes conductive.

When the transistor 24 is conductive, the charging capacitor 21 is charged via a charging resistor 25 which is so dimensioned that the charging time is quick as compared with that of the charging resistor 18, viz., of the order of one millisecond.

A high-valued resistor 20 has, together with the charging capacitor 21, a discharge time constant of several minutes. The signals of the two threshold-value detectors 19 and 24 are integrated over a corresponding period of time.

Transistors 26 and 27, connected to a common emitter resistor 29, from a Schmitt trigger. Normally, the transistor 27 is conductive, and an alarm relay 30 attracted, whereas the transistor 26 is blocked. When the votlage at the charging capacitor 21 reaches the response threshold of the Schmitt trigger 26, 27, the transistor 26 becomes conductive and the voltage drop at a resistor 28 becomes greater, so that the transistor 27 is blocked and the alarm relay 30 drops out. When the charging capacitor 21 has discharged sufficiently, the Schmitt trigger 26, 27 reverts to its normal state, and the alarm relay 30 re-attracts. The Schmitt trigger 26, 27 is preferably so designed that the reversion voltage is substantially lower than the response threshold. The alarm signal is released via a break contact (not shown) of the alarm relay 30.

As may be seen from Figure 2, the emitter and the base of the transistor 27 are connected via the temperature detector 31, represented by a make contact. When the temperature of the acousto-electric transducer 1, which is in contact with the wall of the safe vault, exceeds a predetermined value, the contact 31 closes, the transistor 27 is blocked, the alarm relay 30 drops out, and the alarm signal is released. After the temperature of the acousto-electric transducer 1 has gone back to normal, the contact 31 opens, the transistor 27 becomes conductive, and the relay 30 attracts.

Thus, in the event of a burglary attempt, the apparatus described sets off an alarm not only when mechanical or solid-borne vibrations are produced in the protected object by sawing, filing, drilling, or cutting, but also in the case of an explosion or an attempt to cut through with laser beams, which do not produce mechanical vibrations but only heat.

WHAT WE CLAIM IS: 1. Apparatus for monitoring safes, strong-rooms, vaults, and the like, and for producing an alarm signal in the event of an attempted burglary, comprising an acousto-electric transducer and a first signal path containing an amplifier, a thresholdvalue detector, an integrator connected in after the threshold-value detector, and an output stage for producing the alarm signal, wherein a second signal path comprising a second threshold-value detector and a delay element is connected at the output of the transducer, the first threshold-value detector responding to a transducer-generated signal which is at least one hundred times weaker than the signal to which the second thresholdvalue detector responds, the first integrator causing an alarm-release time-lag of at least five seconds and the delay element causing an alarm-release time-lag of at most 50 milliseconds, and a temperature detector being disposed in the transducer and connected to the output stage for producing the alarm signal when the transducer reaches a predetermined maximum temperature.

2. Apparatus in accordance wtih claim 1, wherein the second signal path further comprises an attenuator for attenuating signals supplied to the second signal path by the transducer.

3. Apparatus in accordance with claim 1, wherein the delay element comprises a second integrator and the first and the second integrator have a common charging capacitor capable of being charged via charging resistors of unequal value, each of the charging resistors being associated with one of the two signal paths.

4. Apparatus in accordance with claim 3, wherein each of the two threshold-value detectors comprises a transistor having a collector-to-emitter path over which the common charging capacitor can be charged.

5. Apparatus in accordance with claim 1, wherein the output stage comprises a Schmitt trigger consisting of an input transistor and an output transistor, the temperature detector being connected in between the emitter and the base of the output transistor.

6. Apparatus in accordance with claim 1, wherein the temperature detector is a temperature-monitoring dry-reed switch.

7. Apparatus in accordance with claim 1, wherein the temperature detector is a bimetal switch.

8. Apparatus in accordance with claim 1, wherein the transducer comprises a piezoelectric cystal or a body of piezoelectric ceramics.

9. Apparatus for monitoring safes, strong-rooms, vaults, and the like, and for producing an alarm signal in the event of an attempted burglary, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. discharged sufficiently, the Schmitt trigger 26, 27 reverts to its normal state, and the alarm relay 30 re-attracts. The Schmitt trigger 26, 27 is preferably so designed that the reversion voltage is substantially lower than the response threshold. The alarm signal is released via a break contact (not shown) of the alarm relay 30. As may be seen from Figure 2, the emitter and the base of the transistor 27 are connected via the temperature detector 31, represented by a make contact. When the temperature of the acousto-electric transducer 1, which is in contact with the wall of the safe vault, exceeds a predetermined value, the contact 31 closes, the transistor 27 is blocked, the alarm relay 30 drops out, and the alarm signal is released. After the temperature of the acousto-electric transducer 1 has gone back to normal, the contact 31 opens, the transistor 27 becomes conductive, and the relay 30 attracts. Thus, in the event of a burglary attempt, the apparatus described sets off an alarm not only when mechanical or solid-borne vibrations are produced in the protected object by sawing, filing, drilling, or cutting, but also in the case of an explosion or an attempt to cut through with laser beams, which do not produce mechanical vibrations but only heat. WHAT WE CLAIM IS:

1. Apparatus for monitoring safes, strong-rooms, vaults, and the like, and for producing an alarm signal in the event of an attempted burglary, comprising an acousto-electric transducer and a first signal path containing an amplifier, a thresholdvalue detector, an integrator connected in after the threshold-value detector, and an output stage for producing the alarm signal, wherein a second signal path comprising a second threshold-value detector and a delay element is connected at the output of the transducer, the first threshold-value detector responding to a transducer-generated signal which is at least one hundred times weaker than the signal to which the second thresholdvalue detector responds, the first integrator causing an alarm-release time-lag of at least five seconds and the delay element causing an alarm-release time-lag of at most 50 milliseconds, and a temperature detector being disposed in the transducer and connected to the output stage for producing the alarm signal when the transducer reaches a predetermined maximum temperature.

2. Apparatus in accordance wtih claim 1, wherein the second signal path further comprises an attenuator for attenuating signals supplied to the second signal path by the transducer.

3. Apparatus in accordance with claim 1, wherein the delay element comprises a second integrator and the first and the second integrator have a common charging capacitor capable of being charged via charging resistors of unequal value, each of the charging resistors being associated with one of the two signal paths.

4. Apparatus in accordance with claim 3, wherein each of the two threshold-value detectors comprises a transistor having a collector-to-emitter path over which the common charging capacitor can be charged.

5. Apparatus in accordance with claim 1, wherein the output stage comprises a Schmitt trigger consisting of an input transistor and an output transistor, the temperature detector being connected in between the emitter and the base of the output transistor.

6. Apparatus in accordance with claim 1, wherein the temperature detector is a temperature-monitoring dry-reed switch.

7. Apparatus in accordance with claim 1, wherein the temperature detector is a bimetal switch.

8. Apparatus in accordance with claim 1, wherein the transducer comprises a piezoelectric cystal or a body of piezoelectric ceramics.

9. Apparatus for monitoring safes, strong-rooms, vaults, and the like, and for producing an alarm signal in the event of an attempted burglary, substantially as hereinbefore described with reference to the accompanying drawings.