ULTRASONIC VOLUMETRIC ALARM SYSTEM

Abstract: Volumetric alarm system based on ultrasonic waves wherein the signal picked up by the receiving station is returned in an amplified form and, on reaching the receiving station, is retransmitted after further amplification, and so on, the phenomenon being continuous and repeated in each cycle, there being created, due to the fact that, while crossing the protected area, the various frequencies composing the signal undergo varying attenuation in relation to a prevailing frequency, a resonance of the entire system on said prevailing frequency which is automatically selected from among the other frequencies, thus further creating a broad signal which is always present, reliability of the system being thereby considerably improved.

Description: ULTRASONIC VOLUMETRIC ALARM SYSTEM The invention concerns an alarm system to prevent the entry of intruders inside an enclosed space. Volumetric alarm systems signal the presence of intruders inside enclosed spaces by detecting the forms of disturbance made by said intruders. Systems based on ultrasonic waves use the Doppler effect .ac- cording to which a change of frequency occurs in an ultra¬ sonic signal when it encounters a moving object. The volume to be protected becomes filled with stationary waves that form a complex 'tangle' because of the way they reflect against the various surfaces within the enclosed space. When the variation in frequency of the return signal , caused by the intruder, reaches the receiving station, it is amplified, filtered and utilized to set off the alarm. The signal picked up by the receiving station is composed of the reflections of the signal emitted by the transmitting station. Therefore, if the signal's frequency is fixed, the environmental changes due to thermal expansion or to other causes may make the system unreliable. Particularly in quartz systems it may happen that, in certain circumstances, the signal picked up by the receiving station is equal to zero thus simulating an act of sabotage which in fact has not occurred. , The above invention improves the reliability and efficiency of alarm systems as will be explained below. Subject of the invention is a volumetric alarm system based on ultrasonic waves in which the signal picked up by the re ¬ ceiving station is re ransmi ed in amplified form by an electronic circuit. On returning to the receiving station, the amplified sig¬ nal becomes further amplified, and so on by continuous and cyclic repetition of the phenomena and by creation of reso- nance. Amplification is preferably attained in three stages. Since, when passing through the enclosed space, the frequen¬ cies forming the signal are varyingly attenuated in relation to a prevailing frequency, resonance occurs on said prevail- ing frequency which is selected automatically from among the component frequencies. If the prevailing frequency becomes attenuated by environ¬ mental variations, thermal expansion or other causes, it will be automatically replaced in the electronic circuit by another which will become the new prevailing frequency. The signal issuing from the circuit that extracts modula¬ tion in amplitude, is filtered to eliminate unwanted sig¬ nals, such as very slow or very rapid variations. Modulation of amplitude, provoked by the presence of an intruder in the enclosed space, is compared in another circuit for this purpose having a reference threshold which can be regulated by the user. The pulse generated by the presence of an intruder deter¬ mines the charge of a certain capacitor in the circuit. A fixed reference threshold is exceeded and the alarm is set off when said capacitor is charged with at least three pulses within a restricted time. By means of the system described above, the presence of a broad signal is assured at the receiving station irrespec- tive of the position of the stations. Reliability and efficiency of the system are considerably improved since practically all uncertain ies and false alarms connected with the systems at. present known are eli¬ minated . If the signal at the receiving station is zero, any simulta¬ neous lack of resonance signal in the circuit would show that non-functioning of the signal was due to malicious cau¬ ses, different therefore from accidental causes. A description, accompanied by an electronic diagram, explains one example of execution of the invention. Fig. 1: Electronic wiring of the system subject of the in.- vention. As shown by the symbols and connecting lines, the circuit in Fig. 1 comprises block A with three amplifiers 12, 13, 14 that amplify the signal picked up by receiving station 10. Said amplified signal, retransmitted by the emitting station 11, returns to the receiving station 10 and is. further ampli ¬ fied arid retransmitted, repetition of said phenomena being continued ad infinitum and a phenomenon of resonance being thereby created. As the signal ,emitted by the transmitting station 11, is formed of frequencies which, when crossing the enclosed space, are subject to varying degrees of attenuation in relation to a prevailing frequency whose amplitude prevails over that of the others, the resonance of the whole system will be established on said prevailing frequency. The signal received and progressively amplified by the recei¬ ving station 10, passes over to block B that extracts the change in amplitude of said signal in accordance with the movements made by objects within the enclosed space. This signal is filtered in block C for elimination of any false signals such as the very slow variations due to move¬ ment of air or the very rapid ones due to disturbance on the feed l ine . The signal passes from the filtering block C to block B where it is compared to a reference which can be regulated by the user. If said reference is exceeded, at the output of block B a zero voltage peak will occur which is passed on to mono- stable block E. For each pulse received, said circuit E supplies a positive pulse at its output equivalent to a time pre-set by compo- nents 15 and 16. Said pulses go to charge a capacitor 17 in block F. In circuit G the charge value of this capacitor is compared with the fixed reference threshold determined by components 18 and 19. If this threshold is exceeded after three pulses the alarm is set off. Detection of possible sabotage is made by evaluating the am¬ plitude of the signal at the output of block B. If said signal falls below the level of a pre-es ablished reference with simultaneous lack of the phenomenon of resonance, the circuit gives the alarm.

Claims: CLAIMS 1. Volumetric alarm system based on ultrasonic waves com¬ prising a transmitting station and a receiving station characterized in that the signal picked up by the receiving station is amplified before retransmission and, on return- " ing to the receiving station, is further amplified before being retransmitted again, and so on, this phenomenon being continuous and repeated in each cycle and, because the var¬ ious frequencies composing the signal crossing the enclosed space are varyingly attenuated in relation to a prevailing frequency, a resonance of the whole system is created on said prevailing frequency, selected automatically in rela¬ tion to the component frequencies, said prevailing frequency being automa ically replaced by another frequency if, due to environmen al variations caused by thermal expansion or by other factors, the first prevailing frequency becomes at¬ tenuated . 2. Alarm system as in claim 1, characterized in that the signal picked up by the receiving station passes through three stages of amplifica ion. 3. Alarm system as in claim 1, characterized in that the signal at the output of the cir¬ cuit that extracts modulation in amplitude, is filtered for elimination of unwanted signals such as very slow or very rapid variations. 4. Alarm system as in claim 1, characterized in that the modulation of amplitude caused by the presence of an intruder inside the protected area, is compared in a special circuit with a reference threshold that can be regulated by the user. 5. Alarm system as in claim 1, characterized in that the modulation of amplitude caused by the presence of an intruder within the protected area determines production of a pulse that charges a capacitor, placed in the circuit for that purpose, so that the fixed threshold of reference is passed and the alarm is given if the charge of said capacitor is completed with at least three pulses within a restricted time.

Inventors: BRUSA PIETRO, PETTINAROLI ROSITA, BRUSA, PIETRO, PETTINAROLI, ROSITA
Applicants: BRUSA PIETRO, PETTINAROLI ROSITA, BRUSA, PIETRO, PETTINAROLI, ROSITA
Application year: 1989
Main classification: G08B13
IPC codes: G01S15, G08B13