Communications – electrical: acoustic wave systems and devices – Echo systems – Presence or movement only detection
Patent
1982-01-07
1985-02-12
Swann, III, Glen R.
Communications, electrical: acoustic wave systems and devices
Echo systems
Presence or movement only detection
340552, 343 5PD, G08B 1316
Patent
active
044995644
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an ultrasonic surveillance system and, more particularly, to an ultrasonic surveillance system utilizing pulse-like ultrasonic waves.
2. Background Art
Ultrasonic waves have often been utilized for modern surveillance systems which produce alarms when an unauthorized person enters into predetermined areas. There has heretofore been proposed an ultrasonic surveillance system of this type utilizing the Doppler effect. According to this system, ultrasonic waves of a predetermined frequency are continuously emitted into an area under surveillance which may be in a room, and when frequency components different from the predetermined frequency are detected being superposed on the waves which are reflected by the objects in the area under surveillance, the presence of said unauthorized person in the area under surveillance is detected, and the alarm, such as a buzzer, is energized. Such a system utilizes the Doppler effect, according to which the frequency of the reflected waves increases when an object approaches the ultrasonic wave emitter, and the frequency of the reflected waves decreases when an object moves away from the ultrasonic wave emitter. In order for the alarm not to operate even when ultrasonic waves (hereinafter referred to as ultrasonic noise) generated by a telephone bell or a bell of fire alarm have infiltrated into the reflected waves, in other words, in order to prevent the alarm from being erroneously operated by ultrasonic noise, the above-mentioned system has been so designed that the received signals are detected in a frequency-modulated manner and are allowed to pass through a low-pass filter to remove the frequency components caused by the ultrasonic noise, since the frequency components (period in the change of frequency) of the ultrasonic noise are much greater than the frequency components of the reflected waves.
There has also been proposed an ultrasonic surveillance system utilizing pulse-like ultrasonic waves. According to this system, pulse-like ultrasonic waves are emitted to an area under surveillance, waves reflected by the objects in the area under surveillance are received to compare the pattern of the reflected waves with a predetermined reference pattern statistically, and an alarm is produced when the two patterns are not in agreement. With this system, however, the ultrasonic noises are not removed even when the received signals are allowed to pass through the low-pass filter, since the frequency components of ultrasonic noises are superposed on the frequency components of reflected waves. Therefore, when the ultrasonic noises infiltrate into the reflected waves, the pattern of the reflected waves is changed to erroneously produce the alarm. Accordingly, in a room where ultrasonic noises are likely to be produced, a limitation is imposed on the place for installing such a surveillance device. Further, even if it is installed at a position which is considered to be acceptable, the surveillance device may erroneously operate, thus decreasing the reliability of the device.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide an ultrasonic surveillance system having high reliability, which will not be erroneously operated by ultrasonic noises that are generated by a telephone bell or by a bell of a fire alarm.
According to the present invention, there is provided an ultrasonic surveillance system comprising a transmitter means which transmits pulse-like ultrasonic waves to an area under surveillance, receiving means which receives ultrasonic waves reflected from the area under surveillance and which subjects the signals of ultrasonic waves to analog-to-digital conversion, and a first operation processing means which compares a pattern of reflected waves established by the digital signals sent from the receiving means with a reference pattern statistically and which produces an alarm signal when the two patterns are not in agreement, wherein the improvement is characterized by the pro
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Secom Co., Ltd.
Swann III Glen R.
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