| 摘要 |
<p>An ultrasonic surveillance system which emits pulse -like ultrasonic waves to an area under surveillance, which statistically compares a reflected-wave pattern established by receiving ultrasonic waves reflected from the under surveillance with a predetermined reference pattern, and which produces an alarm signal when these two patterns are not in agreement. In order to exclude ultrasonic noise having a relatively small amplitude from the reflected-wave pattern, a difference component between a pattern of frequencies of emitted ultrasonic waves and a pattern of the other frequencies is used as the reflected pattern. The frequency components other than those of emitted ultrasonic waves are integrated and, when the integrated value exceeds a predetermined value, the transmission of an alarm signal is interrupted so as to prevent the system from being erroneously operated by ultrasonic noise having a large amplitude. The number of peak values in the reflected pattern is counted and, when the counted value exceeds a predetermined value, the transmission of an alarm signal is also interrupted.</p> |
