Sentrol, Inc.

Richard A Smith

Christopher A Bernhardt

A glass break detector system (10) includes a low frequency (LF) detector (28) that is responsive to a pressure wave transducer (12) to detect the amplitude of a low frequency, generally sinusoidal acoustic wave signal resulting from a physical contact with a glass window. The LF detector includes a peak analyzer (42) that compares absolute values of sequential first and second amplitudes (P1, P2) of a low frequency signal derived from the low frequency acoustic wave signal to determine an appropriate alarm response. The LF detector enables the alarm if the absolute value of the first amplitude (P1) is greater than the absolute value of the second amplitude (P2) or if P1 or P2 amplitudes exceed saturation thresholds. The LF detector also includes a slope analyzer (40) that determines whether the low frequency signal exhibits atypical characteristics that generally indicate glass breakage. The detector system includes mid-frequency and high frequency signal processing circuits to further reduce susceptibility to false alarms.

Glass break detector having reduced susceptibility to false alarms

A glass break detector for detecting the breaking of a window or the like includes an acoustic transducer having a wide band frequency response, coupled to a dual channel filter and signal processing circuit. A low frequency channel detects an initial positive compression wave caused by the inward flex of the window and a high frequency channel detects the acoustic spectrum which is characteristic of breaking glass. The two channels are combined in a logic circuit that is timed so that the low frequency positive flex is detected initially with the high frequency component following shortly thereafter. If both timing conditions are fulfilled, an alarm is initiated. Additional circuitry is provided to inhibit the alarm if a negative compression wave is initially detected. The detection sequence is initiated by a loud sound characteristic of breaking glass.

Growing community of inventors

Portland, OR, United States of America

Richard A Smith