US 5,323,141 A · Glass break sensor having reduced false alarm probability for use with intrusion alarms

Abstract

A sensor has a reduced probability of generating a false alarm in the presence of a strong high frequency acoustic wave, such a false alarm being caused by the saturation of the microphone which is part of a single microphone glass break sensor. The sensor improves an alarm system's immunity to false alarms by using two microphones instead of one, wherein each microphone is used in combination with a filter and a signal processing stage to detect one of the characteristic components of an acoustic wave generated in a glass break event. The microphone used to detect the low frequency component is fitted with an acoustic filter which attenuates the high frequency component of the wave. This reduces the probability of a false alarm by ensuring that the low frequency electrical signals fed to the alarm system's logic and timing circuit are generated by an external event rather than by the microphone itself.

Claims9

Dependent claims

A glass break sensor for use in an intrusion alarm system which detects an intrusion by sensing an acoustic wave produced by a glass break event, said acoustic wave having a low frequency component, the sensor comprising:

first detecting means for detecting said acoustic wave and for generating a first electrical signal in response thereto;
first processing means for receiving said first electrical signal and for processing said first electrical signal to produce a processed first electrical signal;
second detecting means for detecting only said low frequency component of said acoustic wave and for generating a second electrical signal in response thereto;
second processing means for receiving said second electrical signal and for processing said second electrical signal to produce a processed second electrical signal;
and
logic means for receiving said processed first and second electrical signals and for generating an alarm signal in response thereto.

3 more elements

first detecting means for detecting said acoustic wave and for generating a first electrical signal in response thereto;
first processing means for receiving said first electrical signal and for processing said first electrical signal to produce a processed first electrical signal;
second detecting means for detecting only said low frequency component of said acoustic wave and for generating a second electrical signal in response thereto, wherein said second detecting means further comprises:
low pass acoustic filter means for receiving said acoustic wave and for passing said low frequency component of said acoustic wave therethrough;
and
microphone means attached to said acoustic filter means for receiving said low frequency component of said acoustic wave and for generating said second electrical signal in response thereto;
second processing means for receiving said second electrical signal and for processing said second electrical signal to produce a processed second electrical signal;
and
logic means for receiving said processed first and second electrical signals and for generating an alarm signal in response thereto.

6 more elements

Dependencies are inferred from the claim text.

Glass break sensor having reduced false alarm probability for use with intrusion alarms

Life of this patent

Glass break sensor having reduced false alarm probability for use with intrusion alarms

Life of this patent

Abstract

Claims9