ENVIRONMENTAL TEST SWITCH FOR INTRUDER DETECTION SYSTEMS

• US 3,838,408 A
• Filed: 02/09/1973
• Issued: 09/24/1974
• Est. Priority Date: 02/09/1973
• Status: Expired due to Term

• Current Assignee: Richard Laverne Mcmaster
• Original Assignee: Richard Laverne Mcmaster
• Inventors: McMaster, Richard LaVerne
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/331,202
• Time in Patent Office: 592 Days
• Field of Search: 340/258R,258B,258A,214,410,261
• US Class Current: 340/501
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits
• CPC Class Codes: G08B 17/00 Fire alarms; Alarms responsive to explosion
• CPC Class Codes: G08B 29/185 Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system

Abstract

A method and apparatus for optimizing the sensitivity of intruder and fire detection systems for a predesired margin of safety against false alarming. The apparatus comprises means for selectively increasing the system sensitivity by a calibrated amount above an optimum operating level, and means for adjusting the selectively increased system sensitivity, to a level at which the system just responds (or just fails to respond) to the background noise level. Thus, when the sensitivity is returned to its normal operating level, a built-in margin of safety is provided against false alarming from noise signals.

Claims

1. For use in a detection system for sensing the occurrence of an event of interest amid a variety of sources of background noise, the system comprising means for distinguishing electrical signals characteristic of the event of interest from electrical signals characteristic of background noise, and means for activating an alarm in response to the sensing of an electrical signal having an amplitude which rises above or drops below a predefined threshhold level, the improvement comprising, in combination:

switch means for temporarily increasing the level of sensitivity of the system by a predesired factor above an initial level; and

means for setting the sensitivity of the system, at a time when said switch means is effective to produce such a temporary increase in sensitivity, to a level at which electrical signals characteristic of background noise have an amplitude substantially equal to said threshold level of the activating means, whereby the system sensitivity, upon being unaffected by said switch means, is set at a level which provides a predesired margin of safety against alarming due to background noise signals.

2. In an intruder detection system comprising means for transmitting energy waves into a region wherein intrusion is to be detected;

means for receiving said transmitted energy waves upon being reflected and/or modified by objects within said region and for converting said energy waves into a first electrical signal having an instantaneous amplitude and frequency proportional to that of the resultant energy wave received;

detecting means for generating a second electrical signal in response to changes in said first electrical signal;

integrating means operatively coupled to said detecting means for smoothing out rapid variations in the amplitude of said second electrical signal, the degree of such smoothing being governed by the time constant of the integrating circuit, and a threshold sensor operatively coupled to said integrating means for activating an alarm when the amplitude of said second electrical signal exceeds a predefined threshold level, the improvement comprising, in combination;

switch means operatively coupled to said integrating means for temporarily decreasing the time constant of said integrating means by a predetermined factor, thereby temporarily increasing the sensitivity of the system by a predefined factor; and

means operatively coupled to said receiving means for adjusting the amplitude of said first electrical signal, at a time when said switch means is effective to temporarily increase the system sensitivity and when no intruder is present in said region, to a level at which background noise is just effective to produce alarm activation, whereby the system sensitivity, upon being unaffected by said switch means, is set at a level which provides a predesired margin of safety against alarming due to signals characteristic of only background noise.

3. In an intruder detection system comprising means for transmitting energy waves into a region wherein intrusion is to be detected;

means for receiving said transmitted energy waves upon being reflected and/or modified by objects within said region and for converting said energy waves into an electrical signal having an instantaneous amplitude and frequency proportional to that of the resultant energy wave received;

threshold-sensing means operatively coupled to said receiving means for transmitting an alarm activating signal in the event the amplitude of said electrical signal exceeds a predefined threshold level;

the improvement comprising, in combination;

switch means operatively coupled to said threshold-sensing means for temporarily reducing the threshold level of said threshold-sensing means by a predetermined factor, thereby temporarily increasing the sensitivity of the system by said predetermined factor; and

means operatively coupled to said receiving means for adjusting the amplitude of said electrical signal, at a time when said switch means is effective to temporarily increase the system sensitivity and when no intruder is present in said region, to a level at which background noise is just effective to produce alarm activation, whereby the system sensitivity, upon being unaffected by said switch means, is set at a level which provides a predesired margin of safety against alarming due to signals characteristic of only background noise.