Detector-array with mask warning

Details Detector-array with mask warning Detector-array with mask warning

1999-07-12

2001-05-29

Pope, Daryl (Department: 2632)

Communications: electrical

Condition responsive indicating system

With particular system function

Reexamination Certificate

active

06239698

ABSTRACT:

The present invention relates to sensors using detector arrays for identifying the occurrence of events. Such sensors have a variety of applications including flame detection and movement detection. Sensors designed for movement detection are used in security systems and simple examples are the well-known passive infra-red (PIR) intruder detectors. PIR devices detect movement and generate a corresponding alarm signal but they do not give any spatial information within their field of view. We have therefore proposed a sensor which comprises an array of detectors, preferably thermal detectors, with read-out means which monitor signals from each of the various detectors of the array independently and can then identify the occurrence of events by comparison of these signals. Such a sensor provides more information than known PIR devices but has the advantage of being simpler and cheaper to manufacture than known thermal imaging systems, in part because no thermal image is actually provided. A disadvantage of all PIR detectors is that if they are masked in some way, for example by covering them with fabric or by spraying paint over them, they cease to function. The present invention aims to enable the detection of such an event.
With a two dimensional array of thermal detectors, used without chopping the incident radiation, under normal conditions a scene would be focused onto the array and any thermal changes in each area of the scene would be focused onto the corresponding area of the array. With no thermal changes generated by movement or other activity in the scene, the output from the array would be limited to background noise or clutter.
In the event that an attempt was made to disable the sensor for example by covering the sensor with a mask such as a sheet of fabric, or such as paint sprayed across a viewing window, all or the majority of the detector elements would simultaneously detect a significant change in signal. This transient change would take place in the time taken to put the mask in place or the thermal time constant of the detector, whichever is the greater, and might be expected to lie between 0.1 and 10 seconds. Once the mask was in place there would only be background level noise or clutter from each detector. The reservation that not necessarily all but the majority of the detectors exhibit the simultaneous transient signal is made to allow for the coincidence that the temperature and emissivity of a part of the scene and of the mask may be such that no signal results from some of the detectors as the scene is replaced by the mask.
With the foregoing in mind the present invention provides a sensor comprising a two dimensional array of detectors and means for focusing radiation from a scene onto the array, read-out means for monitoring signals from all of the detectors, and means for generating a warning signal. A warning signal is generated in response to a change of signal from a majority of the detectors of the array occurring within a predetermined time period, said warning signal indicating masking of all or part of the sensor. In normal (unmasked) operation, signals from the detectors are monitored whereby to identify other events occurring within the scene.
The masking of a sensor would result in many or all of the detectors simultaneously producing a significant change in signal. This warning condition may be contrasted with the alarm signals generated by an intruder when adjacent elements of the array give successive signals as the intruder moves across the scene, or alarm signals generated by a fire when signals continue to be generated by one element and may spread to adjacent elements successively as the fire itself spreads.
Preferably the warning signal is generated when the signals from a majority of the detectors change by an amount above a predetermined threshold.
Bearing in mind that the masking would usually be followed by background noise only, preferably the warning signal is generated only when a signal within a predetermined time period from a majority of the detectors is followed by a period when these detectors produce only background noise or clutter below a predetermined background value.
It should be noted that the invention can also be used to provide a warning of partial masking if the sensor were to be disabled by a deliberately or inadvertently positioned obstruction. For example if the sensor is mounted in a warehouse it could be inadvertently “blinded” by a tall stack of pallets placed in front of it. In such applications it would again be necessary to specify signals above a threshold from a majority of the detectors, preferably followed by a period of only background noise or clutter from these detectors.
The “majority” may be a numerical majority, eg. more than 50 percent of the total number of detectors, or it may be a subset of the total number of detectors which are adjacent to each other and which cover an area which is larger than the typical “area” of an event to be detected. This latter approach takes account of the fact that a mask or obstruction would effect an area of adjacent detectors ie: a smaller array within the entire array.
Alternatively, a warning signal may be generated in response to a change in signal within a predetermined time period from a majority of detectors within a defined sub array of the sensor, ie. a smaller area within the entire array.
The majority may be defined as a large majority, eg 75 percent or more.
In preferred embodiments of this invention the detector array is formed of thermal, e.g. pyroelectric, detector elements, and is mounted directly onto a silicon integrated circuit which interrogates the output from each element.


REFERENCES:
patent: 5499016 (1996-03-01), Pantus
patent: 2308482 (1977-06-01), None
patent: 2071641 (1981-09-01), None
patent: 2117897 (1983-10-01), None
patent: 2135769 (1984-09-01), None
patent: 0481934 (1992-04-01), None
patent: 0499177 (1992-08-01), None
patent: 0507025 (1992-10-01), None
patent: 0556898 (1993-08-01), None
patent: 0772171 (1996-10-01), None

Affiliated with

Also associated with

Rating

Detector-array with mask warning does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Detector-array with mask warning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Detector-array with mask warning will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2561286