Weight shift detector
First Claim
1. A capacitance activated weight shift detector, especially useful as a security device for detecting intrusion or the like, comprising:
- a mat having first and second sheets of conductive material disposed in superposed positional relationship and a layer of dielectric material disposed intermediate said sheets to maintain the same in separated position even when weight is applied to said mat, said sheets and said intermediate layer forming a capacitor of capacitance dependent on said positional relationship, and said sheets and layer being relatively configured, dimensioned and disposed so that said positional relationship is altered when weight is applied to or removed from said mat;
said positional relationship being altered to give an increasingly greater magnitude of change in said capacitance for an increasingly greater magnitude of weight applied to or removed from said mat; and
electrical circuitry connected to said mat to apply a voltage differential across said sheets and to respond to a change in said capacitance due to alteration of said positional relationship to generate a signal to actuate a desired response, said circuitry including means to give said signal only when said change in capacitance due to application of weight exceeds a first threshold magnitude, or said change in capacitance due to removal of weight exceeds a second threshold magnitude; and
means for enabling independent user selection of said first and second threshold magnitudes.
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Accused Products
Abstract
A device for detecting intrusion for security or inventory control purposes includes a mat having loosely superposed metallic foil sheets separated by a sheet of paper or plastic foil dielectric to form a capacitor, and circuitry connected to provide a voltage differential to the capacitor and to detect a change in capacitance caused by weight applied to or removed from the mat. The circuit includes a voltage regulator to regulate the applied voltage differential, a unity gain amplifier to isolate the mat capacitor from change signal amplifier circuitry, a comparator to compare the amplified change signal with user settable thresholds, and a one-shot multivibrator for initiating an alarm signal pulse when one of the thresholds is exceeded. The sheets are preferably aluminum foil backed with plastic film and, in one form, are wrapped one around the other.
28 Citations
17 Claims
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1. A capacitance activated weight shift detector, especially useful as a security device for detecting intrusion or the like, comprising:
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a mat having first and second sheets of conductive material disposed in superposed positional relationship and a layer of dielectric material disposed intermediate said sheets to maintain the same in separated position even when weight is applied to said mat, said sheets and said intermediate layer forming a capacitor of capacitance dependent on said positional relationship, and said sheets and layer being relatively configured, dimensioned and disposed so that said positional relationship is altered when weight is applied to or removed from said mat;
said positional relationship being altered to give an increasingly greater magnitude of change in said capacitance for an increasingly greater magnitude of weight applied to or removed from said mat; andelectrical circuitry connected to said mat to apply a voltage differential across said sheets and to respond to a change in said capacitance due to alteration of said positional relationship to generate a signal to actuate a desired response, said circuitry including means to give said signal only when said change in capacitance due to application of weight exceeds a first threshold magnitude, or said change in capacitance due to removal of weight exceeds a second threshold magnitude; and
means for enabling independent user selection of said first and second threshold magnitudes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A capacitance actuated weight shift detector, especially useful as a security device for detecting intrusion or the like, comprising:
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a mat having first and second conductive plates superposed in separated positional relationship and a dielectric located between said plates, said plates and dielectric defining a capacitor of a certain capacitance, and said plates and dielectric being relatively configured, dimensioned and disposed so that said sheets remain separated and said capacitance is changed when weight is applied to or removed from said mat; electrical circuitry connected to said mat to apply a voltage differential to said sheets and to respond to said change in capacitance to generate a signal to actuate a desired response, said circuitry comprising voltage regulator means connected for applying a regulated voltage differential from a voltage source to said plates;
means connected for generating a first signal in response to detecting a change in said capacitance;
means connected for amplifying said first signal;
means connected for generating a second signal when said amplified signal exceeds a predetermined threshold magnitude; and
voltage follower means connected to electrically isolate said amplifying means from said means for generating said first signal. - View Dependent Claims (10, 11, 12, 13)
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14. In an intrusion detection system including a mat having first and second sheets of conductive material superposed in spaced positional relationship across a gap and means normally maintaining said sheets in noncontacting relationship, and circuitry connecting said sheets and responsive to a change in said positional relationship due to the application of weight to said mat to provide a signal for activating an alarm or the like, the improvement comprising:
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said means comprising a layer of dielectric material configured, dimensioned and adapted to maintain said sheets in noncontacting relationship, even upon said application of weight, and said layer further being operatively associated with said sheets to define a capacitor having a given capacitance whose magnitude is determined by said positional relationship; and said circuitry being configured and adapted to apply a voltage differential across said sheets, and to detect a change in the magnitude of said capacitance due to a change in said positional relationship to provide said signal; and
said circuitry further including means to provide said signal only when said change in capacitance due to said change in positional relationship exceeds a predetermined threshold magnitude;
user settable means for setting said threshold magnitude; and
a one-shot multivibrator for providing said signal in the form of a timed signal of limited time duration.
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15. A capacitance activated weight shift detector, especially useful as a security device for detecting intrusion or the like, comprising:
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a mat having first and second sheets of conductive material disposed in superposed positional relationship and a layer of dielectric material disposed intermediate said sheets to maintain the same in separated position even when weight is applied to said mat, said sheets and said intermediate layer forming a capacitor of capacitance dependent on said positional relationship, and said sheets and layer being relatively configured, dimensioned and disposed so that said positional relationship is altered when weight is applied to or removed from said mat;
said positional relationship being altered to give an increasingly greater magnitude of change in said capacitance for an increasingly greater magnitude of weight applied to or removed from said mat; andelectrical circuitry connected to said mat to apply a voltage differential across said sheets, to establish a reference value corresponding to an initial positional relationship, and to respond to a change in said capacitance from said reference value to an altered value due to alteration of said positional relationship from said initial positional relationship to generate a signal to actuate a desired response when said change in capacitance due to application of weight exceeds a first threshold magnitude, or said change in capacitance due to removal of weight exceeds a second threshold magnitude; and
means for terminating said signals and for establishing said altered value as said reference value if said altered positional relationship is maintained for a predetermined time increment. - View Dependent Claims (16, 17)
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Specification