Abstract:
A motion detector and a method for detecting a tampering of the motion detector. The tampering can include a spraying or brushing of a lens of the motion detector. The motion detector comprises a lens, a single sensing section for detecting infrared signals within a protected area, and detecting vibrations on the lens in the form of acoustic signals, the vibrations and the infrared signal causing a voltage change in the single sensing section, a first and second amplifier for amplifying the voltage change for processing for tampering and motion, respectively, first and second filter for filtering the voltage change for processing for tampering and motion, respectively, a microcontroller for determining if the detected voltage change is consistent with a pattern that is indicative of tampering or motion and alarm generating section for generating a tamper alarm or a motion alarm based upon the determination by the microprocessor.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to sensors and security systems. More particularly, the present invention relates to a detector that includes a sensing element adapted for detecting a motion within a given area and tampering of the detector. 
       BACKGROUND 
       [0002]    Sensors are used to detect events such as a glass break, motion, asset movement, temperature and impact/shock. These sensors can be used as a standalone device or in combination with a security system. A security system includes a life, safety, and property protection system. The sensors communicate with a control panel when the sensor detects an event. 
         [0003]    Motion sensors or detectors can be masked. Masking of the detector prevents the sensor from correctly detecting motion within a protected area. Spraying or brushing a coating or film on a lens that blocks the infrared signal can mask a detector, such as a PIR sensor. 
         [0004]    Currently, masking is detected by employing multiple sensors to detect signals indicative of the masking. However, this method requires deployment of multiple sensors in an area, where one sensor detects motion and the other sensors are dedicated for the purposes of detecting masking. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention discloses a motion detector that is capable of detecting both masking of a lens and motion within a given protected area. The masking is in the form of spraying or brushing a coating on the lens for the purposes of blocking signals from reaching a sensing element. 
         [0006]    Disclosed is a motion detector for detecting a tampering. The motion detector comprises a lens for focusing infrared signals into an specific area, a sensing section for detecting the focused infrared signals and detecting vibrations on the lens, the vibrations and the infrared signal causes a voltage change in the sensing section, a first amplifier for amplifying the voltage change for processing for tampering, a second amplifier for amplifying the voltage change for processing for motion, a first filter for filtering the voltage change for processing for tampering, a second filter for filtering the voltage change for processing for motion, a microcontroller for determining if the detected voltage change is consistent with a pattern that is indicative of tampering and alarm generating section for generating a tamper alarm based upon the determination by the microcontroller. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text and figures, with like reference numbers referring to like structures across the view, wherein 
           [0008]      FIG. 1  is a block diagram of the motion detector in accordance with an embodiment of the invention; 
           [0009]      FIG. 2  illustrates a block diagram of a microprocessor of the motion detector in accordance with an embodiment of the invention; 
           [0010]      FIG. 3  illustrates a flow chart for the detection method in accordance with an embodiment of the invention; and 
           [0011]      FIG. 4  illustrates a block diagram of a security system with the motion detector in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    In accordance with the invention, the motion detector  100  (as depicted in  FIG. 1 ) is adapted to detect tampering with the motion detector  100 . The motion detector  100  is capable of detecting either a spraying or brushing of a coating on a lens where the spraying or brushing prevents an accurate detection of motion. The motion detector  100  examines or analyzes characteristics of a change in a voltage of a sensing element  110  to determine if a change is indicative of either a brushing or a spraying. 
         [0013]      FIG. 1  illustrates a block diagram of the motion detector  100 . The motion detector  100  includes a sensing element  110 , an optical filter  115 , a lens  120 , a microcontroller  125 , two amplifiers ( 130 ,  135 ), two filters ( 140 ,  145 ) and an indicator  150 . Additionally, the motion detector  100  can include a communication section  155  for transmitting or receiving signals from a security system as will be described in detail later. Additionally, the motion detector  100  will include a power source (not shown). The power source can be an internal power source such as a battery. In another embodiment the microcontroller  125  can perform the filtering without the use of separate filters. In another embodiment, the same amplifier can be used to amplify the signals from both detection channels, i.e., tampering and motion and the microcontroller filters the signal. 
         [0014]    In an embodiment, a Far Infrared (FAR) filter can be used as the optical filter. The motion detector  100  can be a passive infrared detector (PIR). A PIR is responsive to infrared light radiating from objects in a field of view. Motion is detected when an infrared emitting source with one temperature, such as a human body passes in front of a source with another temperature. Motion is detected based on the difference in temperature. The speed of the motion can be detected as a function of the frequencies of the signals received by the sensing element  110 . Other types of motion detectors, which are also shock sensitive can be used. 
         [0015]    In an embodiment of the invention, the sensing element  110  is constructed from a solid-state sensor. More than one solid-state sensor can be used for the sensing element  110 . The sensing element  110  can be manufactured using a material that has both pyro-electric and piezo-electric properties. For example, the sensing element can be constructed from Lithium tantalate (LiTaO 3 ) which is a crystal exhibiting both piezo-electric and pyro-electric properties. However, other materials can be used. Lithium tantalate is presented only as an example and is not an exhaustive list of all of the materials. The sensing element  110  is located within a housing of the motion detector  100 . 
         [0016]    The voltage that is caused by either a spraying or brushing of a coating on the lens is very small and, therefore, the voltage change must be amplified. The voltage change caused by a spraying exhibits different characteristics than a voltage change caused by a brushing. In one embodiment, the gain for the amplification of the voltage change (for tampering processing) is the same for both spraying and brushing. In another embodiment, the gain can be different for the voltage change for spraying and brushing. The gain of the amplifier is variable and can be controlled to vary the sensitivity of the motion detector. For example, a gain can be set at 33000. Amplifier  135  is a dedicated amplifier used to amplify the voltage change for tampering processing. Amplifier  130  is a dedicated amplifier used to amplify the voltage change for motion processing. In an embodiment, the amplification process uses two amplification stages. 
         [0017]    A lens  120  is placed in front of the sensing element  110  to focus the energy onto the sensing element  110 . For example, motion detector  100  can have a Fresnel lens molded externally. The infrared energy or signal will enter the housing of the intrusion detector only through the lens  120 . 
         [0018]    In an embodiment, the lens  120  is adapted to filter the infrared signal. The filter will ideally pass a signal in the range of 750 nm to 1 mm in wavelength, consistent with the “black-body radiation” given off by humans. However, if the lens is sprayed or brushed with a coating, a signal will not pass through. In another embodiment, a separate optical filter  115  (as illustrated in  FIG. 1 ) is placed over the sensing element  110 . The optical filter  115  functions in the same manner as a lens having additional filtering capability. 
         [0019]    Even if a separate optical filter is used, if the lens  120  is sprayed or brushed with a coating, a signal will not pass through. 
         [0020]    The sensing element  110  will exhibit a change in electrical properties such as change in voltage, e.g., voltage change when motion occurs or a spraying or brushing. Specifically, the sensing element  110  exhibits a change in voltage in the presence of vibrations that result from the spraying or brushing, e.g., acoustic signal. 
         [0021]    The microcontroller  125  is configured to determine the source of the change in electrical properties, e.g., motion or tampering, and respond accordingly. The determination is based upon the rate of change, duration, and amplitude of the voltage change. 
         [0022]    The voltage change is processed for motion and tampering using two separate channels, i.e, two different amplifiers and filters. 
         [0023]    Additionally, a filtering occurs for the voltage change. Two filters ( 140 ,  145 ) are used to filter the voltage change. In an embodiment, the filters are bandpass filters which are used to filter two different bands, one band representing a motion and the other band representing a tampering. The voltage change for both spraying and brushing is typically in the same frequency band. In another embodiment, a digital filter can be used to filter the voltage change. 
         [0024]      FIG. 1  depicts that the output of the amplifiers ( 130 ,  135 ) are input into the filters ( 140 ,  145 ). However, in another embodiment, the amplifier ( 130 ,  135 ) and filter ( 140 ,  145 ) can be reversed, i.e., output of the filters ( 140 ,  145 ) input into amplifiers ( 130 ,  135 ). 
         [0025]    The microcontroller  125  receives the amplified and filtered voltage change as an input. 
         [0026]      FIG. 2  is a block diagram of functional blocks in a microcontroller in accordance with an embodiment of the invention. The microcontroller is programmed with software that enables the microcontroller  125  to perform the described functionality herein. As depicted in  FIG. 2 , the microcontroller  125  includes a tampering determining section  200 , a motion determining section  215 , an A/D converter  220 , and a storage section  225 . The tampering determining section  200  includes a spraying determining section  205 , and a brushing determining section  210 . Each determining section ( 205 ,  210 ,  215 ) compares characteristics of a detected voltage change with preset threshold values, i.e., known patterns. 
         [0027]    The storage section  225  includes all preset thresholds, such as rate of change, duration, and the amplitude thresholds for the determining whether the voltage change is indicative of motion or tampering. The storage section  225  can be any type of memory. 
         [0028]    There are three amplitude thresholds: 1 for motion and 2 for tampering. Additionally, there are three duration thresholds: 1 for motion and 2 for tampering. Spraying and brushing exhibits different characteristics and requires two different thresholds. A brushing of a coating may exhibit a longer and stronger voltage change then a spraying. 
         [0029]    As depicted in  FIG. 1 , the indicator  150  outputs a signal indicative of an alarm condition. The indicator  150  can be a light emitting diode (LED), a speaker or a relay. Additionally, a communication section  155  can be used to send an alarm signal  415  or code to a control panel  400  (as depicted in  FIG. 4 ). Additionally, a wired communication path, such as a system communication bus can be used to transmit a code. 
         [0030]    An LED or a speaker is positioned to be a visual or audible signal to a person within a protected premises to notify them of an alarm condition, i.e., motion and/or tampering. The indicator  150  is capable of output at least two different indications, a first indication indicating motion and a second indication indicating tampering. In another embodiment, the indicator  150  can have different indications for spraying and brushing. 
         [0031]      FIG. 3  illustrates a flow chart for an tampering detection method according to an embodiment of the invention. 
         [0032]    At step  300 , a voltage change in the sensing element  110  is detected. In an embodiment of the invention, the voltage change is measured at a source terminal of a source follower. According to an embodiment of the invention, the voltage change is processed in parallel for either motion or tampering. At steps  305  and  305   a , the voltage change is amplified. The amplification for motion is different than the amplification for tampering. In an embodiment, the amplification for motion uses a gain of 10000, whereas the gain for tampering can be 33000. At steps  310  and  310   a , the amplified voltage change is filtered for motion and tampering, respectively. In an embodiment of the invention, two different band pass filters are used, e.g., ( 140 ,  145 ). 
         [0033]    At step  315 , the amplified and filtered voltage changes, i.e., one for motion processing and the other for tampering processing, are converted into a digital signal for processing by a microcontroller  125 . 
         [0034]    At steps  320 ,  320   a  and  320   b , the digitized signals are processed for motion, spraying and brushing, respectively. The processing of the digitized voltage change evaluates the amplitude, frequency, and duration of the detected voltage change. The frequency of a voltage change that is caused by tampering is different from a frequency of the voltage change that is caused by motion. Additionally, as described above, the amplitude and duration of a voltage change that is caused by a spraying of a coating on a lens is different from the amplitude and duration of the voltage change that is caused by brushing. 
         [0035]    At step  320 , the motion determining section  215  processes the digital representation of the voltage change for motion. The motion determining section  215  receives as inputs a digital representation of the voltage change (amplified and filtered) and the preset amplitude and duration thresholds. The motion determining section  215  compares the digital representation of the voltage change with both the amplitude and duration thresholds. If the digital representation of the voltage change is indicative of motion, e.g., meets both thresholds, at step  325 , an alarm is generated, at step  330 . Specifically, the indicator  150  outputs a first signal indicating that motion has been detected. Additionally, the communication section  155  can transmit a first signal to a control panel  400 . 
         [0036]    If at step  325 , the digital representation of the voltage change is not indicative of motion, motion processing phase ends, at step  335 . 
         [0037]    At step  320   a , the spray determining section  205  processes the digital representation of the voltage change for spraying of the lens  120 . The spray determining section  205  receives as inputs a digital representation of the voltage change (amplified and filtered) and the preset amplitude and duration thresholds. At step  320   a , the spray determining section  205  compares the digital representation of the voltage change with both the amplitude and duration thresholds stored in the storage section  225  for spraying. If the digital representation of the voltage change is indicative of spraying, e.g., meets both thresholds, at step  325   a , an alarm is generated, at step  330   a . Specifically, the indicator  150  outputs a second signal indicating that a spraying of the lens  120  has been detected. Additionally, the communication section  155  can transmit a second signal to a control panel  400 . 
         [0038]    If at step  325   a , the digital representation of the voltage change is not indicative of motion, motion processing phase ends, at step  335   a.    
         [0039]    At step  320   b , the brush determining section  210  processes the digital representation of the voltage change for brushing of a coating of the lens  120 . The brush determining section  210  receives as inputs a digital representation of the voltage change (amplified and filtered) and the preset amplitude and duration thresholds. At step  320   b , the brush determining section  210  compares the digital representation of the voltage change with both the amplitude and duration thresholds stored in the storage section  225  for spraying. If the digital representation of the voltage change is indicative of brushing, e.g., meets both thresholds, at step  325   b , an alarm is generated, at step  330   a . Specifically, the indicator  150  outputs a second signal indicating that a spraying of the lens  120  has been detected. Additionally, the communication section  155  can transmit a second signal to a control panel  400 . 
         [0040]    If at step  325   b , the digital representation of the voltage change is not indicative of motion, motion process phase ends, at step  335   a . In another embodiment, if at step  325   b  the digital representation of the voltage change is indicative of brushing, e.g., meets both thresholds, a different alarm signal can be generated, e.g., a third alarm signal. Further, the communication section  155  can transmit a third signal to a control panel  400 . 
         [0041]      FIG. 4  illustrates an exemplary security system with the motion detector  100  according to an embodiment of the invention. 
         [0042]    As depicted, the motion detector  100  can transmit an alarm signal  415  (referenced generically in  FIG. 4 ) to a control panel  400 . As described herein the alarm signal  415  indicates that either motion or a tampering has been detected. In accordance with the invention, a first signal, a second signal, and a third signal can been sent by the motion detector  100  as the alarm signal  415 . Alternatively, the motion detector  100  can transmit the alarm signal  415  to a security system keypad  410 . Additionally, the control panel  400 , upon receipt of the alarm signal  415  can relay the alarm signal to a central monitoring station  405  and a relayed alarm signal  415   a . Additionally, the motion detector  100  may transmit an alarm to a remote keyfob, using the communication section  155 . A property owner will be able to receive alerts and updates regarding a tampering of the motion detector  100  on a bidirectional keyfob. 
         [0043]    The invention has been described herein with reference to a particular exemplary embodiment. Certain alterations and modifications may be apparent to those skilled in the art without departing from the scope of the invention. The exemplary embodiments are meant to be illustrative, not limiting of the scope of the invention, which is defined by the appended claims.