The field of the invention relates to intrusion detection devices and more particularly to passive infrared sensors.
Passive infrared (PIR) sensors or passive infrared detectors (PIDs) are generally known. Such devices find ready use as intrusion detectors in security systems.
A PID device detects intrusion via the infrared radiation emitted by humans. However, PID devices suffer from the difficulty of not being able to differentiate between humans and animals or in not being able to detect humans against hot background surfaces.
One particular type of PID devices is a PID motion detector. A PID motion detector uses a pair of infrared detectors arranged to scan adjacent areas. In this regard, the pair of detectors may be connected in series so that when both areas have the same background temperature, the signal from the one will cancel the signal from the other.
PID motion detectors have been found to be considerably more reliable than when PID detectors are used individually. Since the PIDs of a motion sensor are connected to cancel one another, motion detectors are less vulnerable to transients. For example, flashes of light (e.g., lightning) detected by the pair of detectors is canceled.
Moreover, if a human should appear in one of the two areas, the PID detector on that side would detect the human via the difference in temperature between the human and the background. More importantly, when the human passes from the first of the pair of adjacent areas to the second area, the signal from the pair of detectors will reverse thereby indicating a direction of travel of the human through the pair of areas.
While PID motion detectors are a significant improvement, they are still subject to false alarms. Accordingly, a need exists for more reliable PID motion detectors.
Under one illustrated embodiment, the environmental detector 10 may be provided with one or more optical or sound sensors 110, a vibration or shock sensor 150, a processor 130 and signal processing devices (e.g., amplifiers, filters, etc.) 120, 140. The sensor 110 and vibration sensor 150 may be physically attached to a housing 23 of the PID sensor 10.
The micro processing unit 130 depicted in
In one particular example, the device 10 may be a PIR motion sensor. In this example, the processor 130 receives signals from the one or more PIR sensors 110 and from the vibration sensor 150 and each time the PID motion detector 10 detects an intruder within the secured area 12, the processor 130 sends a motion detected message to a control panel 14 of a security system that protects the secured area 12. The control panel may respond by triggering a local audible or visual alarm and/or notify a local police department.
It has been found that optical (e.g., PID motion) sensors are vulnerable to false alarms triggered by vibration or mechanical shock. Vibration or shock in this case may be created by a person striking the wall on which the PID motion sensor is mounted or slamming a door in the area of the sensor.
Under an illustrated embodiment, the PIR motion detector 10 has at least two operating modes including a first mode where the detector 10 operates under control of the PIR detectors 110 and a second mode where the output of the detectors 110 are blocked. Control of the modes of the detector 10 may be based upon signals processed by one or more of the programmed processors 16 of the processing unit 130.
In this regard, a mode processor of the processing unit 130 may receive signals from one or more signal processors coupled to each of the PIR sensors 110 and vibration sensors 150 and respond accordingly. For example, one of the signal processors may be a PID signal level processor that receives signals from the PID sensors 110, filters and compares the output with a detection threshold to detect the presence of an intruder. The mode processor may also monitor the output of the signal level processor for a signal reversal indicating a direction of travel of the intruder. In the first mode, the mode processor may transmit a message indicating the presence and direction of travel of the intruder through the output 22 of the detector 10 to the control panel 14.
Another one of the signal processors may be a vibration processor that receives signals from the vibration sensor 150 and that processes these signals to determine a type and severity of the vibration. Based upon the type and severity of the vibration, the mode processor may cause the motion detector 10 to switch between the first and second modes.
The bottom line of
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In the case where the vibration detector 150 is an analog device (e.g., an accelerometer), the processor may use a voltage method that compares the amplitude of the voltage of each sample with a vibration threshold value. Alternatively, a level method may be used where the vibration detector 150 is digital device that provides a contact closure type of output for each sample above a threshold value (i.e., each time the vibration detected by the vibration detector 150 exceeds a threshold value). In either case, the vibration processor may collect the number of samples (m) above the threshold for each time period into a sample file. After each sample above the threshold is added to the file, the processor increments a counter 345 and processes the next sample.
At the end of the time period, a comparator of the processor may compare 340 the number (m) of samples above the threshold value during the time period with a vibration activity threshold value. If the number (m) of samples above the threshold value exceeds the activity threshold value, then the processor may instruct the mode processor to enter the second mode blocking the output of the PID motion sensor 10. If the number of samples (m) is below the activity threshold, then the process repeats.
Under another illustrated embodiment, the vibration processor includes an averaging processor that averages the magnitude of a set of accelerometer readings over some number of samples (time m). In this case, if the number of samples averaged is less than m, then the vibration process selects 345 another sample and the process repeats. At the end of the time period m, the average is compared with a vibration amplitude threshold value. If the average is above the threshold then, the device 10 goes into the second mode, blocking the PID motion detection output. If not, then the process repeats.
In a motion detector 10, the first PIR sensor 410 would be directed to a first portion of the secured area 12. A second PIR sensor 410 would also be used to cover a second portion of the secured area 12 directly adjacent to the first portion.
As noted above, a first set of signal processors (of the processing unit 420) would be coupled to the PIR sensors 410 covering the first portion of the area 12 and a second (or same) set of signal processors (of the processing unit 420) would be coupled to the PIR sensor 410 covering the second portion of the area 12. A comparator would receive the processed signals from the first and second set of signal processors and process the signals to detect intruders and direction of travel of the intruders based upon the signal changes from the two PIR detectors 410.
Signals from the PIR sensors 410 and vibration sensors 430 may be processed as discussed above. In the case where three vibration sensors 430 are used, then a first threshold may be used for each individual sensor 430 to trigger the transition to the second mode as well as a cumulative threshold that is compared to the sum of the values from the three sensors 430 to trigger blocking of the output.
The motion detector 10 provides an advance in the technology of environmental detection on any of a number of different levels. The techniques described above in conjunction with
In general, the environmental detector 10 includes an environmental sensor that detects security threats within a secure area, a shock detector that detects vibration of the environmental sensor and a processor that receives an signal from the environmental detector, processes the signal and provides a threat detected signal in response to the signal from the environmental detector wherein the processor also processes a signal from the shock detector, detects vibration and blocks the threat detected signal during the detected vibration.
In other embodiments, the environmental detector includes a passive infrared sensor that detects intruders within a secure area, a shock detector that detects vibration of the passive infrared sensor and a processor that receives an signal from the passive infrared sensor, processes the signal and provides an intruder detected signal in response to the signal from the passive infrared sensor wherein the processor also processes a signal from the shock detector, detects vibration and blocks the intruder detected signal during the detected vibration.
In still other embodiments, the environmental detector includes a pair of passive infrared sensors that detect intruder motion, a shock detector that detects vibration of the passive infrared sensors and a mode processor that receives an intruder detected signal from the passive infrared sensors and a signal from the shock detector, provides a motion detected signal as an output in response to the signal from the passive infrared sensors and blocks the motion detected signal upon detecting vibration from the shock detector.
Although a few embodiments have been described in detail above, other modifications are possible. For example, the logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be added to, or removed from, the described systems. Other embodiments may be within the scope of the following claims.