Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-03-10
2001-10-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06307200
ABSTRACT:
TECHNICAL FIELD
The present invention relates to passive infrared (PIR) motion detectors and, more particularly, to amplifier circuitry for processing signals generated by a PIR sensor.
BACKGROUND
In many security systems, PIR motion detectors are distributed within a monitored area to detect intruders, e.g., for commercial or home security applications. A PIR motion detector is typically mounted on a wall, in a comer of a room, or on a ceiling, to detect motion in a monitored area. A PIR motion detector includes a PIR sensor that generates a sensor signal representing a change in infrared energy, thereby providing an indication of intruder motion within the monitored area. The PIR motion detector typically includes an amplifier circuit that amplifies the sensor signal for analysis. The amplified sensor signal is analyzed by comparison to an amplitude threshold that corresponds to the presence of an intruder.
The output of a PIR sensor can be susceptible to drift, and can introduce dc offset to the sensor signal. Drift can result from environmental effects or component aging. Also, the level of dc offset produced by different PIR sensors can vary due to differences in manufacture or materials. With the introduction of significant dc offset, the amplified sensor signal can communicate inaccurate information relative to the pertinent threshold, causing false alarm triggering or inhibiting proper alarm triggering. Thus, substantial dc offset can cause false triggering when no intruder is present in the monitored area. Also, dc offset can boost sensor signals that ordinarily would fall below the threshold, e.g., signals generated based on the presence of pets or other small animals. In either case, the result is an inability to accurately detect intruders and take appropriate action.
To improve accuracy, PIR motion detectors typically incorporate ac-coupled amplifiers that eliminate dc offset from the PIR sensor signal prior to amplification. AC-coupling also serves to normalize the range of output levels produced by different sensors. The use of ac-coupled amplifiers drives up the cost and complexity of the PIR motion detector, however, due to the need for additional components. Also, ac-coupled amplifiers can be susceptible to “overshoot” problems that undermine the accuracy of the sensors. For example, an ac-coupled amplifier can suffer from overshoot when the PIR sensors generate a strong signal change, and particularly when the amplifier saturates.
Following a significant signal excursion, the amplifier must drive itself back toward a steady state condition. With insufficient damping, the amplifier can be driven beyond steady state and into an overshoot condition. For example, instead of returning from a negative signal excursion to a reference level, the amplifier output may substantially exceed the reference level. A substantial overshoot, when compared to the pertinent alarm threshold, can be misinterpreted as a security event. Consequently, like dc offset, overshoot in the sensor signal produced by an ac-coupled sensor signal can cause false triggering situations.
SUMMARY
The present invention is directed to a PIR sensor apparatus and method that make use of a dc amplifier circuit. The PIR sensor apparatus can be incorporated in a PIR motion detector. The dc amplifier circuit amplifies a dc-coupled sensor signal generated by a PIR sensor for analysis. Each PIR sensor produces a characteristic dc output voltage, along with a signal that varies with the level of infrared energy in the monitored area. This dc output voltage will be referred to herein as dc offset. For improved accuracy, the dc amplifier circuit compensates for the dc offset of the sensor signal. Compensation, as used herein, refers to eliminating, reducing, canceling, or otherwise alleviating adverse effects of the dc offset on sensor signal accuracy. Also, the dc amplifier circuit generally does not suffer from the overshoot problems associated with ac amplifier circuits. In this manner, the dc amplifier circuit is capable of reducing false triggering or inhibited triggering incidents and improving triggering accuracy.
In one embodiment, the present invention provides a passive infrared (PIR) sensor apparatus comprising a PIR sensor that generates a sensor signal, an amplifier, dc-coupled to the PIR sensor, that amplifies the sensor signal, and a circuit that compensates for dc offset in the sensor signal.
In another embodiment, the present invention provides a method for processing a passive infrared (FIR) sensor signal comprising dc coupling a sensor signal from a PIR sensor to an amplifier, amplifying the sensor signal with the amplifier, and compensating for dc offset in the sensor signal.
In an added embodiment, the present invention provides a passive infrared (PIR) sensor apparatus comprising means for generating a PIR sensor signal, means, dc-coupled to the PIR sensor, for amplifying the sensor signal, and means for compensating for dc offset in the sensor signal.
In a further embodiment, the present invention provides a passive infrared (PIR) sensor apparatus comprising a PIR sensor that generates a sensor signal, an amplifier that amplifies the sensor signal to produce an amplified sensor signal, the amplifier being dc-coupled to an output of the PIR sensor to receive the sensor signal, wherein the amplifier includes a differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage, a resistor-capacitor circuit that sets the reference voltage received by the second input of the amplifier, and a detector that detects a level of the dc offset in the sensor signal, and a controller that charges a capacitor in the resistor-capacitor circuit at a duty cycle selected to adjust the reference voltage to compensate for the dc offset in the sensor signal.
In another embodiment, the present invention provides a passive infrared (PIR) sensor apparatus comprising a PIR sensor that generates a sensor signal, an amplifier that amplifies the sensor signal to produce an amplified sensor signal, the amplifier being dc-coupled to an output of the PIR sensor to receive the sensor signal, wherein the amplifier includes a differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage, and a controller that adjusts the reference voltage to compensate for the dc offset in the sensor signal.
In a further embodiment, the present invention provides a passive infrared (PIR) sensor apparatus comprising a PIR sensor that generates a sensor signal, means for amplifying the sensor signal to produce an amplified sensor signal, wherein the amplifying means is de-coupled to an output of the PIR sensor to receive the sensor signal, and means for controlling the amplifier to cancel at least a portion of the dc offset in the sensor signal.
The level of the dc offset in the sensor signal can be detected by reference to the amplified sensor signal produced by the amplifier. Detection and control can be implemented by processes executed by a processor, or by discrete circuitry. The amplifier may take the form of a differential amplifier having a first input that receives the sensor signal and a second input that receives a reference voltage. In this case, the control signal generated by the controller adjusts the reference voltage received by the second input of the differential amplifier to compensate for dc offset in the sensor signal. The reference voltage serves to cancel at least a portion of the dc offset in the sensor signal.
The sensor apparatus may include a resistor-capacitor circuit, for example, that sets the reference voltage for the amplifier. In some embodiments, the controller charges the capacitor in the resistor-capacitor circuit at a duty cycle selected to adjust the reference voltage to compensate for the dc offset. A processor can be programmed to adjust the reference voltage in incremental steps until the dc offset in the sensor signal is canceled to an acceptable level. In particular,
Brunius Robert E.
Kuhnly Keith D.
Saldin Paul G.
Fish & Richardson P.C. P.A.
Hannaher Constantine
Interactive Technologies Inc.
LandOfFree
Passive infrared sensor apparatus and method with DC offset... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Passive infrared sensor apparatus and method with DC offset..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Passive infrared sensor apparatus and method with DC offset... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2612312