Passive infrared detection system and method with adaptive threshold and adaptive sampling

• US 5,870,022 A
• Filed: 09/30/1997
• Issued: 02/09/1999
• Est. Priority Date: 09/30/1997
• Status: Expired due to Term

• Current Assignee: GE Security Incorporated (Carrier Global Corporation)
• Original Assignee: Interactive Technologies, Inc. (Fiserv Incorporated)
• Inventors: Saldin, Paul G., Kuhnly, Keith D.
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US08/941,856
• Time in Patent Office: 497 Days
• Field of Search: 340/567, 340/584, 340/511, 340/521, 340/522, 340/541, 340/552, 340/693
• US Class Current: 340/567
• CPC Class Codes: G08B 13/19 using infrared-radiation detection systems G08B13/194 takes precedence
• CPC Class Codes: G08B 29/26 by updating and storing reference thresholds

Abstract

A detection system and method are capable of reducing the occurrence of false alarms and detection failures by compensating for variations in the amplitude of a detection signal generated by a PIR sensor. An adaptive threshold can be used that varies according to ambient temperature of the detection area and the frequency of the detection signal. Comparison of the detection signal to the adaptive threshold allows compensation for temperature- and/or frequency-induced variations in detection signal amplitude. The adaptive threshold can be configured for standard detection area conditions or calibrated for conditions at the installation site. Relative measurement and adaptive sampling techniques also can be used to compensate for the presence of low frequency shifts in the detection signal. Such techniques can provide an accurate representation of signal amplitude relative to a threshold amplitude despite differences in absolute signal magnitude. The use of an adaptive sampling rate that increases with the onset of a potential intruder event contributes to power conservation in the detector.

Claims

1. A detection system comprising:

a passive infrared sensor for generating a detection signal indicative of a level of infrared radiation within a detection area;

a processor coupled to receive the detection signal, wherein the processor is programmed to execute the steps of;

determining a peak-to-peak amplitude of the detection signal,

comparing the peak-to-peak amplitude of the detection signal to a threshold amplitude, and

generating, in the event the peak-to-peak amplitude is greater than the threshold amplitude, a signal indicative of the presence of the intruder within the detection area.

2. A detection method comprising the steps of:

receiving, from a passive infrared sensor, a detection signal indicative of a level of infrared radiation within a detection area;

determining a peak-to-peak amplitude of the detection signal;

comparing the peak-to-peak amplitude of the detection signal to a threshold amplitude; and

indicating presence of an intruder within the detection area in the event the peak-to-peak amplitude is greater than the threshold amplitude.

3. A detection system comprising:

a passive infrared sensor for generating a detection signal indicative of a level of infrared radiation within a detection area;

a processor coupled to receive the detection signal from the infrared sensor, wherein the processor is programmed to execute the steps of;

determining a peak-to-reference amplitude of the detection signal,

determining a peak-to-peak amplitude of the detection signal,

comparing the peak-to-reference amplitude to a first threshold amplitude,

comparing the peak-to-peak amplitude of the detection signal to a second threshold amplitude greater than the first threshold amplitude, and

indicating, in the event the peak-to-reference amplitude is greater than the first threshold amplitude and the peak-to-peak amplitude is greater than the second threshold amplitude, the presence of the intruder within the detection area.

4. A detection method comprising the steps of:

receiving, from a passive infrared sensor, a detection signal indicative of a level of infrared radiation within a detection area;

determining a peak-to-reference amplitude of the detection signal;

determining a peak-to-peak amplitude of the detection signal;

comparing the peak-to-reference amplitude to a first threshold amplitude;

comparing the peak-to-peak amplitude of the detection signal to a second threshold amplitude greater than the first threshold amplitude; and

indicating, in the event the peak-to-reference amplitude is greater than the first threshold amplitude and the peak-to-peak amplitude is greater than the second threshold amplitude, presence of the intruder within the detection area.

5. A detection system comprising:

a passive infrared sensor for generating a detection signal indicative of a level of infrared radiation within a detection area;

a processor operatively coupled to receive the detection signal from the infrared sensor, wherein the processor is programmed to execute the steps of;

(a) acquiring a plurality of samples of the detection signal representative of slope changes in the detection signal,

(b) analyzing absolute differences between the values of successive samples to identify those samples representative of noise-induced slope changes in the detection signal,

(c) discarding the identified samples, and

(d) comparing the absolute differences between the values of successive remaining samples to a threshold value, and

(e) indicating, in the event one or more of the absolute differences exceeds the threshold value, a condition potentially indicative of the presence of an intruder within the detection area.