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

• US 6,288,395 B1
• Filed: 05/27/1998
• Issued: 09/11/2001
• Est. Priority Date: 09/30/1997
• Status: Expired due to Fees

• Current Assignee: Interactive Technologies, Inc. (Fiserv Incorporated)
• Original Assignee: Interactive Technologies, Inc. (Fiserv Incorporated)
• Inventors: Saldin, Paul G., Kuhnly, Keith D.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US09/085,676
• Time in Patent Office: 1,203 Days
• Field of Search: 250/339.04, 250/339.09, 250/339.11, 250/339.14, 250/340, 250/341.5, 250/342, 250/DIG.1, 250/252.1 A
• US Class Current: 250/339.04
• 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 temperature sensor for generating a temperature signal indicative of a temperature of the detection area; and

a processor coupled to receive the detection signal and the temperature signal, wherein the processor is programmed to;

determining a value of the detection signal,

determining a frequency of the detection signal,

selecting one of a plurality of threshold values based on the frequency of the detection signal and the temperature indicated by the temperature signal, comparing the value of the detection signal to the selected threshold value, and generating, in the event the value of the detection signal is greater than the selected threshold value, a signal indicative of presence of an intruder within the detection area.

2. The system of claim 1, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

3. The system of claim 1, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

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

4. The system of claim 1, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the frequency of the detection signal and the temperature indicated by the temperature signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

generating includes generating, in the event both 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, a signal indicative of the presence of an intruder within the detection area.

5. The system of claim 1, wherein the amplitude of the detection signal varies as a function of the temperature of the detection area and the frequency of the detection signal, and each of the threshold values corresponds to variation of the detection signal for one of a plurality of ranges of the temperature and one of a plurality of ranges of the frequency.

6. A detection method comprising:

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

determining a value of the detection signal;

determining a temperature of the detection area;

determining a frequency of the detection signal;

selecting one of a plurality of threshold values based on the frequency of the detection signal and the temperature;

comparing the value of the detection signal to the selected threshold value; and

indicating presence of an intruder within the detection area in the event the value of the detection signal is greater than the selected threshold value.

7. The method of claim 6, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

8. The method of claim 6, wherein the selected threshold value is a threshold amplitude, and wherein:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

indicating includes indicating the presence of an intruder within the detection area in the event the amplitude of the detection signal is greater than the selected threshold amplitude.

9. The method of claim 6, wherein the selected threshold value is a threshold amplitude, and wherein:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the frequency of the detection signal and the temperature indicated by the temperature signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

indicating includes indicating the presence of an intruder within the detection area in the event both 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.

10. The method of claim 6, wherein the amplitude of the detection signal varies as a function of the temperature of the detection area and the frequency of the detection signal, and each of the threshold values corresponds to variation of the detection signal for one of a plurality of ranges of the temperature and one of a plurality of ranges of the frequency.

11. A method for calibrating a detection system, the method comprising:

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

measuring the values of the detection signal for one or more different conditions within the detection area; and

generating a plurality of threshold values based on the measured values, wherein each of the threshold values represents a value of the detection signal indicative of presence of an intruder within the detection area for a particular combination of the different conditions.

12. The method of claim 11, wherein the different conditions include a plurality of temperatures within the detection area and a plurality of frequencies of the detection signal.

13. The method of claim 11, wherein each of the threshold values represents a value of the detection signal indicative of presence of an intruder within the detection area for one of a plurality of ranges of the temperatures and one of a plurality of ranges of the frequencies.

14. A method for calibrating a detection system, wherein the detection system includes an infrared sensor that generates a detection signal indicative of a level of infrared radiation within a detection area, the method comprising:

generating a plurality of threshold values, wherein each of the threshold values represents a value of the detection signal indicative of presence of an intruder within the detection area for one or more different conditions in the detection area;

installing the detection system within the detection area;

receiving a detection signal from a passive infrared sensor;

measuring the values of the detection signal for each of the one or more different conditions within the detection area; and

adjusting at least some of the threshold values based on the measured values.

15. The method of claim 14, wherein the different conditions include a plurality of temperatures within the detection area and a plurality of frequencies of the detection signal.

16. The method of claim 14, wherein each of the threshold values represents a value of the detection signal indicative of presence of an intruder within the detection area for one of a plurality of ranges of the temperatures and one of a plurality of ranges of the frequencies.

17. A detection system comprising:

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

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

determine value of the detection signal,

determine a frequency of the detection signal,

select one of a plurality of threshold values based on the frequency of the detection signal,

compare the value of the detection signal to the selected threshold value, and

generate, in the event the value of the detection signal is greater than the selected threshold value, a signal indicative of presence of an intruder within the detection area.

18. The system of claim 17, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

19. The system of claim 17, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

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

20. The system of claim 17, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the frequency of the detection signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

generating includes generating, in the event both 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, a signal indicative of the presence of an intruder within the detection area.

21. The system of claim 17, wherein the amplitude of the detection signal varies as a function of the frequency of the detection signal, and each of the threshold values corresponds to variation of the detection signal for one of a plurality of ranges the frequency.

22. 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 temperature sensor for generating a temperature signal indicative of a temperature of the detection area; and

a processor coupled to receive the detection signal and the temperature signal, wherein the processor is programmed to;

determine a value of the detection signal,

select one of a plurality of threshold values based on the temperature indicated by the temperature signal,

compare the value of the detection signal to the selected threshold value, and

generate, in the event the value of the detection signal is greater than the selected threshold value, a signal indicative of presence of an intruder within the detection area.

23. The system of claim 22, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

24. The system of claim 22, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

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

25. The system of claim 22, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further programmed such that:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the temperature indicated by the temperature signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

generating includes generating, in the event both 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, a signal indicative of the presence of an intruder within the detection area.

26. The system of claim 22, wherein the amplitude of the detection signal varies as a function of the temperature of the detection area, and each of the threshold values corresponds to variation of the detection signal for one of a plurality of ranges of the temperature.

27. A detection system comprising:

a passive infrared sensor that generates a detection signal indicative of a level of infrared radiation within a detection area;

a processor that samples the detection signal, the processor being configured to sample the detection signal at a first sampling rate, and sample the detection signal at a second sampling rate greater than the first sampling rate in the event the level indicated by the sampled detection signal changes; and

a temperature sensor that venerates a temperature signal indicative of the temperature within the detection area wherein the processor is further configured to;

determine a value of the detection signal,

determine a frequency of the detection signal,

select one of a plurality of threshold values based on the frequency of the detection signal and the temperature indicated by the temperature signal,

compare the value of the detection signal to the selected threshold value, and

generate, in the event the value of the detection signal is greater than the selected threshold value, a signal indicative of presence of an intruder within the detection area.

28. The detection system of claim 27, wherein the first sampling rate is selected such that the processor samples the detection signal approximately once every sixty milliseconds, and the second sampling rate is selected such that the processor samples the detection signal approximately once every fifteen to twenty milliseconds.

29. The detection system of claim 27, wherein the processor is further configured to resume sampling the detection signal at the first sampling rate when the level indicated by the sampled detection signal remains substantially unchanged for a period of time.

30. The detection system of claim 27, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

31. The detection system of claim 27, wherein the selected threshold value is a threshold amplitude, and wherein the processor is further configured such that:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

generating includes generating, in the event the amplitude of the detection signal is greater than the selected threshold amplitude, the signal indicative of the presence of the intruder within the detection area.

32. The detection system of claim 27, wherein the processor is further configured such that:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the frequency of the detection signal and the temperature indicated by the temperature signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

generating includes generating, in the event both 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 signal indicative of the presence of an intruder within the detection area.

33. The detection system of claim 27, wherein the processor is further configured such that:

selecting one of a plurality of threshold values includes selecting a threshold amplitude based on the frequency of the detection signal and the temperature indicated by the temperature signal,

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

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

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

34. A detection method comprising:

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

sampling the detection signal at a first sampling rate;

sampling the detection signal at a second sampling rate greater than the first sampling rate in the event the level indicated by the sampled detection signal changes;

sensing a temperature within the detection area;

determining a value of the detection signal;

determining a frequency of the detection signal;

selecting one of a plurality of threshold values based on the frequency of the detection signal and the sensed temperature;

comparing the value of the detection signal to the selected threshold value; and

generating, in the event the value of the detection signal is greater than the selected threshold value, a signal indicative of presence of an intruder within the detection area.

35. The detection method of claim 34, wherein the first sampling rate is selected such that the detection signal is sampled approximately once every sixty milliseconds, and the second sampling rate is selected such that the detection signal is sampled approximately once every fifteen to twenty milliseconds.

36. The detection method of claim 34, further comprising resuming sampling the detection signal at the first sampling rate when the level indicated by the sampled detection signal remains substantially unchanged for a period of time.

37. The detection method of claim 34, wherein the value of the detection signal is an amplitude of the detection signal and the threshold value is a threshold amplitude.

38. The detection method of claim 34, wherein the selected threshold value is a threshold amplitude, and wherein:

determining the value of the detection signal includes determining an amplitude of the detection signal,

comparing includes comparing the amplitude of the detection signal to the selected threshold amplitude, and

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

39. The system of claim 34, wherein:

determining the value of the detection signal includes determining both a peak-to-reference amplitude of the detection signal and a peak-to-peak amplitude of the detection signal,

selecting one of a plurality of threshold values includes selecting a first threshold amplitude based on the frequency of the detection signal and the temperature indicated by the temperature signal, and selecting a second threshold amplitude greater than the first threshold amplitude,

comparing includes;

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

comparing the peak-to-peak amplitude to the second threshold amplitude, and

generating includes generating, in the event both 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, a signal indicative of the presence of an intruder within the detection area.

40. The detection system of claim 34, further comprising selecting one of a plurality of threshold values includes selecting a threshold amplitude based on the frequency of the detection signal and the temperature of the detection area, wherein:

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

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

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