Smoke detector for distinguishing between an alarm condition and a nuisance condition

A method for distinguishing between an alarm condition and a nuisance condition in a smoke detector. The smoke detector comprises an illuminator and a light sensor. The method includes measuring a voltage signal in response to an electromagnetic signal emitted by the illuminator, and comparing the voltage signal to an alarm threshold. A rate of change of the voltage signal is determined in response to the comparison of the voltage signal and the alarm threshold. A first frequency component of a first portion of the voltage signal and a second frequency component of a second portion of the voltage signal is determined. The first frequency component and the second frequency component are compared to distinguish between the alarm condition and the nuisance condition. An indication of the alarm condition and the nuisance condition is respectively generated upon an identification of the alarm condition and the nuisance condition.

BACKGROUND

Photoelectric smoke alarms in residential and commercial buildings include a smoke chamber, a light source, and a photodetector. When smoke from a burning object enters the smoke chamber, the photodetector output increases or decreases to a threshold and an alarm is generated to apprise the user of an alarm condition. The photodetector output is also affected when dust gets entrapped in the smoke chamber, resulting in a false alarm.

SUMMARY OF THE EMBODIMENTS

In an embodiment, a method distinguishes between an alarm condition and a nuisance condition in a smoke detector. The smoke detector includes an illuminator and a light sensor. The method includes the step of measuring a voltage signal in response to an electromagnetic signal emitted by the illuminator, and the step of comparing the voltage signal to an alarm threshold. A rate of change of the voltage signal is determined in response to the comparison of the voltage signal and the alarm threshold. A first frequency component of a first portion of the voltage signal and a second frequency component of a second portion of the voltage signal is determined. The first frequency component and the second frequency component are compared to distinguish between the alarm condition and the nuisance condition. An indication of the alarm condition is generated upon an identification of the alarm condition, and an indication of the nuisance condition is generated upon an identification of the nuisance condition.

In another embodiment, a smoke detector includes an illuminator configured to emit an electromagnetic signal, and a light sensor configured to generate a voltage signal in response to the electromagnetic signal. The smoke detector has a memory that stores computer-readable instructions. A processor is configured to execute the instructions to: (i) compare the voltage signal to an alarm threshold; (ii) determine a rate of change of the voltage signal; (iii) compare the rate of change of the voltage signal to a slope threshold; and (iv) determine a first frequency component of a first portion of the voltage signal and a second frequency component of a second portion of the voltage signal.

In yet another embodiment, a method for operating a smoke detector comprising an illuminator and a light sensor comprises the step of measuring a voltage signal in response to an electromagnetic signal emitted by the illuminator. The method includes the step of comparing the voltage signal to an alarm threshold, and the step of determining a rate of change of the voltage signal in response to the comparison of the voltage signal and the alarm threshold. The method comprises the step of determining a first frequency component of a first portion of the voltage signal and a second frequency component of a second portion of the voltage signal upon the determination of the rate of change.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a schematic diagram of an example photoelectric light scattering smoke detector100in a room148that includes smoke150. Smoke detector100includes a smoke chamber102, an illuminator108, and a light sensor130. Illuminator108may include one or more light sources110, which may be a light-emitting diode (LED), laser diode, or other light source known in the art. Light sensor130may include one or more photodetectors.

Illuminator108emits light112, which includes light portions112A and112C. Light portion112A propagates towards the smoke chamber102and light portion112C propagates towards the light sensor130. Light sensor130produces an output voltage140in response to detecting light portion112C. In a “clean-air” condition, when smoke chamber102contains no smoke, light sensor130detects only light portion112C and produces a corresponding clean-air current and associated clean-air voltage114. While in that state, the output voltage140(which is thus at a clean air voltage level) can be thought of as being in a clean air condition. However, when smoke150is in smoke chamber102, smoke150scatters part of light portion112A as scattered light112S toward light sensor130, which increases output voltage140. In the clean-air state, when smoke chamber102contains no smoke, light portion112A does not reach light sensor130.

It is envisioned that the spatial arrangement of smoke chamber102, illuminator108, and light sensor130may differ from the arrangement illustrated inFIG. 1. Without departing from the scope hereof, smoke detector100may be a photoelectric light obscuration smoke detector, such that output voltage140falls below clean-air voltage114when smoke150is in smoke chamber102.

FIG. 2is a schematic diagram of a smoke detector200, which is an example of smoke detector100. Smoke detector200may effectuate smoke detection via at least one of photoelectric light scattering and photoelectric light obscuration. Smoke detector200includes illuminator208, smoke chamber102, a light sensor230, and a nuisance monitor240.

Illuminator208is an example of illuminator108and includes a first light source210. Light sensor230is an example of light sensor130and includes a first photodetector231. Illuminator208may include a second light source220and light sensor230may include a second photodetector232. Light sources210and220are each an example of light source110. In some embodiments, the number of light source(s) and photodetector(s) in the illuminator208and light sensor230, respectively, may be different (e.g., the illuminator208may have two light sources and the light sensor230may have a solitary photodetector).

The size of particles constituting smoke150depends on its source, e.g., on the type of process that produces smoke150. Illuminator208may be configured to emit more than one wavelength of light into smoke chamber102, which enables detection of, and differentiation of, types of smoke that differ in particle size. In an example mode of operation, first light source210emits a first optical signal212having a first center wavelength λ1. Illuminator208, e.g., via second light source220, emits a second optical signal222having a second center wavelength λ2.

In embodiments, second center wavelength λ2exceeds the first center wavelength by at least twenty percent of first center wavelength λ1. For example, light source210emits blue light and light source220emits near-infrared (near-IR) light such that λ1is between 0.40 μm and 0.48 μm and λ2is between 0.66 μm and 1.0 μm. At least one of first center wavelength λ1and second center wavelength λ2may be outside the optical portion of the electromagnetic spectrum without departing from the scope hereof. For example, first center wavelength λ1may be shorter than 0.40 μm and second center wavelength λ2may exceed 1.0 μm.

In embodiments where the smoke detector200includes, in addition to the first light source210and the first photodetector231, the second light source220and the second photodetector232, the first photodetector231is configured to detect first center wavelength λ1and the second photodetector232is configured to detect second center wavelength λ2. For example, first photodetector231includes a bandpass filter that transmits first center wavelength λ1and blocks second center wavelength λ2, while second photodetector232includes a bandpass filter that transmits second center wavelength λ2and blocks first center wavelength λ1. Photodetectors231and232may have spectral response curves optimized for first center wavelength λ1and second center wavelength λ2, respectively.

Light sensor230, specifically the first photodetector231thereof, is configured to produce first voltage214in response to the first optical signal212. The amplitude of the first voltage214is proportional to, or otherwise corresponds to, the first optical signal212. The second photodetector232of the light sensor230is configured to produce second voltage224in response to second optical signal222. The amplitude of the second voltage224is proportional to, or otherwise corresponds to, the second optical signal222.

Nuisance monitor240is a type of computer. In embodiments, nuisance monitor240includes a processor250and a memory260, which are communicatively coupled. Memory260may be transitory and/or non-transitory and may represent one or both of volatile memory (e.g., SRAM, DRAM, computational RAM, other volatile memory, or any combination thereof) and non-volatile memory (e.g., FLASH, ROM, magnetic media, optical media, other non-volatile memory, or any combination thereof). The processor250represents one or more digital processors. The processor250may be a microprocessor, and in embodiments, part or all of memory260may be integrated into processor250. In some embodiments, the processor250may be configured through particularly configured hardware, such as an application specific integrated circuit (ASIC), field-programmable gate array (FPGA), etc., and/or through execution of software to perform functions in accordance with the disclosure herein.

The nuisance monitor240, in the memory260, stores the first voltage214, alarm threshold(s)290, clean air voltage(s)292, and slope threshold(s)293. The alarm threshold290includes a first alarm threshold290A, the clean air voltage292includes a first clean air voltage292A, and the slope threshold293includes a first slope threshold293A, each of which relate to the first light source210and the first photodetector231. In the clean-air condition, when there is no smoke in the smoke chamber102, the first voltage214corresponds to the light portion112C, and has a first value that may be generally equal to first clean air voltage292A. When smoke150enters the smoke chamber102, the photodetector231senses both the light portions112C and112S, which increases the first voltage214to a second value that is greater than the first value/clean air voltage292A. The nuisance monitor240may be configured to generate an alarm where the value of the first voltage214increases to become at least equal to the first alarm threshold290A—unless, as discussed herein, this increase in the first voltage214from the first value to the second value/first alarm threshold290A is attributable to a nuisance condition as opposed to an alarm condition.

The nuisance monitor240includes software270, which may be stored in a transitory or non-transitory portion of the memory260. In an embodiment, the software270includes a primary evaluator272, a companion (or secondary) evaluator278, an alarm generator284, and a calibrator286, each of which may include or have associated therewith machine readable instructions to allow the nuisance monitor240to function as described herein.

The illustrated primary evaluator272includes a comparator274and a nuisance assessor276. The comparator274is configured to compare the first voltage214to the first alarm threshold290A. Under normal conditions, e.g., in the clean-air condition, the first voltage214is below the first alarm threshold290A and is generally equal to the first clean air voltage292A. In an alarm condition, e.g., where a substantial amount of smoke from a burning object enters the chamber102, the first voltage214may begin to increase, and may eventually equal the first alarm threshold290A as smoke continues to enter into the chamber102. The increase in the first voltage214from the clean air voltage292A to the first alarm threshold290A, however, may also be attributable to dust, debris, or another foreign object (i.e., matter other than smoke generated by a burning object) in the chamber102. The slope threshold293may include a first slope threshold293A. The nuisance assessor276may evaluate the rate of change of the first voltage214in the time domain, and where this rate of change of the first voltage214exceeds the first slope threshold293A, the nuisance assessor276may preliminarily determine that the rapid increase in the first voltage214to at least equal the first alarm threshold290A is not attributable to smoke but is attributable to dust, debris, or another foreign object in the chamber102. The primary evaluator272, in response to the preliminary determination by the nuisance assessor276, may call the companion evaluator278for additional evaluation and to confirm that the rapid increase in the first voltage214is due to a nuisance condition.

The primary evaluator272may evaluate the first voltage214in the time domain. Additionally, the companion evaluator278may evaluate the first voltage214in the frequency domain. In an embodiment, the companion evaluator278includes a Fast Fourier Transform module280and a nuisance identifier282. The artisan understands that a signal, such as a signal indicating that the first voltage214is varying over time (herein, the “first voltage214signal”), may be represented in the frequency domain. The Fast Fourier Transform algorithm implemented by the FFT module280is a highly optimized algorithm for identifying the frequency components of a time domain signal. The Fast Fourier Transform module280may, in an embodiment, implement a first time domain to frequency domain transform of the first voltage214signal, a second time domain to frequency domain transform of the first voltage214signal, and a third time domain to frequency domain transform of the first voltage214signal. The first time domain to frequency domain transform may identify the frequency components of a first portion of the first voltage214signal, the second time domain to frequency domain transform may identify the frequency components of a second portion of the first voltage214signal, and the third time domain to frequency domain transform may identify the frequency components of a third portion of the first voltage214signal. In an embodiment, the first portion may correspond to the first voltage214signal before the first voltage214exhibits a rapid increase, the second portion may correspond to the first voltage214signal during the rapid increase, and the third portion may correspond to the first voltage214signal after the first voltage214levels off subsequent to the rapid increase. The nuisance identifier282may compare the first transform, the second transform, and the third transform, and discriminate between a nuisance condition and an alarm condition based on this comparison. Where the nuisance identifier282determines that the rapid increase in the first voltage214is attributable to a nuisance condition, no alarm may be generated and the calibrator286may recalibrate the first alarm threshold290A. Alternately, where the first voltage214at least equals the first alarm threshold290A and a nuisance condition is not identified, the alarm generator284may generate an alarm to apprise the user of the alarm condition.

Smoke detector200may include a network interface202that communicatively couples the nuisance monitor240to data source204A and, in some embodiments, a computing device204B. Remote data source204A is a server, for example. Remote data source204A may provide nuisance monitor240with updated versions of at least one of the alarm threshold290, clean air voltage292, and slope threshold293. Interface202is, for example, a network interface such that remote data source204A and nuisance monitor240communicate via a wired communication channel, a wireless communication channel, or a combination thereof. In an embodiment, remote data source204A includes at least part of nuisance monitor240, such that at least part of nuisance monitor240is remotely located from illuminator208and light sensor230.

When the first voltage214at least equals the first alarm threshold290A, and the preliminary determination of the nuisance assessor276indicates that the rate of change of the first voltage214is less than the first slope threshold293A, the alarm generator284may generate an alarm to apprise the user of the alarm condition. The alarm generator284may also generate an alarm where the nuisance assessor276preliminarily determines a nuisance condition but the nuisance identifier282does not confirm same. The alarm generator284may generate an alarm in one or more of any number of ways. For example, the smoke detector200may include electro-acoustic transducers, and the alarm generator284may cause the smoke detector200to generate an audible alarm where the increase in the first voltage214is determined to not be attributable to a nuisance condition. Additionally or alternately, the smoke detector200may include visual alarms (e.g., LEDs that can flash in different colors) to visually communicate the generated alarm to a user. In some embodiments, the alarm generator284may communicate the alarm (e.g., wirelessly, via the interface202) to the computing device204B of a user or administrator (e.g., a smart phone of the owner of the structure where the smoke detector200is located and/or to the computing device of a third party administrator). In embodiments, the smoke detector200may be communicatively coupled via the interface202to another smoke detector or smoke detectors (e.g., the smoke detector200in room148of a house may be in data communication with the smoke detector in another room of that house); in these embodiments, when an alarm is generated by the alarm generator284of one smoke detector200, the alarms associated with smoke detectors in communication therewith may automatically be activated.

Focus is directed now toFIGS. 3 through 11to illustrate the workings of the smoke detector200, in an embodiment.FIG. 3depicts the time domain output of the first photodetector231in a clean air scenario300.FIG. 4depicts the time domain output of the first photodetector231in an alarm scenario400. And,FIG. 6depicts the time domain output of the first photodetector231in a nuisance scenario600.

In more detail,FIG. 3shows time domain output214A of the first photodetector231in a clean air scenario300where the chamber102is devoid of smoke or another foreign object that affects the first voltage214. In this scenario300, the time domain output of the first photodetector231, i.e., first voltage214A, may be generally equal to the first clean air voltage292A and less than the first alarm threshold290A. For example, as shown, the amplitude of the first voltage214A may be about 0.28V, the first clean air voltage292A may be about 0.29V, and the first alarm threshold290A may be about 0.45V. The clean air voltage292A may be saved in memory upon manufacture of the smoke detector200. A difference (e.g., a difference of 0.01V as shown) between the first clean air voltage292A and the first voltage214A may arise because the output of the photodetector231degrades over time, particularly where the photodetector231is an LED. The primary evaluator272, specifically the comparator274thereof, may compare the first voltage214A to the first alarm threshold290A and determine that the first voltage214A is less than the first alarm threshold290A. No alarm may be generated by the nuisance monitor240so long as the first voltage214A is less than the first alarm threshold290A.

FIG. 4shows a typical alarm scenario400, where an increasing amount of smoke from a burning object progressively enters the chamber102. In the illustrated alarm scenario400, before time T400A, there is no smoke in the chamber102, and output214B of the first photodetector231is generally equal to the first clean air voltage292A and is less than the first alarm threshold290A. For example, before time T400A, as inFIG. 3, the amplitude of the first voltage214B is about 0.28V, the first clean air voltage292A is about 0.29V, and the first alarm threshold290A is about 0.45V. At time T400A, smoke150from a burning object may enter the chamber102and cause the first voltage214B to increase. At time T400B, the first voltage214B may reach the first alarm threshold290A. The comparator274may compare the first voltage214B to the first alarm threshold290A and determine that the first voltage214B at least equals the first alarm threshold290A. The primary evaluator272, in response to a determination by the comparator274that the first voltage214B at least equals the first alarm threshold290A, may call the nuisance assessor276to evaluate the rate of change of the first voltage214B.

The nuisance assessor276may compute the slope of the first voltage214B, e.g., the slope of the first voltage214B between time T400A and time T400B, and compare this slope with the first slope threshold293A. The slope threshold293A, in an embodiment, may be a 0.1V rise in the first voltage214(e.g., first voltage214B) in 0.01 seconds. Because the smoke150from a burning object entering the chamber102increases gradually over time, a generally instantaneous and significant rise (e.g., a 0.1V rise in 0.01 seconds) in the first voltage214B is unlikely to be attributable to smoke. Conversely, a rise in the first voltage214B that is not generally instantaneous (e.g., a rise in the first voltage214B that is less than a 0.1V rise in 0.01 seconds) may indicate smoke from a burning object entering the chamber102. Thus, in an embodiment, the nuisance assessor276may determine that the increase in the first voltage214B to the first alarm threshold290A is attributable to smoke from a burning object (and not to dust, debris, or another foreign object) where the rate of change of the first voltage214B is less than the slope threshold293A (i.e., the increase in the first voltage214B is less than a 0.1V increase in 0.01 seconds). In such case, the alarm generator284may generate an alarm to apprise the user of an alarm condition. Alternately, if the first voltage214B increases to the first alarm threshold290A and the nuisance assessor276determines that the first voltage214B increased by at least 0.1V in 0.01 seconds, the nuisance assessor276may preliminarily determine that the increase in the first voltage214is due to dust, debris, or another foreign object, as opposed to smoke from a burning object; the companion evaluator278may then be called for additional evaluation and verification of a nuisance condition.

With respect to the example alarm scenario400illustrated inFIG. 4, the nuisance assessor276may determine that the rate of change of the first voltage214B is less than the first slope threshold293A. The alarm generator284may consequently generate an alarm to apprise the user of an alarm condition. The artisan will appreciate that the first voltage214B in the alarm scenario400is merely an example and that the smoke150need not cause the first voltage214B to increase linearly as shown; however, smoke150is unlikely to cause the first voltage214B to increase by 0.1V or more in 0.01 seconds.

FIG. 5shows an example smoke chamber102of the smoke detector200. The chamber102may have associated therewith the illuminator208(e.g., the first light source210and, in embodiments, the second light source220), and a light sensor230(e.g., at least one photodetector). The chamber102may include a lid (not shown) and a high density ray region102A. When the smoke150enters the chamber102, e.g., the high density ray region102A thereof, the light scattered thereby (i.e., scattered light112S, seeFIG. 1) may cause the output of the light sensor230to increase.

The skilled artisan understands that a smoke detector, e.g., the smoke detector200, when being installed in a wall, ceiling, or other such structure, may encounter dust (e.g., Gypsum/drywall dust), debris, or other such foreign objects (e.g., wood or silica particles) (collectively, “dust”). The dust, during installation of the smoke detector200, or at some time thereafter, may get entrapped within the smoke chamber102. For example, as shown inFIG. 5, dust particles502and504may get entrapped in the high density ray region102A of the chamber102. The dust particles502and504may affect the amount of light112reaching the light sensor130, and may in-turn cause the first voltage214to increase generally instantaneously to at least equal the first alarm threshold290A.

FIG. 6illustrates the output of the first photodetector231, i.e., first voltage214C, in the nuisance scenario600where dust (e.g., dust particles502and504) has become entrapped in the chamber102. In the illustrated nuisance scenario600, before time T600A, there is no smoke150or dust in the chamber102, and output214C of the first photodetector231is generally equal to the first clean air voltage292A and is less than the first alarm threshold290A. At time T600A, dust enters the chamber102and causes the first voltage214C to increase rapidly such that the first voltage214C equals the first alarm threshold290A at time T600B. The first voltage214C may continue to rapidly increase until time T600C, and level off thereafter. As can be appreciated, the slope of the first voltage214C between time T600A and time T600B in the dust scenario600is greater than the slope of the first voltage214B between time T400A and time T400B in the alarm scenario400ofFIG. 4. The nuisance assessor276may determine that the slope of the first voltage214C is at least equal to the first slope threshold293A (e.g., that the first voltage214C increased by at least 0.1V in 0.01 seconds). The nuisance assessor276may therefore preliminary determine that the rapid increase in the first voltage214C is attributable to a nuisance condition (i.e., to dust in the chamber102). The primary evaluator272may consequently call the companion evaluator278for additional analysis and confirmation of the nuisance condition.

FIGS. 7A-7B, 8A-8B, and 9A-9Beach relate to the nuisance scenario600illustrated inFIG. 6. Specifically,FIGS. 7A-7Brelate to first portion702of first voltage214C signal (i.e., the portion of the first voltage214C signal before the first voltage214C exhibits the rapid increase at T600A),FIGS. 8A-8Brelate to second portion802of first voltage214C signal (i.e., the portion of the first voltage214C signal between time T600A and time T600C, where the first voltage214C exhibits the rapid increase), andFIGS. 9A-9Brelate to third portion902of first voltage214C (i.e., the portion of the first voltage214C signal where the first voltage214C levels off after the rapid increase).FIGS. 7B, 8B, and 9Brespectively illustrate the frequency components of the first portion, second portion, and third portion of the first voltage214C signal.

In more detail, and as illustrated inFIG. 7A, the FFT module280may identify the first portion702of the first voltage214C. The FFT module280may then compute the frequency components of the first portion702, as illustrated inFIG. 7B. The FFT module280may likewise identify the second portion802of the first voltage214C (FIG. 8A) and compute the frequency components thereof (FIG. 8B). The FFT module280may also identify the third portion902of the first voltage214C (FIG. 9A) and identify the frequency components of the third portion902(FIG. 9B). In some embodiments, the FFT module280may implement two time domain to frequency domain transforms instead of three—one transform associated with a portion of the first voltage214C signal before the first voltage214C reaches the alarm threshold290A, and another transform associated with a portion of the first voltage signal214C after the first voltage214C is at least equal to the alarm threshold290A.

As can be appreciated byFIG. 6, and shown more clearly inFIGS. 7A and 9A, the amplitude of the first portion702of the first voltage214C signal is less than the amplitude of the third portion902of the first voltage214C signal. As can further be appreciated byFIGS. 7A, 8A, and 9A, the rate of change of the second portion802of the first voltage214C signal is greater than that of the first portion702and the third portion902. Yet, the frequency components of the first portion702, the second portion802, and the third portion902, as determined by the FFT module280and respectively illustrated inFIGS. 7B, 8B, and 9B, are generally identical (e.g., the dominant frequency component for each of the first portion702, the second portion802, and the third portion902is generally equal to 0 Hz). This is because the entrapped dust in the chamber102is stationary. Consequently, dust increases the amplitude of the first voltage214C signal in the time domain (because of increased scattered light112S) but does not affect the frequency of the first voltage signal214C. Conversely, smoke150has a movement pattern, and as such, an increasing amount of smoke150entering the chamber102may affect both the amplitude and the frequency of the output of the photodetector231. This characteristic may be used by the nuisance monitor240to distinguish a nuisance condition from an alarm condition.

Prior art smoke detectors generate an alarm each time the amplitude of the photodetector output reaches the alarm threshold. The nuisance monitor240, however, via the nuisance identifier282, may compare the frequency components of the first portion702, second portion802, and third portion902, and determine that they are generally identical (e.g., the dominant frequencies of each of the first portion702, the second portion802, and the third portion902are the same). The nuisance identifier282may therefore determine that the increase in the first voltage214C is attributable to a nuisance condition. That is, because the first voltage214C exhibits a rapid increase in the time domain, but exhibits no change in the frequency domain, the nuisance identifier282may attribute the rapid increase in the amplitude of the first voltage214C to a nuisance condition. No alarm may thus be generated, notwithstanding that the first voltage214C is greater than the first alarm threshold290A. In this way, by evaluating the output of the photodetector231in both the time and frequency domains, the nuisance monitor240may significantly reduce false positives as compared to prior art smoke detectors.

In some embodiments, once a nuisance condition (e.g., the nuisance scenario600) is identified, the calibrator286may recalibrate the first alarm threshold290A. In the illustrated embodiment, and with reference toFIG. 10, the calibrator286may determine that the difference between the amplitude of the first portion702and the alarm threshold is 0.17V (i.e., 0.45V (alarm threshold)−0.28 (amplitude of first portion702)=0.17V). The calibrator286may therefore recalibrate the first alarm threshold290A such that it is 0.17V greater than the third portion902of the first voltage214C (i.e., is 0.17V greater than the current steady state value of the first voltage214C). For example, where the amplitude of the third portion902is 0.72V, as shown inFIG. 10, the calibrator286may recalibrate the first alarm threshold290A to the recalibrated first alarm threshold290A′. In the illustrated example, the recalibrated first alarm threshold290A′ may be 0.89V (i.e., 0.72 (third portion902amplitude)+0.17V=0.89V), and this value may replace the first alarm threshold290A in the alarm threshold290. Recalibration of the first alarm threshold290A may allow the smoke detector200to continue to function to detect smoke150as desired, even where dust is entrapped in the chamber102.

FIG. 11shows a flowchart illustrating an example method1100for operating the smoke detector200to distinguish between a nuisance condition (e.g., nuisance condition600) and an alarm condition (e.g., alarm condition400). The method1100may be implemented at least in part by the software270.

At step1102, the first voltage214(FIG. 2) may be communicated to the primary evaluator272. At step1104, the comparator274may compare the first voltage214with the first alarm threshold290A. If it is determined at step1106that the first voltage214does not exceed the first alarm threshold290A, the method1100may return to step1102. Alternately, if the first voltage214exceeds the first alarm threshold290A at step1106, the method1100may move to step1108where the nuisance assessor276may evaluate the rate of change of the first voltage214in the time domain.

If the nuisance assessor276determines at step1110that the rate of change of the first voltage214is greater than the first slope threshold293A, the method1100may move to step1114. Alternately, if the nuisance assessor276determines that the rate of change of the first voltage214is less than the first slope threshold293A, the method1100may move to step1112where the alarm generator284may generate an alarm to indicate an alarm condition.

At step1114, the FFT module280may convert into the frequency domain the time domain signal of the first voltage214. For example, as discussed above, the FFT module280may parse the first voltage214signal into three (or a different number of) portions and determine the frequency components of each. At step1116, the nuisance identifier282may compare the frequency components of different portions of the first voltage214signal (e.g., compare the frequency components of the first voltage214before, during, and after the rapid increase). If the dominant frequency components of the first voltage214before, during, and after the rapid increase are determined by the nuisance identifier282to be generally identical, the nuisance identifier282may ascertain that the increase in the first voltage214is attributable to a nuisance condition. Specifically, if the comparison of the determined frequency components indicates at step1118that the increase in the first voltage214is attributable to a nuisance condition, no alarm may be generated, and the first alarm threshold290A may be recalibrated by the calibrator286to the recalibrated first alarm threshold290A′ at step1122. Alternately, where the nuisance identifier282does not confirm that the increase in the first voltage214is due to a nuisance condition (e.g., where the dominant frequency components of the first voltage214before, during, and after the increase are not generally identical), the alarm generator284may generate an alarm at step1120.

Where the smoke detector200includes the second light source220and the second photodetector232, the nuisance monitor240, in the memory260, may also store the second voltage224, second alarm threshold290B, second clean air voltage292B, and second slope threshold293B. The primary evaluator272, specifically the comparator274thereof, may compare the second voltage224with the second alarm threshold290B in the same way as discussed above for the first voltage214. If the comparator274determines that the second voltage224is greater than the second alarm threshold290B, the nuisance assessor276may identify the rate of change of the second voltage224signal in the time domain and compare same to the second slope threshold293B. Where the rate of change of the second voltage224is greater than the slope threshold293B, the companion evaluator278may be called by the primary evaluator272. The FFT module280may identify the frequency components of the second voltage224signal (e.g., of the first, the second, and the third portions thereof, as discussed above for the first voltage214). Where the nuisance identifier282, via the frequency domain evaluation, determines that the increase in the second voltage224is attributable to a nuisance condition (e.g., is attributable to dust entrapped in the chamber102), the calibrator286may recalibrate the second alarm threshold290B. Alternately, where the nuisance identifier282is unable to confirm that the increase in the second voltage224is due to a nuisance condition, the alarm generator284may generate the alarm. The nuisance monitor240may, in embodiments, process the first voltage214signal and the second voltage224signals in parallel, and an alarm may be generated where either the first voltage214or the second voltage224at least equals its respective alarm threshold290A and290B and a nuisance condition is not identified.

While the disclosure provides specific numerical values (e.g., for the alarm thresholds290, the clean air voltages292, the slope thresholds293, etc.), the artisan will understand that these values are examples only, may depend on the application (e.g., on the configuration of the particular smoke detector at issue), and are not intended to be independently limiting. The artisan may employ the disclosure to, among other things, identify that a change in the photodetector ouput of a smoke detector is attributable to something other than smoke such that an alarm need not be generated.

In some embodiments, the alarm generator284may generate an alarm in response to the identification by the nuisance monitor240of each of the nuisance and alarm conditions. For example, the alarm generator284may generate a warning (or “heads-up”) alarm in response to the identification of a nuisance condition and generate an emergency alarm in response to the identification of an alarm condition. The warning alarm may be configured to be milder than the emergency alarm. For example, in an embodiment, the warning alarm may comprise a gentle beep accompanied by a yellow light, and the emergency alarm may comprise a loud siren accompanied by a red light.

In some embodiments, the warning alarm may comprise a warning message that is transmitted by the alarm generator284to the mobile device204B over the interface202. Additionally or alternately, the smoke detector200may include in memory260a recording of a human voice, which may be audibly conveyed to the user to apprise the user of a nuisance condition. For example, once a nuisance condition is identified by the nuisance monitor240, a recording of a human voice asking the user if he wishes to clean the smoke chamber102(e.g., if he wishes to remove the dust particles502,504therein) may be played. The user may clean the smoke chamber102in response, or alternately, employ an output device (e.g., depress a button on the smoke detector100) to silence or interrupt the warning alarm. In some embodiments, the user may be allowed to silence or interrupt the warning alarm via the mobile device204B (e.g., the smoke detector100may have associated therewith a mobile application installed on the mobile device204B, and the user may use an interface of the application to silence or interrupt the warning alarm). For an emergency situation, the alarm may not be so readily silenced and may require additional steps to be turned off.

As noted, when dust entrapped in the smoke chamber102causes the first voltage214and/or the second voltage224to rapidly increase, the alarm thresholds290A and290B respectively associated with the first voltage214and the second voltage224may be recalibrated (i.e., increased) to allow the smoke detector200to continue to function as desired. In some instances, however, the increase in the first voltage214and/or the second voltage224due to the entrapped dust in the smoke chamber102may be so substantial that the smoke detector200is irreparably damaged. Such may occur, for example, where dust causes either the first voltage214and/or the second voltage224to rapidly increase by about one order of magnitude or more. Therefore, in embodiments, when the first voltage214and/or the second voltage224increases to at least equal the respective alarm thresholds290A and290B, the comparator274may determine if either of the first voltage214and/or the second voltage224increased by at least one order of magnitude. If such a substantial increase is detected, the alarm generator284may generate a head-up alarm (e.g., a visual or audible alarm, a notification to the mobile computing device204B, etc.) to apprise the user that the smoke detector200is irreparably damaged and ought to be replaced.