Source: https://patents.google.com/patent/US6373393
Timestamp: 2018-02-24 14:26:34
Document Index: 731665590

Matched Legal Cases: ['art 23', 'art 24', 'art 25', 'art 26', 'art 25', 'art 32', 'art 33', 'art 32', 'art 34', 'art 35', 'art 34', 'art 36', 'art 35', 'art 35', 'art 40', 'art 40']

US6373393B1 - Flame detection device and flame detection - Google Patents
US6373393B1
US6373393B1 US09321184 US32118499A US6373393B1 US 6373393 B1 US6373393 B1 US 6373393B1 US 09321184 US09321184 US 09321184 US 32118499 A US32118499 A US 32118499A US 6373393 B1 US6373393 B1 US 6373393B1
US09321184
Hidenari Matsukuma
Among conventional infrared ray type flame detection devices (hereinafter, referred to as “flame detection device”), a flame detection device as illustrated in FIG. 8 is known as an example. In FIG. 8, 1 denotes a detection element, 2 denotes a frequency filter, 3 denotes a comparator, and 4 denotes an optical wavelength band pass filter. In practical applications, an amplifier, etc. for signal amplification is included, but omitted here for simplifying the description.
FIG. 9 is a schematic view of how the flame burns. Generally speaking, the flame follows the growing process in which the flame is small immediately after the ignition, then, becomes gradually larger, and smaller as the combustible is exhausted, and is finally extinguished. However, when viewed in a short time, the size of the flame repeats the growth and deflation at a certain period. That is, as indicated in FIG. 9, the periodic fluctuation is repeated, wherein the burned-up flame takes in oxygen therearound and grows, while it becomes smaller for a moment once oxygen in its surrounding is reduced in amount, and then, grows again by the supply of oxygen from its outer side. It is proved that the repetitive cycle (the frequency fc) is characterized in that it is inversely proportional to the square root of the fire length for the combustible, e.g., liquid fuel. For example, the cycle is expressed by the following formula {circle around (1)} according to “Report on Fire-fighting Research, Vol. 53, No. 24 (1982)” (by Kunihiro Yamashita).
fc=k/{square root over ( )}L[Hz] {circle around (1)}
Where, k is a coefficient according to the kind of the fuel, and L is a value to express the quantity (fire length) of the fire. In general fire model, fc is e.g. about 2.5 Hz or 1.8 Hz. Thus, in a construction of FIG. 8, the “flame” caused by a fire can be detected if the passing frequency of a frequency filter 2 is 2.5 Hz, 1.8 Hz or each of these frequencies.
FIG. 10a-c is a diagram to indicate the temporal fluctuation of the infrared ray energy, where (a) denotes a flame, (b) denotes a mercury lamp, and (c) is a rotary lamp. The flame is of course an object to be monitored because the flame detection device is used for detecting the flame, and in addition, the mercury lamp is often used for illumination of roads. The rotary lamp is often used in an emergency car as well as an alarm for an entrance or an exit of a parking lot or for road construction, and for a guide of a store. These mercury lamp and rotary lamp are examples of an infrared ray energy radiation body which are seen in a daily life.
FIG. 10 indicates the output of the infrared ray energy of the flame, the mercury lamp and the rotary lamp taken out through a chopper. In FIG. 10 (a) the infrared ray energy of the flame flickers at the frequency in the frequency band including the extremely low frequency fc, based on the above-mentioned reason. On the other hand, the infrared ray energy of the mercury lamp is maintained at the prescribed level (neglecting the fluctuation in power supply and noise) as indicated in FIG. 10 (b) and the frequency of the flicker is approximately 0 Hz (only DC part). Further, the infrared ray energy of the rotary lamp is clearly accompanied by, the periodic fluctuation as indicated in FIG. 10 (c) and its frequency is synchronous with the revolution of the rotary lamp. The rotary lamp is diversified in kind, including one. In which one lamp is turned in one direction at the prescribed speed (about two turns a second), and one in which a plurality of lamps are turned in a synchronous or asynchronous manner, and their frequency component is also diversified, but the rotary lamp of any kind is same in that it is periodically operated.
FIG. 11a-c shows an observation of the infrared ray energy of the flame, the mercury lamp and the rotary lamp (e.g., the output taken out as the temperature information through the chopper) relative to the frequency axis. Similar to FIG. 10, (a) denotes the flame, (b) denotes the mercury lamp, and (c) denotes the rotary lamp. The axis of abscissa means the frequency, and the origin means 0 Hz (DC part). The level in the vicinity of the origin is fairly large in (a), (b) and (c), and the peak is too high to be described in a graph, and omitted due to limitations of space.
A flame detection device to solve the problem is also proposed. This device made use of not the phenomenon known as the CO2 resonance, but the radiation phenomenon that a peak appears in the vicinity of 4.4 μm in the spectrum distribution of the infrared ray to be irradiated from an infrared ray radiation body accompanied by the flame. This flame detection device comprises, for example, a band pass filter for center extraction to pass the infrared ray of the wavelength around 4.4 μm, and one or a plurality of band pass filters for periphery extraction to pass the infrared ray of the wavelength not including those close to 4.4 μm so that these band pass filters can be switched by a switching mechanism such as a rotary plate. (Japanese Unexamined Patent Publication No. 50-2497, Japanese Unexamined Patent Publication No. 53-44937). Alternatively, the flame detection device comprises a detection element in which a band pass filter for center extraction is arranged on its forward side, and a detection element in which a band pass filter for peripheral extraction is arranged on its forward side.
Among others, U.S. Pat. No. 4,866,420 is given as a fire detection method using the flame flicker frequency spectrum. In the U.S. Pat. No. 4,866,420, a standardized idealized spectrum curve P(f) is compared with the real time spectrum for over 2 seconds. It is then judged whether or not the real time spectrum is deviated by more than the minimum quantity from the idealized spectrum curve P(f), or deviated from the prescribed window and the maximum deviation limit, and the detected signal is a true fire or a mistake. More specifically, as indicated in its flow chart of FIG. 6, it is judged that the detected signal is a true fire when all three limits (steps 34, 37 and 38) are judged to be Yes, while it is judged to be a mistake when any of the three limits are not complied with. In the first step 34, it is judged whether or not the standard deviation is smaller than 7.5 dB in order to roughly confirm a true fire. In the next step 37, it is judged whether or not the number of the curves or parts deviated from a window of 20 dB is smaller than the 25 Hz band width of 19%. In the final step 38, it is judged whether or not two maximum deviations are smaller than 25 dB. The steps 37, 38 are run in order to clearly confirm any mistake.
FIG. 1 is a conceptual view of a first embodiment of the present invention;
FIG. 2 is a graph to indicate the relationship between the signal intensity (obtained by observing the infrared ray from the combustion flame and analyzing the frequency) and the frequency;
FIG. 3 is a flowchart suitable for application to a judgment circuit;
FIG. 4 is a conceptual diagram of a second embodiment;
FIG. 5 is a conceptual diagram of a third embodiment;
FIG. 6 is a conceptual diagram of a fourth embodiment;
FIG. 7 is a conceptual diagram of a fifth embodiment;
FIG. 8 is a conceptual diagram of a conventional flame detection device;
FIG. 9 is a schematic view of how a flame burns;
FIG. 10 is a characteristic figure (time base) of an infrared ray energy radiation body including the flame; and
FIG. 11 is a characteristic figure (frequency base) of an infrared ray energy radiation body including the flame.
FIG. 1 is a conceptual view of the flame detection device in the first embodiment. In the figure, 10 denotes a detection element (not specified, for example, an element using a pyroelectric sensor) to convert the infrared ray energy 11 into the electric signal 12, 13 denotes a first frequency filter, 14 denotes a second frequency filter, 15 denotes a judgment circuit, and 16 denotes an optical wavelength band pass filter.
The first frequency filter 13 has a characteristic to selectively pass the signal in the first prescribed frequency range fCL1-fCH1 (hereinafter, referred to as “first frequency range A”) around the frequency corresponding to the flicker frequency (the frequency fc in the beginning) of the infrared ray energy of the flame. The second frequency filter 14 has a characteristic to selectively pass the signal in the second prescribed frequency range fCL2-fCH2 (hereinafter, referred to as “second frequency range B”) on the higher frequency side adjacent to the first frequency range. The first frequency range A (fCL1-fCH1) is, for example, in a range of 0.5-8.0 Hz, and the second frequency range B (fCL2-fCH2) is, for example, in a range of 8.5-16.0 Hz.
More specifically, the first frequency range of 0.5-8.0 Hz includes both flicker frequencies fc=2.5 Hz and 1.8 Hz under a general condition of the above-mentioned Fire-fighting Certification Standards, and is determined taking into consideration the variance of the frequency due to the difference from other fire conditions and the temporal transition trend of the flicker frequency (the trend in which the flicker frequency becomes smaller as the time is elapsed). This determination is based on the results of several experiments by application, which shows the essential flicker frequency of fire is within 8.0 Hz. The second frequency range of 8.5-16.0 Hz does not include the flicker frequency of fire, and is determined taking into consideration the variance of the frequency similar to the first frequency range, and the temporal transition trend.
FIG. 2 is a graph to indicate the relationship between the signal intensity (obtained by observing the infrared ray from the combustion flame and analyzing the frequency) and the frequency, and the axis of ordinate means the level of the passing signal, and the axis of abscissa means the frequency. In FIG. 2, the crosshatching close to the origin of the frequency axis shows the signal in the first frequency range A passing through the first frequency filter 13. In FIG. 2, the crosshatching on the right side shows the signal in the second frequency range B passing through the second frequency filter 14. As shown in FIG. 2, signal level of a flame fire is high in the first frequency range A, on the other hand, signal level is hardly obtained in the second frequency range B, and also the signal in the range B is extremely lower than signal in the range A. In the figure, the first frequency range A is discontinuous from the second frequency range B, but they can be continuous, or a part of them can be overlapped on each other. The second frequency range B need not be limited to one frequency range, but may be a plurality of frequency ranges. What is important is that the first frequency range A includes the flicker frequency (the frequency fc in the beginning) of the infrared ray energy of the flame, and the second frequency range B does not include the frequency fc, but includes the frequency higher than that in the first frequency range A. Other items can be appropriately regulated according to the requests for the detection performance, etc.
The judgment circuit 15 is a part to judge a fire based on the signal of the first frequency range A and the signal of the second frequency range B, and its preferable algorithm of judgment is described in FIG. 3. The algorithm in FIG. 3 is described by a flowchart, but it does not necessarily mean only the restrictive application to the software processing.
The optical wavelength band pass filter 16 sets the passing characteristic of the wavelength band around the wavelength of 4.4 μm having a high peak through the CO2 resonance radiation specific to the flame, and is provided as necessary.
In FIG. 3, WH dontoes the signal level integrated value of the seconc frequencey range B on the higher frequency side, and WL denotes the signal level integrated value of the first frequency range A on the lower frequency side. The mean value may be used in place of the integrated value. In brief, they may be the generalized energy value of the signal level from which the noise component in each frequency range is removed.
In the flowchart, whether or not WH exceeds the prescribed threshold SLH (S10), the level of SLH is an appropriate level which is higher than WH of the flame, and is lower than WH of other infrared ray energy radiation body with the fluctuation in the infrared ray energy similar to the flame, for example, the “rotary lamp”. Thus, when the judgment is YES in S10, the infrared ray energy radiation body can be identified as another infrared ray energy radiation body with fluctuation in the infrared ray energy similar to the flame, for example, the “rotary lamp”, and in this case, no fire is present, and the flow is completed.
On the other hand, if the judgment is NO in S10, it is proved that the infrared ray energy radiation body is not the “rotary lamp”. However, in only this judgment, it can not be clearly discriminated whether the infrared ray energy radiation body is the “flame” or not. For example, it can not be discriminated whether the body is the flame or other infrared ray energy radiation body without fluctuation in the infrared ray energy, for example, the “mercury lamp”. Thus, for the discrimination, it is judged (S20) whether or not WL exceeds the prescribed threshold SLL. The level of SLL is an appropriate level which is lower than WL of the flame, and higher than WL of other infrared ray energy radiation body without fluctuation in infrared ray energy, for example, the “mercury” lamp. Thus, if the judgment is NO in S20, the infrared ray energy radiation body is identified to be other infrared ray energy radiation body such as a radiation body with the infrared ray energy of only DC part, for example, the “mercury” lamp, and the flow is completed because no fire is present in this case. On the other hand, if the judgment is YES in S20, the infrared ray energy radiation, body is one with WL exceeding SLL i.e., the flame, and the fire detection signal is outputted (S30) and the flow is completed because fire is present.
As mentioned above, in the first embodiment, the output signal of the infrared ray energy detection element 10 is passed through two frequency filters (the first frequency filter 13 and the second frequency filter 14) to extract the representing signal (WL) of the first frequency range A around the frequency corresponding to the flicker frequency (the frequency fc in the beginning) of the infrared ray energy of the flame, and the representing signals (WH) of the second frequency range B on the higher frequency side adjacent to the first frequency range A, and the fire is judged based on these two representing signals (WL, WH) by the judgment circuit 15. Thus, compared with the judgment based on the single signal component, a remarkably advantageous effect of improving the identification performance of other infrared ray energy radiation body with fluctuation in infrared ray energy similar to the flame, for example, the “rotary lamp” in the beginning from the “flame”, can be obtained.
The second embodiment of the present invention described in FIG. 4, is described.
The flame detection device of the present embodiment is provided with the detection element 20, the first frequency filter 21 and the second frequency filter 22 similar to those in the above-mentioned embodiment, and in addition, provided with a first amplification part 23 to amplify the signal (WL) of the first frequency range A to be taken out of the first frequency filter 21, a second amplification part 24 to amplify the signal (WH) of the second frequency range B to be taken out of the second frequency filter 22, a comparison part 25 to judge a fire based on the signals (WL, WH) of these two frequency ranges, and an output part 26 to generate the fire detection signal according to the result of judgment.
The comparison part 25 judges a fire when the ratio of WL to WH (WL/WH) exceeds the prescribed threshold (the third prescribed value). The “flame” and the mercury lamp, and “the flame” and the “rotary lamp” can also be discriminated from each other, respectively. This is because the ratio WL/WH≧4.0 in the case of the “flame” under a certain environment based on the experiment by the inventors, while the ratio WL/WH≦3.0 in the case of the “mercury lamp” and “the rotary lamp”, and the “flame” can be correctly discriminated from other two cases by appropriately setting the threshold according to the experimental results and the environment. That is, the fire can be detected by setting the ratio to the prescribed threshold=4.0. In addition, the threshold may be automatically or manually changed so as to be adapted to the environmental condition, etc.
Next, the third embodiment of the present invention shown in FIG. 5 is described.
The flame detection device of the present embodiment is provided with a detection element 30 similar to that in the above-mentioned embodiment, and also provided with at least a pre-filter 31 to cut the signal of the frequency range exceeding the above-mentioned second frequency range B, an amplification part 32 to amplify the output signal of the pre-filter 31, an AD conversion part 33 to convert the output signal of the amplification part 32 into the digital signal, a digital signal processing part 34 having the function equivalent to the first frequency filter 21 and the second frequency filter 22 in FIG. 4, a judgment part 35 to judge a fire based on the output signal of the digital signal processing part 34—each output signal of the first frequency filter 21 and the second frequency filter 22 in FIG. 4, i.e., the signal corresponding to the signal (WL) of the first frequency range A and the signal (WH) of the second frequency range B, and an output part 36 to output the fire detection signal according to the result of judgment of the judgment part 35.
The judgment part 35 judges a fire when the ratio of WL to WH (WL/WH) is within a range of the prescribed threshold similar to the above-mentioned condition of the second embodiment.
In this example of the embodiment, the function of two filters (equivalent to the first frequency filter 21 and the second frequency filter 22 in FIG. 4) it is important to take out the signal of the first frequency range A and the signal of the second frequency range B, is digitally realized. Thus, a remarkable advantage that the idealized filter characteristic can be easily formed, is obtained. These two filters correctly take out the signal of extremely low frequency (in the vicinity of 1.8 Hz and 2.5 Hz), but in practice, it is fairly difficult to design an analog filter with such a steep cut-off characteristic at such a low frequency. Also, used in the flame detection device are inexpensive, and even if a filter of the desired characteristic is manufactured, its employment is less possible. On the other hand, in the digitally realized filter, the desired filter characteristic can be easily obtained at low cost only by designing the software (program) if its realizing means is a data processing unit for general use, or by achieving the logical design if its realizing means is a programmable logic circuit. Thus, not only the above-mentioned signal of low frequency can be correctly ascertained, but also the DC part can be provided, and flame detection performance can be further improved.
The fourth embodiment of the present invention indicated in FIG. 6 is described.
The present embodiment is a modification of the above-mentioned third embodiment, and different in that a method of the Fast Fourier Transformation (FFT) is adopted in the digital signal processing part 40 so as to take out the signal of the first frequency range A and the signal of the second frequency range B. FFT is a calculation method in which the operational procedures in the discrete Fourier transformation operation are appropriately decomposed, and the number of calculation originally reaching around N2 is reduced to around NlogN, taking into consideration the periodicity and symmetry of the series. The FFT is extensively used as the method to digitally analyze the frequency spectrum X(ω) of the non-periodic time function x(t). The effect similar to that of the above-mentioned third embodiment can also be obtained by using the FFT algorithm. Alternatively, the method of the Maximum Entropy Method (MEM) may be adopted to the digital signal processing part 40. MEM is a method to estimate the spectrum with higher resolution than that of FFT in a short time of measurement.
Next, the fifth embodiment of the present invention indicated in FIG. 7, is described.
Based on the consideration as mentioned above and relationship as sampling frequency=amount of sampling data/sampling time, two suitable conditions can be set as shown in Table 1. In the condition of case 1, sampling time=2 sec, sampling frequency=32 Hz and amount of sampling data=64. In the condition of case 2, sampling time 4 sec, sampling frequency=32 Hz and amount of sampling data=128.
Also, a frequency pitch (a frequency resolving power), which is obtained as a result of the FFT, is an inverse number of sampling time. Thus, the pitch=0.5 Hz in case 1 and the pitch=0.25 Hz in case 2.
Based on the consideration, in condition of case 1, a lowest frequency 0.5 Hz except for the first value is set to fCL1. Also, based on the above consideration of frequency distribution, 8 Hz and 16 Hz are set to fCH1 and fCH2 respectively. Also, fCH1 and frequency pitch make fCL2 as 8.5 Hz.
Based on the same reason, in condition of case 2, 0.25 Hz, 8 Hz, 8.25 Hz and 16 Hz are set to fCL1, FCH1, fCL2, fCH2 respectively.
Second value (1 frequency pitch from the first value, namely, 0.5 Hz in condition of case 1, and 0.25 Hz in condition of case 2 ) might be very larger than other values too, depending on sampling frequency and amount of sampling data etc. In such a case, it is preferable to eliminate the second value too. Thus, 1.0 Hz is set to fCL1 in condition of case 1, and 0.5 Hz is set to fCL1 in condition of case 2.
of Case 1 of Case 2
Sampling Time (sec) 2 4
Sampling Frequency (Hz) 32 32
Amount of Sampling Data 64 128
Frequency Pitch after FFT (Hz) 0.5 0.25
fCL1 0.5 0.25
fCH1 8 8
fCL2 8.5 8.25
fCH2 16 16
a first step to extract the representing signal of a first prescribed frequency range including the flicker frequency fc of the infrared ray energy of the flame and the representing signal of a second prescribed frequency range including no flicker frequency fc of the infrared ray energy of the flame and including the frequency on the higher frequency side than that of said first prescribed frequency range from the output signal of a detection element to convert the infrared ray energy into the electric signal and
a second step to judge that a fire is generated when the representing signal of the second prescribed frequency range extracted is obtained, and said representing signal level is lower than the representing signal of the first prescribed frequency range.
US09321184 1998-06-02 1999-05-27 Flame detection device and flame detection Active US6373393B1 (en)
JP10-153224 1998-06-02
JP15322498 1998-06-02
US6373393B1 true US6373393B1 (en) 2002-04-16
ID=15557778
US09321184 Active US6373393B1 (en) 1998-06-02 1999-05-27 Flame detection device and flame detection
US (1) US6373393B1 (en)
GB (1) GB2338061B (en)
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Owner name: HOCHIKI KAUBSHIKI KAISHA, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:MATSUKUMA, HIDENARI;SHIMA, HIROSHI;AIZAWA, MASATO;REEL/FRAME:010012/0942