Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2002-03-26
2004-06-29
Gagliardi, Albert (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
Reexamination Certificate
active
06756593
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flame sensor. More particularly, the present invention relates to a flame sensor capable of detecting a flame in place where solar rays or artificial rays of light such as halogen lamp are present without being affected by such rays of light.
2. Description of the Related Art
To detect a flame, there is a convenient method that detects resonance radiation generated by a high-temperature carbonic acid gas contained in the flame, as is well known in the art. A line spectrum of resonance radiation of the carbonic acid gas includes many wavelengths. To discriminate the line spectrum from ordinary artificial illumination and solar rays, it is appropriate to utilize a spectral line within the range of the infrared region or the ultraviolet region for detecting the flame. Because optical components belonging to the infrared region or the ultraviolet region do not much exist in artificial rays of light such as illumination, so disturbance by external light when sensing a flame is less in these regions.
To detect a flame in the presence of solar rays, a conventional method detects the line spectrum due to resonance radiation of the carbonic acid gas generated by the flame. To discriminate a continuous spectrum, such as solar rays and artificial light, from the line spectrum of the flame, this method compares and computes a plurality of outputs obtained from a monochromatic filter having a narrow-band that permits the passage of only the line spectrum of the flame and from monochromatic filters of a plurality of narrow-bands, which permit the passage of rays of light having one or a plurality of wavelengths, and the method discriminates whether light is the line spectrum of the flame or the continuous spectrum of the solar rays.
Another method utilizes flicker of light generated by the flame and detects the occurrence of the flame.
Among conventional methods that utilize resonance radiation of the carbonic acid gas, the method using the filter requires at least three monochromatic filters to achieve a flame sensor providing a small number of erroneous detections and capable of reliably sensing a flame. In addition, a computation circuit for sensing is complicated, and the flame sensor is unavoidably expensive.
Flame sensors using two or less filters involve the problem that the number of erroneous detections is great. Though economical, flame sensors utilizing the flicker of the flame also involve the problem that the number of erroneous detections is great.
Solar rays, artificial rays or radiation from a stove emit not only visible rays, but also radiation in the infrared regions. However, this radiation is a continuous spectrum. In contrast, the spectrum of resonance radiation of the carbonic acid gas generated by the flame is a line spectrum in which energy concentrates in extremely narrow regions.
Therefore, a flame sensor, using two filters, capable of reliably detecting a flame with equivalent certainty to the conventional flame sensors using three filters, is proposed (JP-A10-326391, JP-A2000-321132). This flame sensor utilizes the difference between the continuous spectrum and line spectrum for detecting the flame.
In this flame sensor, a broad band filter for permitting the passage of light of a band broader than a spectral line of resonance radiation of the carbonic acid gas generated by the flame and a narrow band filter for permitting the passage of only the spectral line of resonance radiation of the carbonic acid gas, are used. Intensity (optical energy) of light from the flame passing through these two filters is divided by the bandwidth of each filter to determine mean intensities.
When the intensity of the spectrum of light passing through the filters is a straight line-like continuous spectrum, energy of the rays of light passing through the two filters is proportional to the transmission bandwidth. Therefore, the mean intensities obtained by dividing this energy by the bandwidth are equal for the two filters.
However, when the rays of light passing through the filters are the line spectrum of resonance radiation of the carbonic acid gas, both of these two filters allow this line spectrum to pass therethrough and transmission energy is substantially equal. However, optical energy of the light passing through the broad band filter is divided by a greater bandwidth to calculate the mean intensity, whereas optical energy of the light passing through the narrow band filter is divided by a smaller bandwidth. Consequently, a difference develops between these two mean intensities.
Therefore, the flame can be detected by judging whether or not a difference between the two mean intensities exceeds a threshold value.
However, size of a flame which can be detected by the flame detecting device is inverse proportional to square of a distance between the flame and the flame detecting device. Therefore, wide dynamic range is needed in order to detect a flame in a wide range, that is, from a flame which is located near the device to a flame which is located far away from the device. Regarding flame detection signal and noise, the same consideration is needed. The above threshold value is set in accordance with a distance between the flame detecting device and a main (target) position to be detected. However, when the threshold value is set in accordance with a position to be detected which is near the device, a level of the flame detecting signal for a flame located far way from the device becomes too small and therefore detection of the flame becomes impossible or detection error rises. In contrast, when the threshold value is set in accordance with a position to be detected which is far away from the device, a level of the noise for a flame located near the device becomes too large and therefore detection error rises. Accordingly, there is a problem that it is difficult to detect a flame precisely in a wide range.
Further, when light having a large amount of energy in the infrared ray region, such as solar rays or artificial rays of light such as halogen lamp, is incident, due to that temperature of a filter in the flame detecting device rises, secondary radiation is generated from the filter, and therefore, detection error rises due to the secondary radiation being noise. Further, when stray light is incident in the flame detecting device, the stray light is incident from a side surface of the filter therefore detection error rises.
SUMMARY OF THE INVENTION
To solve the problems described above, an object of the present invention is to provide a flame sensor that can accurately detect a flame in a wide range.
Also, another object of the present invention is to provide a flame sensor that can detect a flame without error even when stray light or light having large energy in a range of an infrared region such as solar rays or rays from halogen lamp is incident.
A first aspect of the present invention for accomplishing the objects described above is a flame sensor comprising: a narrow band filter for transmitting only light of a band corresponding to a line spectrum of carbonic acid gas resonance radiation generated by a flame; a broad band filter for transmitting light of a band which includes the band corresponding to the line spectrum and which is broader than the band corresponding to the line spectrum; a first light reception element for converting light transmitted through the narrow band filter to a first electric signal; a second light reception element for converting light transmitted through the broad band filter to a second electric signal; and a judging section for determining whether or not a difference obtained by subtracting a value corresponding to an intensity of the second electric signal from a value corresponding to an intensity of the first electric signal is equal to or greater than a predetermined value, and a ratio between the value corresponding to the intensity of the second electric signal and the value corresponding to the intensity of the first electric signal is wit
Hirasawa Masanori
Nakauchi Shunsaku
Gagliardi Albert
Harness & Dickey & Pierce P.L.C.
Kokusai Gijutsu Kaihatsu Kabushiki Kaisha
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