Flame detector

Abstract

To obtain a flame detector that improves the accuracy of flame detection. [Solution] A flame detector comprising: a first element having spectral sensitivity in a first wavelength region including the CO2 resonance radiation band specific to flames; a second element having spectral sensitivity in a second wavelength region suitable for distinguishing between flames and false alarm sources; and a detection unit that performs a detection process to detect the occurrence of a flame after determining between a flame and a false alarm source from the detection results of the first and second elements, wherein the monitoring range of the flame detector is limited such that the angle of incidence to the first element is limited to a predetermined range in the front direction; the first element has an optical filter with an optimally designed bandwidth that transmits through the CO2 resonance radiation band when the monitoring range is limited; and the optical filter suppresses fluctuations in spectral transmittance characteristics and a decrease in detection sensitivity caused by the angle of incidence to the first element.

Description

Technical Field

[0001] The present disclosure relates to a flame detector that detects the occurrence of a flame after discriminating a false alarm source and a flame.

Background Art

[0002] As an example, in a current flame detector used to detect a fire occurring in a tunnel, a flame is detected using respective detection results by two elements having detection sensitivities in different wavelength bands.

[0003] More specifically, a photodiode is used as a sensor for detecting the near-infrared region, a pyroelectric element is used as a sensor for detecting the mid-infrared region, and discrimination is made between a detected fire and a light source that causes a false detection according to the wavelengths detected by these sensors (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the prior art has the following problems. In order to cope with various site situations that require a flame detector, it is desired to further enhance the function of a conventional flame detector so as to improve the flame detection accuracy. That is, it is desired to improve the flame detection accuracy further after discriminating a false alarm source and a flame with respect to the prior art that detects two wavelengths.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to obtain a flame detector that realizes an improvement in flame detection accuracy.

Means for Solving the Problems

[0007] The flame detector according to this disclosure comprises a first element having spectral sensitivity in a first wavelength region including the CO2 resonance radiation band specific to flames, a second element having spectral sensitivity in a second wavelength region suitable for distinguishing between flames and false alarm sources, and a detection unit that performs a detection process to detect the occurrence of a flame after determining whether it is a flame or a false alarm source from the detection results of the first and second elements, wherein the monitoring range of the flame detector is limited such that the angle of incidence to the first element is limited to a predetermined range in the front direction, and the first element has an optical filter with an optimally designed bandwidth that transmits through the CO2 resonance radiation band when the monitoring range is limited, and the optical filter suppresses fluctuations in spectral transmittance characteristics and a decrease in detection sensitivity caused by the angle of incidence to the first element. [Effects of the Invention]

[0008] According to this disclosure, a flame detector that improves the accuracy of flame detection can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing the configuration of a flame detector in Embodiment 1 of the present disclosure. [Figure 2] This is an explanatory diagram showing the effect of the incident angle on the relative intensity in Embodiment 1 of the present disclosure. [Figure 3] This figure shows the relationship between the monitoring distance and the incident angle in a typical flame detector in Embodiment 1 of the present disclosure. [Figure 4] This diagram illustrates the improvement of detection accuracy when the field of view is limited to a relatively narrow area in Embodiment 1 of the present disclosure. [Figure 5] This diagram summarizes the characteristics of the relative sensitivity to wavelengths for flames and false alarm sources in Embodiment 1 of this disclosure. [Figure 6] This is a diagram showing the configuration of the flame detector in Embodiment 2 of the present disclosure. [Figure 7] This figure shows a flame detector in which two pairs of elements are mounted, according to Embodiment 2 of the present disclosure. [Modes for carrying out the invention]

[0010] Hereinafter, preferred embodiments of the flame detector of this disclosure will be described with reference to the drawings. This disclosure is characterized by achieving improved flame detection accuracy by using an optical filter suitable for transmitting a first wavelength region including the CO2 resonance radiation band specific to flames, assuming that there is a flame in front of it.

[0011] Embodiment 1. Figure 1 is a diagram showing the configuration of a flame detector in Embodiment 1 of the present disclosure. The flame detector according to Embodiment 1 comprises a pair of elements 10 and a detection unit 20. The pair of elements 10 includes a first element 11 and a second element 12.

[0012] The first element 11 is an element that has spectral sensitivity in a first wavelength region that includes the CO2 resonance radiation band characteristic of flames. The second element 12 is an element that has spectral sensitivity in a second wavelength region suitable for distinguishing between flames and false alarm sources.

[0013] The detection unit 20 detects the occurrence of a flame after distinguishing between a flame and a false alarm source based on the detection results of the first element 11 and the second element 12, respectively.

[0014] Flame detectors with this configuration are installed one or more times within the fire monitoring area. Generally, in flame detectors that utilize CO2 resonance, the fire monitoring area for each unit is set to a relatively wide range, for example, a field of view of +45° to -45°. In other words, flame detection is performed even for infrared radiation coming from an oblique angle, such as +45° or -45°, to a pair of elements 10.

[0015] Figure 2 is an explanatory diagram showing the effect of the angle of incidence on relative intensity in Embodiment 1 of this disclosure. The vertical axis represents relative intensity, and the horizontal axis represents wavelength. In Figure 2, three types are shown: dotted line, solid line 1, and solid line 2, each corresponding to the following characteristics.

[0016] Dotted line: It shows the wavelength range of the flame when a heptane fire occurs, and has a peak of relative intensity in the wavelength band of about 4.3 μm to 4.4 μm. Solid line 1: It shows the relative intensity of the element when a flame occurs at the position in the front of the element (corresponding to an incident angle of 0°). Solid line 2: It shows the relative intensity of the element when a flame occurs at the position at the edge of the viewing angle (corresponding to an incident angle of +45°).

[0017] As is clear from FIG. 2, as the incident angle to the element increases, the waveform shifts to the short wavelength side and the relative intensity also tends to decrease. The reason for the decrease in the relative intensity is that due to the oblique incidence, when the incident angle is θ, the area on which the light beam hits decreases by COSθ.

[0018] In addition, in order to detect a flame with high precision by the first element, an optical filter that transmits a first wavelength region including a CO2 resonance emission band peculiar to the flame is used. However, since such an optical filter is based on the principle of interference, the optical path length in the optical thin film changes depending on the incident angle and the interference conditions change, resulting in different spectral transmittance characteristics for each incident angle.

[0019] FIG. 3 is a diagram showing the relationship between the monitoring distance and the incident angle in a general flame detector in Embodiment 1 of the present disclosure. For example, regarding a 15 cm square normal heptane fire pan, a monitoring distance of 25 m can be achieved at an incident angle of 0°, but when the incident angle becomes 45°, the monitoring distance becomes half, decreasing to 12.5 m.

[0020] Similarly, regarding a 33 cm square normal heptane fire pan, a monitoring distance of 60 m can be achieved at an incident angle of 0°, but when the incident angle becomes 45°, the monitoring distance becomes half, decreasing to 30 m.

[0021] That is, considering the characteristics of FIG. 2 and the characteristics of the optical filter described above, as shown in FIG. 3, the larger the incident angle, the shorter the monitoring distance, leading to a decrease in the detection sensitivity.

[0022] Therefore, the flame detector in this embodiment 1 is characterized by limiting the monitoring range to the vicinity of the front of the flame detector, thereby improving detection sensitivity in a region with a relatively narrow field of view compared to conventional devices.

[0023] Figure 4 is an explanatory diagram illustrating the improvement of detection accuracy when the field of view is limited to a relatively narrow area in Embodiment 1 of this disclosure. As shown in Figure 2 above, when the field of view is 45°, the signal waveform shifts and the signal intensity decreases compared to when the field of view is 0°.

[0024] However, by limiting the field of view to near 0°, it becomes unnecessary to consider the shift phenomenon caused by the field of view. Furthermore, as shown in Figure 4, the optical filter provided in the first element can be optimized by widening its bandwidth to cover the entire wavelength range of the flame in a heptane fire, as indicated by the dotted line, thereby increasing the amount of incident energy.

[0025] By optimizing the optical filter design, it is possible to increase the amount of incident energy transmitted through the first wavelength region, which includes the CO2 resonance radiation band that should be detected, while suppressing false detection of wavelengths other than the first wavelength region.

[0026] As a result, detection sensitivity can be improved in areas with a relatively narrow field of view compared to conventional methods. However, limiting the field of view to near 0° will narrow the monitoring range. Nevertheless, by providing a drive mechanism that can move the direction of the flame detector, mounting the flame detector on the drive mechanism, and performing monitoring in multiple directions, it is possible to expand the monitoring range.

[0027] Specifically, the detection unit 20 controls the positioning of a drive mechanism on which a pair of elements 10 are mounted and which can move in the direction of direction of the pair of elements 10. After moving the pair of elements 10 in the desired direction of direction, it can perform flame detection processing based on the detection results of the first and second elements.

[0028] Furthermore, a supplementary explanation will be given regarding the second element that detects a second wavelength region suitable for distinguishing between flames and false alarm sources. Figure 5 is an explanatory diagram summarizing the characteristics of the relative sensitivity to wavelengths for flames and false alarm sources in Embodiment 1 of this disclosure. In Figure 5, "heptane fire" is a detection target that should be identified as a flame, and its relative sensitivity is high in the mid-wavelength band.

[0029] On the other hand, "100°C high-temperature objects" exhibit high relative sensitivity in the long-wavelength band, while "sunlight" and "xenon lamps" exhibit high relative sensitivity in the short-wavelength band. In other words, either or both of the long-wavelength and short-wavelength bands correspond to a second wavelength region suitable for distinguishing between flames and false alarm sources.

[0030] Therefore, as shown in Figure 4 above, by designing an optical filter that appropriately transmits the first wavelength region and applying it to the first element, the wavelength band of the false alarm source can be cut out, and flame detection can be achieved with higher relative sensitivity than before. In other words, assuming that there is a flame near the front, the first element 11 can be optimally designed so that the wavelength region of 4.2 μm to 4.65 μm is the first wavelength region, which is the bandwidth that transmits the CO2 resonance radiation band. By designing the optical filter to encompass the entire CO2 resonance radiation band, the signal-to-noise ratio is also improved.

[0031] As described above, according to Embodiment 1, the first element is provided with an optical filter designed to have an optimal bandwidth for transmitting the CO2 resonance radiation band while limiting the field of view to near 0°. As a result, the effect of the decrease in incident energy as the field of view increases is suppressed, and the amount of incident energy transmitted through the first wavelength region, which includes the CO2 resonance radiation band that should be detected, can be increased by the optical filter with an appropriate bandwidth. This makes it possible to obtain a flame detector that suppresses false detections and improves flame detection accuracy.

[0032] Embodiment 2. In the first embodiment described above, a method was explained to improve the performance of a flame detector by suppressing false detections using a pair of elements consisting of a first element and a second element, thereby improving flame detection accuracy. In this second embodiment, a method for further improving the performance of the flame detector will be described.

[0033] Figure 6 is a diagram showing the configuration of a flame detector in Embodiment 2 of this disclosure. The flame detector according to Embodiment 2 differs from the flame detector according to Embodiment 1 shown in Figure 1 in that it has two pairs of elements 10. Here, both the pair of elements 10a and the pair of elements 10b have the same configuration as the pair of elements 10 described in Embodiment 1, and are configured as two pairs of elements 10a and 10b.

[0034] Figure 7 shows a flame detector in which two pairs of elements 10a and 10b are mounted according to Embodiment 2 of the present disclosure. The first elements 11a and 11b are arranged diagonally to each other, and the second elements 12a and 12b are also arranged diagonally to each other.

[0035] By using two pairs of elements 10a and 10b, the effect of adding two detection results can be obtained with a single detection. If the signal-to-noise ratio (S / N ratio) is defined by the standard deviation, it can be expected that adding K measurement results (where K is an integer greater than or equal to 2) will improve the S / N ratio by a factor of √K.

[0036] Therefore, the detection unit 20 according to this second embodiment can distinguish between a flame and a false alarm source and detect the occurrence of a flame with high accuracy in a single detection timing, based on the result of adding the detection results of the two pairs of elements 10a and 10b.

[0037] As described above, according to Embodiment 2, by using K pairs of elements, the signal-to-noise ratio of the detection signal during the same detection time can be improved by √K times compared to the case where only one pair of elements is used. As a result, a flame detector can be obtained that suppresses false detections and achieves further improvement in flame detection accuracy. [Explanation of Symbols]

[0038] 10 A pair of elements, 11, 11a, 11b First elements, 12, 12a, 12b Second elements, 20 Detection unit.

Claims

[Claim 1] CO specific to flames ２ A first element having spectral sensitivity in a first wavelength region including the resonant radiation band, A second element having spectral sensitivity in a second wavelength region suitable for distinguishing between flames and false alarm sources, A detection unit that performs a detection process to detect the occurrence of a flame after determining the flame and the false alarm source from the detection results of the first element and the second element, respectively. A flame detector equipped with, The flame detector has a limited monitoring range such that the angle of incidence to the first element is restricted to a predetermined range in the forward direction. The first element, in the state where the monitoring range is limited, the CO ２ It has an optical filter with an optimally designed bandwidth that transmits through the resonant radiation band. The optical filter suppresses fluctuations in spectral transmittance characteristics and a decrease in detection sensitivity caused by the incident angle on the first element. Flame detector.

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