JP2740262B2 - Particle size measurement smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Industrial applications]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle size measurement type smoke detector that detects smoke generated in a fire or the like in a building by measuring the particle size of smoke particles.

[Prior art]

2. Description of the Related Art Conventionally, a smoke detector using light scattering by smoke particles has been provided (JP-A-56-147294, JP-A-58-17).
No. 1591, Japanese Unexamined Patent Publication No. 60-109189, Japanese Utility Model Application No. 60-13449
And Japanese Utility Model Application Laid-open No. Sho 62-20358). In a conventionally provided smoke detector, the light projecting means and the light receiving means are arranged so that their optical axes do not coincide with each other, and the light scattered by the smoke particles of the light projected from the light projecting means is received by the light receiving means. Thus, smoke particles are detected based on a change in the amount of received light due to the presence or absence of smoke particles. By the way, since light is scattered not only by smoke but also by water vapor or dust, there is a problem that a false alarm easily occurs in the smoke detector having the above configuration. To solve such a problem,
An accumulation-type smoke detector that emits an alarm only when the change in the amount of received light continues for a predetermined time or more has been put to practical use.

[Problems to be solved by the invention]

The above-mentioned accumulation type smoke detector has a problem that it takes a long time from the generation of smoke to the generation of an alarm, and goes against early detection in a fire or the like. The present invention is aimed at solving the above problems,
By measuring the particle size of the particles that cause scattering, it distinguishes smoke from water vapor and dust to prevent false alarms, and to detect smoke generation at the time of fire etc. at an early stage. It is intended to provide a type smoke detector.

[Means for Solving the Problems]

In the present invention, in order to achieve the above object, a light projecting means for projecting a light beam composed of a parallel light beam having coherence, and scattered light by smoke particles of the light beam arranged opposite to the light projecting means. In a particle diameter measuring type smoke sensor having light receiving means for receiving light and discriminating means for detecting the presence of smoke particles by measuring the particle diameter of the smoke particles based on a light receiving signal from the light receiving means, the light receiving means is projected. A pattern detecting device having a light receiving surface orthogonal to the optical axis of the optical means and detecting the intensity distribution of light on the light receiving surface; and a diffraction image of each order by forward minute angle scattering on the light receiving surface of the pattern detecting device. The Fourier transform lens forms images at equal intervals, and the discriminating means measures the particle diameter based on the intensity distribution of the light received by the pattern detection device.

[Action]

According to the above configuration, since the presence of the smoke particles is detected based on the particle size of the smoke particles, it is possible to prevent false reports due to scattering of other particles having a different particle size from smoke such as water vapor and dust. In addition, since false alarms can be prevented by particles other than smoke, it is not necessary to use a storage-type configuration that emits an alarm when smoke particles are detected for a predetermined time or more. This would enable early detection of fires. Next, the principle of the present invention will be described. As a method for measuring the particle size of fine particles contained in an aerosol (including smoke), a measurement method based on Mie scattering theory is known. Now, the irradiation light to the aerosol is a parallel light beam having coherence, and the particle diameter (diameter) of the scattering particles is D,
The particle diameter parameter α is defined as follows, where λ is the wavelength of the irradiation light. α = πD / λ It is known that when the particle diameter parameter α increases, scattered light concentrates forward and a clear forward lobe is formed. Scattering within this forward lobe is called forward small angle scattering. I have. Since this scattering is due to Fraunhofer diffraction, it is mainly governed by the particle size and is hardly affected by the optical properties of the particles. Therefore, if the diffraction angle is known, the particle size parameter can be known, and the particle size of the particles can be known. However,
Since the aerosol contains particles with various particle sizes, the diffraction angle is not uniquely determined, and the particle size range of the particles contained in the aerosol can be known from the light quantity distribution of the diffraction image. It is. Further, the condition for establishing the Fraunhofer diffraction is α> 1, and the measurement range of the particle size of the target particle depends on the wavelength of the irradiation light.

【Example】

As shown in FIG. 1, a laser light source 1 is provided as a light projecting means, and projects a light beam which is a parallel light beam having coherence. The light receiving means is disposed to face the laser light source 1, and a space between the light receiving means and the laser light source 1 is a monitoring space into which smoke particles a and particles b other than smoke are introduced. The light receiving means includes a pattern detection device 3 in which a large number of circular photocells 2 are arranged concentrically, and a Fourier transform lens 4 disposed in front of the pattern detection device 3. That is, the light beam from the laser light source 1 is scattered by the smoke particles introduced into the monitoring space, and a diffraction image by forward small angle scattering is two-dimensionally Fourier-transformed through the Fourier transform lens 4. Is formed on the light receiving surface of the light emitting element. In the Fourier transform lens 4, the incident angle θ of the light beam with respect to the optical axis, the height h of the image, and the focal length f are defined as h = f · si
When the diffracted light passes through the Fourier transform lens 4, diffraction images of each order are formed at equal intervals when the lens is set to have a relationship of nθ. That is, the distance from the optical axis on the light receiving surface of the pattern detection device 3 becomes a sine function of the scattering angle. By using the Fourier transform lens 4, in the pattern detection device 3, the photocells 2 may be arranged at equal intervals on the light receiving surface, and the design becomes easy. The Fourier transform lens 4 is held by the fine adjustment device 5, and can adjust the angle of the optical axis of the Fourier transform lens 4 with respect to the light receiving surface of the pattern detection device 3 or adjust the distance from the pattern detection device 3. I can do it. The output of the pattern detection device 3 is input to a discrimination device 6 such as a microcomputer constituting a discrimination means. The discriminating device 6 measures the particle size of the smoke particles based on the distribution pattern of the received light intensity by the diffracted light pattern detection device 3, and issues an alarm when it is determined that the particle size corresponds to the smoke particles. The discriminating device 6 discriminates the type of the particle based on the intensity distribution of the diffracted light as described below. That is, when the light intensity distribution in the diffracted image is measured using the light projecting means and the light receiving means having the same configuration as in the above embodiment, the result shown in FIG. 2 is obtained. Here, a helium-neon laser having an output wavelength of 633 nm is used as the laser light source 1, 32 photocells 2 are provided, the focal length of the Fourier transform lens 4 is 63 mm, and the minimum diameter of the measurable particles is about 0.1 μm. 2 (a) to 2 (h), the horizontal axis of the outer graph is the particle diameter (unit: μm), the vertical axis is the particle number density (unit:%),
The horizontal axis of the inner graph is the photocell 2 number, and the vertical axis is the received light intensity. The photocells 2 are arranged concentrically,
Numbered 1,2, ..., 32 from inside. Therefore, for small particles with a large diffraction angle,
Since the light receiving intensity in the photocell 2 with a large number increases, and the diffraction angle decreases in a particle having a large particle size,
The received light intensity at the photocell 2 assigned a small number increases. FIGS. 2 (a) to 2 (e) show the results of measuring the particle size of combustion smoke by heating urethane, kerosene, paper, wood, and cotton wick in an electric furnace at 500 to 600 ° C., respectively. 2 (f) to 2 (h) show the measurement results for smoke, steam and dust of tobacco, respectively. The measured particle sizes are as shown in the following table. From the above measurement results, it can be seen that the particle size is substantially uniform except for dust. The steam has a particle size of 5.0 to 6.4 μm
Since the particle size is larger than that of smoke, it can be distinguished from smoke. In other words, the received light intensity distribution in the pattern detection device 3 changes as shown in FIGS. 2A to 2H depending on the type of the particles. This can prevent false reports from being made. In the above embodiment, the pattern detection device 3 in which a large number of photocells 2 are arranged is used, but an imaging device such as a two-dimensional image sensor may be used. Also, the resolution can be increased by shortening the wavelength of the laser light source 1 and increasing the number of photocells 2. Further, in the case of smoke having a low transmittance such as black smoke generated at the time of a fire, the amount of light received by the pattern detection device 3 becomes small and the distribution of the received light intensity becomes unclear. A method of detecting the particle diameter of smoke particles, deriving reference light from an optical fiber from a laser light source 1 without passing through a monitoring space, and detecting the presence of smoke particles based on an intensity ratio between the reference light and scattered light. When used together, a fire can be reliably detected.

【The invention's effect】

As described above, the present invention provides a light projecting means for projecting a light beam composed of a coherent parallel light beam, and a light receiving means arranged opposite to the light projecting means for receiving light scattered by smoke particles of the light beam. And a discriminating means for detecting the presence of smoke particles by measuring the particle diameter of the smoke particles based on a light receiving signal from the light receiving means. A pattern detector that has a light-receiving surface perpendicular to the axis and detects the intensity distribution of light on the light-receiving surface; and forms diffraction images of each order by forward small-angle scattering at equal intervals on the light-receiving surface of the pattern detector. And a Fourier transform lens for imaging.The discriminating means measures the particle size based on the intensity distribution of the light received by the pattern detection device. Because it detects the presence, There is an advantage that the smoke, such as stiffness can be prevented false alarms due to scattering at different other particles particle sizes. In addition, as a result of preventing false reports due to particles other than smoke,
Since there is no need to use a storage-type configuration that emits an alarm when smoke particles are detected for more than a predetermined time, an early detection of a fire can be performed if used as a fire detector. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, and FIG. 2 is a principle explanatory diagram showing a distribution state of received light intensity corresponding to each particle in the embodiment. DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Photocell, 3 ... Pattern detection device, 4 ... Fourier transform lens, 5 ... Fine adjustment device, 6 ... Determination device.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Akio Takemoto 3-14 Nakahara, Mitaka City, Tokyo Inside the Fire Research Institute of the Fire and Disaster Management Agency of the Ministry of Home Affairs (72) Inventor Yoshihiko Okuda 1048 Kazuma Kazuma, Kadoma City, Osaka Matsushita Electric Works, Ltd. (56) References JP-A-51-15487 (JP, A) JP-A-63-157035 (JP, A) JP-A-59-70944 (JP, A) Kazuhiro Hayashida and two others, “Shimadzu laser diffraction Type particle size distribution analyzer SALD-1000 and its measurement example ", Shimadzu Review, 1988, Vol. 45, Nos. 1, 2 pp. 77-84

Claims (1)

(57) [Claims] 1. A light projecting means for projecting a light beam composed of a parallel light beam having coherence, a light receiving means arranged opposite to the light projecting means for receiving light scattered by smoke particles of the light beam;
A particle diameter measurement type smoke detector having a determination means for detecting the presence of the smoke particles by measuring the particle diameter of the smoke particles based on a light reception signal by the light reception means, wherein the light reception means is located on the optical axis of the light projection means. A pattern detecting device having an orthogonal light receiving surface and detecting the intensity distribution of light on the light receiving surface; and forming a diffraction image of each order by forward small angle scattering at equal intervals on the light receiving surface of the pattern detecting device. A particle size measurement type smoke sensor, comprising: a Fourier transform lens; and a determination unit measuring a particle size based on an intensity distribution of light received by the pattern detection device.