JP2703605B2 - Photoelectric smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a photoelectric smoke detector for detecting smoke generated in a fire or the like in a building.

[Prior art]

2. Description of the Related Art Conventionally, a photoelectric smoke sensor using light scattering by smoke particles has been provided as a smoke sensor (Japanese Patent Application Laid-Open No. 56-1472).
No. 94, Japanese Utility Model Laid-Open No. 58-171591, JP-A-60-109189
No., JP-A-60-13449, JP-A-62-20358, etc.). That is, as shown in FIG. 7, the light projecting element 1 and the light receiving element 8 are arranged so that the optical axes do not coincide with each other, and the light scattered by the smoke particles 3 of the light projected from the light projecting element 1 is received by the light receiving element. 8 to receive light. Therefore, when the smoke particles 3 are present, the amount of light received by the light receiving element 8 increases.
Can be detected.

[Problems to be solved by the invention]

In the above configuration, since the presence or absence of the smoke particles 3 is determined based on the amount of received light, it is not possible to discriminate between reflected light due to insects, water vapor and the like entering the sensor and scattered light due to the smoke particles 3. However, there is a problem that misidentification is likely to occur. Also, since the reflected light in the detector is always incident on the light receiving element 8, the background noise is large, and the signal ratio between the absence of the smoke particles 3 and the presence of the smoke particles 3 is increased. However, there is a problem that the noise margin is small. The present invention is aimed at solving the above problems,
By identifying the size of the scattering smoke particles,
Provide a photoelectric smoke detector that prevents erroneous detection due to scattered light due to water vapor and the like and reflected light due to insects, reduces the effect of background noise due to reflected light inside the detector, and increases the noise margin. It is assumed that.

[Means for Solving the Problems]

In the present invention, in order to achieve the above object, scattered light,
A splitter that separates a polarization component whose electric field is parallel to a plane including the optical axis of the light emitting unit and the optical axis of the light receiving unit into a polarization component whose electric field is parallel and a pair of light receiving elements that respectively receive each polarization component And light receiving means, and a determination means for calculating the ratio of the output levels of the two light receiving elements and determining that smoke particles are present when the ratio is within a predetermined range is provided.

[Action]

According to the above configuration, the particle size of the smoke particles is obtained based on the ratio of the intensities of the polarization components orthogonal to each other included in the scattered light due to the smoke, and when the particle size is within a predetermined range, the smoke particles are present. As a result, the particle size of the scattering particles is reflected, and it becomes easy to distinguish between scattering by smoke particles and reflection by other substances. That is, in general, the aerosol is irradiated with light having no polarization, and the polarization component of the scattered light is converted into a polarization component (TE) in which the electric field is parallel to a plane containing the irradiation light and the scattered light (hereinafter referred to as an observation plane). When polarized light and magnetic field are separated into parallel polarized light components (TM polarized light), the ratio of the intensity between TE polarized light and TM polarized light is a function of the wavelength of light and the particle size of aerosol particles.
Known by e-scattering theory. Therefore, if the polarization component of the scattered light is separated into TE polarized light and TM polarized light, and the intensity ratio (polarization ratio) is obtained, the particle size of the aerosol particles can be known. Now, assuming that the intensities of the TE-polarized light and the TM-polarized light are Ip and Is, respectively, the polarization ratio ρ (θ) at the angle (scattering angle) θ of the scattered light with respect to the traveling direction of the incident light is given by ρ (θ) = Ip (θ ) / Is (θ). Here, the intensity Ip, Is of the TE polarized light and the TM polarized light depends on the scattering angle θ. Further, the following values are defined as the particle diameter (diameter) of the aerosol particles that cause scattering, the wavelength of the irradiation light as λ, and the particle diameter parameter α. α = πD / λ There is a relationship as shown in FIG. 5 between the thus defined polarization ratio ρ (θ) and the particle diameter parameter α. Here, the fifth
In the figure, the scattering angle θ is set to 90 °. In FIG. 5, the particle diameter parameter α is a function of the radius a of the particle.
In general, the polarization ratio ρ (θ) is a complicated function with respect to the particle diameter parameter α, but in the region of α <2, it can be regarded as almost monotonic increase as shown in FIG. In this region, if the wavelength of the irradiation light is 0.80 to 0.95 μm, the maximum measurable particle diameter D is 0.51 to 0.61 μm. Here, the general wavelength of infrared light emitting diode and infrared semiconductor laser is
Since the thickness is 0.80 to 0.95 μm, these elements can be used as an irradiation light source. In addition, when a light emitting element having a wavelength of 1.30 μm or 1.55 μm, which is recently used in optical communication, is used, the maximum measurable particle diameter D is 0.83 μm or 0.95 μm. On the other hand, since the size of the smoke particles is 0.1 to 1 μm, the presence or absence of the smoke particles can be determined by determining the polarization ratio. The method of determining the particle size of the aerosol particles in this manner is called a polarization ratio method.

【Example】

As shown in FIG. 1, the light projecting means includes a light emitting element 1 and a light projecting lens 2. As the light emitting element 1, a light emitting diode or a semiconductor laser is used, and emits light of a single color or a narrow band. The light projecting lens 2 is a condenser lens,
The light from the light emitting element 1 is guided to a space region where the smoke particles 3 are introduced. Here, the optical axis of the light emitting element 1 and the light projecting lens 2 is defined as a light projecting axis lt, and the traveling direction of light is defined as 0 °. The light receiving means sets an optical axis forming a predetermined angle θ with respect to the light projecting axis lt as a light receiving axis lr, and on the light receiving axis lr, a light receiving lens 4 as a condenser lens, a diffraction grating 5, a light receiving element 7, Is arranged. Further, the light receiving element 6 is disposed at a position deviated from the light receiving axis lr in a plane (observation plane) including the light projecting axis lt and the light receiving axis lr.
As the light receiving elements 6, 7, a phototransistor, a photodiode, or the like is used. As shown in FIG. 2, the diffraction grating 5 has many grooves on the surface.
5a are formed, and the grooves 5a are arranged so as to be orthogonal to the observation surface. About such a diffraction grating 5,
The following properties are known: That is, the diffraction efficiency is defined as diffraction wave intensity / incident wave intensity, and the wavelength λ and the lattice constant d
When the first-order diffraction efficiency with respect to the ratio (λ / d) is measured, characteristics as shown in FIG. 3 are obtained. Here, FIG. 3A shows that the ratio (h / d) of the depth h of the groove 5a to the lattice constant d is 1.0.
FIG. 3 (b) shows the first-order diffraction efficiency when the same is set to 1.5, and FIG. 3 (c) shows the first-order diffraction efficiency when the same is set to 2.0. Here, the solid line indicates the intensity of the polarization component whose electric field is parallel to the groove 5a of the diffraction grating 5 (TE polarized light with reference to the groove of the diffraction grating), and the broken line indicates the polarization component whose magnetic field is parallel to the groove 5a of the diffraction grating 5. (TM polarized light with reference to the groove of the diffraction grating). As is clear from this figure, the diffraction efficiency depends on the polarization component (K. Yokomori: Appl. Opt .; 23, 14, 2303 (198
Four). That is, if λ / d> 1.6, a sufficiently high diffraction efficiency can be obtained with a polarization component whose electric field is parallel to the groove 5a,
The diffraction efficiency is almost zero for the polarized light component parallel to 5a. In other words, most of the first-order diffracted light is considered to be a polarization component whose electric field is parallel to the groove 5a, and most of the light on the light receiving axis lr is considered to be a polarization component whose magnetic field is parallel to the groove 5a. It is done. Therefore, the diffraction grating 5 can be used as a splitter for separating the TE polarized light and the TM polarized light. That is, according to the configuration of FIG. 1, since the groove 5a of the diffraction grating 5 is orthogonal to the observation surface (paper surface), the polarization component (TE polarization) whose electric field is parallel to the observation surface is on the light receiving axis lr. Light receiving element 7
Polarization component (TM)
(Polarized light) is received by the light receiving element 6 away from the light receiving axis lr. The outputs Is and Ip of the light receiving elements 6 and 7 are as shown in FIG.
The output voltages Vs, Vp of the light receiving circuits 11, 12, which are input to the light receiving circuits 11, 12, respectively and correspond to the amounts of light received by the light receiving elements 6, 7, are logarithmically amplified by logarithmic amplifiers 13, 14, respectively. The outputs of the log-log amplifying circuits 13 and 14 are input to a subtracting circuit 15, and the output of the subtracting circuit 15 is the logarithm of the ratio of the output voltages Vs and Vp of the light receiving circuits 11 and 12 (ie, In (Vp / Vs)) can get. Therefore, the output value of the subtraction circuit 15 is the logarithm of the intensity ratio (polarization ratio) between TE polarized light and TM polarized light. In the comparison circuit 16, the subtraction circuit 15
It is determined whether or not the output value is within a predetermined range set in advance. If the output value is within the predetermined range, the output circuit 18 is operated via the signal processing circuit 17. That is, the comparison circuit 16 functions as a determination unit. Here, the set value of the comparison circuit 16 can be adjusted by the variable resistor VR. The output of the oscillation circuit 19 for intermittently lighting the light emitting element 1 is input to the signal processing circuit 17, and only the scattered light of the light emitted from the light emitting element 1 is synchronized by synchronizing the light receiving system with the blinking of the light emitting element 1. Is processed, and a noise component is removed. A drive circuit 20 for amplifying the output of the oscillation circuit 19 is inserted between the oscillation circuit 19 and the light emitting element 1. As described above, if the light is separated into the TE polarized light and the TM polarized light using the diffraction grating 5, the distance between the light receiving elements 6 and 7 can be reduced. Therefore, the optical system and the signal processing circuit unit are hybridized. A one-chip optoelectronic integrated circuit can be configured. In the above embodiment, the diffraction grating 5 is arranged so that the groove 5a is orthogonal to the observation surface. However, when the diffraction grating 5 is arranged so that the groove 5a is parallel to the observation surface, the TE polarized light and the diffracted light are combined. Therefore, the light receiving element 7 for receiving the TE polarized light is arranged at a position different from the observation surface in a plane orthogonal to the groove 5a, and is positioned on the light receiving axis lr.
What is necessary is just to arrange the light receiving element 6 which receives TM polarized light. Instead of using the diffraction grating 5, as shown in FIG. 6, a beam splitter including a half mirror 21 and a mirror 22, and a pair of polarizing plates 23 and 24 are used to convert scattered light into an observation surface. And the magnetic vector separates into a polarization component parallel to the observation plane.
Smoke particles can be detected based on the principle described in the section of “action”. In the case of this configuration, the number of parts is increased, and the beam splitters and the polarizing plates 23 and 24 are relatively large, so that it is difficult to form one chip. This makes it possible to prevent erroneous detection due to reflected light or insects in the detector.

【The invention's effect】

As described above, the present invention provides a splitter that separates scattered light into a polarization component whose electric field is parallel to a plane including the optical axis of the light projecting unit and the optical axis of the light receiving unit, and a polarization component whose magnetic field is parallel to the plane. ,
A light-receiving means is constituted by a pair of light-receiving elements for receiving the respective polarized light components. A discriminating circuit for calculating the ratio of the output levels of the two light-receiving elements and determining that smoke particles are present when the ratio is within a predetermined range. The particle diameter of the smoke particles is determined based on the ratio of the intensity of the polarization components orthogonal to each other contained in the scattered light due to the smoke, and when the particle diameter is within a predetermined range, the smoke particles Since it is determined that there is a particle, the particle size of the scattering particle is reflected, and it becomes easy to distinguish between scattering by smoke particles and reflection by other objects such as the inner peripheral surface of the detector and insects. Because As a result, there is an advantage that erroneous detection is prevented and reliability is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a sectional view of a principal part of the diffraction grating used in the above embodiment, FIG. 3 is an operation explanatory diagram of the diffraction grating used in the embodiment, and FIG. FIG. 5 is a diagram illustrating the principle of the above, FIG. 6 is a schematic configuration diagram showing another embodiment of the present invention, and FIG. 7 is a schematic sectional view showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... Light-emitting element, 2 ... Projection lens, 3 ... Smoke particle, 4 ... Light-receiving lens, 5 ... Diffraction grating, 6, 7 ... Light-receiving element, 13, 14 ... Logarithmic amplifier circuit, 15 ... Subtraction circuit, 16 ... Comparison circuit .

Claims (1)

(57) [Claims] A light projecting means for projecting a light beam; and a light receiving means arranged such that an optical axis forms a predetermined angle with respect to an optical axis of the light projecting means. In a photoelectric smoke sensor in which scattered light is received by a light receiving means, the light receiving means converts the scattered light into polarized light whose electric field is parallel to a plane including the optical axis of the light projecting means and the optical axis of the light receiving means. A splitter that separates the component into a parallel polarization component and a magnetic field, and a pair of light receiving elements that respectively receive the respective polarization components.When the ratio of the output levels of both light receiving elements is calculated and the ratio is within a predetermined range, A photoelectric smoke detector characterized in that a determination means for determining that smoke particles are present is provided in the smoke detector.