JPH033277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scattered light type smoke sensor in which smoke is detected by a light source emitted from a light source being scattered by smoke, and the scattered light is detected by a light receiver.

In general, in a scattered light type smoke detector, in addition to the original signal light scattered by the smoke, the light from the light source is also diffusely reflected inside the dark box, which becomes noise light and enters the light receiver. Therefore, improving the signal-to-noise ratio, or S/N ratio, of the sensor,
To produce a highly sensitive sensor, noise light must be suppressed as much as possible. Therefore, in order to reduce the diffused reflection inside the dark box, it has been necessary to apply a matte black coating to the inner surface of the dark box. However, applying this matte black coating hinders the simplification of the manufacturing process, which in turn becomes an obstacle to lowering the price of the sensor. Furthermore, the matte black coating does not sufficiently absorb noise light, making it difficult to obtain a highly sensitive sensor.

Therefore, the scattered light type smoke detector according to the present invention sufficiently suppresses noise light entering the light receiver without applying a matte black coating as in the conventional case.
As a result, the S/N ratio is improved and the structure is extremely simple to manufacture.

Next, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows a longitudinal cross-sectional view of an embodiment of the scattered light type smoke detector of the present invention, and FIG.
-A cross-sectional view taken along line A', the sensor as a whole includes a cover 1, a dark box 2, a light source 3 that irradiates light into the dark box 2, and is arranged in a position where it does not receive direct light from the light source 3. and a light receiver 4.

Furthermore, the dark box 2 is made up of a cylindrical side wall 22 whose both ends are closed by end walls 20 and 21, and this cylindrical side wall 22 is made up of an aggregate of a plurality of thin plates 7 each having a glossy surface. There is. Each of the thin plates is set parallel to a line connecting both end walls 20 and 21, and is also set diagonally toward the center of the dark box. The thin plates 7 are arranged at intervals from each other, and serve as ventilation holes 6 through which smoke can enter the dark box. The light source 3 has its optical axis aligned with the thin plate 7.
It is fixed to the support 5 so that it is oriented. The support 5 integrates the light source 3 and the light receiver 4 and is arranged on one end wall 21 side.

With the configuration of the dark box 2 as described above, the light rays from the light source 3 are reflected by the surface 9 of the thin plate 7 without being diffusely reflected because the surface 9 of the thin plate 7 is a glossy surface.
Since the light is set obliquely toward the center of the dark box, the light is converged in the trough 8 and is not reflected in the direction of the light receiver 4. The valley 8 created between the thin plates 7 therefore acts as if it were a light trap.

In this way, the surface 9 of the thin plate 7 must be a reflective surface, such as a glossy surface. This is also demonstrated by the graph in FIG.

FIG. 3 is a graph showing the relationship between the noise level and the degree of surface finish of the thin plate 7 shown in FIG. This graph shows how the surface of a glossy thin plate obtained by molding synthetic resin was roughened using sandpaper of different roughness (the roughness of the sandpaper is displayed as a mesh). Occasionally,
This was obtained by measuring the respective noise optical outputs.

As you can see from this graph, the better the surface finish, the lower the noise level. This means that there is no need to roughen the surface by applying matte black paint, etc., as in the past, and the surface condition produced by molding with synthetic resin can be used as is. ing.
It can be seen that the finish should be a glossy surface that is denser than the surface roughened with an 800-mesh file.

As explained above, in the scattered light smoke detector of the present invention, the cylindrical side wall is composed of an assembly in which a plurality of thin plates each having a glossy surface are arranged at intervals, and each of the thin plates is It was set parallel to the line connecting both end walls and diagonally toward the center of the dark box, so that the optical axis of the light source was oriented toward the thin plate.
The entire side wall 22 of the dark box 2 has a structure that has a light trap-like effect, and there is no need to go to the trouble of painting it matte black as in the past.
Even if the surface 9 of some of the thin plates 7 is somewhat dirty or rough, a sufficient S/N ratio can be obtained. Therefore, the painting process can be omitted in the manufacturing process, and when cleaning the sensor during maintenance and inspection, there is no need to take care of the painted surface, etc., and the dark box 2 can be easily cleaned with alcohol or the like. Can be cleaned. Furthermore, since the structure of the dark box 2 has ventilation holes 6 uniformly around the side wall with the center as an axis,
It is useful for disaster prevention because it has excellent effects such as not having to consider the direction of smoke inflow.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view showing an embodiment of the scattered light type smoke detector of the present invention, Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1, and Fig. 3 is a surface of the thin plate of the dark box. Graphs showing the relationship between the noise level and the finish are shown respectively. DESCRIPTION OF SYMBOLS 1...Cover, 2...Dark box, 3...Light source, 4...Receiver, 7...Thin plate, 8...Trough, 20, 21...End wall, 2
2...Side wall.

Claims (1)

[Claims] 1 A dark box formed by a cylindrical side wall closed at both ends by end walls is provided, a light source and a light receiver are arranged on one of the end walls, and the light source illuminates the inside of the dark box and emits light into the dark box. In the scattered light type smoke detector, the light receiver receives light scattered by smoke particles in the dark box without being directly irradiated by the light source, and the cylindrical side wall includes a plurality of thin plates. The surface of each of the thin plates is polished to a glossy surface with a file of 800 or more meshes, and each of the thin plates is parallel to the line connecting the two end walls and the center of the dark box. A scattered light type smoke detector characterized in that the light source is set obliquely toward the thin plate, and the optical axis of the light source is oriented toward the thin plate.