JPS5833599B2 - Scattered light smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a scattered light type smoke detector that aims to improve the S/N ratio by extremely suppressing stray light in a smoke-sensitive room.

As shown in FIG. 1, the scattered light type smoke detector has a light emitting element 3 and a light receiving element 4 separately disposed inside a housing 2 having a smoke inlet hole 1, and a primary light limiting edge 6 of an irradiation window 5. , 6 are the primary light limiting edges 6, 6 where the light emitted from the light emitting element 1
The light beam L1 is prevented from hitting the view-limiting edges 8, 8 of the light receiving window 7, and the light beam L2 is prevented from irradiating the opposing wall surface B.
From there, the opposing wall surface B can be seen through the visibility limiting edges 8, 8, and the light beam L2 passes through the primary light limiting edges 6, 8.
6, and the light beam L4 is not emitted from the opposite wall surface A (reflected light does not enter the light receiving element 4). The light radiated from the smoke particles is scattered by the smoke particles and enters the light receiving element 4, which also senses the presence of smoke.

In the conventional example with the above configuration, even when there is no smoke, the light reflected once and multiple times from the wall surface of the smoke sensitive chamber enters the light receiving element, so it always appears as noise, and the noise is It had the disadvantage of poor S/N ratio and low reliability.

In view of these points, the present invention provides a light emitting element and a light receiving element that are separately disposed inside a housing having a smoke infiltration hole, and a primary light limiting edge that forms an irradiation window of the light emitting element and a light receiving window of the light receiving element. In a scattered light optical system consisting of a visibility-restricting edge that forms a field of view, a convex portion is provided at the boundary so that the opposing wall surface on which direct light from the light emitting element enters and the opposing wall surface that can be seen from the light receiving element do not face each other. , which prevents reflected light inside the smoke-sensitive room and improves the S/N ratio.

FIG. 2 shows an embodiment of the present invention, in which a light emitting element 3 and a light receiving element 4 are arranged separately in a housing 2 having a smoke infiltration hole 0, and the primary light of the irradiation window 5 of the light emitting element 3 is The light rays pass through the limiting edges 6, 6 and irradiate the opposing wall surface A through the -order light limiting edges, so that the light rays do not touch the visibility limiting edges 8, 8 of the light receiving window 7, and the light rays L3 pass through the light-facing wall surface A. B, and pass the visibility limiting edges 8, 8 of the light receiving window 7 from the light receiving element 4 through the visibility limiting edges 8, 8 to the opposing wall B.
The scattered light optical system is constructed so that the light ray L2 does not touch the primary light limiting edges 6, 6, and the light ray L4 does not emit from the opposing wall surface A (the reflected light does not enter the light receiving element 4). The boundary between opposing wall surfaces A and B is set so that the direct light from the light emitting element 3 entering the optical system does not reflect once on the opposing wall surface and reflect twice on the opposing wall surface that can be seen from the light receiving element 4 and enter the light receiving element 4. A convex portion 10 is provided on the opposite wall surface A.
and B are respectively tapered surfaces inclined outward, and the opposing wall surface A
The opposite wall surface B is not visible from the outside.

Instead of making the opposing wall surfaces A and B sloped surfaces, the convex portion 10 at the boundary may be made high as shown in the third figure.

As explained above, in this invention, a convex portion is provided at the boundary of the opposing wall surface of the scattered light optical system so that the opposing wall surface B cannot be directly seen from the opposing wall surface A, and the light reflected once on the opposing wall surface A is reflected from the opposing wall surface. While preventing the light from being reflected twice by B and entering the light receiving element, not only the once reflected light but also the twice reflected light can be completely prevented, easily improving the S/N, and preventing malfunctions due to dust accumulation, etc. This has the effect of improving reliability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a partial block diagram showing another embodiment. 1 is a smoke infiltration hole, 2 is a housing, 3 is a light emitting element, 4 is a light receiving element, 5 is an irradiation window, 6, 6 are primary light limiting edges, 7 is a light receiving window, 8, 8 are visibility limiting edges, A, B is the opposite wall,
10 is a convex portion.

Claims (1)

[Claims] 1 A light emitting element and a light receiving element are arranged separately inside a housing having a smoke infiltration hole, and are composed of a primary light limiting edge forming an irradiation window for the light emitting element and a visibility limiting edge forming a light receiving window for the light receiving element. A scattered light optical system characterized in that a convex portion is provided at the boundary so that the opposing wall surface into which direct light from the light emitting element enters and the opposing wall surface visible from the light receiving element do not face each other. Smoke detectors.