JPS6114460B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insect repellent device for an optical smoke detector. Optical smoke detectors direct the light beam into a dark room where it is shielded as much as possible from ambient light. The opening allows smoke to pass into the dark room, but insects must be excluded. The reason for this is that smoke or insects scatter light onto the photocells in the dark room, which are shielded from the light source but still visible in the light path.

An object of the present invention is to provide a device for excluding insects from a dark room and also for blocking light.

A photodetector according to the invention includes a housing forming a darkroom, a light source directed into a light path within the darkroom, and a photocell facing the light path and responsive to light scattered by smoke in the light path and triggering an electrical alarm signal. , the housing includes an outer wall exposed to ambient light and an inner wall proximate the darkroom, each of the outer and inner walls having a smoke opening offset circumferentially with respect to the darkroom and a smoke opening extending between the outer wall and the inner wall and extending into the darkroom. and a wire mesh device that prevents the passage of insects, the wire mesh device being angled relative to the external opening, and the wires preventing external light rays from passing directly into the internal opening.

The present invention will be described in detail below with reference to Examples.

The optical smoke detector shown consists of a circular substrate 1 having a flange 2 abutting a circular housing 3. The optical smoke detector shown in FIG.

The substrate and housing can be rectangular or other shapes. The illustrated housing consists of a lower wall 4 with a peripheral surface 5 of an optical block 6 which includes a light emitting diode (LED) source 7,
It houses a smoke sensing cell 17 and a compensation cell 21.
Source 7, as detailed in U.S. Patent No. 3,863,076
Light from inside the darkroom 12 is surrounded by the lower wall 4 and the substrate 1, the outer wall 13 exposed to ambient light, the inner wall 14 around the darkroom 12, and the cover 16 covering the inner and outer walls standing from the surface 5 of the lower wall 4. is guided along the path indicated by the axis 11. optical block 6
The smoke detection photocell 17 in the dark room 1 is located along an axis 18 that intersects the light source axis 11 in the smoke detection area.
Facing 2. The light from the source 7 is spread by a diffuser 19 on the second photocell 21 which compensates for variations in the smoke sensing cell 17, as is well known in the smoke detection art. Additionally, as is well known, there is a need to exclude insects from the darkroom 12 while allowing as much airborne smoke as possible, and at the same time to shield ambient light from the darkroom so that such light or insects may cause smoke detection cells to It is necessary to avoid triggering false alarms.

According to the invention, the exclusion of insects and ambient light is made possible by the provision of radially spaced outer walls 13 and inner walls 14 within the dark room, it being understood that the outer and inner walls can also be rectangular. Furthermore, a smoke inlet/outlet opening 22 is provided in the outer wall 13 . These external openings 22 are circumferentially offset from internal smoke openings 23 in the internal wall 14. As shown in Figure 2, 4
A set of external and internal openings are arranged symmetrically about the circumference of the darkroom housing. Outer wall 13 and inner wall 14
form a passageway 15 between them, which terminates in an end wall 25 forming a light trap (valve) with the other wall beyond the internal opening. Wire mesh screen 24
are mounted between adjacent ends 22 ^* and 23 ^* of offset apertures 22 and 23 as shown in detail in FIG. The mesh is typically composed of closely spaced longitudinal and transverse members 24 ^* . A typical mesh screen is a square inch (6.45 mm) wire with a diameter of 0.011 inch (0.254 mm).
It has 18 x 16 holes per square centimeter (cm 2 ) and consists of aluminum wire weave coated in matte black. Such a screen or array of vent holes in the 5 inch (12.7 centimeter) diameter detector housing provides an opening for smoke to pass through almost as freely as without the screen. This is because the total number of openings in the screen is approximately equal to the cross-sectional area of the passage between the outer and inner walls. The screen also excludes direct light rays from the internal aperture 23. Due to the offset of the outer and inner openings and the slope of the wire screen with respect to the inner opening, the wires of the mesh prevent the light rays 25 from passing directly through the mesh. Some light scattered beyond the screen is optically unavoidable, but most of the direct light rays are rejected by the tilted screen.

It is understood that the disclosure of the invention is for the purposes of the drawings only and that the invention includes all modifications within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is an isometric view of an optical smoke detector according to the invention. FIG. 2 is a partially removed plan view of the detector showing the screen device. FIG. 3 is a sectional view taken along line 3--3 in FIG. 2. FIG. 4 is an enlarged detailed view of the screen device. (Description of symbols), 1: Circular board, 2: Flange,
3: Circular housing, 6: Optical block, 7: Light emitting diode, 12: Dark room, 13: External wall, 14:
Inner wall, 17: smoke detection photocell, 24: wire mesh screen.

Claims (1)

Claims: 1. A housing forming a darkroom, a light source directed into a light path within the darkroom, and an electrical alarm facing the light path and responsive to light scattered by smoke in the light path. a photocell that triggers a signal, the housing including an outer wall exposed to ambient light and an inner wall adjacent a darkroom, the outer wall and the inner wall having a smoke opening circumferentially offset relative to the darkroom. An optical smoke detector, wherein the outer wall and the inner wall form a passageway therebetween, and a wire mesh device is disposed between the outer wall and the inner wall at an angle with respect to the smoke opening in the outer wall, so that a dark room is detected. an optical smoke detector, characterized in that the wire of the wire mesh device prevents external light from passing directly into the smoke opening of the inner wall.