CA1254970A - Photoelectric smoke detector - Google Patents
Photoelectric smoke detectorInfo
- Publication number
- CA1254970A CA1254970A CA000489719A CA489719A CA1254970A CA 1254970 A CA1254970 A CA 1254970A CA 000489719 A CA000489719 A CA 000489719A CA 489719 A CA489719 A CA 489719A CA 1254970 A CA1254970 A CA 1254970A
- Authority
- CA
- Canada
- Prior art keywords
- light
- measuring space
- smoke detector
- front wall
- photoelectric smoke
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- Investigating Or Analysing Materials By Optical Means (AREA)
- Fire-Detection Mechanisms (AREA)
Abstract
ABSTRACT
A photoelectric smoke detector equipped with a light emitter which radiates light into a measuring space and a light receiver which detects scattered light caused by entry of smoke into the measuring space. A dark chamber which forms the above space has a front wall with a plane or curved surface which is arranged in front of the light emitter so that the light from the light emitter is reflected at a predetermined angle to the optical axis and side walls which are arranged nearly in parallel with the optical axis. A rear wall may also be provided which has a plane or curved surface and arranged in the rear of the light emitter so as to reflect the reflected light from the side walls at such an angle that the reflected light does not directly irradiate the light receiver. The above walls preferably have mirror-like surfaces with good absorbance.
A photoelectric smoke detector equipped with a light emitter which radiates light into a measuring space and a light receiver which detects scattered light caused by entry of smoke into the measuring space. A dark chamber which forms the above space has a front wall with a plane or curved surface which is arranged in front of the light emitter so that the light from the light emitter is reflected at a predetermined angle to the optical axis and side walls which are arranged nearly in parallel with the optical axis. A rear wall may also be provided which has a plane or curved surface and arranged in the rear of the light emitter so as to reflect the reflected light from the side walls at such an angle that the reflected light does not directly irradiate the light receiver. The above walls preferably have mirror-like surfaces with good absorbance.
Description
1 ~ 5 L~
Title of Invention Photoelectric Smoke Detector Field of Invention The present invention rel~tes to a small-sized photoelectric smoke detector.
Background of Invention Dark chambers of conventional photoelectric smoke detectors have a complicated labyrinth construction or double covers to prevent the environmental light from entering the dark chamber but to facilitate entry of smoke into the same.
However, those detectors with the above-mentioned dark chamber construction, being large in size, are not suitable for use as detectors built in equipment such as electronic computers or installed in lavatories in aircrafts. They also have such a shortcoming that miniaturizing them by merely reducing the sizes of their dark chambers results in lowering the SN ratio.
Summar~ of Invention The present invention relates to a photoelectric smoke detector equipped with a light emitter which radiates light into a measuring space and a light receiver which detects scattered light caused by entry of smoke into the measuring space, and characterized in that a dark chamber which forms the above space at least comprises a front wall with a plane or curved surface which is arranged in front of the light emitter so that the light from the light emitter is reflected at a predetermined angle to the optical axis and side walls which are arranged nearly in parallel with the optical axis. ~ rear wall may also be provided which has a plane or curved surface and arranged in the rear of the light emitter so as to reflect the reflected light from the side walls at such an angle that the reflected light does not directly irradiate the light receiver. The above walls preferably have mirror-like surfaces with good absorbance.
The photoelectric smoke detector according to the present invention is equipped with a dark chamber of the above composition whereby the dark chamber itself is capable of performing a light trap function. More specifically, the dark chamber is designed in such a way that the light beam radiated by the light emitter is reflected from the wall surfaces of the dark chamber several times without allowing the initially reflected light to reach the light receiving element of -the light receiver, and that reflected light reaching the light receiving element, if any, is attenuated to a very weak one.
Reflection of the beam is enhanced by having side walls with mirror-like surfaces with good absorbance. Therefore, it is not necessary to specially provide a light trap meansl thus a small-sized photoelectric smoke detector with a narrow measuring space is obtained.
Drawings The invention is illustrated by way of example in the accompanying drawings wherein Figures 1 through 3 are schematic diagrams of the photoelectric smoke detector according to the present inven-tion in each case (a) being a cross-section, and (b) a transverse section; and Figure 4 shows characteristics including a graph.
Preferred embodiment The following describes an embodiment of the photoelectric smoke detector according to the present invention in reference to Figures l through 3. In these figuresl (a) is a cross section and (b) is a transverse section of the dark chamber according to the present invention, wherein the components are indicated by numerals as follows: 1 - a light emitter which is 3~
equipped with a light source such as light emitting diode and a lens, and radiates a convergent light beam; 2 - a light receiver comprising a light receiving element such as solar cell and a lens; 3 - a light shielding plate provided between the light emitter 1 and the light receiver 2; 4, 5 - side walls arranged nearly in parallel with the optical axis of the light beam radiated from the light emitter 1; 6 - a front wall with a plane or curved survace which is arranged in front of the light emitter 1 to reflect the light at a predetermined angle to the optical axis; 7 - a rear wall with plane or curved surface which is arranged in the rear of the light emitter 1 to reflect the reflected light from side walls 4, 5 at a predetermined angle so that the reflected light does not directly irradiate the light receiving element of the light receiver 2; 8, 9 - a bottom wall and a top wall with apertures through which smoke can flow in (not shown on the drawing) and which are provided in the center of the bottom wall 8 and near both ends of the top wall 9. The wall surfaces are of a color having a good absorbance, for example, black color and finished up like a mirror. Further in the figures, s - a starting point of the light beam; arrow - a point where the light beam reaches; black dots - reflection points on the side wall 4; white dots - reflection points on the side wall 5; triangle - a reflaction point on the top wall 9O
Fig. 1 shows a case where the optical axis is in the slightly lef-t direction toward the light receiver 2 and 0 = 150. Fig. 2 shows a case where the optical axis is in the left direction at an angle of 5 to the light receiver 2 and 0 = 150. Fig. 3 shows a case where the angle of the light emitter 1 shown in Fig. l-is set further upward.
Function of the dark chamber is described below. In Fig.
1, for example, the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, and from the left wall 4, the right and left walls 5, 4, further from the top wall 9, the right wall 5, the left wall 4, the left side of the rear wall 7, and impinges on the outer wall of the light receiver 2. As can be seen from the above description, the dark chamber acts as light trap, where the light radiated from the 3','~
light emitter 1 is attenuated while being reflected from the side walls 4, 5 several times, and eventually becomes a very weak light.
In the case of black surfaces, the convergent light beam radiated from the light emitter 1 impinges on the left side surface of the front wall 6 and is absorbed by the black surface. Unabsorbed light is reflected from the mirror-like surface nearly as it is, i.e. in the form of convergent light beam without being diffused, and from the left wall 4, the right and left walls 5, 4, further from the top wall 9, the right wall 5, the left wall 4, the left side of the rear wall 7, and then impinges on the outer wall of the light receiver 2. As can be seen from the above description, the dark chamber acts as light trap, where the light radiated from the light emitter 1 is absorbed by the black surfaces and attenuated while being reflected several times, and eventually becomes a very weak light.
Further describing the invention in reference to Fig. 29 -~
the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, the left wall 4, the right, left, right walls, the top wall 9, the left wall ~, the right wall 5, and the right side of the rear wall 7, and then impinges on the outer wall of the light receiver 2. In Fig. 3, the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, the left wall 4, the top wall 9, the right, left, right left walls and the left of the rear wall 7, and then impinges on the outer wall of the light emitter 1, thus being attenuated to a very weak light~
On the other hand, if a fire breaks out and smoke enters the dark chamber, scattered light irradiates the light receiving element of the light receiver 2, where an output to give a fire alarm develops. Fig. 4 shows characteristics of the dark chamber, with S representing output of the light receiving element when a predetermined density of smoke for decision on fire entered the dark chamber, N representing the output of the 3'o~f~
light receiving element in normal condition, and 0 representing angles of the front and rear walls 6, 7. According to this figure, a sufficient SN ratio for practical use is obtained at 0 of not more than 140 and not less than 210~.
The photoelectric smoke detector according to -the present invention is equipped with a d-ark chamber of the above composition whereby the dark chamber itself is capable of performing a light trap function. More specifically, the dark chamber is designed in such a way that the light beam radiated by the light emitter is reflected several times from the side walls having mirror-like surEaces with good absorbance via the front and rear walls, without allowing the initially reflected light to reach the light receiving element of the light receiver, and that reflected light reaching the light receiving element if any is attenuated to a very weak one. Therefor, this invention has such an effect that a small-sized photoelectric smoke detector which has a narrow measuring space and does not require special provision of a light trap means is obtained,
Title of Invention Photoelectric Smoke Detector Field of Invention The present invention rel~tes to a small-sized photoelectric smoke detector.
Background of Invention Dark chambers of conventional photoelectric smoke detectors have a complicated labyrinth construction or double covers to prevent the environmental light from entering the dark chamber but to facilitate entry of smoke into the same.
However, those detectors with the above-mentioned dark chamber construction, being large in size, are not suitable for use as detectors built in equipment such as electronic computers or installed in lavatories in aircrafts. They also have such a shortcoming that miniaturizing them by merely reducing the sizes of their dark chambers results in lowering the SN ratio.
Summar~ of Invention The present invention relates to a photoelectric smoke detector equipped with a light emitter which radiates light into a measuring space and a light receiver which detects scattered light caused by entry of smoke into the measuring space, and characterized in that a dark chamber which forms the above space at least comprises a front wall with a plane or curved surface which is arranged in front of the light emitter so that the light from the light emitter is reflected at a predetermined angle to the optical axis and side walls which are arranged nearly in parallel with the optical axis. ~ rear wall may also be provided which has a plane or curved surface and arranged in the rear of the light emitter so as to reflect the reflected light from the side walls at such an angle that the reflected light does not directly irradiate the light receiver. The above walls preferably have mirror-like surfaces with good absorbance.
The photoelectric smoke detector according to the present invention is equipped with a dark chamber of the above composition whereby the dark chamber itself is capable of performing a light trap function. More specifically, the dark chamber is designed in such a way that the light beam radiated by the light emitter is reflected from the wall surfaces of the dark chamber several times without allowing the initially reflected light to reach the light receiving element of -the light receiver, and that reflected light reaching the light receiving element, if any, is attenuated to a very weak one.
Reflection of the beam is enhanced by having side walls with mirror-like surfaces with good absorbance. Therefore, it is not necessary to specially provide a light trap meansl thus a small-sized photoelectric smoke detector with a narrow measuring space is obtained.
Drawings The invention is illustrated by way of example in the accompanying drawings wherein Figures 1 through 3 are schematic diagrams of the photoelectric smoke detector according to the present inven-tion in each case (a) being a cross-section, and (b) a transverse section; and Figure 4 shows characteristics including a graph.
Preferred embodiment The following describes an embodiment of the photoelectric smoke detector according to the present invention in reference to Figures l through 3. In these figuresl (a) is a cross section and (b) is a transverse section of the dark chamber according to the present invention, wherein the components are indicated by numerals as follows: 1 - a light emitter which is 3~
equipped with a light source such as light emitting diode and a lens, and radiates a convergent light beam; 2 - a light receiver comprising a light receiving element such as solar cell and a lens; 3 - a light shielding plate provided between the light emitter 1 and the light receiver 2; 4, 5 - side walls arranged nearly in parallel with the optical axis of the light beam radiated from the light emitter 1; 6 - a front wall with a plane or curved survace which is arranged in front of the light emitter 1 to reflect the light at a predetermined angle to the optical axis; 7 - a rear wall with plane or curved surface which is arranged in the rear of the light emitter 1 to reflect the reflected light from side walls 4, 5 at a predetermined angle so that the reflected light does not directly irradiate the light receiving element of the light receiver 2; 8, 9 - a bottom wall and a top wall with apertures through which smoke can flow in (not shown on the drawing) and which are provided in the center of the bottom wall 8 and near both ends of the top wall 9. The wall surfaces are of a color having a good absorbance, for example, black color and finished up like a mirror. Further in the figures, s - a starting point of the light beam; arrow - a point where the light beam reaches; black dots - reflection points on the side wall 4; white dots - reflection points on the side wall 5; triangle - a reflaction point on the top wall 9O
Fig. 1 shows a case where the optical axis is in the slightly lef-t direction toward the light receiver 2 and 0 = 150. Fig. 2 shows a case where the optical axis is in the left direction at an angle of 5 to the light receiver 2 and 0 = 150. Fig. 3 shows a case where the angle of the light emitter 1 shown in Fig. l-is set further upward.
Function of the dark chamber is described below. In Fig.
1, for example, the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, and from the left wall 4, the right and left walls 5, 4, further from the top wall 9, the right wall 5, the left wall 4, the left side of the rear wall 7, and impinges on the outer wall of the light receiver 2. As can be seen from the above description, the dark chamber acts as light trap, where the light radiated from the 3','~
light emitter 1 is attenuated while being reflected from the side walls 4, 5 several times, and eventually becomes a very weak light.
In the case of black surfaces, the convergent light beam radiated from the light emitter 1 impinges on the left side surface of the front wall 6 and is absorbed by the black surface. Unabsorbed light is reflected from the mirror-like surface nearly as it is, i.e. in the form of convergent light beam without being diffused, and from the left wall 4, the right and left walls 5, 4, further from the top wall 9, the right wall 5, the left wall 4, the left side of the rear wall 7, and then impinges on the outer wall of the light receiver 2. As can be seen from the above description, the dark chamber acts as light trap, where the light radiated from the light emitter 1 is absorbed by the black surfaces and attenuated while being reflected several times, and eventually becomes a very weak light.
Further describing the invention in reference to Fig. 29 -~
the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, the left wall 4, the right, left, right walls, the top wall 9, the left wall ~, the right wall 5, and the right side of the rear wall 7, and then impinges on the outer wall of the light receiver 2. In Fig. 3, the light radiated from the light emitter 1 is reflected from the left side of the front wall 6, the left wall 4, the top wall 9, the right, left, right left walls and the left of the rear wall 7, and then impinges on the outer wall of the light emitter 1, thus being attenuated to a very weak light~
On the other hand, if a fire breaks out and smoke enters the dark chamber, scattered light irradiates the light receiving element of the light receiver 2, where an output to give a fire alarm develops. Fig. 4 shows characteristics of the dark chamber, with S representing output of the light receiving element when a predetermined density of smoke for decision on fire entered the dark chamber, N representing the output of the 3'o~f~
light receiving element in normal condition, and 0 representing angles of the front and rear walls 6, 7. According to this figure, a sufficient SN ratio for practical use is obtained at 0 of not more than 140 and not less than 210~.
The photoelectric smoke detector according to -the present invention is equipped with a d-ark chamber of the above composition whereby the dark chamber itself is capable of performing a light trap function. More specifically, the dark chamber is designed in such a way that the light beam radiated by the light emitter is reflected several times from the side walls having mirror-like surEaces with good absorbance via the front and rear walls, without allowing the initially reflected light to reach the light receiving element of the light receiver, and that reflected light reaching the light receiving element if any is attenuated to a very weak one. Therefor, this invention has such an effect that a small-sized photoelectric smoke detector which has a narrow measuring space and does not require special provision of a light trap means is obtained,
Claims (6)
1. A photoelectric smoke detector, comprising:
a front wall, two opposite side walls, a rear wall, a top wall and a bottom wall bounding a measuring space;
a light emitter for radiating light into said measuring space along a predetermined optical axis;
a light receiver for detecting scattered light scattered in the presence of smoke from the light radiated into said measuring space;
at least said front wall and said two opposite side walls possessing reflective surfaces facing said measuring space;
said front wall being arranged substantially opposite to said light emitter for receiving said light radiated by said light emitter and reflecting said received light at a predetermined angle relative to said predetermined optical axis;
said two opposite side walls being arranged substantially parallel to said predetermined optical axis;
said reflective surfaces of said front wall and said -two opposite side walls constituting light trap means for said light radiated from said light emitter and which light trap means multiply reflect said light through said measuring space; and said light receiver being arranged outside the path of said multiply reflected light.
a front wall, two opposite side walls, a rear wall, a top wall and a bottom wall bounding a measuring space;
a light emitter for radiating light into said measuring space along a predetermined optical axis;
a light receiver for detecting scattered light scattered in the presence of smoke from the light radiated into said measuring space;
at least said front wall and said two opposite side walls possessing reflective surfaces facing said measuring space;
said front wall being arranged substantially opposite to said light emitter for receiving said light radiated by said light emitter and reflecting said received light at a predetermined angle relative to said predetermined optical axis;
said two opposite side walls being arranged substantially parallel to said predetermined optical axis;
said reflective surfaces of said front wall and said -two opposite side walls constituting light trap means for said light radiated from said light emitter and which light trap means multiply reflect said light through said measuring space; and said light receiver being arranged outside the path of said multiply reflected light.
2. The photoelectric smoke detector as defined in claim 1, wherein:
said front wall possesses a substantially planar surface constituting said reflective surface facing said measuring space.
said front wall possesses a substantially planar surface constituting said reflective surface facing said measuring space.
3. The photoelectric smoke detector as defined in claim 1, wherein:
said front wall possesses two adjacent substantially planar side surfaces forming between themselves a predetermined angle and constituting said reflective surface facing said measuring space.
said front wall possesses two adjacent substantially planar side surfaces forming between themselves a predetermined angle and constituting said reflective surface facing said measuring space.
4. The photoelectric smoke detector as defined in claim 3, wherein:
said two adjacent side surfaces of said front wall form between themselves an angle which is smaller than 140° and greater than 210°.
said two adjacent side surfaces of said front wall form between themselves an angle which is smaller than 140° and greater than 210°.
5. The photoelectric smoke detector as defined in claim 1, wherein:
said light emitter for radiating light into said measuring space along said predetermined optical axis, emits a convergent light beam.
said light emitter for radiating light into said measuring space along said predetermined optical axis, emits a convergent light beam.
6. The photoelectric smoke detector as defined in claim 1, wherein:
said light receiver is placed outside said predetermined optical axis along which said light is radiated by said emitter.
said light receiver is placed outside said predetermined optical axis along which said light is radiated by said emitter.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP13058784U JPS6146454U (en) | 1984-08-30 | 1984-08-30 | photoelectric smoke detector |
| JP17940084A JPS6157835A (en) | 1984-08-30 | 1984-08-30 | Photoelectric smoke detector |
| JP59-179400 | 1984-08-30 | ||
| JP59-130587 | 1984-08-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254970A true CA1254970A (en) | 1989-05-30 |
Family
ID=26465680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000489719A Expired CA1254970A (en) | 1984-08-30 | 1985-08-29 | Photoelectric smoke detector |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1254970A (en) |
-
1985
- 1985-08-29 CA CA000489719A patent/CA1254970A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |