Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-03-01
2001-02-27
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S628000, C340S629000, C250S574000
Reexamination Certificate
active
06195014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fire detector for sensing a fire by detecting a smoke caused by the fire.
2. Description of Related Art
According to an earlier development, a smoke-detecting type of the fire detector which senses a fire by detecting a smoke caused by the fire by using a light emitting element and a light detecting element is often attached to one member having a disk shape so that the light emitting element is placed at a certain angle with respect to the light detecting element, for example as described in Japanese Patent Application No. Tokukai-Hei 8-166347.
However, in case that a fire detector having such a structure identified above is miniaturized, it is difficult to prepare an enough smoke detecting area because it is inevitable to shorten a distance in a radial direction, and then a distance between the light emitting element and the light detecting element becomes shorter.
Contrarily, a fire detector as described in Japanese Patent Application No. Tokukou-Sho 57-22157, has a structure where an axis of the light emitting element are approximately perpendicular to that of the light detecting element in a height direction. It is possible to miniaturize the fire detector in the radial director by sacrificing the height, that is, a thickness of the detector because of the structure thereof.
However, in case that the fire is miniaturized in the radial direction, it is necessary to prepare the smoke detecting area as large as possible.
Alternatively, the distance between the light emitting element and a wall of the smoke chamber storing the light emitting element necessarily becomes shorter by miniaturizing the detector. A reflected light generated by a reflection of a light from the light emitting element on the wall or the like is not reduced. Such a reflected light is detected by the light detecting element as a noise light, and a problem including a decrease of an S/N ratio occurs.
Further, each part of the fire detector may be located accurately in assembly process in order to stabilize the performance of the fire detector. However, regarding the assembly of the smoke chamber, when the detector is miniaturized, a space for a screw nut used frequently in a fire detector according to an earlier development, must be needed. Therefore, it is not preferred because of the restriction of the space.
SUMMARY OF THE INVENTION
The present invention was developed in view of the above problem. An object of the present invention is to provide the fire detector which can prepare the smoke detecting area enough when miniaturized, and to provide the fire detector which senses the fire at the high S/N ratio when miniaturized. Further, another object is to provide the fire detector in which the smoke chamber can be attached the smoke chamber accurately without the unneeded space when miniaturized.
In order to solve the above problem, in accordance with one aspect of the present invention, a fire detector for sensing a fire, comprises;
a smoke chamber,
a light emitting element, and
a light detecting element for detecting a scattered light caused by scattering a light emitted by the light emitting element with a smoke which enters in the smoke chamber,
wherein a wall part of the smoke chamber is formed in a shape based on a circle having a predetermined size, and comprises a projecting portion which projects from at least a part of the circle to an outside of the circle,
the light emitting element is disposed on the projecting portion of the smoke chamber, and
the light detecting element is arranged out of the smoke chamber and an optical axis thereof is approximately perpendicular to a plane including the circle.
According to the present invention, because the axis of the light emitting element crosses the axis of the light detecting element along with a vertical direction, it is possible to miniaturize the fire detector in a horizontal direction. Further, because the light emitting element is arranged in the projecting portion, the distance between the axis of the light detecting element and the light emitting element can be prepared well, for example, in comparison with a case that the light emitting element and the light detecting element are arranged in the vertical direction by using the circular smoke chamber. Therefore, the large smoke detecting area can be prepared.
Accordingly, the small fire detector having the large smoke detecting area is provided.
The optical axis of the light detecting element may pass through an approximate center of the circle.
An optical axis of the light emitting element may be approximately parallel to the plane including the circle and may be approximately perpendicular to the optical axis of the light detecting element in the smoke chamber.
A circuit board for connecting with the light emitting element and the light detecting element may be disposed on a rear face of the smoke chamber, and the light detecting element may be surface-mounted on the circuit board.
According to the present invention, because the light detecting element is surface-mounted on the circuit board, an assembly process becomes simple. Besides, the storing efficiency of the circuit board is increased.
The circuit board may be disposed apart from a rear surface of the smoke chamber at a predetermined interval, a surrounding member for surrounding the light detecting element, which has a height which is approximately equivalent to the predetermined interval, is provided between the rear face of the smoke chamber and the circuit board.
According to the present invention, because the surrounding member for surrounding the light detecting element, which has a height which is approximately equivalent length to the predetermined interval, is arranged between the rear face of the smoke chamber and the circuit board, a noise light, such as a light entering into the rear face of the smoke chamber through various holes formed on the smoke chamber according to the necessity of some situations and a light emitted by the light source except the light emitting element disposed on the circuit board, is not detected by the light detecting element. Therefore, the S/N ratio is increased and a high detecting accuracy is achieved.
Hereupon, the present invention is not limited to a concrete shape of the surrounding member. However, for example, the shape thereof may be cylindrical so as to surround the light detecting element or may be a frame having a rectangular sectional shape. The surrounding member may be disposed doubly or triply.
The surrounding member may be formed on the smoke chamber in one body. A light is shielded more. Therefore, the higher S/N ratio is achieved.
A surface of the circuit board, which faces to the smoke chamber may be black. Therefore, a light reflected on the circuit board or the like is shielded as possible. The S/N ratio is increased.
A lead hole through which a lead wire led from the light emitting element is connected to the circuit board may be formed in the smoke chamber.
When the fire detector is equipped on a ceiling, the fire detector is placed so as to direct toward a surface facing to the light emitting element in the smoke chamber upwardly. However, when an inner surface of the smoke chamber, which faces to the light detecting element, is made smooth, an influence caused by a reflection of a light emitted by the light emitting element can be relatively reduced as compared to a case that a structure on which an edge portion or the like is formed is provided. Therefore, the S/N ratio is increased on this point.
In accordance with another aspect of the present invention, a fire detector for sensing a fire, comprises;
a smoke chamber,
a light emitting element,
a light detecting element for detecting a scattered light caused by scattering a light emitted by the light emitting element with a smoke which enters into the smoke chamber, an optical axis of the light detecting element crossing an optical axis of the light emitting element in a predetermined position, and
a plurality of light shiel
Sakurai Kazuyoshi
Tsubouchi Seiji
Nguyen Phung
Nittan Company Limited
Staas & Halsey , LLP
Wu Daniel J.
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