JP3131886B2 - Photoelectric smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric smoke detector, and more particularly to a shield structure.

[0002]

2. Description of the Related Art In a photoelectric smoke detector, light emitted from a light emitting element is reflected by smoke entering a dark box, and the minute scattered light is detected by a light receiving element, and the light output is amplified by an amplifier circuit. Then, a fire is judged based on the amplified output, or a digital signal is converted into a physical quantity signal by an analog / digital converter and transmitted to a receiving unit such as a fire receiver or a repeater.

For this reason, when electromagnetic noise enters the sensor, a false alarm is generated or a physical quantity signal different from the actual one is transmitted to the receiver.

In order to prevent false information and transmission of different physical quantity signals of smoke due to the electromagnetic noise, a photoelectric smoke detector in which the dark box is made of a conductive resin and the dark box has a shielding function is disclosed in Japanese Utility Model Application Laid-Open No. 2-111896. No. has been proposed.

[0005]

SUMMARY OF THE INVENTION
The photoelectric smoke detector of No. 896 has excellent shielding characteristics because the entire dark box is made of a conductive resin.

However, since the entire dark box is made of a conductive resin, when used in a place where corrosive gas is likely to be generated, such as a hot spring area or a factory, metal powder mixed with the resin to obtain conductivity is used. And conductive materials such as metal fibers are subject to corrosion. For this reason, the inner wall surface and the outer wall surface of the dark box that comes into contact with the outside air are corroded to generate irregularities, and the irregularities gradually increase.

As a result, noise light generated on the inner wall surface of the dark box when the light emitting element emits light when smoke does not invade gradually increases due to the occurrence of irregularities and its progress, so-called sensitivity disorder occurs, and normality occurs. There is a problem that the fire monitoring is not performed.

[0008] Moreover, since the sensitivity deviation is caused by a change in the shape of the inner wall surface of the dark box which directly affects smoke detection, there is a disadvantage that the sensitivity cannot be recovered unless the dark box is replaced with a new one.

[0009]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a photoelectric type having a dark box which has a shielding function and which does not change the shape of the inner wall surface which affects the monitoring of smoke due to corrosion. It is intended for smoke detectors.

[0010] For this reason, the present invention, on the lower surface side of the main body,
A printed circuit board on which electric circuit components are mounted, and a dark box provided with a light emitting element and a light receiving element and into which smoke flows are sequentially provided, and a cover surrounding the printed circuit board and the dark box is detachably engaged with the main body. In the photoelectric smoke detector according to the present invention, the dark box has an inner surface formed of a non-conductive resin and an outer surface formed of a conductive resin.

The dark box includes an optical table provided with the light emitting element and the light receiving element and having an open lower surface, and a lid covering an open portion of the lower surface of the optical table. The table is characterized in that its upper surface is made of a conductive resin and its lower surface is made of a non-conductive resin.

The dark box is mounted and fixed on the lower surface of the printed circuit board, and a shield case is provided on the upper surface side of the printed circuit board. The conductive resin portion of the dark box is directly connected to the shield case. Alternatively, they are connected through a wiring pattern of the printed circuit board.

[0013]

[Function] The outside or top surface of the dark box into which smoke flows is formed of conductive resin, and the inner wall of the dark box, which directly affects smoke monitoring, is formed of corrosion-resistant non-conductive resin. Even when the dark box is used in a bad environment, the inner wall surface of the dark box is not corroded by corrosive gas or the like, and a good shielding property can be obtained by the conductive resin on the outside or the top surface.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a first embodiment, in which 10 is a photoelectric smoke detector, 11 is a main body, and 12 is a cover.

Reference numeral 20 denotes a printed circuit board on which circuit components (not shown) such as a light emission control circuit, an amplification circuit, a fire determination circuit, an analog / digital converter, and a microcomputer are mounted. This printed circuit board 20 has a hook 1
3 attaches to the lower surface side of the main body 11.

Numeral 30 denotes a dark box mounted and fixed on the lower surface of the printed circuit board 20, 31 denotes an optical table on which the light emitting element 22 and the light receiving element 23 are provided and the peripheral wall is formed of labyrinth, and 32 denotes a lower surface of the optical table 31. It is a removable lid that covers the opening. The optical bench 31 has an upper surface portion 33 on the side facing the printed circuit board 20 formed of conductive resin, and a lower surface portion 34 including the inner wall surface of the dark box formed of non-conductive resin by integral molding. Engagement piece 35 for attaching optical table 31 to printed circuit board 20
Is provided. The lid 32 is formed of a non-conductive resin similarly to the lower surface portion 34 of the optical bench 31. Reference numeral 36 denotes a concave portion provided on the upper surface of the optical bench 31 and surrounded by the upper surface portion 31.

Reference numeral 40 denotes a shield case provided on the upper surface side of the printed circuit board 20. This shield case 40
The engaging piece 42 of the optical bench 31 inserted through the insertion hole 24 of the printed circuit board 20
5 is pressed into contact with the ground wire 25 provided on the printed circuit board 20. Thereby, the ground wire 25, the conductive resin of the upper surface portion 33 of the optical bench 31,
Conduction with the shield case 40 is established.

In FIG. 1, reference numeral 14 denotes a smoke inlet of the cover 12, 15 denotes a blade for electrically and mechanically connecting to a sensor base (not shown), and 26 denotes a light receiving element 2.
The shield cover 34 for 3 is a portion extending upward from the lower surface portion 34 in order to prevent the lead wires of the light emitting element 22 and the light receiving element 23 from contacting the upper surface portion 33 made of a conductive resin.

With such a configuration, circuit components susceptible to electrical noise, such as an amplifier circuit provided on the printed circuit board 20, include an upper surface portion 33 made of conductive resin of the optical table 31 of the dark box 30. Since electromagnetic shielding is performed by the shield case 40, malfunction can be prevented. Further, since the lower surface portion 34 of the optical bench 31 which is the inner wall surface of the dark box 30 which affects smoke monitoring is formed of a non-conductive resin, it is not corroded even when exposed to corrosive gas. Further, the lower surface of the printed circuit board 20 surrounded by the concave portion 36 can also be used as an electromagnetically shielded mounting surface of a circuit component such as a chip component.

In this embodiment, the optical table 31 and the shield case 40 are electrically connected by the engaging pieces 35 of the optical table 31.
5 may be engaged with and connected to the ground wire 25 of the printed circuit board 20, and the shield case 40 may be connected to the ground wire 25 at another portion on the printed circuit board 20.

FIG. 2 shows a second embodiment, in which parts common to those of the first embodiment are denoted by the same reference numerals, and a main body 11 and a cover 1 are provided.
2 is not shown.

In this embodiment, the optical table 31 is formed integrally with the upper surface portion 33 and the outer wall portion, that is, the outer surface side 33 'is made of a conductive resin, and the inner surface 37, which is the inner portion, is made of a non-conductive resin. Is formed. Also, the lid 32
Is formed by integrally molding the outer surface side 38 of a conductive resin and the inner surface side 39 of a non-conductive resin.

With this configuration, the dark box 30
Since the inner surfaces 37 and 39 are made of a non-conductive resin, and the outer surfaces 33 'and 38 are made of a conductive resin,
The inside of the dark box 30 can be electromagnetically shielded, and the light receiving element 2
3 can be shielded. In addition, since the inner surfaces 37 and 39 of the dark box 30 that affect smoke monitoring are non-conductive resins, they are not corroded by corrosive gas or the like, so that irregularities are not generated.

In each of the above embodiments, when it is necessary to shield the entire lower surface of the printed circuit board, a flange made of a conductive resin is provided on the dark box or the upper surface of the dark box so as to cover the entire printed circuit board. I just need.

[0026]

According to the present invention, the outside or top surface of the dark box into which smoke flows is formed of conductive resin, and the inner wall of the dark box which directly affects smoke monitoring is formed of non-conductive resin which is resistant to corrosion. Even if it is used in places with bad environment such as hot springs and factories, the inner wall surface is not corroded by corrosive gas etc. Also, a dark box with good shielding properties with conductive resin on the outside or top surface There is an effect that a photoelectric smoke detector provided with the sensor can be obtained.

Further, since the dark box has a shielding property, it is not necessary to provide a shield pattern having a large area such as a solid ground on the lower surface side of the printed circuit board, so that both sides of the printed circuit board can be effectively used. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention.

FIG. 2 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoelectric smoke detector 11 main body 12 cover 13 hook 20 printed circuit board 21 circuit component 22 light emitting element 23 light receiving element 24 insertion hole 25 earth wire 30 dark box 31 optical table 32 lid 33 upper surface part 33 ′, 38 inner surface side 34 lower surface part 35 engagement piece 36 concave portion 37, 39 outer surface side 40 shield case 42 engagement hole

Claims (3)

(57) [Claims] 1. A printed circuit board on which electric circuit components are mounted, and a dark box provided with a light emitting element and a light receiving element and into which smoke flows are provided in this order on the lower surface side of the main body. In a photoelectric smoke detector in which an enclosing cover is detachably engaged with the main body, the dark box may be formed with a non-conductive resin on the inner surface side and formed with a conductive resin on the outer side. Features a photoelectric smoke detector. 2. A printed circuit board on which electric circuit components are mounted, and a dark box provided with a light emitting element and a light receiving element and into which smoke flows are provided in this order on the lower surface side of the main body. In a photoelectric smoke detector in which an enclosing cover is detachably engaged with the main body, the dark box is provided with the light emitting element and the light receiving element, and an optical table having an open lower surface, and an open lower surface of the optical table. And an optical table of the dark box, wherein the optical box of the dark box is integrally formed with a conductive resin on an upper surface portion and a non-conductive resin on a lower surface portion thereof. Type smoke detector. 3. The dark box is mounted and fixed on the lower surface of the printed circuit board, and a shield case is provided on the upper surface side of the printed circuit board. The conductive resin portion of the dark box is directly connected to the shield case. The photoelectric smoke sensor according to claim 1, wherein the photoelectric smoke detector is connected through a wiring pattern of the printed circuit board.