JPS5825513Y2 - photoelectric smoke detector - Google Patents

Description

[Detailed description of the invention] This invention relates to protection measures against electromagnetic noise in a photoelectric smoke detector.

Recently, smoke detectors have been developed in which a light receiving part receives light from a light emitting part through smoke, and detects smoke based on the amount of received light.

This type of photoelectric smoke detector operates by detecting minute electrical signals obtained from the light receiving section using a circuit, so the optical system consists of a smoke detecting section and a minute signal consisting of a light emitting section and a light receiving section. The detection circuit, including the amplifier circuit, must be protected from external electromagnetic noise to prevent malfunction. Conventional photoelectric smoke detectors require a synthetic resin case and cover to house the entire device. Some are coated with a conductive material to provide electromagnetic shielding, or the detection circuit is integrated into a small shielded case.

However, in the former structure, the case and cover are very expensive, and it is necessary to consider reliable electrical contact between the case and the cover.In addition, in the latter structure, the electromagnetic shield is attached to the leads of the light emitting part and the light receiving part. There were some shortcomings such as not being as good as .

The present invention was developed in view of the above drawbacks, and by covering the electric circuit section with the metal mounting plate of the smoke detection section to which the light emitting section and light receiving section are attached, a good electromagnetic shielding effect can be achieved with an extremely simple structure. The present invention provides a photoelectric smoke detector that can

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a cross-sectional view of a photoelectric smoke detector according to the present invention.
FIG. 2 is a front view with the cover removed.

Case 1 is the basic case of this smoke detector. Case 1 is made of heat-resistant synthetic resin and is shaped like a cylindrical container.
The upper wall 1a side is attached to the ceiling or the like.

Reference numeral 2 denotes a circuit board fixed to the lower surface of the upper wall 1a of the case 1 with screws 3, and although detailed illustration is omitted, a large number of circuit elements are attached to this circuit board 2, such as a detection circuit and the like. An output circuit is configured and serves as an electronic circuit section 4.

Note that a ground line is formed on the circuit board 2 over a wide area.

5 is a mounting plate formed in the shape of a shallow container with a conductive metal plate;
This mounting plate 5 is fixed to the projection 1b of the case 1 with screws 6, and the electronic circuit section 4 at the bottom of the circuit board 2 is housed inside the container-shaped mounting plate 5, and its bottom surface 5a and peripheral surface 5b
covered by.

Furthermore, a light emitting section 7, a light receiving section 8, and two light shielding plates 9 and 10 are attached to the bottom surface 5a of the mounting plate 5, as shown in FIG. 2, to constitute a smoke sensing section 11 of an optical system.

The light emitting unit 7 has a light emitting element 7a such as a light emitting diode attached via a mounting base 7b, and irradiates the measuring light beam A toward the aperture windows 9a and 10a of the light shielding plates 9 and 10.

The light receiving section 8 has a light receiving element such as a phototransistor (not shown) and a condensing lens 8a built into a mounting base 8b, and is designed to receive the scattered light B when the measurement light beam A is scattered by smoke. It has become.

The light shielding plates 9 and 10 prevent unnecessary reflected light of the measurement light beam A from entering the light receiving section 8 .

Further, the electrical connection between the light emitting element 7a and the light receiving element and the electronic circuit section 4 is made through the mounting plate 5 over the shortest distance.

Further, the mounting plate 5 is electrically connected to the ground line of the circuit board 2.

A synthetic resin cover 12 covers the entire lower part of the case 1, and is detachably fitted to the case 1.

This cover 12 prevents external light from entering the interior, and allows smoke to easily enter through a labyrinth portion 12a formed on its lower surface.

When smoke enters the internal smoke sensing section 11 with this cover 12 attached, the measuring light beam A from the light emitting section 7 is scattered by the smoke, and this scattered light B enters the light receiving section 8.

The resulting minute signal from the light receiving element is amplified and detected in the electronic circuit section 4, and its output circuit is operated to send out a smoke detection signal.

As shown in the above embodiments, in the photoelectric smoke sensor according to this invention, the electronic circuit section is covered by the metal mounting plate of the smoke sensor section to which the light emitting section, the light receiving section, etc. are attached, so as to provide electromagnetic shielding. Therefore, not only the electronic circuit section but also the node section connecting the electronic circuit section with the light emitting section and the light receiving section are well shielded by the mounting plate, and accurate operation can be obtained without being affected by external electromagnetic noise.

Furthermore, since the shield structure is made up of a single mounting plate, assembly is easy, and maintenance and inspection are also easy.

[Brief explanation of the drawing]

The drawings show an embodiment of the photoelectric smoke detector according to the present invention, and FIG. 1 is a sectional view thereof, and FIG. 2 is a front view with the cover removed. 1... Case, 2... Circuit board, 4.
...Electronic circuit section, 5...Mounting plate, 7...
... Light emitting section, 8 ... Light receiving section, 9 ...
- Light shielding plate, 10... Light blocking plate, 11...
Smoke sensitive section, 12...Cover.

Claims (2)

[Scope of utility model registration request] (1) A photoelectric smoke detector characterized in that the electronic circuit section of the photoelectric smoke detector is covered by a metal mounting plate of the smoke sensor to which a light emitting section, a light receiving section, etc. are attached, thereby providing electromagnetic shielding. . (2) The photovoltaic device according to claim 1, wherein the mounting plate is curved around its periphery to form a container shape, and the electronic circuit portion is covered so as to be housed inside the container-shaped mounting plate. type smoke detector.