JP2008250852A - Smoke detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a smoke detector for selectively fetching only the necessary rays of light of a scattering angle without receiving any noise light from an unintended direction such as stray light reflected inside a labyrinth or incident light incoming from the outside, and for having a simple labyrinth structure. <P>SOLUTION: This smoke detector is provided with a smoke detection part; a light emitting device installed in the smoke detection part; and a light receiving device installed in the smoke detection part. The smoke detector is provided with an optical filter through which only a peak emission wavelength band emitted by the light emitting device is transmitted in front of the light reception face of the light emitting device. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a smoke detector.

A conventional scattered light type smoke detector has a labyrinth member that covers the outer periphery of the smoke detection chamber with a plurality of labyrinth members that are shielded from light, and a light-emitting element and a light-receiving element are provided toward the inside. A gap that further limits the light receiving field area of the light receiving element with respect to the smoke detection chamber determined by the light receiving holder opening of the light receiving element is formed by the tip and a light shielding plate that blocks light reaching the light receiving element from the light emitting element, In normal times, stray light from the light emitting element to the light receiving element is reduced to reduce the zero point level to improve reliability (for example, see Patent Document 1).
Japanese Patent No. 3389227

  In the above conventional example, much of the light from the light emitting element is blocked by the tip of the labyrinth member and the light shielding plate, and in order to obtain a stable light receiving output, it is necessary to increase the amount of light emission. There is a problem that stray light increases.

  That is, in the above conventional example, in order to limit the light receiving field by the arrangement of the labyrinth member or the like, the light receiving field region is narrowed with respect to noise light from an unintended direction due to reflection inside the labyrinth, and light having a necessary scattering angle. There is a problem that it is not possible to selectively capture only.

An object of the present invention is to provide a smoke detector that can selectively capture only light having a necessary scattering angle without receiving noise light from an unintended direction due to reflection inside the labyrinth or the like.

The present invention relates to a smoke detector having a smoke detector, a light emitting element provided in the smoke detector, and a light receiving element provided in the smoke detector, wherein the light emission is provided in front of the light receiving element. An optical filter that transmits only the peak emission wavelength band of the element is provided.

According to the present invention, noise light inside the labyrinth (stray light by a light emitting element and external incident light) can be reduced, detection accuracy can be improved, and the labyrinth structure can be simplified. Play.

  The best mode for carrying out the invention is the following examples.

  FIG. 1 is a cross-sectional view showing a smoke detector of a smoke detector SE1 that is Embodiment 1 of the present invention.

  The smoke detector SE1 includes a case 10, a light emitting element 20, a light receiving element 30, and an optical filter 40. Further, although not shown, the smoke detector SE1 is provided with a light receiving amplification circuit, a CPU, and the like.

  A labyrinth member 11 and a smoke detector 12 are provided inside the case 10 that opens the outer periphery.

  The smoke detector 12 is provided with a light emitting element 20 and a light receiving element 30.

  The light emitting element 20 is configured by, for example, an LED that emits infrared light having a peak emission wavelength of 900 nm.

  The light receiving element 30 is constituted by a PD having a light receiving sensitivity to infrared rays, and receives scattered light from smoke particles that have received light emitted from the LED when smoke enters. The light receiving element 30 forms a predetermined optical axis angle with the light emitting element 20.

  The light receiving amplification circuit amplifies the output signal of the light receiving element 30. The CPU has an A / D conversion function and a fire discrimination function, and the A / D conversion function converts a signal of the light receiving amplification circuit into a detection level as data. If the detection level is equal to or higher than the threshold value, the fire discrimination function discriminates a fire and outputs a fire signal.

  The optical filter 40 is disposed in the opening of the light receiving element storage portion in front of the light receiving surface of the light receiving element 30. The optical filter 40 is configured by an interference filter, and this interference filter is a filter that limits the incidence of scattered light caused by smoke reaching the light receiving element 30. The interference filter is a filter in which a thin film material (silica, titanium dioxide, etc.) is laminated in multiple layers on a substrate such as glass, and the spectral characteristics can be arbitrarily set. For example, only the peak emission wavelength band of the light emitting element 20 can be set. Can be transmitted.

  In this case, the other wavelength bands are reflected by the interference action by the surface of the substrate or film.

  Next, the operation of the first embodiment will be described.

  FIG. 2 is a diagram for explaining the operation of the first embodiment.

  As shown in FIG. 2A, when light in the peak emission wavelength band of the light emitting element 20 is incident at right angles to the surface of the optical filter 40, the light is transmitted through the optical filter 40. However, as shown in FIG. 2B, when light in the peak emission wavelength band of the light emitting element 20 is incident on the surface of the optical filter 40 obliquely, the light is reflected by the surface of the optical filter 40, and the optical filter 40. Does not pass through.

  This is because the transmission wavelength band of the optical filter 40 is shifted to the short wavelength side due to the incident angle θ.

  The magnitude of this shift is determined by the refractive index of the optical filter 40. If this refractive index is low, this shift amount becomes large. The shift amount of the optical filter 40 is calculated by the following formula.

_{λ θ = {λ 0 · (} n e 2 -sin 2 θ) 1/2} / n e ... formula (1)
here,
theta = angle of incidence n e ₌ refractive index lambda _{0 =} front direction (θ = 0 °) the center wavelength lambda _theta = is "" the optical filter when the angle of incidence of 40 degree of the optical filter 40 at the angle of incidence of the optical filter 40 Therefore, if the light emitting element 12 and the light receiving element 30 are arranged so that the incident angle θ is increased, the optical filter 40 can block incident light from an oblique direction of the peak emission wavelength band of the light emitting element 11. it can.

  FIG. 3 is a diagram illustrating a state in which the internal stray light L of the LEDs constituting the light emitting element 20 does not reach the light receiving element 30 in the smoke detector SE1.

  The internal stray light L of the LED constituting the light emitting element 20 reflects the labyrinth member 11 and reaches the optical filter 40 provided in the light receiving element 30, but the stray light is incident at an angle orthogonal to the surface of the optical filter 40. Therefore, the light is reflected on the surface of the optical filter 40 and does not reach the light receiving element 30. Therefore, there is no false detection of fire due to the internal stray light L of the LED, that is, no false alarm.

  FIG. 4 is a diagram illustrating a state where the incident light N from the outside does not reach the light receiving element 30 in the smoke detector SE1.

  When the incident light N enters the smoke detector 12 from the outside of the smoke detector SE1, the light reaches the optical filter 40 after being reflected by the labyrinth member 11, but the incident light has the same band as the peak emission wavelength of the light emitting element 20. Even if it exists, since it does not enter at an angle orthogonal to the surface of the optical filter 40, it is reflected by the surface of the optical filter 40 and does not reach the light receiving element 30. Therefore, there is no false detection of fire due to incident light N from the outside, that is, no false alarm.

  3 and 4, even if the stray light L and the incident light N in the same band as the peak emission wavelength of the light emitting element 20 are incident so as to be orthogonal to the optical filter 40, by that time, the labyrinth member 11 In this case, the light receiving element 30 does not detect them.

  That is, according to the above embodiment, the light from the light emitting unit is selectively received with the light having the necessary scattering angle, so that the noise light inside the labyrinth (the internal stray light L of the LED and the incident light N from the outside) is generated. The detection accuracy can be improved. Moreover, a labyrinth structure can be simplified and the directionality of the inflow characteristic (responsiveness) of the smoke with respect to the smoke detection part from the peripheral direction can be eliminated.

  The optical filter 40 may be a band pass filter.

In any case, by using the optical filter 40 having a spectral characteristic that transmits only the light emission wavelength band of the light emitting element 20, the peak light emission wavelength band of the light emitting element 20 is transmitted while the light receiving wavelength sensitivity of the light receiving element 30 is narrowed. Therefore, the amount of noise light can be reduced, and the smoke detector SE1 having an excellent S / N ratio can be obtained.

It is sectional drawing which shows smoke detector SE1 which is Example 1 of this invention. FIG. 6 is a diagram illustrating the operation of the first embodiment. FIG. 3 is a diagram illustrating a trajectory in which internal stray light of an LED constituting the light emitting element 20 reaches the light receiving element 30 in the smoke detector SE1. In smoke detector SE1, it is a figure which shows the locus | trajectory in which the incident light from the outside arrives at the light receiving element 30. FIG.

Explanation of symbols

SE1: Smoke detector,
10 ... Case,
11 ... Labyrinth member,
12 ... smoke detector,
20 ... light emitting element,
30. Light receiving element,
40: Optical filter.

Claims (2)

A smoke detector;
A light emitting device provided in the smoke detector;
A light receiving element provided in the smoke detector;
In smoke detectors with
A smoke detector, wherein an optical filter that transmits only the peak emission wavelength band of the light emitting element is provided in front of the light receiving element. In claim 1,
The smoke sensor, wherein the optical filter is an interference filter.

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