RU2262745C2 - Smoke fire alarm - Google Patents

Abstract

FIELD: automatic fire alarm.

SUBSTANCE: device has optical couple, positioned in sensitive chamber, and additional chamber, with at least three ribs, one of which is positioned between the other two, positioned on the opposite wall of chamber. Outer wall of additional chamber is made perforated and is positioned inclined to base.

EFFECT: higher efficiency, higher resistance to interference.

2 cl, 3 dwg

Description

The invention relates to the field of automatic fire alarms, and more particularly to fire detectors that detect the appearance of smoke in the area of their installation.

Smoke detectors operating on the principle of recording scattered radiation are widely known. For example, a smoke detector by a.s. USSR No. 575672, G 08 B 17/10; smoke detector USSR No. 1265821, G 08 B 17/10; scheme for detecting a decrease in the sensitivity of a photoelectric smoke detector, Japanese application No. 4-60276, No. 4-60277, G 08 B 17/107.

These detectors use a built-in emitting LED and a recording photodiode located in a sensitive camera at an obtuse angle to one another. Under clean air conditions, the photodiode does not detect the emission of the LED. When smoke enters through openings in the walls of the sensitive chamber, the LED radiation scattered by the smoke particles is detected by the photodiode. The signal from the photodiode is transmitted to a decisive device, and when the signal reaches a predetermined threshold level, the detector switches to an alarm state. However, the luminous flux incident on the photodiode may also be due to the reflection of the LED radiation from the dusty walls of the sensitive chamber or to the light penetrating through its openings.

The closest to the proposed technical essence and the achieved result is a smoke optical-electronic smoke detector ECO2003 by System Sensor [Specialized Information and Technical Journal for Fire and Security Protection, Information and Communication, December 1997 / February 1998, p. 13; European Patent Application EP 1049060 A2]. The detector contains an emitting LED that detects a photodiode, i.e. an optical pair housed in a sensitive chamber that is directly connected to an additional chamber for dust collection.

The aerodynamic resistance of the additional chamber (Ω ₁ ), which affects the speed and nature of the propagation of air flows through the chamber, is proportional to the ratio of the path length (L ₁ , figure 2), which must be passed through the air flow from the analyzed volume to the sensitive element (optical pair), and the surface area of the additional chamber (S ₁ ) in contact with the analyzed volume:

Ω ₁ ~ L ₁ / S ₁

The surface area of the additional chamber (S ₁ ) is determined by the following ratio:

S ₁ = 2πR ₁ H ₁ ; Where

R ₁ - the distance from the geometric axis of the detector to the outer wall of the additional camera (figure 2).

H ₁ - the height of the smoke channel in the additional chamber (figure 2).

The problem is solved in that in a smoke fire detector containing an optical pair located in a sensitive chamber, and an additional chamber equipped with at least three ribs, one of which is located between two others located on the opposite wall of the chamber, the sensitive chamber is separated from the additional chamber by one of the mentioned ribs, while the smoke passes through the perforated outer wall of the additional chamber, collides with the ribs and passes into the sensitive chamber.

In accordance with claim 2, the outer wall of the additional chamber is inclined to the base.

It is obvious that the placement of additional ribs, which significantly increases the path (L _{2 of} FIG. 3) of smoke passage from the analyzed volume to the sensitive chamber compared to the prototype, ceteris paribus would increase the aerodynamic drag of the additional chamber (Ω ₂ ), spreading the spread of smoke through the smoke channel.

L ₁ <L ₂

However, with the claimed solution, the surface area (S ₂ ) of the additional camera, which is in direct contact with the analyzed volume, is also increased by increasing the distance from the geometric axis of the detector to the outer wall of the additional camera (R ₂ , Fig. 3):

R ₁ <R ₂

S ₂ = 2πR ₂ H ₂

Where:

H ₂ - the height of the smoke channel in the additional chamber.

The surface area S _{2 is} increased so that the aerodynamic drag of the additional chamber (Ω ₂ ):

Ω ₂ ~ L ₂ / S ₂

remained at least unchanged, and therefore the sensitivity of the detector did not deteriorate. Those. the technical contradiction has been eliminated and it should be concluded that the proposed solution meets the criterion of "inventive step".

The invention is illustrated in the drawing, which shows:

Figure 1 - diagram of the proposed detector;

Figure 2 - diagram of the passage of the analyzed air in the prototype;

Figure 3 - diagram of the passage of the analyzed air in the proposed detector.

The smoke fire detector contains (Fig. 1) a sensitive chamber 1 in which an optical pair 2 is placed. The sensitive chamber is separated from the secondary chamber 3 by a rib 4. In the secondary chamber 3 there are ribs 4, 5 and 6 and a perforated outer wall 7 inclined to the base The rib 6 is located on the opposite wall 8 of the additional chamber 3. The number of ribs can be increased (not shown in the drawing), then two ribs will be located on the wall 8, and three on the opposite wall. Wall 8 is the base of the smoke detector, with which the detector is mounted in the analyzed volume.

The inclined location of the perforated outer wall 7 allows you to increase sensitivity to both horizontal and vertical streams of smoke.

The detector operates as follows.

Under clean air conditions, the photodiode does not detect the emission of the LED, since in the optical pair 2 located in the sensitive chamber 1, the emitting LED and the recording photodiode are at an obtuse angle to one another. When a fire occurs, smoke passes through the perforated outer wall 7 of the additional chamber 3, collides with the ribs 4, 5 and 6 and passes into the sensitive chamber 1. At each collision, heavy dust particles settle in special cavities of the additional chamber and do not enter the sensitive chamber. Thus, contamination of the sensitive chamber is minimized. When smoke enters the sensitive chamber 1, the scattered light is detected by the photodiode of the optical pair 2. The signal from the photodiode enters the device, which makes a decision about the alarm when the specified signal level is reached.

Claims (2)

1. A smoke fire detector containing an optical pair located in a sensitive chamber and an additional chamber provided with at least three fins, one of which is located between two others located on the opposite wall of the chamber, the sensitive chamber is separated from the additional chamber by one of the said ribs, while the smoke passes through the perforated outer wall of the additional chamber, collides with the ribs and passes into the sensitive chamber. 2. The detector according to claim 1, characterized in that the outer wall of the additional camera is located obliquely to the base.

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