RU2613274C2 - Optic smoke sensor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: smoke sensor contains a light source with the power unit and a reflector optically coupled to the light source, a support receiving channel optically coupled to the light source, the output of which is connected to the input of the power supply, a measuring receiving channel optically coupled to the light source through the reflector. The smoke presence in the measuring channel is determined by the exceeding of the threshold value Δ, the difference between the current signal value Φ_c of the measuring channel and the dynamic signal value _F0, where

, *Φ₀ - the initial signal level; Φ_i - the instantaneous signal value;

, i - the sample number; n - the number of samples for averaging the dynamic signal level; k - the number of samples for averaging the current signal level.

EFFECT: high measurement accuracy.

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Description

The technical solution relates to developments in the field of security and fire-fighting systems and can be used in aircraft, shipbuilding and other industries.

Known smoke sensor [1], taken as an analogue. The specified sensor at a sufficiently low sensitivity has a complex structure. In addition, the presence of a number of reflectors with both spherical and aspherical surfaces significantly complicates the alignment of the device, and also reduces its operational characteristics - resistance to changes in temperature, pressure, humidity.

The closest to the invention in technical essence is a smoke detector with self-monitoring [2], which contains two optical receiving channels - a reference and a measuring channel, as well as a radiator channel (based on the LED), and consists of a housing, inside of which there is an LED, a prism for removal radiation into the reference channel, the photodiode receiver of the reference channel, the forming optical system, an adjustable reflector, a measuring photodiode receiver optically coupled to it through a receiving lens, and an electronic circuit boots and control.

The presence of smoke in the chamber is detected by the difference between the signals of the reference and measuring receiving channels. In this case, before reaching the operating mode, the signals in the receiving channels are aligned electronically. This principle of operation requires high stability of the emitter, due to the unevenness of the receiving channels, the influence of the instability of the LED radiation flux on the signals in the channels will be different, which will inevitably lead to the appearance of a mismatch signal between them and, as a result, to the appearance of a false alarm. To ensure the unchanged characteristics of the LED radiation during operation, the device has a complex thermal stabilization system, the presence of which leads to a significant increase in both the cost of the device and its energy consumption.

An important aspect is the following fact. The stabilization of the reference signal is carried out in a certain range of dF. As a rule, the sensitivity of the sensor cannot be less than dF.

The above disadvantages can be eliminated by the fact that in the optical smoke detector containing a radiation source with a power supply and a reflector optically coupled to a radiation source, a reference receiving channel optically coupled to a radiation source, the output of which is connected to the input of the power supply, a measuring receiving channel, optically coupled to the radiation source through the reflector, the presence of smoke is determined in the measuring channel by exceeding the threshold value Δ, the difference between the value of the current signal level F _t measuring channel and the value of the dynamic signal level f ₀ , where

* Ф ₀ - initial signal level;

F _i is the instantaneous value of the signal;

i is the sample number;

n is the number of samples for averaging the dynamic signal level;

k is the number of samples to average the current signal level.

Moreover, k << n.

The dynamic signal level characterizes the reference signal in the system. The introduction of averaging over a sample of n measurements makes it possible to exclude random outliers of the reference signal when making a decision. The current signal level is also averaged. His sample is k measurements, with k << n.

With such a processing algorithm, the value of the threshold value Δ can ideally be arbitrarily small. It can be limited only by the intrinsic noise of the electronic processing system. The dF value, which determines the stabilization range of the reference signal, is not critical, i.e. Δ may be less than dF. Therefore, the proposed set of distinctive features allows us to achieve two positive effects, firstly, to increase the sensitivity of the smoke sensor (i.e., to ensure Δ << dF), and secondly, to reduce the likelihood of false alarms of the device due to random emissions of both the reference and current signals (by introducing averaging of the reference and current signals).

The drawing shows a diagram of an optical smoke detector.

It uses a circuit with two receiving channels, one of which is a measuring channel. In this case, an LED is used as a radiator 1 in the transmitting channel, the radiation of which passes through the diaphragm 2 and is additionally collimated by the optical system 3. The focused radiation of the LED is incident on an adjustable reflector 4, which sets the initial value of the flux entering the measuring channel. In turn, the receiving measuring channel includes an optical system 5 and a radiation receiver 6 (photodiode). When smoke enters the chamber on its particles, additional scattering of the LED radiation occurs, and the flux entering the measuring channel increases, which can be detected by increasing the signal from the photodiode radiation receiver by the processing and control unit 7.

The second receiving channel is a reference (reference) channel, which is made on the basis of photodiode 8 and is optically connected to the LED due to its wide radiation pattern, and is also electrically connected through the processing and control unit 7 to the emitter. Its task is to stabilize the radiation of the LED, which is achieved electronically - the sensor provides current control through the LED. Therefore, any change in the emitting characteristics of the LED, both due to external influences (temperature, pressure, etc.), and during degradation of the emitter crystal itself, is almost instantly compensated by an increase or decrease in the current through it. In addition, the LED radiation is modulated in the kilohertz range - amplification paths with high quality factor of both measuring channels located in the processing and control unit 7 are tuned to the same frequency, which allows you to move away from all external background illumination of both natural and artificial origin.

Information sources

1. RF patent 2037883, IPC G08B 17/10, publ. 06/19/1995.

2. US patent US 4870394 from 09/26/1989, IPC G08B 17/10, NKI 340/630.

Claims (8)

A smoke detector comprising a radiation source with a power supply and a reflector optically coupled to a radiation source, a reference receiving channel optically coupled to a radiation source whose output is connected to an input of the power supply, a measuring receiving channel optically coupled to a radiation source through a reflector, characterized in that the presence of smoke is determined in the measuring channel by exceeding the threshold value Δ, the difference between the value of the current signal level Ф _{t of the} measuring channel and the dynamic signal level f ₀ , where

^* Ф ₀ - initial signal level; F _i is the instantaneous value of the signal;

i is the sample number; n is the number of samples for averaging the dynamic signal level; k is the number of samples to average the current signal level.

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