SU1550555A1 - Method and apparatus for checking presence of smoke in medium under check - Google Patents

Abstract

The invention relates to a fire alarm technique and can be used in fire protection to detect fires at an early stage even before the occurrence of an open flame. The aim of the invention is to increase the reliability of control and functional reliability. The essence of the invention is that the method of detecting smoke is based on passing a reference luminous flux through a controlled medium, measuring the diffused luminous flux of the controlled medium at the same acute angle in the forward and reverse directional luminous flux, converting the forward and backward diffused Light fluxes into electrical signals form their difference, and the magnitude of the difference between electrical signals is compared to the level of a reference electrical signal. In a device for carrying out a method comprising two optical emitters connected to a pulse generator, a photodetector installed at an acute angle to the luminous flux of the emitter, the output of the photodetector is connected to a comparator connected to the source of the reference signal, in order to protect against spurious device triggers element, the emitters are arranged in such a way that their optical axes are aligned, and the radiating surfaces are facing towards each other and are removed at an equal distance from the point ne the cross section of the optical emitters and photodetector, the output of which is connected through a separating element to the comparator. 2 sec. f-ly, 2 ill.

Description

In the absence of smoke, the light from source 1 does not reach the photodetectors 2 and 3. The output electrical signals of the photodetectors 2 and 3 are absent, therefore the output signal of the subtractor 4 is also absent. At the output of comparator 5, a smoke detection signal is absent, since it is less than the value of the reference signal of the source K 3 fr.

When smoke appears in a sensitive area with a center at point O, smoke particles most intensively scatter light in the direction of the control light flux of source 1 (in Fig. 1 the indicatrix 8 scatters 1 smoke particles), and a large fraction of

light smoke (vector 0V indicatrix 8), and a photodetector less than the amount of light scattered by smoke (vector OA indicatrix 8), therefore, the output electric signal of the photodetector 3 exceeds the output signal of the photodetector 2. At the output of the subtractor 4, a signal proportional to electrical signals of photodetectors 2 and 3, which exceeds the threshold value of the reference source signal 6. At the same time, at the output of comparator 5, a smoke detection signal is generated.

When water aerosols (fog, vapor) appear in a sensitive area with a center at the point O, the spatial distribution of the scattered light possesses symmetry with respect to the incident light flux from the source 1 (figure 1 shows the indicatrix 7 scattered particles of water aerosols), therefore the proportion of scattered light (vector OD of indicatrix 7) falling on the photodetector 3 is equal to the fraction of scattered light (vector OS Indicator 7) falling on the photodetector 2. The output signals of the photodetectors 2 and 3 are the same, therefore output signal subtracted conductive device 4 is missing, ie, does not exceed the threshold value of the reference signal source 6. The output of the comparator 5 smoke detection signal is absent.

The device (figure 2) contains optical emitters 9 and 10, the photodetector 11, the generator 12 pulses, the comparator 13, the source 14 of the reference signal and the driver J 5 difference

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signal. Optical emitters 9 and 10 create a luminous flux transmitted through a controlled environment, and are arranged so that their optical axes are combined, and the radiating surfaces are facing one another. The photodetector 11 is installed at an angle of 30e to the axis of the emitters 9 and 10, and its

10 the optical axis intersects with the axis of the emitters 9 and 10, at point 0, which is the center of the smoke-sensitive region formed by the intersection of the solid angles of the field of view.

15 photodetector 11 and emitters 9 and 10, which are at equal distance from point O. Figure 2 also shows the indicatrices 16, 17 and 18.

Emitters 9 and 10 are connected to the outputs of the pulse generator 12, while at the time of switching on the radiator 9 there is no radiation of the radiator 10 and vice versa.

The imaging unit 15 extracts only the variable component from the output signal of the photodetector 1-1. To perform this function can be

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a transformer or filter tuned to the frequency of the generator 12.

The device (figure 2) that implements the proposed method works as follows.

In the absence of smoke, the light from the alternately switched on radiators 9 and 10 does not reach the photodetector, the output signal of which is absent, i.e. less than the threshold value of the reference signal of the source 14, while the output of the comparator 13 is no smoke detection signal.

When smoke appears in the sensitive area with the center at point 0 with the emitter switched on, smoke particles most intensively scatter light in the direction of the light flux of the emitter 9 (Fig. 2, indicatrix 17), while the photodetector 11 hits less than the amount of light diffused by the smoke (Fig .2, OA indicatrix vector 17), and when the emitter 10 is turned on, smoke particles most intensively scatter light in the direction of the light flux of the emitter 10 (FIG. 2, indicatrix 16), while a large proportion of the light diffused by the smoke detector hits (FIG. 2, vector 0B indicatrix 16). A driver 15 connected to the output of the photodetector 11 forms

an electrical signal in the form of pulses with a frequency of the generator 12, which passes through the driver 15 and exceeds the threshold value of the reference signal of the source 14. At the output of the comparator 13 a smoke detection signal is generated. The amplitude of the pulses at the output of the photodetector 1 1 is equal to the difference of the electrical signals corresponding to the forward and backscattered light flux.

When water aerosols (fog, vapor) appear in a sensitive area with a center at point O, the spatial distribution of the scattered light is symmetrical with respect to the incident light flux (Fig. 2, indicatrix 18) both with the emitter 9 on, and with the emitter 10 turned on, “ at the same time, the same fraction of scattered light hits the photodetector 11 (Fig. 2, the OS of the indicatrix 18), therefore a constant electric signal is formed on the driver 15 connected to the output of the photo receiver 1 1 that does not pass through the driver 15 which has no signal at the output, i.e. less than the threshold value of the reference signal of the source 14, while the output of the comparator 13 is no smoke detection signal.

The invention allows, at minimum cost, to distinguish smoke from other aerosols, for example, from sea mist, steam, etc., which ensures the reliability of the detection of smoke and eliminates false alarms and associated material damage.

Claims (2)

In addition, the invention makes it possible to detect smoke in the presence of aqueous aerosols in a controlled environment, which increases the detectability of smoke detectors and the effectiveness of automatic fire protection. Invention Formula one . The way to control the presence of smoke in a controlled environment based five 0 five on passing the light drip through the controlled medium, measuring one light scattered by the medium being monitored at an acute angle to one direction of the light flux, converting the scattered light flux into the first electrical signal, generating an information signal whose Q level is compared with the reference signal level and when exceeding the level of the reference signal of the formation of a signal about the presence of smoke, which is due to the fact that, in order to increase the reliability of the control, the second luminous flux is measured, Assa nny controlled environment measurement produced at an acute angle in the other direction relative to the direction of the light flux; the second light flux is converted into a second electrical signal, respectively; the information signal is generated by determining the difference between the first and second electrical signals. 2. A device for monitoring smoke in a controlled environment, containing two optical emitters connected to a pulse generator, a photo0 receiver mounted at an acute angle to the optical axis of the emitter, a comparator, to one input of which a reference source is connected, the output of the comparator is 5 signal output of the device, which is due to the fact that, in order to increase the functional reliability of the device, a differential shaper is inserted into it, the emitters are arranged so that the optical axes are aligned, and the radiating surfaces of the emitters face opposite to the other, the photoreceiver is placed so that its optical axis crosses the optical axis of the optical emitters at a point equidistant from their emitting surfaces, the output of the photodetector is connected to the differential signal former of the 0 which is connected to the other input of the comparator. 1  Smoke detection eight , Smoke detection signal