BG67306B1 - Multifunctional optical fire detector - Google Patents

Abstract

The invention relates to a multifunctional optical fire detector. Its multifunctionality relates to the ability to detect carbon monoxide, smoke and temperature simultaneously and continuously. The detection is entirely performed by optical methods, which means that no electrical voltage is applied to the detection device and no electricity is flowing therein. This allows the detector to be used in explosive production or storage areas, as well as in the presence of other aggressive agents. The detector can be integrated into a large premise fire protection system. This is easy and inexpensive, since it is based on technological solutions used in optical communications. Due to its multifunctionality, the detector is versatile and satisfies the commonly conflicting requirements for fire protection of different sites.

Description

Field of technology

The invention relates to a multifunctional optical fire detector, which detector simultaneously and continuously carbon monoxide (CO), smoke and temperature, as the detection is entirely optical in the detector no voltage is applied and no electric current flows. It is used in fire alarm systems for all types of premises, as well as those with explosive and aggressive environments.

BACKGROUND OF THE INVENTION

The invention aims to create a universal and multifunctional fire sensor:

- for fire protection of sites with various applications;

- which simultaneously and continuously detects carbon monoxide, smoke and temperature;

- which is fully optical, with the light in the detector being fed through optical fibers; the detection of CO, smoke and temperature is based on optical principles; there is no voltage in the detector and no electric current flows as with conventional detectors.

CO detection is mandatory when using solid fuel heating, according to the regulations of many countries. The installation of a CO sensor in the fire sensor is the most effective. All known sensors are electrochemical - the sensor operates at an electrical voltage and an electric current flows through it.

The power supply of the sensor is provided either by connection to the mains or by a battery. In both cases, these sensors are dangerous for use in potentially explosive atmospheres or in areas with aggressive chemical environments, as it has been shown that an electric spark can cause an explosion.

Document DE102011088850 BZ reports a smoke detector in a fire alarm system which is based on the principle of light scattering of a directed beam of light in a direction different from its direction of propagation. The disadvantage of this type of sensors is the occurrence of a false signal - dust in the air leads to the same effect.

Document EP0248723 A1 reports a sensor for detecting critical temperature in a fire-protected room. Optical fibers are placed in the room, the polymer reflective coating of which is destroyed at a certain temperature. At the same time, the intensity of the light passing through the optical fibers decreases sharply, which serves as an indication of the temperature caused by fire. The disadvantage of this method is the detection of a certain temperature, which is considered critical. This does not meet modern requirements for fire protection systems, which require continuous temperature measurement and hazard criteria is the gradient of temperature change.

Document RU2336573 C1 reports a fire sensor that alerts the occurrence of smoke and gases in the initial stages of a fire. The sensor consists of two optical channels. One is the wavelength that is absorbed by the detectable gas, and its presence is judged by the reduction in light intensity. The other channel is at a different wavelength, and the decrease in intensity can only be due to the presence of smoke. Disadvantage of the sensor is the detection of changes in light intensity. This

BG 67306 Bl change may be due to many factors unrelated to the phenomena to be controlled. This determines the low reliability of the sensor.

Document US4839527 reports a system that detects gases and smoke by spectral analysis, the presence of which is a fire criterion. The registration takes place in a sensor placed in the guarded room. Light with a certain spectrum is fed to the sensor and is removed from it by optical fibers. It is possible to install another sensor to measure temperature, but the principle of operation is not specified. The essential differences from our detector are that the measurement of smoke, CO and temperature takes place simultaneously in one device. The proposed measurement of the presence of gases along their absorption spectrum cannot be performed with optical fibers, because they have large losses for those wavelengths that are informative for the gases. Probably no attention was paid to this at the time of the application (1989) as fiber optics was at an early stage of development at that time. An essential difference of our invention is that the measured spectral response is not due to the spectral properties of the gas, but to the result of its interaction with a recognizing substance, which greatly facilitates the practical implementation.

Such an approach is disclosed in JPH1096690 (A), where a carbon monoxide sensor is reported. The gas is detected by its interaction with inorganic recognition elements. The difference from our detector is that it uses organic matter to detect CO, as it measures both smoke and temperature.

The fire sensor disclosed in GB2310726 (A) detects CO on the same principle. Its difference from our detector is that the sensor is not fully optical - it requires power to operate.

The tasks solved by the present invention are:

Early warning of a fire requires early detection of smoke and gases released in the initial phase of the fire - incomplete combustion. These gases are different in different combustion products, but all emit carbon monoxide. Their simultaneous detection allows the sensor to be universal - to be used for fire protection of objects with different purposes and storing different products, as well as to reduce to virtually zero the possibility of false signals. The present invention relates to an all-optical fire detector, which allows the security of premises for the production of explosives, warehouses for such materials, warships, submarines, chemical plants, mines and mines, transport tunnels.

Technical essence of the invention

The object of the invention is to provide a universal and multifunctional fire detector, which detects simultaneously and continuously CO, smoke and temperature, the detection being performed entirely on optical principles.

The listed disadvantages of the prior art are overcome by creating a new method for measuring CO and combining it with known methods for measuring smoke and temperature in a designed new device, which is a fire detector.

The new method for measuring CO is based on recording the interaction of the CO molecule with a substance (recognizing) that has a strong affinity for interaction with CO. The recognizing substance can

BG 67306 B1 is Ag-YSZ (silver with stabilized yttrium and zirconium), tin dioxide or synthetic hemoglobin. The registration of the interaction with CO is performed by a surface plasmon wave excited on the surface of a gold diffraction grating, on the surface of which the recognition substance is applied, as shown in Figure 1. The surface plasmon wave is excited by a beam of white light falling at a specific angle θ (figure 1). At this angle of incidence, the spectrum of the reflected light has a minimum at a precisely defined wavelength (curve 1, Fig. 2). This phenomenon is called plasmon resonance. The angle of incidence θ and the wavelength λ at which a minimum of intensity is observed (ie at which resonance occurs) are related to the formula:

A / X * ²

Λ = - ί—-) -sin (0) \\ ^mn !

where Λ is the lattice constant, £ _m is the dielectric constant of the metal, and ε _η is the dielectric constant of the recognition substance. In Figure 1, the resonant wavelength (Figure 1) is: 728.0 nm. It can be seen from the formula that it changes when the dielectric constant of the recognizing substance changes, which occurs upon interaction with even several CO molecules - the registration of the interaction with plasmon resonance is extremely sensitive. Curve 2 in Figure 2 shows the plasmon resonance upon interaction with CO at a concentration of 100 ppm (0.01%) - the plasmon resonance was displaced by 10.4 nm. The displacement depends only on the CO concentration. The dependence - spectral shift of plasmon resonance / CO concentration is calibrated in advance. The spectral shift and hence the CO concentration are measured. Plasma resonance (ie the spectrum of light reflected from the diffraction grating) is measured with a standard spectrometer.

Free access of air from the guarded room is provided to the recognizing substance. The presence of CO is always associated with a combustion process and when it is registered, a fire alarm is given.

Smoke is detected by a known method: the amplitude of the light reflected from the diffraction grating is monitored. The amplitude of the light does not depend on the concentration of CO, but only on the presence of smoke particles in the air of the guarded room. Figure 26, curve 3 shows the plasmon resonance signal at a concentration of 100 ppm and the presence of smoke. The amplitude of the signal decreases due to the absorption and scattering of light by the smoke particles, but the spectral position of the resonance is preserved. The decrease in the amplitude of the optical signal is always associated with the presence of smoke. When the signal amplitude is reduced by more than 10%, a fire hazard signal is given.

The registration of CO and smoke is reflected at the same time as an absolutely certain sign of a fire with the appropriate alarm. Combining the two registrations allows to eliminate false signals in the presence of dust instead of smoke.

The principle of temperature measurement is based on the temperature dependence of the band gap of a GaAs semiconductor:

αΤ ²

Eg (T) = Eg (0) - - where Eg is the band gap, T is the temperature, and E _e (0), and β are material-specific parameters. For GaAs their values are E _e (0) = 1.519 eV, a = 5.41 x 10 ' ⁴ eV / K, β = 204 K. From the equation we can get the theoretical dependence of the band gap and the wavelength λ ( Τ) from which

BG 67306 Bl starts the optical transmission of GaAs from the temperature. The experimentally measured change in the optical transmission of the light passing through the semiconductor wafer is shown in Figure 3. The increase in temperature leads to a shift of the transmission arm to greater wavelengths. This displacement, relative to a temperature of 18 ° C, is shown in Figure 4 and measures the temperature of the semiconductor. It is in contact with the environment of the guarded room and thus the temperature is continuously measured. This allows not only to signal a fire hazard when a certain critical temperature is reached, but also to monitor the temperature gradient over time. If this value deviates from the usual for the guarded room, a warning signal is given at the beginning of combustion.

Explanation of the attached figures

Figure 1 - gold diffraction grating with a coating on it that interacts with CO;

Figure 2a is a graph of the spectral shift at a CO concentration of 100 ppm;

Figure 2c - graph of the plasmon resonance signal at a concentration of 100 ppm and the presence of smoke;

Figure 3 is a graph of the change in the spectrum of light passing through a GaAs semiconductor with a change in temperature;

Figure 4 is a graph of the displacement of the optical transmission arm with a change in temperature relative to a temperature of 18 ° C;

Figure 5 - exemplary embodiment of the multifunction detector;

Figure 6 - another embodiment of the multifunction detector;

Figure 7 is another embodiment of the multifunction detector;

An embodiment of the invention

The detector consists of three modules:

Module 1: delivers the light signal to the other two modules, which operate with a light signal in different spectral ranges. The role of module 1 is to direct and spectrally separate the light to the respective modules, then combine the light signals and send them to the spectrometer. Module 1 includes lenses, dichroic mirrors and ordinary mirrors. Module 2, measures the concentration of CO and the presence of smoke, working with a light signal with a spectrum of 700-800 nm. The module includes a gold diffraction grating coated with a recognizing substance that interacts with CO (Fig. 1). The recognition substance is organic, applied in such a way that the layer is not dense, but nanostructured - on "islands" with a size of 70 nm to 120 nm, with an average thickness between 270 nm and 320 nm. At these parameters, the substance has a maximum activity of interaction with CO, which provides high sensitivity and accuracy of measurement. A surface plasmon wave is excited on the surface of the golden lattice when the light falls at a precisely defined angle θ = 38.4 ° on it, which is adjusted by the inclination of the dichroic mirrors relative to the diffraction grating. The diffraction grating has a period A ⁼ 1.52 μm and a groove depth of 120 nm. In the absence of CO, plasmon resonance was observed at λ = 728.0 nm. The spectral position of the surface plasmon resonance changes upon interaction of the recognizing substance with CO. At a CO concentration of 100 ppm, plasmon resonance occurs at 717.6 nm (Fig. 2a). When smoke occurs, the light intensity decreases, but the spectral position of the plasmon resonance is preserved - Figure 26.

BG 67306 Bl

Module 3 measures the temperature and operates with a light signal with a spectrum of 880-920 nm. The module includes a GaAs plate between 200 and 300 pm thick, placed perpendicular to the incident beam.

An embodiment of the multifunction detector is shown in FIG. 5. The light, the spectrum of which is in the range 700-800 nm and 880 - 920 nm, reaches the detector on optical fiber 1 standard 62.5 / 125 pm or 105/125 pm. The collimator 2 is a lens (or system of lenses) that forms an optical beam, and after passing through modules 2 and 3 it is focused by light into optical fiber 1. The dichroic mirror 30 deflects half of the optical beam and only light in the spectral range 700-800 nm to module 2. The dichroic mirror 30 is placed at a precisely defined angle to excite a surface plasmon wave in the gold diffraction grating 4 on which the recognition substance 5 is placed. The dichroic mirror 31 receives the light reflected by the diffraction grating 4 and directs it to focus in the optical fiber 1. In the other half of the optical beam is placed the plate GaAs 6, which transmits part of the spectrum in the range 880-920 nm depending on its temperature. The transmitted light is focused in the optical fiber 1.

The light passing through modules 2 and 3 is transmitted along the optical fiber to a spectrometer, which measures the displacement of the plasmon resonance in the spectral range 700-800 nm and the spectrum in the spectral range 880-920 nm. The first measures the concentration of CO, and the second - the temperature. As an additional function, the spectrometer measures the signal intensity in the spectral range 700-800 nm and monitors changes in time. When the intensity decreases, the presence of smoke is alerted.

Figure 6 and Figure 7 show other possible embodiments of the multifunction detector. The main difference with the one shown in Figure 5 is that an optical fiber is used to supply light to the detector and to receive the light after passing it through modules 2 and 3 of the detector. The function of the individual elements is the same as in Figure 5. The optical fibers 1 supply light in the spectral ranges 700-800 nm and 880-920 nm and receive the light signal after passing through module 2 and module 3 of the detector. The collimating module 2 forms a parallel beam of light as it passes through modules 2 and 3, and focuses the light into the optical fibers after passing through modules 2 and 3. In Figure 6, the dichroic mirror 30 deflects half of the optical beam with a spectrum of 700-800 nm to the diffraction grating 4 with a recognition substance on it 5 to excite the plasmon resonance. The light reflected from the grating is reflected back from the mirror 7 and is focused in the optical fiber 1. In the other half of the optical beam is placed the plate GaAs (gallium arsenide) 6 on the back of which is placed a mirror 8. The light passed through the plate with spectrum , depending on its temperature, but in the range 880-920 nm, is reflected by the mirror, passes again through the plate and focuses in the optical fiber 1. In figure 7, the dichroic mirror 30 is placed in the entire optical beam, transmitting light in the range 700 -800 nm to module 2 - the diffraction grating 4 (with the recognition substance 5 placed on it), which is placed at the necessary angle to excite the surface plasmon resonance. The mirror 7 reflects the light reflected from the grating, returns it back and it is focused back into the optical fiber 1. The dichroic mirror 30 reflects the light in the spectral range 880-920 nm to module 3 - the GaAs plate 76 on the back of which has a mirror 8. The path of the beams in module 3 is the same as in module 3 of figure 6.

Claims (1)

Multifunctional optical fire detector, characterized in that it consists of optical fibers (1) connected to collimators (2), in which in the lower half and between them are placed inclined dichroic mirrors (30) and (31), and under a gold diffraction grating (4) is placed on them, which has an excited plasmon wave on it and a layer (5) applied on its upper surface and a GaAs plate (6) is placed in the upper half of the collimators.