BG112583A - Multifunctional optical fire detector - Google Patents

Abstract

The invention relates to a multifunctional optical fire detector. Its multifunctionality refers 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. 4 claims, 7 figures

Description

Multifunctional optical fire detector

I. Field of the Technique

The invention relates to a multifunctional optical fire detector that simultaneously and continuously detects carbon monoxide (CO), smoke and temperature, and the detection is entirely optical - no electrical voltage is applied in the detector 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.

II. Prior art

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

- for fire protection of objects with various applications;

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

- Which is entirely optical, as the light in the detector is guided by optical fibers; detection of CO, smoke and temperature is based on optical principles; in the detector there is no electric voltage 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. Incorporating a CO sensor into the fire detector is most effective. All sensors known to date are electrochemical - the sensor works with an electric voltage and an electric current flows through it.

The sensor is powered either by connecting to the mains or by using a battery. In both cases, these sensors are dangerous for use in potentially explosive areas or in areas with aggressive chemical environments, as it has been shown that an electrical spark that could cause an explosion is possible.

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

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

In document RU2336573 C1, a fire sensor is reported which gives an alarm for the occurrence of smoke and gases in the initial stages of a fire. The sensor consists of two optical channels. One is at a wavelength that is absorbed by the detectable gas, its presence judged by a decrease in light intensity. The other channel is on a different wavelength, and the reduction in intensity can only be due to the presence of smoke. A disadvantage of the sensor is the detection of changes in light intensity. This variation may be due to many factors unrelated to the phenomena under control. This determines the low reliability of the sensor.

Document US4839527 reports a system that registers gases and smoke by spectral analysis, their presence being fire criteria. Registration takes place in a sensor placed in the guarded room. Light of a certain spectrum is brought to the sensor and taken away from it by optical fibers. It is possible to place 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 and in one device. The proposed measurement of the presence of gases by their absorption spectrum cannot be carried out with optical fibers because they have high losses for those wavelengths that are informative for gases. It is likely that this was not addressed at the time of filing (1989) as fiber optic optics was at an early stage of development at that time. A significant 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 recognition substance, which greatly facilitates practical implementation.

Such an approach is disclosed in JPH1096690 (A), which reports a sensor for measuring carbon monoxide. The gas is detected by its interaction with inorganic sensing elements. The difference from our detector is that it uses an organic substance to detect CO, and it measures both smoke and temperature at the same time.

The fire sensor disclosed in GB2310726(A) detects CO on the same principle. Its difference from our detector is that the sensor is not entirely optical - it requires an electrical power supply for its operation.

The tasks that the present invention solves are:

Early warning of fire requires early detection of smoke and gases released in the initial phase of fire - during incomplete combustion. These gases are different for different products of combustion, but they all emit carbon monoxide CO. 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 the possibility of false signals to practically zero. The present invention relates to an all-optical fire detector, which allows the protection of premises for the production of explosive materials, warehouses for such materials, warships, submarines, chemical plants, mines and mining plants, transport tunnels.

III. Technical essence of the invention

The task of the invention is to create a universal and multi-functional fire detector that can simultaneously and continuously detect CO, smoke and temperature, and the detection is carried out 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 of measuring CO is based on registering the interaction of the CO molecule with a substance (detector) that has a strong affinity of interaction with CO. The recognition substance can be Ag-YSZ (silver with stabilized yttrium and zirconium), tin dioxide, or synthetic hemoglobin. The registration of 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 Fig.1. The surface plasmon wave is excited by a beam of white light falling at a precisely defined angle 0 (Fig. 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 0 and the wavelength λ at which a minimum of the intensity is observed (i.e. at which resonance occurs) are related by the formula: λ// \ ^1/2 \

Γ = — —-sin(0) where A is the lattice constant, ε _t is the dielectric permittivity of the metal, and ε _π is the dielectric permittivity of the sensing substance. In fig. 1 resonance wavelength (fig.1) is: 728.0 nm. It can be seen from the formula that it changes when the dielectric permittivity of the recognition substance changes, which happens when it interacts with even a few molecules of CO - the registration of interaction with plasmon resonance is extremely sensitive. Curve 2 in Fig.2 shows the plasmon resonance when interacting with CO with a concentration of 100 ppm (0.01%) - the plasmon resonance is shifted by 10.4 nm. The offset depends solely on the CO concentration. The plasmon resonance spectral shift/CO concentration dependence is calibrated in advance. The spectral shift and hence the CO concentration is measured. The plasmon resonance (ie the spectrum of light reflected from the diffraction grating) is measured with a standard spectrometer.

Free air access from the guarded room is provided to the identifying substance. The presence of CO is always associated with a combustion process and when it is detected, a fire hazard signal is issued.

Smoke is registered by a known method: the amplitude of the light reflected by 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 protected 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. A decrease in the amplitude of the optical signal is always associated with the presence of smoke. When the signal amplitude decreases by more than 10%, a fire hazard signal is given.

The registration of CO and smoke at the same time is reflected as an absolutely sure sign of fire with the corresponding alarm system. Combining the two registrations allows to eliminate false alarms in the presence of dust instead of smoke.

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

аТ ² Е _d (Г> = Е _d Ю~ — where Е _d is the bandgap width, Т is the temperature, and Е _d (0), а and β are parameters specific to the material. For GaAs, their values are Е _d ( 0)=1.519 eV, a=5.4М0' ⁴ eV/K, β= 204 K. From the equation we can obtain the theoretical dependence of the width of the forbidden zone and the wavelength λ(Τ), from which the optical transmission begins of GaAs, from the temp.

The experimentally measured change in the optical transmittance of light passing through a semiconductor wafer is shown in Fig. 3 the increase in temperature causes the transmission arm to shift to longer wavelengths. This shift, relative to a temperature of 18 °C, is shown in Fig. 4 and on it the temperature of the semiconductor is measured. 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 the occurrence of combustion.

IV. Description of attached figures

Fig.1 - a gold diffraction grating with a cover on it, which interacts with CO;

Fig. 2a - graph of the spectral shift at a CO concentration of 100 ppm;

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

Fig. 3 - a graph of the change in the spectrum of the light passed through the GaAs semiconductor with a change in temperature;

Fig. 4 - a graph of the shift of the optical transmission arm with temperature change, relative to a temperature of 18 °C;

Fig. 5 - exemplary implementation of the multifunctional detector;

Fig.6 - another implementation of the multifunctional detector;

Fig.7 - another implementation of the multifunctional detector;

V. Sample Performance

The detector consists of three modules:

Module 1: supplies the light signal to the other two modules, which work with a light signal in different spectral ranges. The role of module 1 is to direct and spectrally split 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 CO concentration and 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 recognition substance that interacts with CO (Fig.1). The recognition substance is organic, it is applied so that the layer is not dense, but nanostructured - on "islands" with a size of 70 nm to 120 nm, with an average thickness of between 270 nm and 320 nm. At these parameters, the substance has maximum activity of interaction with CO, which ensures high sensitivity and measurement accuracy. A surface plasmon wave is excited on the surface of the gold grating when light falls on it at a precisely defined angle 6=38.4°, which is adjusted by the tilt of the dichroic mirrors relative to the diffraction grating. The diffraction grating has a period A=1.52 pm and a groove depth of 120 nm. In the absence of CO, the plasmon resonance is observed at λ=728.0 nm. The spectral position of the surface plasmon resonance changes when the recognition substance interacts with CO. At a CO concentration of 100 ppm, the 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 - Fig. 2b.

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

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

The light passed through modules 2 and 3 is transmitted along the optical fiber to a spectrometer that measures the plasmon resonance shift in the 700-800 nm spectral range and the spectrum in the 880-920 nm spectral range. The CO concentration is measured on the first, and the temperature on the second. As an additional function, the spectrometer measures the signal intensity in the spectral region 700-800 nm and monitors changes over time. When the intensity decreases, an alarm is given for the presence of smoke.

In Fig. 6 and Fig. 7 other possible implementations of the multifunctional detector are presented. The main difference with that shown in Fig. 5 is that an optical fiber is used to guide the light to the detector and to receive the light after passing through the detector module 2 and 3. The function of the individual elements is the same as in fig. 5. Optical fibers 1 mislead light in the spectral ranges 700-800 nm and 880-920 nm and receive the light signal after passing it through module 2 and module 3 of the detector. The collimating module 2 forms a parallel beam of light for its passage through modules 2 and 3, and focuses the light into the optical fibers after its passage through modules 2 and 3. In FIG. 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 thereon 5 to excite plasmon resonance. The light reflected from the grating is reflected back by the mirror 7 and focused in the optical fiber 1. In the other half of the optical beam, the GaAs (gallium arsenide) plate 6 is placed on the back side of which a mirror 8 is placed. The light that passed through the plate, with a spectrum , depending on its temperature, but in the range 880-920 nm, is reflected by the mirror, passes through the plate again and is focused in the optical fiber 1. In fig. 7, the dichroic mirror 30 is placed in the entire optical beam, passing the light in the range 700-800 nm to the module 2 - the diffraction grating 4 (with the recognition substance 5 placed on it), which is placed at the necessary angle to excite surface plasmon resonance.. The mirror 7 reflects the light reflected from the grating, brings it back and it focuses back into the optical fiber 1. The dichroic mirror 30 reflects the light in the spectral range 880-920 nm to the module 3 - the GaAs plate 76 on the back side of which has mirror 8. The ray path in module 3 is the same as in module 3 in fig. 6.

Claims (4)

1. Multifunctional optical fire detector, characterized in that it consists of a module for collimating, forming and adjusting an optical beam with a spectrum in the range of 700-800 nm and 880-920 nm by reaching the light through an optical fiber (1) and a module 2 for measuring the concentration of CO and module 3 for measuring the temperature, and in module 2 the spectrum is in the range 700-800 nm, formed after deflecting half of the optical beam from the dichroic mirror (30) placed at a certain angle to a gold diffraction grating (4) , where a surface plasmon wave is excited, penetrating a biologically active recognition substance (5) placed on the diffraction grating interacting with CO, and the light reflected from the diffraction grating (4) is directed by a dichronic mirror (31) to a collimator (2), which focuses it in the optical fiber (1) and is transmitted to a spectrometer measuring the plasmon resonance shift in the spectral range 700-800 nm, on module 3 for measuring temp. erature falls the other half of the optical beam with a spectrum in the range 700-800 nm and 880-920 nm, the GaAs plate (6), passes part of the spectrum in the range 880 - 920 nm depending on its temperature, the beam with this spectrum directed to the collimator (2) which focuses it in the optical fiber (1) and the light is transmitted to a spectrometer measuring the spectrum in the spectral range 880-920 nm, while simultaneously measuring the light intensity in the spectral range 700-800 nm, as in the decrease in intensity is interpreted as caused by smoke, at which point it is signalled. 2. Multifunctional optical fire detector according to claim 1, characterized in that one optical fiber (1) is used, and a collimator (2) is used, which forms a parallel beam of light with a spectrum range of 700-800 nm and 880-920 nm, half of the beam and in the spectral range 700-800 nm is deflected by the dichroic mirror (30), passing through the module 2 for measuring the concentration of CO, and the light reflected by the diffraction grating (4) is returned in the opposite way by the mirror (7 ), and the other half of the parallel beam of light passes through the temperature measuring module 3, consisting of a GaAs plate (6), which passes part of the spectrum in the range 880-900 nm, returning from the mirror (8) and focusing in the optical fiber (1) and are transmitted to the spectrometer. 3. Multifunctional optical fire detector according to claim 1, characterized in that one optical fiber (1) is used, and a collimator (2) is used, which forms a parallel beam of light with a spectrum in the range 700-800 nm and 880- 920 nm, a dichroic mirror (30) which is placed throughout the optical beam, transmitting light in the range 700-800 nm incident on the CO concentration measuring module, the diffraction grating (4) being placed so that the incident light excites surface plasmon resonance, and the light reflected from the grating is reflected back by a mirror (7) and focused into a fiber (1), and the light reflected from the dichroic mirror (30) in the range 880-920 nm is directed to module 3 for measurement of the temperature, passes through it and is reflected by the mirror (8), returns on the reverse path and is focused in the optical fiber (1), and the two beams in the spectral ranges 700 - 800 nm and 880-900 nm are transmitted to the spectrometer. . 4. Multifunctional optical fire detector according to claim 1, characterized in that the recognition substance deposited on the diffraction grating (4) can be an organic biologically active substance deposited so as to be nanostructured, i.e. of "islands" with a size of 70 nm to 120 nm, with an average thickness between 270 nm and 320 nm, providing high sensitivity and accuracy of CO measurement. Fig. A beam of white falls