Fully-distributed optical fiber COsensor for fire early warning and control method of fully-distributed optical fiber COsensor

Abstract

The invention belongs to the technical field of mine fire early warning, and discloses a fully-distributed optical fiber CO2 sensor for fire early warning and a control method thereof.According to the sensor, sensing optical fibers are arranged at an underground fire early warning monitoring site; acquiring a signal by using an optical frequency domain reflectometer system and carrying out fast Fourier transform to obtain distance domain information; intercepting effective sensing data in a distance domain to enter loop operation; performing fast Fourier inversion on the data in the cyclic window and performing cross-correlation operation to obtain a cross-correlation spectrum offset result; a CO2 cross-correlation spectrum offset coefficient alpha co2 is obtained through a correction experiment, and distributed measurement of CO2 is achieved. According to the system, the underground large-range fully-distributed CO2 concentration is monitored on line at any time, accurate early warning of underground fire accidents can be achieved, and the problems that a current fire early warning system cannot achieve distributed measurement and is high in networking cost can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mine fire warning, and particularly relates to a fully distributed optical fiber CO2 sensor for fire warning and its control method. Background Art

[0002] Mine fires are usually triggered by factors such as electrical equipment failures, coal dust accumulation, and combustible gas leakage. If not detected and effectively addressed in a timely manner, fires not only pose a serious threat to the lives of miners but may also lead to severe damage to mining facilities, suspension of production activities, and even have a profound impact on the sustainable mining of the mine. Traditional fire monitoring technologies, such as temperature sensors, smoke detectors, and gas detectors, although able to provide early warnings to a certain extent, often fail to capture the weak signs in the initial stage of a fire in a timely manner due to their slow response speed and certain limitations, thus missing the best opportunity for fire fighting.

[0003] In recent years, with the rapid development of technologies such as sensor technology, the Internet of Things, big data analysis, and artificial intelligence, fire warning systems have gradually developed towards intelligence and automation. Especially in the underground environment, fire warning technologies based on gas concentration distribution have received increasing attention. CO2 is a typical gas in the initial stage of a fire, and its concentration change usually provides important warning information in the initial stage of a fire. The concentration change of CO2 is closely related to the generation of the fire source and the spread of the fire. Therefore, by real-time monitoring the concentration of CO2 gas, the potential risks of fire occurrence can be effectively identified and early warning can be achieved. Combining big data analysis and machine learning algorithms can process multi-dimensional data of the underground environment in real time, thereby improving the accuracy and response speed of the fire warning system, providing strong support for mine safety management. Especially in fire prevention and control, it can effectively gain precious escape time for miners.

[0004] Traditional CO2 gas monitoring technologies are mainly based on optical and chemical principles, such as optical spectroscopy, infrared spectroscopy, fluorescence detection, and electrochemical sensors. Although these sensors have high selectivity and sensitivity in gas detection, their complex operation procedures, high equipment costs, and high requirements for the working environment limit their application in special environments such as mines. In addition, optical fiber gas sensing technology has become a monitoring technology that has received much attention due to its anti-electromagnetic interference, corrosion resistance, compact structure, and high safety. Optical fiber gas sensors based on different principles, such as etched optical fibers, optical fiber tip processing, hollow optical fibers, and microbubble optical fibers, although able to meet the gas monitoring requirements to a certain extent, usually adopt fine structural designs, which limit their application in complex underground environments.

[0005] The main limitation of existing fiber optic CO2 sensors is their inability to achieve distributed gas measurement, which directly affects the overall construction of the underground fire warning system. To improve the accuracy and real-time performance of fire warning, it is urgent to develop fiber optic gas sensing technology with distributed measurement capabilities. This can not only meet the needs of multi-point gas concentration monitoring underground but also enable multi-directional and three-dimensional early warning of fire occurrence, thereby significantly enhancing the efficiency and reliability of fire prevention and control. Therefore, how to break through the bottleneck of current fiber optic gas sensing technology, especially in the construction of distributed gas detection and monitoring networks, has become a key research problem that needs to be solved urgently.

[0006] Through the above analysis, the problems and defects existing in the prior art are as follows:

[0007] (1) Traditional fire monitoring technologies have a slow response speed and certain limitations, often unable to promptly detect weak signs in the initial stage of a fire, thus missing the best opportunity for fire fighting.

[0008] (2) Traditional CO2 gas monitoring technologies have complex operation processes, high equipment costs, and high requirements for the working environment. At the same time, they adopt delicate structural designs, which limit their application in complex underground environments.

[0009] (3) Existing fiber optic CO2 sensors cannot achieve distributed CO2 monitoring, which affects the overall construction of the underground fire warning system, and adding additional sensors requires huge costs. Summary of the Invention

[0010] To overcome the problems existing in the related technologies, the disclosed embodiments of the present invention provide a fully distributed fiber optic CO2 sensor for fire warning and its control method. The technical solutions are as follows:

[0011] The present invention is implemented as follows. The control method of the fully distributed fiber optic CO2 sensor for fire warning includes:

[0012] S1, laying a sensing optical fiber at the underground fire warning monitoring location and protecting it with a metal spiral spring tube;

[0013] S2, connecting the sensing optical fiber to an optical frequency domain reflectometer system, collecting a signal once after the sensing optical fiber is installed as a reference signal; collecting signals in real-time online as measurement signals, and transmitting the measurement signals to the processing end through the underground network;

[0014] S3, performing a fast Fourier transform on the signals collected by the optical frequency domain reflectometer system to obtain distance domain information, intercepting effective sensing data in the distance domain according to the layout position of the optical fiber underground, and entering a loop operation;

[0015] S4. In the loop operation, select C data points as the loop window size. The distance domain information of the reference signal and the measurement signal is intercepted starting from the real position using the loop window. Perform an inverse fast Fourier transform on the data within the window to obtain the time domain information of the local reference signal and the measurement signal.

[0016] S5. Perform a cross-correlation operation on the obtained time domain information of the local reference signal and the measurement signal to obtain the cross-correlation spectrum offset result.

[0017] S6. Repeat steps S4 - S5 to obtain the cross-correlation spectrum offset result Δλ at each corresponding position along the entire sensing optical fiber.

[0018] S7. Obtain the CO2 cross-correlation spectrum offset coefficient α through a calibration experiment co2 , and achieve distributed measurement of CO2. Use the obtained CO2 concentration information as the basis for underground fire warning.

[0019] In step S1, the sensing optical fiber uses a polarization-maintaining fiber coated with commercial polyimide. The coating has CO2 sensitivity and is used to adsorb CO2 molecules in the environment to cause volume changes.

[0020] In step S3, the fast Fourier transform operation process is as follows:

[0021] Given a time domain sequence x[c] of length C, the formula for the discrete Fourier transform is:

[0022]

[0023] where X[k] is the k-th frequency component, x[c] is the c-th value of the input sequence, j is the imaginary unit, is the rotation factor, C is the length, and e is the natural constant;

[0024] The calculation of the FFT is performed recursively by splitting the sequence into even and odd parts.

[0025] In step S4, the window size determines the spatial resolution of the system measurement. The spatial resolution is the product of the spatial length ΔZ of a single data point and the number of points M within the loop window, and the expression is:

[0026] ΔZ = c / 2nΔv

[0027] where Δv is the tuning range of the tunable light source, c is the speed of light in vacuum, and n is the refractive index of the optical fiber.

[0028] In step S4, the inverse fast Fourier transform operation process is as follows:

[0029] Given a frequency domain sequence X[k] of length C, the formula for the discrete inverse Fourier transform is:

[0030]

[0031] The calculation of the IFFT is performed recursively by splitting the sequence into even and odd parts.

[0032] In step S5, the cross-correlation operation process is as follows:

[0033] Given two discrete signals x[c] and y[c] of length C, the cross-correlation function r xy [m] is:

[0034]

[0035] In the formula, r xy [m] is the value of the cross-correlation function at the offset m, and (c + m) mod C represents the modulo operation on the index C to achieve circular cross-correlation.

[0036] In step S7, the distributed measurement of CO2 is realized, and the expression is:

[0037] ΔCO2 = α co2 *Δλ

[0038] In the formula, ΔCO2 is the change in the carbon dioxide concentration, Δλ is the wavelength offset, and α co2 is the CO2 - spectral offset sensitivity coefficient.

[0039] In step S7, the calibration experiment is to mix N2 / CO2 with different ratios using a gas mixing instrument to determine the cross-correlation spectral offset caused by different CO2 concentrations, so as to determine the sensitivity coefficient α co2 , and the CO2 concentration information is demodulated through the calibrated standard sensitivity coefficient.

[0040] Another object of the present invention is to provide a fully distributed optical fiber CO2 sensor system for fire warning, which is used to control the fully distributed optical fiber CO2 sensor control method for fire warning. The system includes: a tunable laser, a coupler one, a coupler two, a circulator, a Mach - Zehnder interferometer, a polarization controller one, a polarization controller two, a coupler three, a polarization beam splitter, a detector, a data acquisition card, a sensing optical fiber, and a Fresnel ring;

[0041] The tunable laser emits linearly frequency - swept light, and the output is divided into two parts by the coupler one. One part, 10%, is incident on the unbalanced Mach - Zehnder interferometer composed of delay optical fibers, serving as an auxiliary interferometer to provide a trigger signal for the data acquisition card, and the remaining light enters the coupler two;

[0042] It is divided into two parts by coupler two. Among them, 1% of the output is adjusted by polarization controller one so that the p-light component and the s-light component have the same power. 99% enters the sensing optical fiber for detection through the circulator and polarization controller two. A Fresnel loop is made at the end of the sensing optical fiber to suppress Fresnel reflection;

[0043] The Rayleigh scattering signal of the detection optical fiber returns through the circulator and is combined with the interference signal obtained by combining 1% of the optical output from coupler three. The interference signal is decomposed into a p-light component and an s-light component by a polarization beam splitter; finally, the p-light component and the s-light component are detected by a detector and collected by a data acquisition card to obtain the required signal.

[0044] Further, coupler one is a 10 / 90 optical coupler, coupler two is a 1 / 99 optical coupler, and coupler three is a 50 / 50 optical coupler.

[0045] Combining all the above technical solutions, the advantages and positive effects of the present invention are as follows:

[0046] First, the present invention provides a distributed optical fiber monitoring method that can online and at any time monitor the large-scale fully distributed CO2 concentration in the mine, and further realizes the accurate early warning of underground fire events, and can solve the problems that the current fire early warning system cannot achieve distributed measurement and has a high networking cost.

[0047] Second, the fully distributed optical fiber CO2 sensor for fire early warning of the present invention can realize online monitoring and distributed measurement, and has a low cost.

[0048] Third, after the technical solution of the present invention is transformed, it can provide a recyclable and low-cost CO2 monitoring device for underground fire monitoring, and realize fire monitoring and early warning. The price of commercial polyimide is low, and the fire early warning of the whole well can be realized at a very low cost, greatly reducing the cost of fire early warning. Brief Description of the Drawings

[0049] The accompanying drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present disclosure, and are used together with the specification to explain the principles of the present disclosure;

[0050] Figure 1 It is a flowchart of the control method of the fully distributed optical fiber CO2 sensor for fire early warning provided by an embodiment of the present invention;

[0051] Figure 2 It is a schematic structural diagram of the fully distributed optical fiber CO2 sensor for fire early warning provided by an embodiment of the present invention;

[0052] Figure 3 It is a schematic diagram of the experimental result of single sensitivity verification provided by an embodiment of the present invention;

[0053] Figure 4 It is a schematic diagram of the demodulation result provided by the embodiment of the present invention;

[0054] In the figure: 1. Tunable laser; 2. Coupler 1; 3. Coupler 2; 4. Circulator; 5. Mach-Zehnder interferometer; 6. Polarization controller 1; 7. Polarization controller 2; 8. Coupler 3; 9. Polarization beam splitter; 10. Detector; 11. Acquisition card; 12. Sensing optical fiber; 13. Fresnel ring. Specific embodiments

[0055] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0056] The innovation points of the present invention are as follows:

[0057] 1. Distributed CO2 measurement is achieved using polyimide optical fiber and OFDR, which is convenient for constructing downhole distributed fire warning

[0058] 2. Due to the CO2 absorption and expansion characteristics of polyimide, the polyimide coating can transfer strain to the optical fiber itself, thereby indirectly demodulating the CO2 concentration

[0059] Example 1, as Figure 1 shown, the full-distributed optical fiber CO2 sensor control method for fire warning provided by the embodiment of the present invention includes the following steps:

[0060] S1. Lay the sensing optical fiber 12 at the downhole fire warning monitoring location and protect it with a metal spiral spring tube;

[0061] Among them, the sensing optical fiber 12 uses a commercially available polarization-maintaining optical fiber coated with polyimide, and the coating has CO2 sensitivity and can adsorb CO2 molecules in the environment to cause volume changes.

[0062] S2. Connect the sensing optical fiber 12 to the optical frequency domain reflectometer system, collect a signal once after the sensing optical fiber 12 is installed as a reference signal; collect signals in real time and online as measurement signals, and the measurement signals are transmitted to the processing end through the downhole network;

[0063] S3. Perform a fast Fourier transform on the signals collected by the optical frequency domain reflectometer system to obtain distance domain information, intercept effective sensing data in the distance domain according to the layout position of the optical fiber downhole, and enter the loop operation;

[0064] Preferably, the fast Fourier transform operation process is as follows:

[0065] Given a time-domain sequence x[c] of length C, the formula for the discrete Fourier transform is:

[0066]

[0067] where X[k] is the k-th frequency component, x[c] is the c-th value of the input sequence, j is the imaginary unit, is the rotation factor, and e is the natural constant;

[0068] The calculation of the FFT is performed recursively by splitting the sequence into even and odd parts.

[0069] S4. In the loop operation, select C data points as the loop window size, and the distance domain information of the reference signal and the measurement signal is intercepted starting from the real position using the loop window; perform an inverse fast Fourier transform on the data within the window to obtain the time-domain information of the local reference signal and the measurement signal;

[0070] where the window size determines the spatial resolution size of the system measurement.

[0071] Preferably, the spatial resolution is the product of the spatial length ΔZ of a single data point and the number of points M within the loop window, and the expression is:

[0072] ΔZ = c / 2nΔv

[0073] where Δv is the tuning range of the tunable light source, c is the speed of light in vacuum, and n is the refractive index of the optical fiber.

[0074] Preferably, the inverse fast Fourier transform operation process is as follows:

[0075] Given a frequency-domain sequence X[k] of length C, the formula for the discrete inverse Fourier transform is:

[0076]

[0077] The calculation of the IFFT is performed recursively by splitting the sequence into even and odd parts.

[0078] S5. Perform a cross-correlation operation on the obtained time-domain information of the local reference signal and the measurement signal to obtain the cross-correlation spectrum offset result;

[0079] Preferably, the cross-correlation operation process is as follows:

[0080] Given two discrete signals x[c] and y[c] of length C, their cross-correlation function r xy [m] is:

[0081]

[0082] Wherein, r xy [m] is the value of the cross-correlation function at the offset m, and (c + m) mod C represents the modulo operation of the index on C to achieve cyclic cross-correlation;

[0083] S6. Repeat steps S4 - S5 to obtain the cross-correlation spectrum offset result Δλ at each corresponding position along the entire sensing optical fiber 12;

[0084] S7. Obtain the CO2 cross-correlation spectrum offset coefficient α through calibration experiments co2 , realize the distributed measurement of CO2, and use the obtained CO2 concentration information as the basis for underground fire warning;

[0085] Preferably, to realize the distributed measurement of CO2, the expression is:

[0086] ΔCO2 = α co2 *Δλ

[0087] Wherein, ΔCO2 is the change in carbon dioxide concentration, Δλ is the wavelength offset, and α co2 is the CO2 - spectrum offset sensitivity coefficient.

[0088] Preferably, the calibration experiment is to use a gas mixing instrument to mix N2 / CO2 in different proportions, and determine the cross-correlation spectrum offset caused by different CO2 concentrations by using the proposed method, so as to determine the sensitivity coefficient. During the use of the method, the CO2 concentration information is demodulated by the calibrated standard sensitivity coefficient.

[0089] The obtained CO2 concentration information can be used as the basis for underground fire warning.

[0090] Example 2, as Figure 2 shown, the fully distributed optical fiber CO2 sensor for fire warning provided by the embodiment of the present invention includes:

[0091] The linearly swept-frequency light emitted by the tunable laser 1 is output and divided into two parts by coupler 1 2 (10 / 90 optical coupler). One part, which is 10%, is incident on an unbalanced Mach-Zehnder interferometer 5 composed of delay fibers, serving as an auxiliary interferometer to provide a trigger signal for the acquisition card 11. The remaining light enters coupler 2 3; then it is divided into two parts by coupler 2 3 (1 / 99 optical coupler). Among them, 1% of the output is adjusted by polarization controller 1 6 so that the p-light component and the s-light component have the same power. 99% passes through circulator 4 and polarization controller 2 7 and enters the sensing fiber 12 for detection. A Fresnel loop 13 is made at the end of the sensing fiber 12 to suppress Fresnel reflection. The Rayleigh scattering signal of the detection fiber returns through circulator 4 and is combined with the interference signal obtained by combining the 1% light output from coupler 3 8 (50 / 50 optical coupler), and is decomposed into a p-light component and an s-light component by polarization beam splitter 9; finally, the p-light component and the s-light component are collected by the acquisition card 11 to obtain the required signal.

[0092] The simulation experiment uses Figure 2 the system shown in the figure. Place the last two meters of the sensing fiber 12 in the gas chamber. First, introduce pure N2, N2:CH4 = 90:10 mixed gas, and N2:CO2 = 80:20 mixed gas respectively to test the independent sensitivity of the sensor to CO2 and prevent CH4 in the mine from affecting the fire warning result. The results can be obtained as Figure 3 shown in the figure. The experimental results show that only carbon dioxide can cause spectral shift, verifying the excellent single-selection sensitivity of the sensor designed by the present invention to nitrogen dioxide.

[0093] Then, using the pure N2 environment as a reference, collect the reference signal. The measurement signals are collected at 10%, 20%, 30%, 40%, 50%, and 60% CO2 concentrations, and the obtained demodulation results are shown in Figure 4 the figure.

[0094] From Figure 4 the following results can be obtained:

[0095] 1. The measurement range of the sensor is 0%-40% CO2 concentration, and the measurement is inaccurate when it exceeds 40%.

[0096] 2. The sensitivity of the sensor is 1.039 pm / CO2%.

[0097] As described above, only the relatively optimal specific implementation manner of the present invention is provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A fully distributed optical fiber CO2 sensor control method for fire warning, characterized in that: The control method includes: S1, laying out a sensing optical fiber (12) at a fire early warning monitoring location underground and using a metal spiral spring tube for protection; S2, connecting the sensing optical fiber (12) to the optical frequency domain reflectometer system, collecting a signal once after the sensing optical fiber (12) is installed as a reference signal; collecting the signal online in real time as a measurement signal, and transmitting the measurement signal to a processing end through a downhole network; S3, performing fast Fourier transform on the signal collected by the optical frequency domain reflectometer system to obtain distance domain information, and intercepting effective sensing data in the distance domain according to the layout position of the optical fiber in the well, and entering a loop operation; S4, in the loop operation, C data points are selected as the loop window size, and the distance domain information of the reference signal and the measurement signal is intercepted from the real position using the loop window; the data in the window is subjected to inverse fast Fourier transform to obtain the time domain information of the local reference signal and the measurement signal; S5, performing a cross-correlation operation on the obtained local reference signal and the time domain information of the measurement signal to obtain a cross-correlation spectrum shift result; S6, repeating steps S4 to S5 to obtain a cross-correlation spectrum shift result Δλ at each corresponding position along the entire sensing optical fiber (12); S7, obtain the CO2 cross-correlation spectrum shift coefficient α through calibration experiment co2 , realize distributed measurement of CO2, and use the obtained CO2 concentration information as the basis for underground fire warning.

2. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 1 is characterized in that: In step S1, the sensing optical fiber (12) adopts a commercially available polyimide-coated polarization-maintaining optical fiber, the coating of which is CO2-sensitive and is used to adsorb CO2 molecules in the environment to generate volume changes.

3. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 1 is characterized in that: In step S3, the fast Fourier transform operation process is: Given a time domain sequence x[c] of length C, the formula for the discrete Fourier transform is: Where X[k] is the kth frequency component, x[c] is the cth value of the input sequence, and j is the imaginary unit. is the rotation factor, e is the natural constant; The FFT is calculated recursively by splitting the sequence into even and odd parts.

4. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 1 is characterized in that: In step S4, the window size determines the spatial resolution of the system measurement. The spatial resolution is the product of the spatial length ΔZ of a single data point and the number of points M in the cyclic window, and the expression is: ΔZ=c / 2nΔv Where Δv is the tuning range of the tunable light source, c is the speed of light in a vacuum, and n is the refractive index of the optical fiber.

5. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 3 is characterized in that: In step S4, the inverse fast Fourier transform operation process is: Given a frequency domain sequence X[k] of length C, the formula for the discrete inverse Fourier transform is: The IFFT calculation is performed recursively by splitting the sequence into even and odd parts.

6. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 5 is characterized in that: In step S5, the cross-correlation operation process is: Given two discrete signals x[c] and y[c] of length C, the cross-correlation function r xy [m] is: In the formula, r xy [m] is the value of the cross-correlation function at offset m, and (c+m)modC represents the modulo operation of the index on C to achieve cyclic cross-correlation.

7. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 1 is characterized in that: In step S7, the distributed measurement of CO2 is realized, and the expression is: ΔCO2=a co2 *Dl In the formula, ΔCO2 is the change in carbon dioxide concentration, Δλ is the wavelength shift, and α co2 is the CO2-spectrum shift sensitivity coefficient.

8. The fully distributed optical fiber CO2 sensor control method for fire warning according to claim 7 is characterized in that: In step S7, the calibration experiment is to use a gas mixing instrument to mix N2\CO2 in different proportions, determine the cross-correlation spectrum shift caused by different CO2 concentrations, and thus determine the sensitivity coefficient α co2 , the CO2 concentration information is obtained by demodulating the measurement through the calibrated standard sensitivity coefficient.

9. A fully distributed optical fiber CO2 sensor for fire warning, characterized in that: The sensor is used to control the fully distributed optical fiber CO2 sensor control method for fire warning according to any one of claims 1 to 8, and the system comprises: a tunable laser (1), a coupler 1 (2), a coupler 2 (3), a circulator (4), a Mach-Zehnder interferometer (5), a polarization controller 1 (6), a polarization controller 2 (7), a coupler 3 (8), a polarization beam splitter (9), a detector (10), an acquisition card (11), a sensing optical fiber (12), and a Fresnel ring (13); The tunable laser (1) emits a linear frequency sweep light, and the output is divided into two parts through a coupler (2), one part is 10% and is incident on an unbalanced Mach-Zehnder interferometer (5) composed of a delay optical fiber, which serves as an auxiliary interferometer to provide a trigger signal for an acquisition card, and the rest of the light enters a coupler (3); After being divided into two parts by coupler 2 (3), 1% of the output is adjusted by polarization controller 1 (6) so that the p-light component and the s-light component have the same power, and 99% of the output is detected by circulator (4) and polarization controller 2 (7) and enters the sensing optical fiber (12). A Fresnel ring (13) is formed at the end of the sensing optical fiber (12) to suppress Fresnel reflection; The Rayleigh scattered signal of the detection optical fiber is returned through the circulator (4) and combined with 1% of the light output from the coupler three (8) to obtain an interference signal, which is decomposed into a p light component and an s light component through a polarization beam splitter (9); finally, the p light component and the s light component are detected by a detector (10) and collected by an acquisition card (11) to obtain the required signal.

10. The fully distributed optical fiber CO2 sensor for fire warning according to claim 9, characterized in that: Coupler one (2) is a 10 / 90 optical coupler, coupler two (3) is a 1 / 99 optical coupler, and coupler three (8) is a 50 / 50 optical coupler.

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