Composite mine smoke sensor and detection method thereof

Abstract

The invention relates to the technical field of coal mine underground smoke detection, in particular to a composite mining smoke sensor and a detection method thereof. A composite mine smoke sensor comprises a mounting frame, a shell, a protective net, a circuit board and an optical labyrinth piece, the mounting frame is a hollow piece with two open ends, one end of the shell is open and sleeved on the periphery of the lower portion of the mounting frame, the optical labyrinth piece is arranged on the inner bottom face of the shell, and T-shaped smoke inlet grids are evenly distributed on the edge of the optical labyrinth piece. The top of the optical labyrinth piece is connected with a circuit board located in the installation frame, an optical smoke sensor and a gas-sensitive sensor are installed on the circuit board, and a protective net is arranged between the optical labyrinth piece and the shell. The optical smoke sensor and the gas-sensitive sensor are combined for smoke detection, the optical smoke sensor identifies smoke by distinguishing particle sizes of particulate matters by using an optical dual-wavelength detection technology, and the gas-sensitive sensor detects the content of some gases generated along with the smoke, so that the situation of false alarm of a single sensor can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of coal mine underground smoke detection, in particular to a composite mine smoke sensor and a detection method thereof. Background Art

[0002] Mine fire is one of the main threats to coal production safety in my country. Before a fire occurs, smoke will be generated. Therefore, smoke alarms can be used to monitor the occurrence of fire so that emergency measures can be taken in time. There are currently three types of smoke sensors used in mines: ion smoke sensors, optical smoke sensors, and gas-sensitive smoke sensors. Faced with the harsh environment of high heat, high humidity, high dust, paint interference, etc. in coal mines, all three detection methods have certain limitations. The ion type has high accuracy, but there are radioactive substances inside; the traditional optical type uses a single infrared light source and is easily affected by particulate matter such as water vapor and dust; the gas-sensitive type is easily affected by flammable volatile gases, such as alcohol and paint. The above three types of coal mine smoke sensors often cause false alarms.

[0003] The ignition source of a solid material fire usually needs to go through three stages: early stage, smoldering, flame and heat release. In the early stage, invisible particles with a particle size of 0.001μm-0.05μm and gases such as CO, CO2, H2 are produced, there is no visible smoke and flame, and the heat release is very low. In the smoldering stage, more gas is released, visible smoke is produced, no flame appears, and the temperature rises slowly. It is the primary stage of the fire. Therefore, smoke is an extremely important fire signal generated in the early stage of a fire. Optical smoke sensors are more reliable in detecting common fires and can handle smoldering fires faster, but due to the harsh environment of high temperature and humidity in coal mines, dew and condensation may form on the inner surface of the optical smoke sensor chamber, resulting in light scattering. In relatively humid coal mines, condensation often forms, and this light scattering problem is particularly serious.

[0004] In coal mines, smoke sensors are often used to monitor the safe operation of belt conveyors. In this area, the large amount of coal ash dust floating in the air and the workers' flushing of the tunnels are major hidden dangers that affect the operation of smoke sensors. Workers flush the tunnels with water, causing water mist to float in the air, and even water directly splashes into the smoke detection chamber, causing the sensor to be corroded and damaged. The floating water mist and coal ash enter the detection chamber, and for traditional single infrared optical smoke sensors, they will be identified as smoke, causing serious misjudgment. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in order to solve the problems existing in the prior art in the above-mentioned background technology, a composite mine smoke sensor is provided.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a composite mine smoke sensor, including a mounting frame, a shell, a protective net, a circuit board and an optical labyrinth. The mounting frame is a hollow member with openings at both ends, and the shell is open at one end and is mounted on the lower periphery of the mounting frame. The optical labyrinth is placed on the inner bottom surface of the shell, and its edges are evenly distributed with "T"-shaped smoke inlet grilles. The top of the optical labyrinth is connected to the circuit board located in the mounting frame, and the optical smoke sensor and the gas sensor are installed on the circuit board. A protective net is arranged between the optical labyrinth and the shell, and a plurality of smoke inlets are opened on the periphery of the shell.

[0007] Furthermore, the optical labyrinth is made of black plastic, and its bottom surface is a cone.

[0008] Furthermore, the housing and the mounting frame are connected via threads.

[0009] Furthermore, the circuit board includes a first circuit board and a second circuit board, the first circuit board is the minimum unit circuit board of the single-chip microcomputer, the optical smoke sensor and the gas sensor are installed on the second circuit board, the first circuit board and the second circuit board are riveted by copper columns, and the second circuit board and the optical maze are connected to the copper columns by screws.

[0010] Furthermore, a black light-absorbing paint layer is sprayed on the circuit board.

[0011] Furthermore, the optical smoke sensor is an integrated dual-wavelength photoelectric smoke sensor, which has a transmitting end and a receiving end, and a grid is provided between the transmitting end and the receiving end. A lens protection cover is provided outside the optical smoke sensor, and the lens protection cover includes a lens frame and a first lens and a second lens installed on the lens frame. The first lens and the second lens are respectively arranged on the transmitting end and the receiving end, and the first lens and the second lens are both made of quartz glass, K9 optical glass or sapphire glass with a wavelength range of 400 to 900 nm and high transmittance.

[0012] Furthermore, the bottom edge of the optical labyrinth has a flange for placing a protective net, one end of the protective net abuts against the flange, and the other end of the protective net abuts against the lower opening edge of the mounting frame.

[0013] Furthermore, the protective net is made of 304 stainless steel with a thickness of 0.1-0.15 mm, and its surface is evenly distributed with through holes processed by etching process, and the aperture of the through holes is 40 meshes.

[0014] A detection method of a composite mine smoke sensor is also mentioned, comprising the following steps: S1. Perform calibration in a smoke-free environment to obtain optical background signals and gas-sensitive background signals: Power on the optical smoke sensor and gas-sensitive sensor, initialize the optical smoke sensor with the program, and start collecting light signals after initialization. Every 100ms, the microcontroller collects light signals. After a period of time, the real-time value within this period of time is average-filtered to obtain the blue light background signal PTR of the current smoke-free environment. BLUE0 and infrared background signal PTR IR0 ,PTR BLUE0 and PTR IR0 The calculation formulas are: and , Among them, PTR BLUES For blue light real-time signal, PTR IRS It is the real-time signal of infrared light. n is the number of samples, i For the i sampling points; At the same time, the gas sensor is preheated first, and then waits for calibration. After receiving the calibration command, it is calibrated, and then the gas sensor signal is collected every 1s. After a period of time, the real-time value during this period is averaged and filtered to obtain the gas sensor background resistance R0 in the current smoke-free environment. The calculation formula of R0 is: , Among them, R s is the real-time resistance value of the gas sensor, n is the number of samples, i For the i sampling points; S2. Determine the concentration trend of particles in the optical maze: calculate the change in blue light signal PTR ⊿BLUE And infrared light signal change PTR ⊿IR ,PTR ⊿BLUE and PTR ⊿BLUE and PTR ⊿IR The calculation formulas are: and , Then PTR ⊿BLUE and PTR ⊿IR Compare with the set threshold value. If the threshold value is exceeded, the concentration of particles in the optical maze is increasing, and it is necessary to determine whether there is smoke; S3. Determine particle size: Calculate the ratio of the scattering intensity of blue light to infrared light. When the ratio exceeds the set threshold, it is determined that the particle size is small and there is smoke. The calculation formula of the ratio is: ; S4, Gas-sensing auxiliary judgment: Calculate the real-time resistance value R of the gas-sensing s , R s The calculation formula is: , Among them, R L is the load resistance, V C is the supply voltage, V TGS is the load resistance R L The voltage across the terminals, Then calculate the gas-sensitive resistance change rate α, the calculation formula for α is: , If α exceeds the set threshold, it is determined that there is smoke.

[0015] Furthermore, in step S1, PTR is a power transfer ratio, which is calculated as follows: , Among them, I LED_PK is the LED peak current, which is configured by setting the optical smoke sensor register and calculated based on the current proportional factor; R PD is the photodiode responsivity; η LED is the LED efficiency, calculated based on the LED gain calibration and derating factors in its manual; I PD is the photodiode current, which is calculated as: , Among them, ADCdata is the accumulated sum of the sampled data of a group of light pulses; Q is the resolution of the analog-to-digital converter; pulse_num is the number of pulses; Then test the optical signal size of the optical smoke sensor in different temperature environments of -10 to 50°C, draw a fitting curve, determine the temperature response value β relative to the reference temperature point 25°C, and correct the photodiode current I PD补偿 , and its calculation formula is as follows: , Will I PD补偿 Substituting into the PTR calculation formula, the corrected power transfer ratio of the optical smoke sensor is obtained.

[0016] Beneficial effects of the present invention: 1. The composite mining smoke sensor of the present invention uses an optical smoke sensor and a gas sensor in combination for smoke detection. The optical smoke sensor uses optical dual-wavelength detection technology to identify smoke by distinguishing the particle size. The gas sensor detects the content of certain gases produced with smoke, which can avoid the situation of false alarms by a single sensor. 2. The optical smoke sensor in the composite mining smoke sensor of the present invention detects two wavelengths of light signals scattered by particulate matter. Compared with the traditional single-wavelength infrared optical sensor, it can significantly distinguish dust, water mist and smoke according to the particle size, and can avoid the occurrence of false alarms; 3. The composite mining smoke sensor of the present invention protects the transmitting end and the receiving end of the optical smoke sensor in the humid environment of coal mines, so as to prevent dust and water, and avoid corrosion and damage caused by water vapor; by adding a protective cover, the sensor can be put into use again by workers cleaning the dust in the later maintenance; 4. The composite mining smoke sensor of the present invention is designed for protection in the water mist and dust environment of coal mines: the fine holes of the protective net and the "T"-shaped optical grid can block most of the particle dust and water mist from entering the sensor, and a large dust holding space is set inside the optical labyrinth. The housing and the optical labyrinth are easy to disassemble, making it simple for workers to clean the dust on site; 5. The detection method of the composite mining smoke sensor of the present invention adopts a relative measurement method, and the reference background signal value changes flexibly with the environment, which can avoid the problem of frequent calibration and maintenance of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0018] Figure 1 It is a schematic structural diagram of the composite smoke sensor for mining of the present invention.

[0019] Figure 2 yes Figure 1 sectional view of .

[0020] Figure 3 It is a schematic diagram of the structure of the optical labyrinth component in the composite smoke sensor for mining of the present invention.

[0021] Figure 4 The present invention is a schematic diagram of the structure of the lens protection cover in the composite smoke sensor for mining.

[0022] Figure 5 The invention discloses a driving circuit diagram of an optical smoke sensor in a composite smoke sensor for mining.

[0023] Figure 6 The present invention discloses a level conversion circuit diagram of an optical smoke sensor in a composite smoke sensor for mining.

[0024] Figure 7 The invention discloses a detection circuit diagram of a gas sensor in a composite smoke sensor for mining.

[0025] Figure 8The present invention is a flow chart of the composite mining smoke sensor detection method.

[0026] Fig. 9 It is a fitting curve of the temperature response value β relative to the reference temperature point 25° C. in the detection method of the composite mining smoke sensor of the present invention.

[0027] Fig.10 It is a curve diagram of the light signal of the optical smoke sensor and the smoke concentration in the composite mining smoke sensor detection method of the present invention.

[0028] Fig.11 It is a curve diagram of the gas sensitive resistance value and smoke concentration of the gas sensor in the composite mining smoke sensor detection method of the present invention.

[0029] In the figure: 1, mounting frame; 2, housing; 21, smoke inlet; 3, protective net; 4, circuit board; 41, first circuit board; 42, second circuit board; 5, optical maze; 51, smoke inlet grille; 52, flange; 6, copper column; 7, lens protection cover; 71, lens frame; 72, first lens; 73, second lens. DETAILED DESCRIPTION

[0030] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0031] like Figure 1 to Figure 3 As shown, a composite smoke sensor for mining includes a mounting frame 1, a housing 2, a protective net 3, a circuit board 4 and an optical labyrinth 5. The mounting frame 1 is a hollow member with openings at both ends. The housing 2 is open at one end and is threadedly connected to the lower periphery of the mounting frame 1. The optical labyrinth 5 is placed on the inner bottom surface of the housing 2, and its edges are evenly distributed with "T"-shaped smoke inlet grilles 51. The top of the optical labyrinth 5 is connected to the circuit board 4 located in the mounting frame 1, and the circuit board 4 is installed with an optical smoke sensor and a gas sensor. A protective net 3 is arranged between the optical labyrinth 5 and the housing 2, and a plurality of smoke inlets 21 are opened on the periphery of the housing 2. The housing is reinforced with reinforcing ribs for structural reinforcement, and the smoke inlet 21 is provided with a large opening to facilitate smoke inlet, so that smoke can rise from the bottom and dust can fall.

[0032] like Figure 2 As shown, the circuit board 4 includes a first circuit board 41 and a second circuit board 42. The first circuit board 41 is the minimum unit circuit board of the single chip microcomputer. The optical smoke sensor and the gas sensor are mounted on the second circuit board 42. The first circuit board 41 and the second circuit board 42 are riveted by copper pillars 6. The second circuit board 42 and the optical labyrinth 5 are connected to the copper pillars 6 by screws. A black light-absorbing paint layer is sprayed on the circuit board 4.

[0033] like Figure 3 As shown, the optical labyrinth 5 is made of black plastic, which blocks ambient light from entering the optical labyrinth 5. The bottom surface of the optical labyrinth 5 is a conical surface. On the one hand, the conical surface allows the large dust particles that fall to slide to the sides of the optical labyrinth 5, and not to accumulate in the middle of the optical labyrinth 5 where the light is strong and easy to cause light reflection; on the other hand, the light irradiated here is reflected to the smoke inlet grille 51 for absorption. The optical labyrinth 5 is large in size, fully considering the accumulation of coal mine dust inside the optical labyrinth 5. The internal space is large, and a certain amount of coal ash can be allowed to accumulate. The bottom edge of the optical labyrinth 5 has a circle of flanges 52 for placing the protective net. One end of the protective net 3 is against the flange 52, and the other end is against the lower opening edge of the mounting frame 1 to block dust or insects from entering and prevent false triggering of the alarm. The protective net 3 is made of 304 stainless steel, with a thickness of 0.1-0.15 mm, and its surface is evenly covered with through holes processed by etching technology, and the aperture of the through holes is 40 mesh.

[0034] The optical labyrinth 5 of such a structure has the following advantages: 1) It prevents external light from directly shining into the darkroom from any direction; 2) The light emitted by the LED light emitting diode of the optical smoke sensor cannot be directly or indirectly reflected on the photodiode; By increasing the effective detection space inside the optical labyrinth 5 as much as possible, the sensitivity to the directionality of LED light emission and photodiode reception can be reduced; 3) The inner surface treatment of the optical labyrinth 5 should be as close to the ideal black body as possible to increase the absorption of light and reduce reflection; 4) The effective detection space of the optical labyrinth 5 and the geometric boundary of the optical labyrinth 5 are kept at an appropriate distance, so that the optical smoke sensor has a more consistent background light signal; Generally speaking, the smaller the background light, the better the dynamic detection response performance; At the same time, the background light should be stable and consistent within an acceptable range; 5) The unidirectionality of the airflow makes it easy for smoke to enter the detection room and not easy to disperse; 6) Ensure the smoothness of the airflow and sufficient smoke intake efficiency, and have a rapid response characteristic to changes in smoke concentration; At the same time, it has a consistent response characteristic to smoke in all directions.

[0035] The optical smoke sensor is an integrated dual-wavelength photoelectric smoke sensor, which has a transmitter and a receiver. The transmitter has two LEDs, and the receiver is a silicon photodiode (PD). There is a 0.7mm grid between the transmitter and the receiver to block light from directly entering the receiver from the transmitter. When the optical smoke sensor is used underground in a coal mine, water vapor will corrode and damage the device, and the accumulation of coal ash particles inside the device will affect the emission and reception of optical signals. Therefore, a lens protective cover 7 is set outside the optical smoke sensor.

[0036] like Figure 4As shown, the lens protective cover 7 includes a lens frame 71 and a first lens 72 and a second lens 73 mounted on the lens frame 71. The height of the lens protective cover 7 is 0.5 mm. It is made of aluminum parts and the surface is matte black. A concave platform with a depth of 0.2 mm and a width of 0.2 mm is milled at the lens installation position. The concave platform is used to place the lens and is fixed with glue. The thickness of the lens is 0.2 mm. The lens material is quartz glass, K9 optical glass, sapphire glass, etc. with high transmittance in the wavelength range of 400 to 900 nm. The lens can include an anti-reflection film and a hydrophobic treatment. The lens protective cover 7 is glued to the optical smoke sensor, and UV glue is used to reinforce the structure with the circuit board 4 on the periphery. The lens protective cover 7 isolates the transmitting end and the receiving end in two independent areas. There is no light reflection condition between the two areas, so the background light signal will be greatly reduced.

[0037] The optical smoke sensor integrates a high-efficiency photoelectric measurement front end, two light-emitting diodes (LEDs) and two photodiodes (PDs). Figure 5 As shown, the driving circuit of the optical smoke sensor has three power supplies. 1.8V powers the analog front end and the communication interface, and 5V and 3.3V power the two LED light sources respectively. A large μF capacitor and a small nF capacitor are configured at each of the three power pins for noise reduction and to meet the 300mA pulse current drive requirement of the LED lamp. The CS selection pin is pulled high to enable I2C communication with the microcontroller. For the unused communication pins SCLK and MOSI, a pull-down resistor is used to ground to avoid external interference and false triggering of signal reception. The communication interface of the optical smoke sensor is powered by 1.8V, which is different from the 3.3V level of the microcontroller I2C interface, so level conversion is required. The level conversion circuit is shown in Figure 6 As shown, the chip is used for level conversion, and R9 and R10 resistors divide the voltage so that the level conversion chip is always in the enabled state.

[0038] like Figure 7 As shown in the figure, the detection circuit of the gas sensor is powered by a 5V power supply. A μF-class large capacitor and a nF-class small capacitor are configured at the power pins for noise reduction. The 1st and 4th pins of the gas sensor are the sensor heater pins. The 5V heating voltage generates a heating current of about 56mA. The 2nd and 3rd pins of the gas sensor are the sensor sensitive element pins. R4 is the load resistor. The voltage signal on the resistor can be collected to deduce the change in the resistance of the gas sensor, thereby obtaining the change in the concentration of the combustible gas in the air. Resistors R5, R6 and resistors R7, R8 are sampled by voltage division to obtain the 5V voltage value and the voltage value on the load resistor R4.

[0039] The two LED light-emitting diodes of the optical smoke sensor emit light pulses in two independent time slots (short-wavelength blue light and long-wavelength infrared light, respectively). The emitted light is scattered back to the photodiode by the particles in the air, generating a proportional output current, which is amplified by the operational amplifier and converted into a digital signal output. When the LED light power remains constant, the output current of the optical smoke sensor increases over time, indicating that the concentration of particles in the air is increasing. The optical smoke sensor is mounted face down on the second circuit board 42, and the LED emits light pulses downward. When there are particles in the space below, the scattered light signal enters the photodiode to generate current output. The higher the smoke concentration, the stronger the light signal. The gas sensor is also mounted face down on the second circuit board 42 to detect the combustible gas released during the smoldering stage and entering the optical maze with the smoke particles. The higher the concentration of combustible gas, the lower the resistance of the gas sensor.

[0040] Optical smoke sensors use a backscattering layout. Regardless of the particle size, the large scattering angle (backward) signal is generally smaller than the small scattering angle (forward) signal. As the angle increases, the scattered light intensity decreases and reaches the minimum value. As the angle increases, the light intensity will increase again. Compared with forward scattering, backscattering can significantly reduce the absolute value of scattered light by increasing the scattering angle. Backscattering is not as sensitive to changes in different particle sizes as forward scattering, so the sensitivity to various types of smoke can be uniformed.

[0041] like Figure 8 As shown, the composite mining smoke sensor detection method includes the following steps: S1. Perform calibration in a smoke-free environment to obtain optical background signals and gas-sensitive background signals: Power on the optical smoke sensor and gas-sensitive sensor, initialize the optical smoke sensor with the program, and start collecting light signals after initialization. Every 100ms, the microcontroller collects light signals. After a period of time, the real-time value within this period of time is average-filtered to obtain the blue light background signal PTR of the current smoke-free environment. BLUE0 and infrared background signal PTR IR0 ,PTR BLUE0 and PTR IR0 The calculation formulas are: and , Among them, PTR BLUES For blue light real-time signal, PTR IRS It is the real-time signal of infrared light. n is the number of samples, i For the i sampling points; At the same time, the gas sensor is preheated first, and then waits for calibration. After receiving the calibration command, it is calibrated, and then the gas sensor signal is collected every 1s. After a period of time, the real-time value during this period is averaged and filtered to obtain the gas sensor background resistance R0 in the current smoke-free environment. The calculation formula of R0 is: , Among them, R s is the real-time resistance value of the gas sensor, n is the number of samples, i For the i sampling points; S2. Determine the concentration trend of particles in the optical maze: calculate the change in blue light signal PTR ⊿BLUE And infrared light signal change PTR ⊿IR ,PTR ⊿BLUE and PTR ⊿BLUE and PTR ⊿IR The calculation formulas are: and , Then PTR ⊿BLUE and PTR ⊿IR Compare with the set threshold value. If the threshold value is exceeded, the concentration of particles in the optical maze is increasing, and it is necessary to determine whether there is smoke; S3. Determine particle size: Calculate the ratio of the scattering intensity of blue light to infrared light. When the ratio exceeds the set threshold, it is determined that the particle size is small and there is smoke. The calculation formula of the ratio is: ; S4, Gas-sensing auxiliary judgment: Calculate the real-time resistance value R of the gas-sensing s , R s The calculation formula is: , Among them, R L is the load resistance, V C is the supply voltage, V TGS is the load resistance R L The voltage across the terminals, Then calculate the gas-sensitive resistance change rate α, the calculation formula for α is: , If α exceeds the set threshold, it is determined that there is smoke.

[0042] The calculation of PTR in step S1 is as follows: the two LED light-emitting diodes of the optical smoke sensor emit light pulses in two independent time slots, that is, they emit short-wavelength blue light and long-wavelength infrared light respectively, and they are emitted alternately, and the emitted light power P PD It is related to the pulse peak current and the luminous efficiency of the LED light emitting diode. The light is scattered and irradiated onto the photodiode to generate photocurrent, which is amplified across the impedance and collected by the analog-to-digital converter (ADC). The received optical power P LED The power transfer ratio (PTR) of each LED is calculated as follows: , Among them, I LED_PK is the LED peak current, which is configured by setting the optical smoke sensor register and calculated based on the current proportional factor; R PD is the photodiode responsivity; η LED is the LED efficiency, calculated based on the LED gain calibration and derating factors in its manual; I PD is the photodiode current, which is calculated as: , Among them, ADCdata is the accumulated sum of the sampled data of a group of light pulses; Q is the resolution of the analog-to-digital converter; and pulse_num is the number of pulses.

[0043] The entire process of transmitting and receiving the optical signal of the LED light emitting diode will be affected by the change of ambient temperature. The photodiode photocurrent signal collected by the ADC can comprehensively reflect the impact of temperature on the optical signal. For infrared light, the temperature response curve is independent of the current of the LED light emitting diode. For blue light, its temperature response curve will vary according to the current of the LED light emitting diode used, so compensation is required. Specifically: test the size of the optical signal of the optical smoke sensor in different temperature environments of -10 to 50°C, and draw a fitting curve, such as Fig. 9 As shown in the figure, the temperature response value β relative to the reference temperature point 25°C is determined, and the photodiode current I is corrected PD补偿 , and its calculation formula is as follows: , Will I PD补偿 Substituting into the PTR calculation formula, the corrected power transfer ratio of the optical smoke sensor is obtained.

[0044] In a smoke-free state, the blue light and infrared light emitted by the optical smoke sensor will be scattered or reflected onto the PD (silicon photodiode) receiving surface when encountering particles floating in the air or irradiating the wall of the smoke chamber. At this time, the optical background signal is calculated from the optical module. The optical background signal reflects the particle concentration in the environment where the sensor is located and the reflected light signal of the smoke chamber wall.

[0045] The blue light background signal PTR of the current smoke-free environment is obtained through step S1 BLUE0 and infrared background signal PTR IR0 After that, due to the constant change of water mist and dust concentration in the air of coal mines, the particle concentration, temperature and humidity in the detection chamber environment are also changing slowly, and the background signals of light and gas sensors need to be continuously updated during the program operation. However, in the presence of smoke, the background signal will not be updated until the smoke dissipates. After testing, if Fig.10 As shown, when the optical signal driving pulse and driving current are fixed, the change trend of the particle concentration is positively correlated with the change amount of the optical signal, so the blue light signal change amount PTR is calculated respectively in step S2 ⊿BLUE And infrared light signal change PTR ⊿IR .

[0046] The optical smoke sensor uses two light sources, blue light (470nm) and infrared light (850nm), which are emitted alternately at a very high frequency. When particles in the air pass through the optical path, scattered light is generated. The short wavelength of blue light has a large scattering intensity for particles with a particle size of less than 1μm, and the long wavelength of infrared light has a large scattering intensity for particles with a particle size of more than 1μm. According to sample statistics, most of the particle sizes of combustion smoke particles are in the range of 0.1 to 0.4μm, while the particle sizes of common water mist, dust and other particles in coal mines are usually greater than 1μm. The ratio of the scattering intensity of blue light to infrared light is calculated by step S3. When the particles entering the optical labyrinth 5 are smoke with a smaller particle size, the scattering intensity of blue light is larger and the ratio is larger; when the particles entering the optical labyrinth 5 are dust or water mist with a larger particle size, the scattering intensity of blue light is smaller and the ratio is smaller. By measuring a variety of smoke and particulate matter, the threshold of Ratio can be determined. The Ratio values ​​of water mist, dust and smoke are clearly distinguished according to the actual test results.

[0047] When used underground in coal mines, workers often flush water and the environment is humid, which will form condensation or mist on the surface of the components, which may cause the optical smoke sensor to mistakenly identify smoke. Therefore, it is necessary to add a gas sensor for auxiliary judgment. Because when encountering smoke, the resistance of the gas sensor will have a significant trend of decreasing, such as Fig.11As shown, the gas sensor uses the gas-sensitive resistance change rate as a judgment basis, and calculates the gas-sensitive resistance change rate α through step S4.

[0048] In addition, both optical smoke sensors and gas sensors may fail in coal mines. It is very important to introduce fault diagnosis to the sensors and timely judge the sensor status to avoid false alarms of smoke. The main fault of the optical smoke sensor is the abnormal light signal caused by the obstruction of the light signal propagation path, including the optical labyrinth 5 dust accumulation causing the background light signal abnormality and the optical smoke sensor surface adhering to dust affecting the light emission and reception. The optical labyrinth 5 is seriously dusted, resulting in the light signal being emitted back to the receiving end by the dust accumulation instead of reflecting out of the optical labyrinth in the absence of smoke, making the light background signal abnormally large, affecting the response change of the light signal when smoke enters. Therefore, when the light background signal is large, it can be considered that the optical sensor has a fault and needs to be cleaned. The surface of the optical smoke sensor is adhered by moist coal ash dust, the light signal propagation path is blocked, the transmitting end cannot emit light, and the receiving end cannot receive light. At this time, the light background signal will be small, and the response change of the light signal when smoke enters will also be small and no alarm can be generated; therefore, when the light background signal is small, the dust cleaning operation should also be considered.

[0049] The main malfunction of the gas sensor is heater damage, etc. When the heater is damaged, the dirt on the surface of the sensitive element cannot be removed, and the sensitive element cannot fully exert its detection performance. At this time, the sensitive element will always be in a high-resistance state. According to experience, the voltage signal on the load resistor will be lower than 50mV. At this time, it can be determined that the gas sensor is faulty.

[0050] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A composite smoke sensor for mining, characterized in that: It includes a mounting bracket (1), a housing (2), a protective net (3), a circuit board 4, and an optical maze component (5). The mounting bracket (1) is a hollow component with openings at both ends. One end of the housing (2) is open and sleeved on the outer periphery of the lower part of the mounting bracket (1). The optical maze component (5) is placed on the inner bottom surface of the housing (2), and smoke inlet grilles (51) in a "T" shape are evenly distributed on its edge. The top of the optical maze component (5) is connected to the circuit board (4) located inside the mounting bracket (1). An optical smoke sensor and a gas sensor are installed on the circuit board (4). A protective net (3) is arranged between the optical maze component (5) and the housing (2), and a plurality of smoke inlets (21) are provided on the outer periphery of the housing (2).

2. The composite mine smoke sensor according to claim 1 is characterized in that: The material of the optical maze component (5) is black plastic, and its bottom surface is a conical surface.

3. The composite mine smoke sensor according to claim 1 is characterized in that: The housing (2) and the mounting bracket (1) are connected by threads.

4. The composite smoke sensor for mining according to claim 1 is characterized in that: The circuit board (4) includes a first circuit board (41) and a second circuit board (42). The first circuit board (41) is a minimum unit circuit board of a single chip microcomputer. The optical smoke sensor and the gas sensor are installed on the second circuit board (42). The first circuit board (41) and the second circuit board (42) are riveted by copper columns (6). The second circuit board (42) is connected to the optical maze component (5) through screws and copper columns (6).

5. The composite mine smoke sensor according to claim 1 or 4, characterized in that: A black light-absorbing paint layer is sprayed on the circuit board (4).

6. The composite smoke sensor for mining according to claim 1 is characterized in that: The optical smoke sensor is an integrated dual-wavelength photoelectric smoke sensor, which has a transmitting end and a receiving end, and a grille is arranged between the transmitting end and the receiving end. A lens protection cover (7) is arranged outside the optical smoke sensor. The lens protection cover (7) includes a lens frame (71) and a first lens (72) and a second lens (73) installed on the lens frame (71). The first lens (72) and the second lens (73) are respectively arranged on the transmitting end and the receiving end. The first lens (72) and the second lens (73) are both made of quartz glass, K9 optical glass or sapphire glass with a wavelength range of 400 - 900nm and high transmittance.

7. The composite smoke sensor for mining according to claim 1 is characterized in that: A flange (52) for placing the protective net (3) is provided on the bottom edge of the optical maze component (5). One end of the protective net (3) abuts against the flange (52), and the other end abuts against the lower opening edge of the mounting bracket (1).

8. The composite smoke sensor for mining according to claim 1 is characterized in that: The protective net (3) is made of 304 stainless steel, with a thickness of 0.1 - 0.15mm. Through holes processed by an etching process are evenly distributed on its surface, and the aperture of the through holes is 40 meshes.

9. A detection method for a composite mine smoke sensor as claimed in any one of claims 1 to 8, characterized in that: It includes the following steps: S1. Perform calibration in a smoke-free environment to obtain optical background signals and gas-sensitive background signals: Power on the optical smoke sensor and gas-sensitive sensor, initialize the optical smoke sensor with the program, and start collecting light signals after initialization. Every 100ms, the microcontroller collects light signals. After a period of time, the real-time value within this period of time is average-filtered to obtain the blue light background signal PTR of the current smoke-free environment. BLUE0 and infrared background signal PTR IR0 ,PTR BLUE0 and PTR IR0 The calculation formulas are: and , Among them, PTR BLUES For blue light real-time signal, PTR IRS It is the real-time signal of infrared light. n is the number of samples, i For the i sampling points; Meanwhile, the gas sensor is preheated first. After the preheating ends, it waits for calibration. After receiving the calibration command, it performs calibration, and then starts to collect gas sensor signals, collecting once every 1s. After a period of time, the real-time values during this period are subjected to mean filtering to obtain the gas background resistance value R0 of the current smokeless environment. The calculation formula for R0 is: ， Among them, R s is the real-time resistance value of the gas sensor, n is the number of samples, i For the i sampling points; S2. Determine the concentration trend of particles in the optical maze: calculate the change in blue light signal PTR ⊿BLUE And infrared light signal change PTR ⊿IR ,PTR ⊿BLUE and PTR ⊿BLUE and PTR ⊿IR The calculation formulas are: and , Then PTR ⊿BLUE and PTR ⊿IR Compare with the set threshold value. If the threshold value is exceeded, the concentration of particles in the optical maze is increasing, and it is necessary to determine whether there is smoke; S3. Judge the particle size: Calculate the ratio Ratio of the scattering intensities of blue light and infrared light. When Ratio exceeds the set threshold, it is determined that the particle size is small and there is smoke. The calculation formula for Ratio is: ； S4, Gas-sensing auxiliary judgment: Calculate the real-time resistance value R of the gas-sensing s , R s The calculation formula is: ， Among them, R L is the load resistance, V C is the supply voltage, V TGS is the load resistance R L The voltage across the terminals, Then calculate the change rate α of the gas sensor resistance value. The calculation formula for α is: ， If α exceeds the set threshold, it is determined that there is smoke.

10. The detection method of the composite mining smoke sensor according to claim 9, characterized in that: In step S1, PTR is the power transfer ratio, which is calculated as follows: ， Among them, I LED_PK is the LED peak current, which is configured by setting the optical smoke sensor register and calculated based on the current proportional factor; R PD is the photodiode responsivity; η LED is the LED efficiency, calculated based on the LED gain calibration and derating factors in its manual; I PD is the photodiode current, which is calculated as: ， Among them, ADCdata is the accumulated sum of the sampled data of a group of light pulses; Q is the resolution of the analog-to-digital converter; pulse_num is the number of pulses; Then test the optical signal size of the optical smoke sensor in different temperature environments of -10 to 50°C, draw a fitting curve, determine the temperature response value β relative to the reference temperature point 25°C, and correct the photodiode current I PD补偿 , and its calculation formula is as follows: ， Will I PD补偿 Substituting into the PTR calculation formula, the corrected power transfer ratio of the optical smoke sensor is obtained.

Images