Airflow protection type optical fiber probe, powder concentration measurement system and method

Abstract

The present invention belongs to the field of optical sensors, and specifically relates to an airflow protection type fiber optic probe, a powder concentration measurement system and method. The airflow protection type fiber optic probe includes a probe body, an airflow duct, and a four-way valve. Among them, at least one group of first through holes and second through holes connected to the airflow cavity of the reflection end are respectively opened on the measuring tube of the probe body; a plurality of third through holes and a plurality of fourth through holes connected to the airflow cavity of the optical fiber end are also opened on the measuring tube. The airflow duct adopts an F-type pipeline and is inserted into the measuring tube along each through hole; the four-way valve is used to connect the F-type pipeline to the gas source of clean gas, the atmosphere or keep it sealed. In the airflow protection type fiber optic probe of the present invention, the airflow duct cleans the mirror window by spraying clean gas into the measuring tube during measurement, and forms a protective atmosphere to prevent dust from intruding during measurement. The present invention overcomes the problem that the existing fiber optic probe type dust concentration sensor is not suitable for high-concentration aerosol environment monitoring.

Description

Technical Field

[0001] The invention belongs to the field of optical sensors, and in particular relates to an airflow protection type optical fiber probe, a powder concentration measurement system using the airflow protection type optical fiber probe, and a corresponding measurement method. Background Art

[0002] In industrial production, environmental monitoring, fire safety and other aspects, powder environments are widely present. In order to ensure the safety of the working environment and the health of personnel during the operation, real-time monitoring of powder concentration is very important. For powder monitoring in environmental space, relatively mature dust monitoring equipment is currently widely used. However, when encountering extreme particulate matter concentration conditions such as sandstorms and high-dust construction sites, it is easy for the optical path receiver and the airflow bend to be contaminated with dust, which may affect its measurement accuracy and fail to meet the high-reliability measurement requirements. Therefore, the powder concentration detection equipment needs to ensure its own tolerance to high-concentration dust and long-term stability to ensure the reliability of the measurement results.

[0003] Local confined spaces such as fluidized beds, reactors, and aircraft engine compartments usually require real-time monitoring of dust concentration. In such application scenarios, dust concentration sensors based on miniaturized fiber optic probes have excellent measurement advantages. This type of sensor places the fiber optic probe in a small test space. Through the transmission of optical signals, it can effectively avoid the instability of the detector and signal processing circuits in complex and special environments. However, there is also the problem of high-concentration powder contamination during the powder testing process in local spaces. Aerosol powders in such confined spaces have a higher initial velocity. Therefore, during the measurement process, powder particles are easily diffused in the internal cavity of the fiber optic probe, which in turn causes contamination to the optical mirror window inside the fiber optic probe, which significantly reduces the detection accuracy of the sensor and makes the monitoring function ineffective. Summary of the invention

[0004] In order to solve the problem that the fiber optic probe type dust concentration sensor is easily contaminated by dust in the high concentration aerosol environment monitoring, thereby causing the failure of the detection function; the present invention provides an airflow protection type fiber optic probe, a powder concentration measurement system and method.

[0005] The present invention is implemented by the following technical solutions:

[0006] An airflow protection type optical fiber probe comprises a probe body, at least one pair of airflow conduits, and a plurality of four-way valves corresponding to the number of the airflow conduits.

[0007] Wherein, at least one group of first through holes and second through holes connected to the airflow cavity at the reflection end are respectively provided on the measuring tube of the probe body; the first through holes and the second through holes are respectively located near the mirror window at the reflection end and near the gradually expanding cavity at the reflection end. A plurality of third through holes and a plurality of fourth through holes connected to the airflow cavity at the optical fiber end are also provided on the measuring tube; the third through holes and the fourth through holes are respectively located near the mirror window at the optical fiber end and near the gradually expanding cavity at the optical fiber end.

[0008] The airflow duct adopts an F-type duct, which includes a main pipe with one end open and two branch pipes perpendicular to the main pipe and connected to the main pipe. The airflow duct is divided into a first duct and a second duct. Each first duct is connected to the airflow cavity at the reflection end and the airflow cavity at the optical fiber end of the measuring tube through a group of first through holes and a third through hole; each second duct is connected to the airflow cavity at the reflection end and the airflow cavity at the optical fiber end of the measuring tube through a group of second through holes and a fourth through hole.

[0009] The four-way valve is used to switch the main pipe of each gas flow duct between three states: connected to the gas source of clean gas, connected to the atmosphere, and kept sealed.

[0010] In the airflow protection type optical fiber probe provided by the present invention, the probe body includes a reflective structural member, a measuring tube and a wire tube fixing member. The internal cavity of the measuring tube includes a reflective end airflow cavity, a reflective end gradually expanding cavity, a measuring cavity, an optical fiber end gradually expanding cavity and an optical fiber end airflow cavity which are interconnected and symmetrically distributed in a diabolo shape. The two ends of the measuring tube are sealed by a reflective end mirror window and an optical fiber end mirror window respectively. A measuring hole connected to the measuring cavity is also provided on the measuring tube.

[0011] The wire tube fixing part is located on one side of the optical fiber end mirror window and is used to fix the transmission optical fiber and the airflow duct. The detection signal emitted by the transmission optical fiber is incident along the central axis of the internal cavity of the measuring tube. The reflection structure is located on one side of the reflection end mirror window and is used to reflect the incident detection signal back along the central axis of the measuring tube.

[0012] As a further improvement of the present invention, the number of the first through hole, the second through hole, the third through hole and the fourth through hole are all multiple. Each type of through hole is distributed in an annular manner at different positions in the axial direction of the measuring pipe. Among them, the first through hole and the third through hole correspond one to one, and the two are respectively located at designated positions in the circumference of the measuring pipe; the second through hole and the fourth through hole correspond one to one, and the two are respectively located at designated positions in the circumference of the measuring pipe. And the distribution positions of the first through hole and the third through hole and the second through hole and the fourth through hole along the circumference of the measuring pipe do not overlap.

[0013] As a further improvement of the present invention, the spraying directions of the two branches in the first conduit are respectively directed to the reflective end mirror window and the optical fiber end mirror window; the spraying directions of the two branches in the second conduit are respectively directed to the reflective end gradually expanding cavity and the optical fiber end gradually expanding cavity.

[0014] As a further improvement of the present invention, the gas source is connected to the inlet of the four-way valve via a flow valve; the flow valve is used to adjust the flow of the clean gas introduced into the first conduit or the second conduit.

[0015] As a further improvement of the present invention, the airflow protection type optical fiber probe also includes a controller, which is electrically connected to each four-way valve and the flow valve. The controller switches the connection relationship between the inlet and outlet of each four-way valve to achieve: (a) connecting some or all of the airflow ducts to the air source before measurement to clean the probe. (b) During the measurement process, several designated first ducts are connected to the air source, and several designated second ducts are connected to the atmosphere, thereby forming a clean pressure environment that can isolate dust at the airflow cavity at the reflection end and the airflow cavity at the optical fiber end. The controller is also used to dynamically adjust the flow rate of the clean gas output by the air source according to the number of airflow ducts connected to the air source.

[0016] The present invention also includes a powder concentration measurement system, which includes: the aforementioned airflow protection type optical fiber probe; and a composite wire tube and a detection module. The composite wire tube includes a transmission optical fiber and an air tube; and the transmission optical fiber adopts a Y-type optical fiber.

[0017] The detection module includes an air source, a laser light source, a signal receiving module and a signal processing module. The air source is used to provide high-pressure clean gas; the air source is connected to one of the inlets of the four-way valve of each airflow duct in the airflow protection type optical fiber probe through the air pipe. The single-port side of the transmission optical fiber is installed at the optical fiber end mirror window of the measuring tube through the wire tube fixture, one end of the double-port side is connected to the laser light source, and the other end is connected to the signal receiving module. The laser light source is used to transmit a detection signal to the measuring tube through the transmission optical fiber; the signal receiving module is used to receive the echo signal received by the transmission optical fiber. The signal processing module is used to process the echo signal to obtain the powder concentration of the aerosol diffused into the measuring tube.

[0018] The present invention also provides a method for measuring powder concentration, which uses the aforementioned powder concentration measurement system to measure the concentration of powder contained in the gas in the measurement space. The measurement method comprises the following steps:

[0019] S1: Adjust the conduction state of each four-way valve and the opening of the flow valve so that a number of designated airflow ducts in the airflow protection optical fiber probe are connected to the air source, and the remaining airflow ducts remain closed. In this state, ventilate the measuring tube for a specified period of time to achieve self-cleaning of the measuring tube.

[0020] S2: Adjust the conduction state of each four-way valve and the opening of the flow valve, first connect a number of designated first conduits in the airflow protection optical fiber probe to the air source, then connect a number of designated second conduits to the atmosphere, and keep the remaining airflow conduits closed; thereby maintaining the two ends of the measuring cavity in the measuring tube at a balanced pressure state of the designated pressure to isolate dust;

[0021] S3: Place the airflow protection optical fiber probe into the measurement environment, turn on the detection module, and complete the powder concentration detection of the measurement environment;

[0022] S4: After the powder concentration measurement is completed, the airflow protection type optical fiber probe is taken out from the measurement environment, and step S1 is repeated, and then the air source is turned off and all airflow ducts are switched to a closed state.

[0023] As a further improvement of the present invention, in step S2, the number N1 of first conduits connected to the gas source, the number N2 of second conduits connected to the atmosphere, and the flow rate Q of the clean gas discharged by the flow valve are pre-set according to the gas pressure P in the current measurement environment; the relevant parameters are obtained by querying a "P-N1-N2-Q mapping table"; the P-N1-N2-Q mapping table is a data comparison table established through pre-tested experimental data, which can characterize the mapping relationship between parameters P, N, N2 and Q under ideal dust prevention effect.

[0024] The technical solution provided by the present invention has the following beneficial effects:

[0025] The airflow protection type fiber optic probe provided by the present invention has a plurality of through holes at the positions of the airflow cavity at the fiber end and the airflow cavity at the reflection end corresponding to the measuring tube of the existing fiber optic probe, and an F-type conduit connected to the internal cavity of the measuring tube is installed at the through hole. Before the airflow protection type fiber optic probe is used, clean gas can be sprayed into the measuring tube through the F-type conduit to achieve the purge of the mirror window at the reflection end and the mirror window at the fiber optic probe, so as to achieve self-cleaning of the mirror window. When the airflow protection type fiber optic probe performs the detection task, the air can be released into the measuring tube through the F-type conduit, and then a protective gas valve composed of clean gas is formed outside the measuring cavity of the measuring tube to inhibit the aerosol in the measuring environment from diffusing to the mirror windows on both sides. Thereby, the purpose of protecting the mirror window from contamination is achieved.

[0026] Since the airflow-protected optical fiber probe provided by the present invention has the performance of self-cleaning and dust-proof during use, the dust concentration sensor designed using the airflow-protected optical fiber probe can overcome the problem that existing sensors cannot be applied to high-concentration and high-rate aerosol concentration monitoring, and thus has broad application prospects in the fields of fluidized beds, reactors, and aircraft engine compartments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 It is a schematic diagram of the structure of an existing optical fiber probe for dust concentration sensors.

[0029] Figure 2 This is a schematic diagram of the structure of the airflow protection type optical fiber probe provided in Example 1 of the present invention.

[0030] Figure 3 This is a schematic diagram of the cross-sectional structure of the airflow protection type optical fiber probe provided in Example 1 of the present invention.

[0031] Figure 4 It is a schematic cross-sectional view of a measuring tube equipped with multiple groups of airflow ducts in Example 1 of the present invention.

[0032] Figure 5 Two typical activation states of the first catheter in the sweeping mode.

[0033] Figure 6 Schematic diagram of beveling the end of a branch pipe in an airflow duct to change the direction of the airflow at the end in Example 1 of the present invention.

[0034] Figure 7 Schematic diagram of the connection between the air flow duct and the air source in Example 1 of the present invention.

[0035] Figure 8 This is a schematic diagram of the powder concentration measurement system provided in Example 2 of the present invention.

[0036] Fig. 9 This is a flow chart of the steps of a powder concentration measurement method based on a powder concentration measurement system in Example 2 of the present invention.

[0037] The markings in the figure are:

[0038] 1. Probe body; 3. Four-way valve; 4. Flow valve; 5. Gas source; 11. Reflection structure; 12. Measuring tube; 13. Wire tube fixing part; 2. Airflow duct; 21. First duct; 22. Second duct; 100. Airflow protection fiber optic probe; 110. Reflector mounting seat; 111. Concave reflector; 120. Measuring hole; 121. Airflow cavity at the reflecting end; 122. Gradual expansion cavity at the reflecting end; 123. Measuring cavity; 124. Gradual expansion cavity at the optical fiber end; 125. Airflow cavity at the optical fiber end; 200. Composite wire tube; 201. Air tube; 202. Transmission optical fiber; 300. Detection module; 301. Laser light source; 302. Signal receiving module; 1201. First through hole; 1202. Second through hole; 1203. Third through hole; 1204. Fourth through hole. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Example 1

[0041] This embodiment provides an airflow protection type optical fiber probe 100, which is obtained by improving the probe body 1 of a conventional optical fiber probe. The structure of a conventional optical fiber probe is as follows: Figure 1 As shown, the probe body 1 includes a measuring tube 12, and a reflective structure 11 and a wire tube fixing member 13 connected to both sides of the measuring tube 12. The interior of the measuring tube 12 is composed of multiple sections of cavities with different functions; in order from the side of the reflective structure 11 to the side of the wire tube fixing member 13, it includes a reflective end airflow cavity 121, a reflective end gradually expanding cavity 122, a measuring cavity 123, a fiber end gradually expanding cavity 124 and a fiber end airflow cavity 125 that are interconnected. The sections where the two ends of the measuring tube 12 are connected to the reflective structure 11 and the wire tube fixing member 13 are sealed by a high-transmittance reflective end mirror window and a fiber end mirror window respectively. The reflective end airflow cavity 121, the fiber end airflow cavity 125 and the measuring cavity 123 are cylindrical with constant diameter, while the reflective end gradually expanding cavity 122 gradually expands in diameter from the side of the measuring cavity 123 to the side of the reflective end airflow cavity 121, and the fiber end gradually expanding cavity 124 gradually expands in diameter from the side of the measuring cavity 123 to the side of the fiber end airflow cavity 125. The interconnected cavities inside the measuring tube 12 are symmetrically distributed in a diabolo shape. A measuring hole 120 communicating with the measuring cavity 123 is provided on the outer wall of the measuring tube 12 at a position corresponding to the measuring cavity 123 .

[0042] In the probe body 1 of the conventional optical fiber probe, the wire tube fixture 13 is located on one side of the optical fiber end mirror window and is used to fix the transmission optical fiber 202. The detection signal emitted by the transmission optical fiber 202 is incident along the central axis of the internal cavity of the measuring tube 12. The reflective structure 11 is located on one side of the reflective end mirror window, and includes a reflector mounting seat 110 and a concave reflector 111. The concave reflector 111 is fixedly connected to the measuring tube 12 through the reflector mounting seat 110, and the reflective curved surface of the concave reflector 111 faces the reflective end mirror window of the measuring tube 12. The reflective structure 11, the measuring tube 12 and the wire tube fixture 13 are aligned and matched in sequence in the coaxial direction. On this basis, the detection signal emitted from the transmission optical fiber 202 in the wire tube fixture 13 passes through the optical fiber end mirror window, the optical fiber end airflow cavity 125, the optical fiber end gradually expanding cavity 124, the measuring cavity 123, the reflective end gradually expanding cavity 122, and the reflective end airflow cavity 121 in sequence. Then, after being converged and reflected by the concave reflector 111 in the reflective structure 11, it passes through the reflective end airflow cavity 121, the reflective end gradually expanding cavity 122, the measuring cavity 123, the optical fiber end gradually expanding cavity 124, the optical fiber end airflow cavity 125 and the optical fiber end mirror window in sequence, and finally, it is received by the signal receiving module 302 on the other side of the optical fiber end mirror window to obtain the corresponding echo signal. In this process, the aerosol to be detected will diffuse into the measuring cavity 123 of the measuring tube 12 along the measuring hole 120 in the optical fiber probe, and the emitted detection signal and the received echo signal will pass through the aerosol to be detected in the measuring cavity 123 twice and attenuate, so the powder concentration in the aerosol can be measured according to the signal intensity change between the detection signal and the echo signal.

[0043] exist Figure 1 Based on the conventional optical fiber probe shown in FIG. 1 , the structure of the improved airflow protection optical fiber probe 100 provided in this embodiment is as follows: Figure 2 As shown, it includes a probe body 1, at least one pair of airflow conduits 2, and a plurality of four-way valves 3 corresponding to the number of the airflow conduits 2. Specifically, as Figure 3 As shown, in this embodiment, at least one group of first through holes 1201 and second through holes 1202 are respectively provided on the measuring tube 12 of the probe body 1, which are connected to the airflow cavity 121 at the reflection end; the first through holes 1201 and the second through holes 1202 are respectively located near the mirror window at the reflection end and near the gradually expanding cavity 122 at the reflection end. A plurality of third through holes 1203 and a plurality of fourth through holes 1204 are also provided on the measuring tube 12, which are connected to the airflow cavity 125 at the optical fiber end; the third through holes 1203 and the fourth through holes 1204 are respectively located near the mirror window at the optical fiber end and near the gradually expanding cavity 124 at the optical fiber end.

[0044] Each pair of airflow ducts 2 used in the optical fiber probe of this embodiment includes a first duct 21 and a second duct 22. The first duct 21 and the second duct 22 are both F-type ducts. Each F-type duct includes a main duct with one end open and two branch ducts perpendicular to the main duct and connected to the main duct. The two branch ducts of each first duct 21 are respectively inserted into one group of first through holes 1201 and third through holes 1203 of the measuring tube 12, and then communicated with the reflecting end airflow cavity 121 and the optical fiber end airflow cavity 125 in the measuring tube 12. The two branch ducts of each second duct 22 are respectively inserted into the second through hole 1202 and the fourth through hole 1204, and then communicated with the reflecting end airflow cavity 121 and the optical fiber end airflow cavity 125 in the measuring tube 12.

[0045] In practical applications, in order to facilitate the installation of the first conduit 21 and the second conduit 22, the first through hole 1201 and the third through hole 1203 should be located at the same position of the measuring tube 12 in the circumferential direction, while the second through hole 1202 and the fourth through hole 1204 should be located at the same position of the measuring tube 12 in the circumferential direction, and the positions of the first through hole 1201 and the third through hole 1203 and the second through hole 1202 and the fourth through hole 1204 in the circumferential direction of the measuring tube 12 do not overlap. At this time, both the first conduit 21 and the second conduit 22 can be made of hard pipes, and the distance between the two branches in the first conduit 21 is relatively far, and is equal to the spacing between the first through hole 1201 and the third through hole 1203 on the measuring tube 12. Correspondingly, the distance between the two branches in the second conduit 22 is relatively close, and is equal to the spacing between the second through hole 1202 and the fourth through hole 1204 on the measuring tube 12. The connection between each airflow conduit 2 and the measuring tube 12 is kept sealed.

[0046] In this embodiment, the four-way valve 3 includes three inlets and one outlet. One of the inlets of each four-way valve 3 is used to connect to the gas source 5 storing high-pressure clean gas, the second inlet is sealed, and the third inlet is connected to the atmosphere; the outlets of each four-way valve 3 are respectively connected to the open end of the main pipe in one of the air flow conduits 2. On this basis, when a certain four-way valve 3 is switched to the first inlet and outlet to be connected, the clean gas in the gas source 5 will be sprayed into the reflection end air flow cavity 121 and the optical fiber end air flow cavity 125 of the measuring tube 12 along the first conduit 21 or the second conduit 22. When a certain four-way valve 3 is switched to the second inlet and outlet to be connected, the retention pipeline remains closed. When a certain four-way valve 3 is switched to the third inlet and outlet to be connected, the high-pressure gas in the reflection end air flow cavity 121 and the optical fiber end air flow cavity 125 of the measuring tube 12 will be discharged into the atmosphere along the corresponding first conduit 21 or the second conduit 22.

[0047] In addition, it should be additionally explained that: compared with the traditional fiber optic probe, the wire tube fixing member 13 in the fiber optic probe used in this embodiment is not only required to fix the transmission optical fiber 202, but also needs to fix the additional components such as the airflow duct 2.

[0048] Based on the various additional through holes on the measuring tube 12, and the installed airflow duct 2 and four-way valve 3, this embodiment provides two typical working modes for the airflow protection type optical fiber probe 100, namely, a cleaning mode and a dustproof mode. Among them, the cleaning mode is used to clean the optical fiber probe that has been contaminated or may be contaminated with the split body and restore it to a clean state. The dustproof mode is a mode that prevents the optical fiber probe from being contaminated by dust during use.

[0049] In the cleaning mode, it is necessary to adjust the connection direction of each four-way valve 3 so that all or part of the airflow ducts 2 on the measuring tube 12 are connected to the gas source 5, and all the airflow ducts 2 are prohibited from connecting to the atmosphere. In this state, the clean gas introduced will comprehensively clean the inner cavity of the measuring tube 12, and then blow off the powder contaminated on the reflection end mirror window and the optical fiber end mirror window and the inner wall of each cavity in the measuring tube 12, and discharge the powder along the measuring hole 120 at the measuring cavity 123 in the middle section of the measuring tube 12. In actual application, each time the optical probe is placed in the measuring space to start the powder concentration measurement, the optical fiber probe should be cleaned once to ensure that the reflection end mirror window and the optical fiber end mirror window of the optical fiber probe are clean before the measurement. In addition, after each measurement, one side cleaning can also be performed to discharge a small amount of powder that may be contaminated during the actual measurement.

[0050] In the dustproof mode, it is necessary to adjust the connection direction of each four-way valve 3, first connect the first conduit 21 on the measuring tube 12 to the gas source 5, and pre-introduce clean gas into the inner cavity of the measuring tube 12, and then connect the second conduit 22 on the measuring tube 12 to the atmosphere to discharge the high-pressure clean gas in the inner cavity of the measuring tube 12. The ventilation flow of the first conduit 21 into the measuring tube 12 is balanced with the exhaust flow of the second conduit 22 and the measuring hole 120 to the outside of the measuring tube 12, and a specified pressure state can be maintained in the reflection end gas flow cavity 121 and the reflection end gradual expansion cavity 122 on both sides of the measuring cavity 123 in the measuring tube 12, as well as the optical fiber end gradual expansion cavity 124 and the optical fiber end gas flow cavity 125. On this basis, when the aerosol in the measuring environment passes through the measuring cavity 123 along the measuring hole 120, its diffusion effect to the reflection end gradual expansion cavity 122 and the optical fiber end gradual expansion cavity 124 on both sides of the measuring cavity 123 will be suppressed. That is, the protective atmosphere with a certain pressure formed by the clean gas in the cavities at both ends of the measuring tube 12 by the first conduit 21 and the second conduit 22 can prevent the powder from entering the two ends of the measuring tube 12, thereby achieving dust prevention. In practical applications, the fiber optic probe should be cleaned first, then switched to the dust prevention mode, and finally sent to the measurement environment for dust concentration monitoring. When the dust concentration monitoring task is completed, the fiber optic probe should be removed from the measurement environment first, and then the dust prevention mode of the fiber optic probe should be turned off. If necessary, the fiber optic probe removed from the measurement environment can be cleaned again.

[0051] In the airflow protection type optical fiber probe 100 provided in this embodiment, in order to improve the cleaning effect of the airflow conduit 2 in the cleaning mode and improve the dustproof effect of the airflow conduit 2 in the dustproof mode, multiple pairs of airflow conduits 2 can be arranged along the circumferential direction on the same measuring tube 12. For example, Figure 4 A cross-sectional view of a measuring tube 12 is shown in which four first conduits 21 and four second conduits 22 are reserved for installation on one measuring tube 12. Accordingly, the number of the first through hole 1201, the second through hole 1202, the third through hole 1203 and the fourth through hole 1204 provided on each measuring tube 12 is also multiple. Each type of through hole is distributed in an annular manner at different positions in the axial direction of the measuring tube 12. In particular, in order to avoid interference between the installation positions of different airflow conduits 2, the distribution positions of each first through hole 1201 and the third through hole 1203 and each second through hole 1202 and the fourth through hole 1204 along the circumference of the measuring tube 12 do not overlap.

[0052] When multiple sets of airflow ducts 2 are installed on the measuring tube 12 at the same time, the number of airflow ducts 2 to be enabled can be flexibly selected as needed to meet the needs of different pressure measurement scenarios. In addition, when multiple sets of airflow ducts 2 are installed on the measuring tube 12 at the same time, the direction of the airflow ejected by different airflow ducts 2 can be adjusted in the cleaning mode or dust prevention mode to achieve differentiated cleaning effects or dust prevention effects. For example, Figure 5 The state diagrams are shown respectively when two V-shaped first conduits 21 are enabled in the cleaning mode and two straight-line first conduits 21 are enabled. The two V-shaped first conduits 21 can generate a stronger cleaning airflow at the opposite side of the measuring tube 12, which is suitable for use in scenarios where the powder is unevenly contaminated when the fiber optic probe is used. By calling the two opposite first conduits 21, the area with more serious dust contamination can be cleaned strongly. The two straight-line first conduits 21 can generate a more uniform cleaning airflow in the measuring tube 12, which is suitable for use in scenarios where the powder contamination is relatively uniform and relatively light.

[0053] In a more optimized solution of this embodiment, the injection direction of the ends of the branches in the first duct 21 and the second duct 22 can also be adjusted. By optimizing the direction of the airflow injected or discharged by the airflow duct 2, the clean gas forms an airflow circulation in the cavity of the measuring tube 12 in the desired direction, thereby achieving a better cleaning or dust prevention effect. Specifically, considering that the reflection end mirror window and the optical fiber end mirror window are mainly kept clean during the cleaning process, and the dust prevention process mainly requires that the dust in the middle measuring cavity 123 be isolated outside the two gradually expanding cavities. Therefore, in this embodiment, the injection directions of the two branches in the first duct 21 are respectively directed to the reflection end mirror window and the optical fiber end mirror window; the injection directions of the two branches in the second duct 22 are respectively directed to the reflection end gradually expanding cavity 122 and the optical fiber end gradually expanding cavity 124.

[0054] In practical applications, the directional control of the airflow direction sprayed from the ends of the branch pipes in the first conduit 21 and the second conduit 22 can be achieved in a variety of ways. For example, Figure 6 The example of beveling the ends of the branch pipes in the first conduit 21 and the second conduit 22 to change the direction of the airflow injection is shown. If the airflow needs to be deflected to a certain side, a portion of the end of the branch pipe is cut off obliquely on that side. In other embodiments, the end of the branch pipe can also be directly bent in the corresponding direction to achieve control of the airflow injection direction. Figure 6 The upper middle part is a schematic diagram of the first conduit 21 spraying clean gas to the reflection end mirror window and the optical fiber end mirror window respectively. Figure 6 The lower middle part is a schematic diagram of the second conduit 22 discharging clean gas close to the measuring chamber 123 .

[0055] In a more optimized solution of this embodiment, Figure 7As shown, a flow valve 4 is further provided between the gas source 5 and the inlet of each four-way valve 3; the flow valve 4 is used to adjust the flow of the clean gas introduced into the first conduit 21 or the second conduit 22. The foregoing describes the case where the flow of the clean gas introduced into the measuring tube 12 is adjusted by changing the number of activated gas flow conduits 2. In the optimized later scheme, the flow of the clean gas released by the gas source 5 can also be adjusted by the flow valve 4, and the flow of the clean gas discharged from the gas flow conduit 2 into the measuring tube 12 can be indirectly changed to meet the needs of different application scenarios.

[0056] In combination with the above, it can be seen that the airflow protection type optical fiber probe 100 provided in this embodiment switches different working modes mainly by adjusting the conduction direction of the four-way valve 3. The above content does not limit the switching mode of each four-way valve 3. In practical applications, the four-way valve 3 can be a manually adjusted valve, and the technician can manually switch it according to the needs. In a more optimized solution, each four-way valve 3 can also be an electrically controlled valve, and a controller such as a PLC controller is added to the airflow protection type optical fiber probe 100. The controller is electrically connected to each four-way valve 3 and the flow valve 4. The controller switches the connection relationship between the inlet and outlet of each four-way valve 3 to achieve: (a) Before measurement, some or all of the airflow conduits 2 are connected to the air source 5 to clean the probe. (b) During the measurement process, the specified number of first conduits 21 are connected to the air source 5, and the specified number of second conduits 22 are connected to the atmosphere, thereby forming a clean pressure environment that can isolate dust at the reflection end airflow cavity 121 and the optical fiber end airflow cavity 125. The controller is also used to dynamically adjust the flow rate of the clean gas output by the gas source 5 according to the number of gas flow conduits 2 connected to the gas source 5 .

[0057] Example 2

[0058] Based on the solution of Example 1, this embodiment further provides a powder concentration measurement system, such as Figure 8 As shown, it includes: a composite line tube 200, a detection module 300, and an airflow protection type optical fiber probe 100 as in Example 1. The composite line tube 200 includes a transmission optical fiber 202 and an air tube 201; the detection module 300 includes an air source 5, a laser light source 301, a signal receiving module 302 and a signal processing module.

[0059] Among them, the gas source 5 is used to provide high-pressure clean gas; the gas source 5 is connected to one of the inlets of the four-way valve 3 of each gas flow conduit 2 in the gas flow protection type optical fiber probe 100 through the gas pipe 201; or, the gas source 5 is indirectly connected to the four-way valve 3 through the flow valve 4. The transmission optical fiber 202 adopts a Y-type optical fiber, and its single-port side is installed at the optical fiber end mirror window of the measuring tube 12 through the wire tube fixing member 13, and one end of the double-port side is connected to the laser light source 301, and the other end is connected to the signal receiving module 302. The laser light source 301 is used to transmit a detection signal to the measuring tube 12 through the transmission optical fiber 202; the signal receiving module 302 is used to receive the echo signal through the transmission optical fiber 202. The signal processing module is used to process the echo signal to obtain the powder concentration in the gas diffused into the measuring tube 12.

[0060] like Fig. 9 As shown, the aforementioned powder concentration measurement system is used to implement a method for measuring the concentration of powder contained in the gas in the measurement space, which includes the following steps:

[0061] S1: Adjust the conduction state of each four-way valve 3 and the opening degree of the flow valve 4 so that a specified number of airflow conduits 2 in the airflow protection type optical fiber probe 100 are connected to the air source 5, and the remaining airflow conduits 2 remain closed. In this state, the measuring tube 12 is ventilated for a specified time to achieve self-cleaning of the measuring tube 12.

[0062] S2: Adjust the conduction state of each four-way valve 3 and the opening of the flow valve 4, first connect a number of designated first conduits 21 in the airflow protection type optical fiber probe 100 to the air source 5, then connect a number of designated second conduits 22 to the atmosphere, and keep the remaining airflow conduits 2 closed; thereby maintaining the two ends of the measuring cavity 123 in the measuring tube 12 at a balanced pressure state of the designated pressure to isolate dust.

[0063] In step S2, the number N1 of the first conduits 21 connected to the gas source 5, the number N2 of the second conduits 22 connected to the atmosphere, and the flow rate Q of the clean gas discharged by the flow valve 4 are pre-set according to the gas pressure P in the current measurement environment; the relevant parameters are obtained by querying a "P-N1-N2-Q mapping table"; the P-N1-N2-Q mapping table is a data comparison table established through pre-tested experimental data, which can characterize the mapping relationship between parameters P, N, N2 and Q under ideal dust prevention effect.

[0064] S3: placing the airflow protection type optical fiber probe 100 into the measurement environment, turning on the detection module 300, and completing the powder concentration detection of the measurement environment;

[0065] S4: After the powder concentration measurement is completed, the airflow protection type optical fiber probe 100 is taken out from the measurement environment, and step S1 is repeated. Then, the air source 5 is turned off, and all the airflow ducts 2 are switched to a closed state.

[0066] The measurement principle of the dust concentration measurement system provided in this embodiment is: the laser light source 301 is turned on by its driving module and emits an initial measurement light, the intensity of which is I The initial measurement light is transmitted through the transmission optical fiber 202 and reaches the outside of the optical fiber end mirror window of the measuring tube 12, and is emitted to the side of the reflective structure 11 of the measuring tube 12 as a detection signal. The detection signal first passes through the optical fiber end mirror window in the measuring tube 12 and enters the interior of the measuring tube 12. At the optical fiber end mirror window, the detection signal is first attenuated, which is recorded as .

[0067] Then, the detection signal passes through the fiber end airflow cavity 125, the fiber end gradually expanding cavity 124, the measuring cavity 123, the reflection end gradually expanding cavity 122, and the reflection end airflow cavity 121 in sequence. In this process, the fiber end airflow cavity 125, the fiber end gradually expanding cavity 124, the reflection end gradually expanding cavity 122, and the reflection end airflow cavity 121 are filled with a protective atmosphere formed by clean gas, and the detection signal is not affected by the powder here, and the attenuation can be ignored. In the detection cavity, the detection signal will encounter the aerosol diffused from the measurement environment, so the more serious attenuation in this part can be recorded as .

[0068] Next, the detection signal will pass through the reflection end mirror window, and the influence of the reflection end mirror window will be attenuated here. The attenuation here is recorded as After passing through the reflective end mirror window, the detection signal converges at the concave reflector 111 and then reflects back to the measuring tube 12. The attenuation at the concave reflector 111 can be expressed as .

[0069] Then, the reflected detection signal will pass through the reflection end mirror window again, which is the same as the detection signal passing through the reflection end mirror window last time. The attenuation in this process is recorded as Later, the detection signal will pass through the reflection end airflow cavity 121 and the reflection end gradually expanding cavity 122, the measurement cavity 123, the optical fiber end gradually expanding cavity 124, and the optical fiber end airflow cavity 125 in sequence. Similarly, the attenuation in this process is still recorded as Finally, the detection light will pass through the optical fiber end mirror window again, and then be received by the signal receiving module 302 on the other side of the optical fiber end mirror window. In this case, the detection signal is attenuated at the optical fiber end mirror window and is still recorded as .

[0070] In the signal detection process of the measuring device, for the signal receiving module 302, the echo signal received is the initial measurement light emitted by the light source passing through the , , , , , , After seven attenuations, the signal strength of the echo signal is I 0 The signal strength of the initial measurement light I The following equation is satisfied:

[0071] .

[0072] In the above formula, and Usually it is only related to the material and thickness of the optical fiber end mirror window and the reflection end mirror window. For a specified optical fiber probe, the two are constants. Similarly, It is only related to the structure, material and optical performance of the concave reflector 111 and is also a constant. I 0 The signal strength of the initial measurement light I The main differences between related. It is also related to the concentration of powder in the aerosol in the measurement environment diffused from the detection cavity, so the signal processing module can be combined with I 0 and I The current environment can be calculated Then according to Get the aerosol powder concentration in the current measurement environment.

[0073] In summary, combined with the above measurement principle and the performance description of the airflow protection type optical fiber probe 100 provided by the present invention, it can be found that:

[0074] For the conventional fiber optic probe type powder concentration sensor, the reflective end mirror window and the fiber optic end mirror window in the measuring tube 12 do not have a self-cleaning function. and The actual size is not a fixed value, but a variable that changes with the degree of dust contamination on the mirror surface. In addition, the reflection end airflow cavity 121, the reflection end gradually expanding cavity 122, the fiber end gradually expanding cavity 124 and the fiber end airflow cavity 125 inside the measuring tube 12 of the traditional fiber optic probe type powder concentration sensor are not filled with clean gas, so this area may also be invaded by the dust-carrying aerosol entering from the measuring cavity 123 and be contaminated. This will also cause the detection signal to attenuate in the inner cavity of the detection tube. It is not only related to the aerosol in the detection cavity, but may also be affected by the powder contamination caused by the aerosol entering from other cavities. In summary, when there is a high-concentration, high-speed dust-carrying aerosol in the measurement environment, the detection accuracy of the traditional fiber optic probe that does not have self-cleaning and protective atmosphere will drop significantly until it fails. The airflow-protected fiber optic probe 100 and its corresponding powder concentration measurement device provided by the present invention can achieve self-cleaning of the lens and use clean gas as a protective atmosphere to isolate the cavity outside the measurement cavity 123 from dust, thereby avoiding the above phenomenon. All of these make the product provided in the scheme of the present invention have good measurement accuracy and reliability even in a high-concentration, high-speed dust-carrying aerosol environment. It solves the problem of difficulty in long-term monitoring of powder concentration in confined spaces in the prior art.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An airflow protection type optical fiber probe, which is used to measure the concentration of powder, comprises a probe body; the probe body comprises a measuring tube; the internal cavity of the measuring tube comprises a reflection end airflow cavity, a reflection end gradually expanding cavity, a measuring cavity, an optical fiber end gradually expanding cavity and an optical fiber end airflow cavity which are interconnected and symmetrically distributed in a diabolo shape; the reflection end airflow cavity, the optical fiber end airflow cavity and the measuring cavity are cylindrical with constant caliber; the characteristics are: A plurality of first through holes and a plurality of second through holes connected to the airflow cavity at the reflection end are respectively provided on the measuring tube of the probe body; the first through holes and the second through holes are respectively located near the mirror window at the reflection end and near the gradually expanding cavity at the reflection end; a plurality of third through holes and a plurality of fourth through holes connected to the airflow cavity at the optical fiber end are also provided on the measuring tube; the third through holes and the fourth through holes are respectively located near the mirror window at the optical fiber end and near the gradually expanding cavity at the optical fiber end; various through holes are respectively distributed in an annular manner at different axial positions of the measuring pipeline; it also includes: A plurality of pairs of airflow ducts; the F-type ducts include a main pipe with one end open and two branch pipes perpendicular to the main pipe and connected to the main pipe; the airflow ducts are divided into a first duct and a second duct; each first duct is connected to one group of the first through holes and the third through holes; each second duct is connected to one group of the second through holes and the fourth through holes; and A plurality of four-way valves corresponding to the number of the gas flow conduits, the four-way valves being connected to the inlet of the gas source via a flow valve; the four-way valves are used to switch each gas flow conduit between three states: connected to the gas source of clean gas, connected to the atmosphere, and kept sealed; A controller is electrically connected to each four-way valve and a flow valve; the controller is realized by switching the connection state of each four-way valve: before measurement, a plurality of designated first conduits and second conduits are first connected to the gas source, and the remaining gas flow conduits are kept closed to achieve self-cleaning; then a plurality of designated first conduits and second conduits are respectively connected to the gas source and the atmosphere, and the remaining gas flow conduits are kept closed, so that the two ends of the measurement cavity are maintained in a balanced pressure state of a designated pressure; finally, the gas flow protection type optical fiber probe is placed in the measurement environment; after measurement, the probe is first taken out of the measurement environment, and then the self-cleaning step is performed, and finally all the gas flow conduits are closed.

2. The airflow protection optical fiber probe according to claim 1, characterized in that: The probe body includes a reflective structure, a measuring tube and a wire tube fixing part; The two ends of the measuring tube are sealed by a reflection end mirror window and an optical fiber end mirror window respectively; the measuring tube is also provided with a measuring hole connected to the measuring cavity; The wire tube fixing part is located on one side of the optical fiber end mirror window and is used to fix the transmission optical fiber and the airflow duct; the detection signal emitted by the transmission optical fiber is incident along the central axis of the internal cavity of the measuring tube; The reflective structural component is located on one side of the reflective end mirror window and is used to reflect the incident detection signal back along the central axis of the measuring tube.

3. The airflow protection type optical fiber probe according to claim 2, characterized in that: The first through hole and the third through hole correspond one to one, and are respectively located at designated positions in the circumference of the measuring tube; the second through hole and the fourth through hole correspond one to one, and are respectively located at designated positions in the circumference of the measuring tube; and the distribution positions of the first through hole and the third through hole and the second through hole and the fourth through hole along the circumference of the measuring tube do not overlap.

4. The airflow protection type optical fiber probe according to claim 1, characterized in that: The spray directions of the two branches in the first conduit are respectively directed to the reflection end mirror window and the optical fiber end mirror window; the spray directions of the two branches in the second conduit are respectively directed to the reflection end gradually expanding cavity and the optical fiber end gradually expanding cavity.

5. The airflow protection type optical fiber probe according to claim 4, characterized in that: The ends of the branch pipes in the first conduit and the second conduit are beveled or bent to achieve a designated spraying direction.

6. The airflow protection type optical fiber probe according to claim 1, characterized in that: The flow valve is used to adjust the flow of the clean gas introduced into the first conduit or the second conduit.

7. The airflow protection optical fiber probe according to claim 6, characterized in that: The controller is also used to dynamically adjust the flow rate of the clean gas output by the gas source according to the number of gas flow conduits connected to the gas source.

8. A powder concentration measurement system, characterized in that: It includes: The airflow-protected optical fiber probe according to any one of claims 1 to 7; Composite line tubes, including transmission optical fibers and air tubes; The transmission optical fiber adopts a Y-type optical fiber; and The detection module comprises an air source, a laser light source, a signal receiving module and a signal processing module; the air source is used to provide high-pressure clean gas; the air source is connected to one of the inlets of the four-way valve of each airflow duct in the airflow protection type optical fiber probe through the air pipe; the single-port side of the transmission optical fiber is installed at the optical fiber end mirror window of the measuring tube through a wire tube fixture, one end of the double-port side is connected to the laser light source, and the other end is connected to the signal receiving module; the laser light source is used to transmit a detection signal to the measuring tube through the transmission optical fiber; the signal receiving module is used to receive the echo signal received by the transmission optical fiber; the signal processing module is used to process the echo signal to obtain the powder concentration of the aerosol diffused into the measuring tube.

9. A method for measuring powder concentration, characterized in that: The powder concentration measurement system as claimed in claim 8 is used to measure the concentration of powder contained in the gas in the measurement space; the measurement method comprises the following steps: S1: Adjust the conduction state of each four-way valve and the opening of the flow valve so that a number of designated airflow ducts in the airflow protection optical fiber probe are connected to the air source, and the remaining airflow ducts remain closed; ventilate the measuring tube for a specified time to achieve self-cleaning of the measuring tube; S2: Adjust the conduction state of each four-way valve and the opening of the flow valve, first connect a number of designated first conduits in the airflow protection optical fiber probe to the air source, then connect a number of designated second conduits to the atmosphere, and keep the remaining airflow conduits closed; thereby maintaining the two ends of the measuring cavity in the measuring tube at a balanced pressure state of the designated pressure to isolate dust; S3: Place the airflow protection optical fiber probe into the measurement environment, turn on the detection module, and complete the powder concentration detection of the measurement environment; S4: After the powder concentration measurement is completed, the airflow protection type optical fiber probe is taken out from the measurement environment, and step S1 is repeated, and then the air source is turned off and all airflow ducts are switched to a closed state.

10. The method for measuring powder concentration according to claim 9, characterized in that: In step S2, the number N1 of the first conduits connected to the gas source, the number N2 of the second conduits connected to the atmosphere, and the flow rate Q of the clean gas discharged by the flow valve are pre-set according to the gas pressure P in the current measurement environment; the relevant parameters are obtained by querying a "P-N1-N2-Q mapping table"; the P-N1-N2-Q mapping table is a data comparison table established through pre-tested experimental data, which can characterize the mapping relationship between parameters P, N, N2 and Q under the ideal dust prevention effect.

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