A device and method for monitoring blockage of a filling pipe based on a low-frequency magnetic field

Abstract

The application discloses a device and method for monitoring blockage of filling pipeline based on low-frequency magnetic field, which comprises a pipeline to be monitored, a low-frequency magnetic field control circuit, a low-frequency magnetic field generating device, a monitoring mechanism and a feedback control module. The filling pipeline at the long-distance straight transportation is placed in the uniform magnetic field, and whether the pipeline is blocked is judged by monitoring the numerical change of the uniform magnetic field. Since the raw material for forming the filling slurry contains magnetic substances, the filling slurry is prone to segregation and precipitation at the long-distance transportation filling pipeline under the influence of gravity. At this time, the slurry concentration at the bottom of the pipeline gradually increases, the content of magnetic substances gradually increases, and the uniform magnetic field intensity around the pipeline is affected. Therefore, the filling pipeline is monitored according to the size of the magnetic field intensity. The device can realize non-contact monitoring of the filling pipeline, can accurately monitor the blockage of the filling pipeline and rapidly process it, is convenient and fast to install, and improves the service life of the filling pipeline and the operation efficiency of the filling operation.

Description

Technical Field

[0001] This invention relates to a device and method for monitoring blockages in filling pipelines based on low-frequency magnetic fields, belonging to the field of monitoring and treatment of blockages in mine filling pipelines. Background Technology

[0002] Coal, as my country's primary energy source and an important chemical raw material, saw its production increase from 2.15 billion tons in 2005 to 3.9 billion tons in 2020. With the continuous increase in coal mining volume, easily mined coal resources across the country are almost exhausted. Therefore, it is necessary to shift mining targets to "three-under" coalfields with abundant high-quality coal reserves. "Three-under" coalfields generally refer to coal stored under villages, railways, and water bodies. These typically require backfilling mining to ensure the stability of the goaf. Cemented backfilling mining is one of the commonly used methods. Its working principle mainly involves pumping a slurry, primarily composed of cement, coal gangue, fly ash, and additives mixed with water, into the goaf through backfilling pipelines. After curing and solidification, it supports the overlying rock strata. However, segregation and sedimentation are prone to occur during slurry transportation, especially over long distances. Due to gravity, large particles gradually accumulate at the bottom of the pipeline, causing blockages and, in severe cases, pipeline rupture, resulting in significant economic losses. Therefore, in order to ensure the safe operation of mine backfilling operations, it is necessary to monitor the status of the slurry during the transportation process in real time and deal with pipeline blockages in a timely manner to prevent a series of impacts caused by pipeline blockages.

[0003] Currently, there is extensive research on monitoring technology for filled pipelines both domestically and internationally. Based on the installation location of the monitoring device and whether it affects the pipeline's foundation design, these technologies are broadly categorized into two types: contact monitoring and non-contact monitoring. Methods that typically involve installing sensors inside the pipeline or require altering the original pipeline size and structure are classified as contact monitoring methods, such as pressure sensors, electromagnetic flowmeters, and resistivity sensors. Chinese patent CN202210629246.X discloses an online rheological testing method for transporting solid waste paste slurry in pipelines. This method utilizes two pressure sensors and a resistivity tomography electrode sensor for monitoring. When the slurry flows stably inside the tested pipeline, the pressure and slurry velocity distribution curves are measured and recorded. The shear stress distribution expression at any point on the pipeline cross-section is obtained, and a more accurate slurry rheological model is constructed based on the obtained data, providing support for monitoring technology in filled pipelines. Chinese patent CN201810984338.3 discloses a test device and method for monitoring the segregation of paste-filled slurry in pipelines. It mainly uses a resistivity measuring device installed on the inner wall of the pipeline to monitor the segregation state of the filling slurry. The resistivity measuring device includes a measuring electrode, a multiplexer, a multi-channel resistivity testing module, and a data acquisition and processing module. The measuring electrode is installed on the inner wall of the pipeline, and the wire passes through a through-hole and is sequentially connected to the multiplexer, the multi-channel resistivity testing module, and the data acquisition and processing module to form an overall monitoring circuit system. The above-mentioned contact-type monitoring devices typically install the sensor inside the pipeline and require modification to the pipeline size or structure, resulting in high costs and inconvenience for widespread use. Another type of non-contact monitoring device generally does not require changes to the original pipeline structure. The measuring sensor and other materials are installed on the outside of the monitoring pipeline, allowing direct monitoring of the internal conditions of the pipeline, such as ultrasonic monitoring. Chinese patent CN201710174967.5 discloses a device and method for monitoring blockage in paste-filled pipelines. This device has a magnetic material concentration testing device installed on the outside of the pipeline. During use, a certain proportion of magnetite sand needs to be added to the filling paste. The blockage is determined by monitoring the concentration of the magnetic material inside the pipeline. In addition, Chinese patent CN201710174436.6 discloses a non-invasive device and method for monitoring blockage in paste-filled pipelines. This device mainly places the transmitting and receiving ends of an ultrasonic sensor on both sides of the pipeline. Different wave velocities are calculated by measuring the signals to reflect the flow of the filling slurry inside the pipe. While these methods are convenient and quick, and do not require replacing the original pipeline, the overall monitoring accuracy is low. To achieve the desired monitoring effect, some filling material needs to be added to the slurry, which increases the cost and hinders widespread application.

[0004] In conclusion, monitoring of mine backfill pipelines is of great significance to the backfilling industry. Therefore, it is necessary to seek green and efficient innovative technologies for pipeline monitoring devices and methods, and to develop a new device and method based on low-frequency magnetic field monitoring for monitoring and handling backfill pipeline blockages. This could effectively reduce backfilling costs, improve monitoring efficiency and response speed, more quickly determine pipeline blockage conditions, and comprehensively solve the problem of backfill pipeline blockages. Summary of the Invention

[0005] The present invention aims to provide a device and method for monitoring blockage in filling pipelines based on low-frequency magnetic fields, which can monitor the operation of filling pipelines and accurately determine blockage.

[0006] The principle of this invention is as follows: The filling pipe at a long-distance linear transport point is placed in a uniform magnetic field. Changes in the uniform magnetic field value are monitored to determine if blockage has occurred. Since the raw materials constituting the filling slurry contain charged metal ions, such as iron, aluminum, and calcium ions, after being stirred with water, the slurry is prone to segregation and precipitation at long-distance transport points due to gravity. At this time, the slurry concentration at the bottom of the pipe gradually increases, and the accumulation of metal ions leads to a gradual increase in the content of magnetic material at the bottom of the pipe, affecting the strength of the uniform magnetic field around the pipe. Therefore, the filling pipe can be monitored based on the magnitude of the magnetic field strength. This invention provides a non-contact monitoring mechanism. During transport, the slurry undergoes segregation and precipitation, and the density of the deposited material at the bottom of the pipe gradually increases. The composition of all materials in the slurry increases at the deposition site. Therefore, changes in the magnetic field value are monitored to determine if the filling slurry has accumulated; the monitoring accuracy is high. Furthermore, in practical applications, the addition of magnetic materials can be considered to improve monitoring accuracy.

[0007] This invention provides a device for monitoring blockage in filling pipes based on low-frequency magnetic field, including a low-frequency magnetic field control circuit, a low-frequency magnetic field generator, a monitoring mechanism, and a feedback control module;

[0008] The pipeline to be monitored is arranged along a long horizontal straight transport path in the goaf area; the low-frequency magnetic field control circuit is connected to the low-frequency magnetic field generator, and the uniform magnetic field is arranged outside the pumping filling pipeline to be monitored. The pumping pipeline is located at the center horizontal position of the uniform magnetic field. The monitoring mechanism is installed on both sides of the pipeline in the horizontal direction and connected to the feedback control module, thereby realizing the monitoring and blockage of the filling pipeline.

[0009] The low-frequency magnetic field control circuit consists of a function generator, a sliding rheostat, a benchtop digital multimeter, and a power supply. The function generator provides sinusoidal signals of different amplitudes and frequencies for the low-frequency magnetic field. The positive wire in the circuit on one side of the coil is connected to the sliding rheostat, and the benchtop digital multimeter is connected in parallel with the sliding rheostat. The voltage across the sliding rheostat can be monitored and adjusted using the benchtop digital multimeter. The power supply connects to each electrical appliance and provides power support for it.

[0010] The low-frequency magnetic field generator consists of a Helmholtz coil and a coil insulation support. Two wires led out from the low-frequency magnetic field control circuit are respectively connected to the two conductor coils of the Helmholtz coil. The coil insulation support is used to fix the position and angle of the two conductor coils to ensure the stability of the uniform magnetic field generated.

[0011] The monitoring mechanism consists of two probes and an insulating mounting bracket. The probes are installed on both sides of the pipeline to be monitored in the horizontal direction, in the monitoring area of ​​a uniform magnetic field, and are responsible for monitoring the changes in the magnetic field strength near the pipeline. The probes are fixed by the insulating mounting bracket.

[0012] The feedback control module mainly consists of a PC computer, a PLC, and a filling pump. The signal output by the probe is connected to the PC computer via an optical cable. The PC computer processes and analyzes the transmitted data to determine whether the pipeline is blocked. It can also control the filling pump to adjust the pumping flow rate through the PLC to quickly deal with the pipe blockage problem.

[0013] In this invention, the device for monitoring blockages in filling pipelines based on low-frequency magnetic fields is uniformly and continuously arranged along a long horizontal straight transport path in the goaf area, which can realize the monitoring and precise location of pipeline blockages.

[0014] In the aforementioned device, the pipeline to be monitored is arranged in a long-distance straight transport section and is composed of multiple pipeline sections of equal length, facilitating pipeline installation and subsequent maintenance and replacement. Each pipeline section is 7–15 meters long, with an inner radius of 7.5 cm and a thickness of 1.5 cm. The pipeline to be monitored is made of acrylic or PVC to reduce the impact on low-frequency magnetic fields and improve monitoring accuracy. The multiple pipeline sections are connected by flanges, with long screws passing through the flanges of two adjacent pipelines and secured with bolts. The long screws and nuts in the monitoring area are also made of acrylic or PVC, materials that have minimal impact on magnetic field strength.

[0015] In the above-mentioned device, while meeting the requirements for slump and compressive strength of the filling slurry, conductive materials can be added to the slurry to increase the conductivity of the mixed material, such as sodium sulfate, sodium chloride, calcium chloride, etc. In order to save costs, some industrial waste, such as steel slag, can also be used, as long as it contains metallic conductive elements.

[0016] In the above-mentioned device, the output frequency provided by the function generator can be set from 1.0Hz to 25.0MHz; the frequency of the low-frequency magnetic field is set from 10.0Hz to 400.0kHz, and is usually monitored using three frequency bands: 10.0kHz, 50.0kHz, and 100.0kHz.

[0017] In the above device, the maximum resistance of the sliding rheostat is 50Ω, and the maximum allowable current is 1.5A.

[0018] In the aforementioned device, the Helmholtz coils are a pair of parallel and interconnected coaxial circular coils with the same current direction and magnitude within both coils. The distance between the coils is equal to the radius of the circular coils, ensuring a broad and uniform magnetic field is generated near the midpoint of their common axis. The output port of the function generator is connected to the circular Helmholtz coils, which have a radius of 0.25m. A benchtop digital multimeter is connected to the two ends of the sliding rheostat in the circuit. The low-frequency magnetic field can be adjusted by monitoring the voltage reading across the two ends. The specific calculation principle is as follows.

[0019] According to the calculation standard for low-frequency magnetic fields:

[0020]

[0021] In equation (1), H is the magnetic field strength at the center of the coil, in A / m (1A / m=1.256μT); N is the number of turns of the coil; I is the magnitude of the current passing through the coil, in A; and r is the radius of the coil, in m.

[0022] From the above formula, we can derive:

[0023]

[0024] The actual required voltage can be obtained according to Ohm's law:

[0025] U=I·R (3)

[0026] In equation (3), R is the resistance of the sliding rheostat, in Ω; U is the voltage across the sliding rheostat monitored by the benchtop multimeter, in V.

[0027] In the aforementioned device, the monitoring of low-frequency magnetic field strength at different frequencies can be achieved by adjusting the number of turns of the Helmholtz coil. The coil turns typically range from 3 to 50. A typical 5-turn coil can monitor the frequency response from 10.0Hz to 100.0kHz. When monitoring frequencies of 50Hz or 60Hz, a 40-turn coil can be used for specialized measurement, providing high accuracy and good performance. Ordinary copper wire can be used as the material for the Helmholtz coil.

[0028] In the above device, the Helmholtz coil is installed in the coil housing. The coil housing has an outward-facing annular groove that is coaxial with the center of the coil housing at both ends, and is used to wind coils with different numbers of turns. The coil housing is made of non-metallic insulating materials such as plastic or PVC. To satisfy the uniform magnetic field generated by the Helmholtz coil, the inner radius of the annular groove is 24.5 cm, the outer radius is 25.5 cm, and the groove depth is 2 cm.

[0029] In the above-mentioned device, a set of Helmholtz coils is installed on the outside of each set of pipelines to be monitored. Each set consists of two parallel Helmholtz coils. The upper and lower ends of the coils are connected by parallel insulating brackets. The material used is the same as the coil shell, such as plastic or PVC, which are non-metallic insulating materials.

[0030] In the above device, a pair of probes are installed on both sides of the pipeline to be monitored. The probes are installed at equal intervals in the center of each coil group, about 3cm away from the outer wall of the pipeline, to prevent the monitoring accuracy of the pipe wall from being affected by the vibration of the pipeline when they are close to the pipeline.

[0031] In the aforementioned device, the probe has a cubic structure with a height of approximately 9.0 cm. The probe transmits data via optical fiber and has an internal shielded power supply, which is charged through the probe's charging interface. To ensure monitoring effectiveness, the probe charging cable casing is made of shielded insulating material. During filling operations, the power supply stops charging the probe, and the probe uses its built-in shielded power supply to provide monitoring data to the PC computer via optical fiber. When not filling operations are in progress, the charging cable is connected to charge the probe, preventing charging during monitoring from affecting the monitoring results.

[0032] In the aforementioned device, since the raw materials of the filling slurry are mostly conductive substances and contain a large amount of magnetic materials, based on the principle analysis, the blockage status of the pipeline can be reflected by measuring the magnitude of the magnetic field strength. Probes on both sides of the pipeline can monitor the time-domain and frequency-domain data of the field strength in real time, and perform real-time calculations based on the measured spectrum data to obtain the final stable value. With the slurry conveying direction set forward, i.e., the left and right probes respectively, the magnetic field strength values ​​on the left and right sides of the empty filling pipeline are recorded as H. 0left With H 0right During normal operation, the magnetic field strength on both sides of the filling pipe is H. 1left With H 1right At this point, the influence rate β of the magnetic field strength of the probes on both sides of the slurry conveying can be calculated separately. left and β right The calculation is as follows.

[0033]

[0034]

[0035] In equations (4)-(5), r p R is the radius of the filling pipe, and R is the radius of the Helmholtz coil (coil spacing).

[0036] Because the slurry mix ratio varies in pipelines and the conditions during transport are diverse, the location and nature of blockages are also unpredictable. Therefore, the impact rate of the most significant blockage is selected for calculation to obtain the extreme value β of the impact rate under this condition. max .

[0037] β max ={β left ,β right} (6)

[0038] After obtaining the above parameters, the pipe blockage can be determined. If either equation (7) or equation (8) is satisfied, the filling pipe can be determined to be blocked.

[0039] H′ left ≥H 1left ·(1+β max +ξ) (7)

[0040] H′ right ≥H 1right ·(1+β max +ξ) (8)

[0041] In equations (7)-(8), H′ left With H′ right These represent the real-time monitoring values ​​of the magnetic field strength of the probes on both sides of the pipeline; ξ is the error influence parameter of the monitoring, which is usually taken as 0.05-0.1.

[0042] This invention provides a method for monitoring blockage in filling pipes based on low-frequency magnetic fields, comprising the following steps:

[0043] S1: Install the filling pipeline and fix the monitoring mechanism. Connect the power supply line and signal transmission line. Install the monitoring mechanism at the long-distance straight transport point, so that the pipeline passes through the central axis of the Helmholtz coil of the monitoring mechanism. Connect the power supply to the function generator, benchtop digital multimeter, probe, PC computer, and PLC respectively to provide power for their operation. Connect the function generator to both ends of the Helmholtz coil with wires, and connect a sliding rheostat in series in the circuit on one side. Connect the benchtop digital multimeter in parallel on both sides of the sliding rheostat. Connect the probe to the PC computer through optical fiber, and connect the PC computer to the PLC to complete the overall wiring of the monitoring mechanism.

[0044] S2: Use a benchtop digital multimeter to adjust the low-frequency magnetic field output signal, and calculate whether the measured field strength meets the standard value according to formula (1)-(3) and the monitoring agency parameters; when the measurement result meets the standard calculated value, monitoring can be carried out directly; when the measurement result does not meet the standard value, the input parameters need to be adjusted.

[0045] The standard value is calculated by connecting the parameters of the circuit components. When the desired magnetic field value is 3μT and the range of the sliding rheostat is 0-20Ω, the voltage range corresponding to the linear magnetic field strength at 50Hz and 60Hz is 0.1-0.6V.

[0046] S3: Prepare the filling slurry. A magnetic additive can be added to improve the monitoring effect. Generally, the mass ratio of coal gangue to water is 4-6, the mass ratio of cement to fly ash is 0.4-0.6, and the mass ratio of water to fly ash is 0.2-0.5. Mix the coal gangue, cement, fly ash and water according to the ratio. Add 80-120g of magnetic additive to each kilogram of the prepared slurry to complete the preparation of the filling slurry.

[0047] S4: No-load monitoring, record the required judgment parameter data; when the power is turned on, record the magnetic field strength value H of the probes on both sides of the pipeline before the slurry pumping starts. 0left With H 0right ;

[0048] S5: Begin filling operation and monitor the pipeline in real time; record the magnetic field strength H values ​​of the probes on both sides of the pipeline when no segregation or sedimentation of the slurry occurs. 1left With H 1right ;

[0049] S6: When the slurry segregates, the density of the slurry accumulated at the bottom of the pipe gradually increases. At this time, the magnetic material in the material gradually accumulates, which has a greater impact on the uniform magnetic field between the coils. The magnetic field strength affected by the blockage of the pipe is monitored in real time by probes on both sides of the pipe. The magnetic field strength influence rate and magnetic field strength extreme value are calculated by PC computer, and the blockage of the filling pipe is determined according to the calculation formulas (7) and (8).

[0050] S7: When the judgment formula determines that the pipeline is blocked, the PC computer transmits a signal to the PLC to control the filling pump to increase the pumping flow rate to deal with the pipeline blockage; when the monitored field strength data gradually decreases and falls below the calculated monitoring value, the PC computer transmits a signal to the PLC again to control the filling pump to decrease the pumping flow rate, thus completing one pipeline blockage treatment.

[0051] S8: When pipe blockage occurs again, repeat steps S6 and S7 to achieve closed-loop control of pipeline monitoring and blockage handling.

[0052] The beneficial effects of this invention are:

[0053] (1) This invention provides a device and method for monitoring blockage in filling pipes based on low-frequency magnetic field. It can determine whether the pipe is blocked by monitoring the change in magnetic field strength near the pipe. The method is easy to install, has high monitoring accuracy, can accurately locate the blockage location, and controls the pump flow rate through PC computer and PLC feedback, thus solving the problem of monitoring and handling blockage in filling pipes.

[0054] (2) The device of the present invention adopts non-contact monitoring, which does not require redesigning the pipe size and shape. It only needs to be installed on the outside of the pipe to realize the monitoring of pipe blockage. The device and method can improve the service life of the pipe and the operating efficiency of the filling operation, and save a lot of the cost of cleaning the pipe. It is of great significance in the monitoring and treatment of pipe blockage in filling pipes. Attached Figure Description

[0055] Figure 1 This is a three-dimensional structural diagram of the device for monitoring blockages in filling pipes based on low-frequency magnetic fields in this invention.

[0056] Figure 2 This is a plan view of the device for monitoring blockages in filling pipes based on low-frequency magnetic fields in this invention.

[0057] Figure 3 This is a front view of a set of monitoring devices connected to the outside of the pipeline in this invention.

[0058] Figure 4 This is a cross-sectional view of a set of monitoring devices outside the pipeline in this invention.

[0059] Figure 5 This is a schematic diagram of the Helmholtz coil structure dimensions in this invention.

[0060] In the diagram: 1 is the pipeline to be monitored, 2 is the coil, 3 is the coil housing, 4 is the probe, 5 is the coil insulation support, 6 is the insulation mounting bracket, 7 is the mounting base, 8 is the power supply, 9 is the function generator, 10 is the sliding rheostat, 11 is the benchtop digital multimeter, 12 is the PC computer, 13 is the PLC, 14 is the parallel insulation support, 15 is the flange, 16 is the long screw, and 17 is the bolt. A indicates the direction of power supply; B indicates the direction of slurry flow. Detailed Implementation

[0061] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0062] Example 1:

[0063] like Figures 1-5 As shown, a device for monitoring blockage in filling pipes based on low-frequency magnetic field includes a low-frequency magnetic field control circuit, a low-frequency magnetic field generator, a monitoring mechanism, and a feedback control module.

[0064] The pipeline to be monitored, 1, is arranged along a long horizontal straight transport path in the goaf area; the low-frequency magnetic field control circuit is connected to the low-frequency magnetic field generator, and the uniform magnetic field is arranged outside the pumping filling pipeline to be monitored. The pumping pipeline is located at the center horizontal position of the uniform magnetic field. The monitoring mechanism is installed on both sides of the pipeline in the horizontal direction and connected to the feedback control module, thereby realizing the monitoring and blockage of the filling pipeline.

[0065] The low-frequency magnetic field control circuit consists of a function generator 9, a sliding rheostat 10, a benchtop digital multimeter 11, and a power supply 8. The function generator provides sinusoidal signals of different amplitudes and frequencies for the low-frequency magnetic field. The positive wire in the circuit on one side of the coil is connected to the sliding rheostat, and the benchtop digital multimeter is connected in parallel with the sliding rheostat. The voltage across the sliding rheostat can be monitored and adjusted using the benchtop digital multimeter. The power supply connects to each electrical appliance and provides power support for it.

[0066] The low-frequency magnetic field generator consists of a Helmholtz coil 2 and a coil insulation support 5. Two wires led out from the low-frequency magnetic field control circuit are respectively connected to the two conductor coils of the Helmholtz coil. The coil insulation support is used to fix the position and angle of the two conductor coils to ensure the stability of the uniform magnetic field generated.

[0067] The monitoring mechanism consists of two probes 4 and an insulating bracket 6. The probes 4 are installed on both sides of the pipeline 1 to be monitored in the horizontal direction, in the monitoring area of ​​the uniform magnetic field, and are responsible for monitoring the changes in the magnetic field strength near the pipeline. They are fixed by the insulating bracket 6.

[0068] The feedback control module mainly consists of a PC computer 12, a PLC 13, and a filling pump. The signal output by the probe is connected to the PC computer via an optical cable. The PC computer processes and analyzes the transmitted data to determine whether the pipeline is blocked. It can also control the filling pump to adjust the pumping flow rate through the PLC to quickly handle the pipe blockage problem.

[0069] In this invention, the device for monitoring blockages in filling pipelines based on low-frequency magnetic fields is uniformly and continuously arranged along a long horizontal straight transport path in the goaf area, which can realize the monitoring and precise location of pipeline blockages.

[0070] In the aforementioned device, the pipeline to be monitored is arranged in a long-distance straight transport section and is composed of multiple pipeline sections of equal length, facilitating pipeline installation and subsequent maintenance and replacement. Each pipeline section is 7–15 meters long, with an inner radius of 7.5 cm and a thickness of 1.5 cm. The pipeline to be monitored is made of acrylic or PVC to reduce the impact on low-frequency magnetic fields and improve monitoring accuracy. The multiple pipeline sections are connected by flanges, with long screws passing through the flanges of two adjacent pipelines and secured with bolts. The long screws and nuts in the monitoring area are also made of acrylic or PVC, materials that have minimal impact on magnetic field strength.

[0071] In the above-mentioned device, while meeting the requirements for slump and compressive strength of the filling slurry, conductive materials can be added to the slurry to increase the conductivity of the mixed material, such as sodium sulfate, sodium chloride, calcium chloride, etc. In order to save costs, some industrial waste, such as steel slag, can also be used, as long as it contains metallic conductive elements.

[0072] In the above-mentioned device, the output frequency provided by the function generator can be set from 1.0Hz to 25.0MHz; the frequency of the low-frequency magnetic field is set from 10.0Hz to 400.0kHz, and is usually monitored using three frequency bands: 10.0kHz, 50.0kHz, and 100.0kHz.

[0073] In the above device, the maximum resistance of the sliding rheostat is 50Ω, and the maximum allowable current is 1.5A.

[0074] In the aforementioned device, the Helmholtz coils are a pair of parallel and connected coaxial circular coils with the same direction and magnitude of current in both coils. The distance between the coils is equal to the radius of the circular coils, ensuring a broad and uniform magnetic field is generated near the midpoint of their common axis. Figure 5 The output port of the function generator is connected to a circular Helmholtz coil with a radius of 0.25m. A benchtop digital multimeter is connected to the two ends of the sliding rheostat in the circuit. The low-frequency magnetic field can be adjusted by monitoring the voltage reading at both ends. The specific calculation principle is as follows.

[0075] According to the calculation standard for low-frequency magnetic fields:

[0076]

[0077] In equation (1), H is the magnetic field strength at the center of the coil, in A / m (1A / m=1.256μT); N is the number of turns of the coil; I is the magnitude of the current passing through the coil, in A; and r is the radius of the coil, in m.

[0078] From the above formula, we can derive:

[0079]

[0080] The actual required voltage can be obtained according to Ohm's law:

[0081] U=I·R (3)

[0082] In equation (3), R is the resistance of the sliding rheostat, in Ω; U is the voltage across the sliding rheostat monitored by the benchtop multimeter, in V.

[0083] In the aforementioned device, the monitoring of low-frequency magnetic field strength at different frequencies can be achieved by adjusting the number of turns of the Helmholtz coil. The coil turns typically range from 3 to 50. A typical 5-turn coil can monitor the frequency response from 10.0Hz to 100.0kHz. When monitoring frequencies of 50Hz or 60Hz, a 40-turn coil can be used for specialized measurement, providing high accuracy and good performance. Ordinary copper wire can be used as the material for the Helmholtz coil.

[0084] In the above device, the Helmholtz coil 2 is installed in the coil housing 3. The coil housing 3 has an annular groove facing outward, which is coaxial with the center of the coil housing at both ends, and is used to wind coils with different numbers of turns. The coil housing is made of non-metallic insulating materials such as plastic or PVC. In order to satisfy the uniform magnetic field generated by the Helmholtz coil, the inner radius of the annular groove is 24.5cm, the outer radius is 25.5cm, and the groove depth is 2cm.

[0085] In the above-mentioned device, a set of Helmholtz coils is installed on the outside of each set of pipelines to be monitored. Each set consists of two parallel Helmholtz coils. The upper and lower ends of the coils are connected by parallel insulating brackets. The material used is the same as the coil shell, such as plastic or PVC, which are non-metallic insulating materials.

[0086] In the above device, a pair of probes are installed on both sides of the pipeline to be monitored. The probes are installed at equal intervals in the center of each coil group, about 3cm away from the outer wall of the pipeline, to prevent the monitoring accuracy of the pipe wall from being affected by the vibration of the pipeline when they are close to the pipeline.

[0087] In the aforementioned device, the probe has a cubic structure with a height of approximately 9.0 cm. The probe transmits data via optical fiber and has an internal shielded power supply, which is charged through the probe's charging interface. To ensure monitoring effectiveness, the probe charging cable casing is made of shielded insulating material. During filling operations, the power supply stops charging the probe, and the probe uses its built-in shielded power supply to provide monitoring data to the PC computer via optical fiber. When not filling operations are in progress, the charging cable is connected to charge the probe, preventing charging during monitoring from affecting the monitoring results.

[0088] In the aforementioned device, since the raw materials of the filling slurry are mostly conductive substances and contain a large amount of magnetic materials, based on the principle analysis, the blockage status of the pipeline can be reflected by measuring the magnitude of the magnetic field strength. Probes on both sides of the pipeline can monitor the time-domain and frequency-domain data of the field strength in real time, and perform real-time calculations based on the measured spectrum data to obtain the final stable value. With the slurry conveying direction set forward, i.e., the left and right probes respectively, the magnetic field strength values ​​on the left and right sides of the empty filling pipeline are recorded as H. 0left With H 0right During normal operation, the magnetic field strength on both sides of the filling pipe is H. 1left With H 1right At this point, the influence rate β of the magnetic field strength of the probes on both sides of the slurry conveying can be calculated separately. left and β right The calculation is as follows.

[0089]

[0090]

[0091] In equations (4)-(5), r p R is the radius of the filling pipe, and R is the radius of the Helmholtz coil (coil spacing).

[0092] Because the slurry mix ratio varies in pipelines and the conditions during transport are diverse, the location and nature of blockages are also unpredictable. Therefore, the impact rate of the most significant blockage is selected for calculation to obtain the extreme value β of the impact rate under this condition. max .

[0093] β max ={β left ,β right} (6)

[0094] After obtaining the above parameters, the pipe blockage can be determined. If either equation (7) or equation (8) is satisfied, the filling pipe can be determined to be blocked.

[0095] H′ left ≥H 1left ·(1+β max +ξ) (7)

[0096] H′ right ≥H 1right ·(1+β max +ξ) (8)

[0097] In equations (7)-(8), H′ left With H′ right These represent the real-time monitoring values ​​of the magnetic field strength of the probes on both sides of the pipeline; ξ is the error influence parameter of the monitoring, which is usually taken as 0.05-0.1.

[0098] This invention provides a method for monitoring blockage in filling pipes based on low-frequency magnetic fields, comprising the following steps:

[0099] S1: Install the filling pipeline and fix the monitoring mechanism. Connect the power supply line and signal transmission line. Install the monitoring mechanisms at 8m intervals along the long-distance straight transport route, ensuring the pipeline passes through the central axis of the Helmholtz coil of the monitoring mechanism. Figure 2 Connect the power supply to the function generator, benchtop digital multimeter, probe, PC, and PLC respectively to provide power for their operation; connect the function generator to both ends of the Helmholtz coil via wires, and connect a sliding rheostat in series in the circuit on one side; connect the benchtop digital multimeter in parallel on both sides of the sliding rheostat; connect the probe to the PC via optical fiber, and connect the PC to the PLC to complete the overall wiring of the monitoring mechanism. Figure 3 .

[0100] S2: Use a benchtop digital multimeter to adjust the low-frequency magnetic field output signal. Calculate whether the measured field strength meets the standard value according to equations (1)-(3) and the monitoring mechanism parameters. After testing and calculation, when the desired magnetic field value is 3μT and the resistance of the sliding rheostat is 10.76Ω, the voltage corresponding to the 50Hz and 60Hz linear magnetic field strength should be 0.224V. See Table 1 for the voltage table corresponding to the specific magnetic field strength. When the measurement result meets the standard calculated value, monitoring can be performed directly. If the measurement result does not meet the standard value, the input parameters need to be adjusted.

[0101] Table 1

[0102] Desired magnetic field value 50Hz corresponding voltage 60Hz corresponding voltage 3μT 0.224V 0.224V 5μT 0.374V 0.374V 8μT 0.599V 0.599V 10μT 0.748V 0.748V 30μT 2.248V 2.248V 50μT 3.742V 3.742V 80μT 5.987V 5.987V 100μT 7.483V 7.483V

[0103] Table 1 shows the voltmeter values ​​corresponding to the 50Hz and 60Hz linear magnetic field strengths in this invention.

[0104] The desired magnetic field value refers to the magnitude of the magnetic field generated in the magnetic field generator. It is achieved by adjusting some parameters of the circuit to ensure that the generated magnetic field strength value is an integer, which facilitates the monitoring and comparison of numerical changes.

[0105] S3: Prepare the filling slurry. A magnetic additive can be added to improve the monitoring effect. Mix coal gangue, cement, fly ash, and water in a mass ratio of 5:2:4:1. Add 100g of iron powder per kilogram of the prepared slurry to complete the preparation of the filling slurry.

[0106] S4: No-load monitoring, record the required judgment parameter data; when the power is turned on, record the magnetic field strength value H of the probes on both sides of the pipeline before the slurry pumping starts. 0left With H 0right ;

[0107] S5: Begin filling operation and monitor the pipeline in real time; record the magnetic field strength H values ​​of the probes on both sides of the pipeline when no segregation or sedimentation of the slurry occurs. 1left With H 1right ;

[0108] S6: When the slurry segregates, the density of the slurry accumulated at the bottom of the pipe gradually increases. At this time, the magnetic material in the material gradually accumulates, which has a greater impact on the uniform magnetic field between the coils. The magnetic field strength affected by the blockage of the pipe is monitored in real time by probes on both sides of the pipe. The magnetic field strength influence rate and magnetic field strength extreme value are calculated by PC computer, and the blockage of the filling pipe is determined according to the calculation formulas (7) and (8).

[0109] S7: When the judgment formula determines that the pipeline is blocked, the PC computer transmits a signal to the PLC to control the filling pump to increase the pumping flow rate to deal with the pipeline blockage; when the monitored field strength data gradually decreases and falls below the calculated monitoring value, the PC computer transmits a signal to the PLC again to control the filling pump to decrease the pumping flow rate, thus completing one pipeline blockage treatment.

[0110] S8: When pipe blockage occurs again, repeat steps S6 and S7 to achieve closed-loop control of pipeline monitoring and blockage handling.

Claims

1. A method for monitoring the blockage of a filling pipe based on a low-frequency magnetic field, using a device for monitoring the blockage of a filling pipe based on a low-frequency magnetic field, characterized in that The method comprises the following steps: S1: install the filling pipe and fix the monitoring mechanism, connect the power supply circuit and the signal transmission circuit, install the monitoring mechanism at the long-distance straight transportation position, so that the pipe passes through the center axis position of the monitoring mechanism Helmholtz coil; connect the power supply with the function generator, the table digital multimeter, the probe, the PC computer and the PLC respectively to supply power for their work; the function generator is connected with the two ends of the Helmholtz coil through wires, and a sliding resistor is connected in series in the circuit on one side; the table digital multimeter is connected in parallel on both sides of the sliding resistor; the probe is connected with the PC computer through an optical fiber, and the PC computer is connected with the PLC to complete the wiring of the whole monitoring mechanism; S2: adjust the low-frequency magnetic field output signal by using the table digital multimeter, and calculate whether the measured field strength meets the standard value according to formulas (1)-(3) and the monitoring mechanism parameters; when the measurement result meets the standard calculation value, directly monitor; when the measurement result does not meet the standard value, adjust the input parameters for adjustment; （1） In the above formula, H is the magnetic field strength at the center of the coil, with units of A / m; N is the number of turns of the coil; I is the current through the coil, with units of A; r is the radius of the coil, with units of m; According to Ohm's law, the actual required voltage is obtained: （2） S3: prepare the filling slurry, and add part of the magnetic admixture to improve the monitoring effect; （3） In the above formula, R is the resistance of the slide rheostat, unit ; V is the voltage monitored by the bench multimeter across the slide rheostat, unit V; S6: when the slurry is separated, the slurry density at the bottom of the pipe gradually increases, at this time, the magnetic substances in the material gradually accumulate, which affects the uniform magnetic field between the coils; the magnetic field strength affected by the pipe blockage is monitored in real time by the probes on both sides of the pipe, the magnetic field strength influence rate and the magnetic field strength extreme value are calculated by the PC computer, and the determination of the filling pipe blockage is realized according to the calculation formulas (7) and (8); S4: Idling monitoring, recording required decision parameter data; switch on power supply, record the magnetic field strength value of the probes on both sides of the pipeline when the slurry has not started pumping With ; S5: Start filling operation, real-time monitoring of the pipeline; record the magnetic field strength values of the probes on both sides of the pipeline when the slurry does not precipitate With ; Influence rate of magnetic field intensity of both sides of slurry conveying probe and The calculation is as follows: （4） （5） In the above equation, R is the radius of the Helmholtz coil; After the above parameters are obtained, the determination of the pipe blockage is continued, when one of the following formulas (7) and (8) is met, it is determined that the filling pipe is blocked: Because of the different proportion of pipeline slurry and the diversification of state during transportation, the position and situation of blockage are irregular, so the influence rate of the large blockage is selected to calculate and get the extreme value of influence rate under this state : （6） S7: when it is determined that the pipe is blocked through the judgment formula, the PC computer transmits a signal to the PLC to control the filling pump to increase the pumping flow to handle the pipe blockage; when the monitoring field strength data gradually decreases and is lower than the calculated monitoring value, the PC computer transmits a signal to the PLC again to control the filling pump to reduce the pumping flow, that is, the treatment of the pipe blockage is completed once; （7） （8） In formula (7)-(8), With Respectively, the real-time monitoring value of the magnetic field strength of the probe on both sides of the pipeline; Error influence parameter for monitoring, value 0.05-0.1; S8: when the pipe blockage occurs again, repeat steps S6 and S7 to realize the closed-loop control of pipe monitoring and pipe blockage treatment; The device for monitoring the filling pipe blockage based on the low-frequency magnetic field comprises a low-frequency magnetic field control circuit, a low-frequency magnetic field generating device, a monitoring mechanism and a feedback control module; The pipe to be monitored is arranged on the long-distance horizontal straight transportation path in the goaf; the low-frequency magnetic field control circuit is connected with the low-frequency magnetic field generating device, the uniform magnetic field is arranged outside the pump type filling pipe to be monitored, the pump type pipe is located at the center horizontal position of the uniform magnetic field, the monitoring mechanism is installed on both sides of the pipe in the horizontal direction and is connected with the feedback control module, so that the monitoring and blockage of the filling pipe are realized. ​ The low-frequency magnetic field control circuit is composed of a function generator, a slide rheostat, a desk digital multimeter and a power supply; the function generator provides sine wave signals with different amplitudes and different frequencies for the low-frequency magnetic field; the positive lead in the circuit on one side of the coil is connected with the slide rheostat, the desk digital multimeter is connected in parallel with the slide rheostat, the voltage across the slide rheostat is monitored through the desk digital multimeter, and the slide rheostat is adjusted; the power supply connects various electrical appliances and provides power support for them; The low-frequency magnetic field generating device is composed of a Helmholtz coil and a coil insulation support, two wires led out by the low-frequency magnetic field control circuit are connected to the two conductor coils of the Helmholtz coil respectively, and the coil insulation support is used to fix the positions and angles of the two conductor coils to ensure the stability of the generated uniform magnetic field; The monitoring mechanism is composed of two probes and an insulating fixing frame, the probes are installed on the two sides of the pipeline to be monitored in the horizontal direction and in the monitoring area of the uniform magnetic field, and are responsible for monitoring the change of the magnetic field intensity near the pipeline, and are fixed through the insulating fixing frame; The feedback control module is composed of a PC computer, a PLC and a filling pump, the signals output by the probes are connected to the PC computer through an optical cable, the transmitted data are processed and analyzed by the PC computer, it is judged whether the pipeline is blocked, and the filling pump is controlled by the PLC to adjust the pumping flow to quickly handle the pipe blocking problem.

2. The method of claim 1, wherein: The pipeline to be monitored is arranged in a long-distance straight transportation section and is composed of multiple pipe sections with equal lengths, the length of each pipe section is 7-15 meters, the inner diameter of the pipeline is 7.5 cm, and the pipe thickness is 1.5 cm; the material of the pipeline to be monitored is selected from acrylic material or PVC material to reduce the influence on the low-frequency magnetic field and improve the monitoring accuracy; the multiple pipe sections are connected through flanges, long screws are used to pass through the flanges of two adjacent pipe sections, and are fixed through bolts; the long screws and nuts in the monitoring area are also selected from acrylic material or PVC material which has little influence on the magnetic field intensity.

3. The method for monitoring a blockage of a filling conduit based on a low frequency magnetic field according to claim 1, characterized in that: The output frequency provided by the function generator is set at 1.0 Hz-25.0 MHz; the frequency of the low-frequency magnetic field is set at 10.0 Hz-400.0 kHz; the maximum resistance value of the sliding rheostat is 50 , and the maximum current value allowed to pass is 1.5 A.

4. The method for monitoring a blockage of a filling conduit based on a low frequency magnetic field according to claim 1, characterized in that: The Helmholtz coil is a pair of coaxial circular coils parallel to each other and connected, the current directions in the two coils are consistent and the sizes are the same; the distance between the two coils is equal to the radius of the circular coil to ensure that a wide uniform magnetic field is generated near the midpoint of the common axis; the output port of the function generator is connected with the circular Helmholtz coil, the coil radius is 0.25 m, the desk digital multimeter is connected across the slide rheostat in the circuit, and the low-frequency magnetic field is adjusted by monitoring the voltage reading.

5. The method for monitoring a blockage of a filling conduit based on a low frequency magnetic field according to claim 1, characterized in that: The number of turns of the Helmholtz coil is adjusted to realize the monitoring of the low-frequency magnetic field intensity at different frequencies, the range of the number of turns of the coil is 3-50 turns; the 5-turn coil can be used for frequency response monitoring of 10.0 Hz-100.0 kHz, when the monitoring frequency is 50 Hz or 60 Hz, the 40-turn coil is used for special monitoring, and the monitoring accuracy is high; the material of the Helmholtz coil is copper wire.

6. The method of monitoring a blockage of a filling conduit based on a low frequency magnetic field according to claim 5, characterized in that: The Helmholtz coil is installed in the coil shell, the coil shell has a circular groove in the outward direction, which is coaxial with the centers of the coil shells at both ends, and is used for winding coils with different numbers of turns; the coil shell is made of plastic or PVC, in order to meet the generation of the uniform magnetic field by the Helmholtz coil, the cross-sectional size of the circular groove is: inner diameter 24.5 cm, outer diameter 25.5 cm, groove depth 2 cm.

7. The method for monitoring blockage of a filling conduit based on low frequency magnetic field according to claim 1, characterized in that: A set of Helmholtz coils are arranged outside the pipeline to be monitored, each set of coils is composed of two parallel Helmholtz coils, the upper and lower ends of the coils are connected by parallel insulation support, the material is the same as the coil shell, which is plastic or PVC; A pair of probes are installed on both sides of the pipeline to be monitored, the probes are installed at the center of each set of coils at equal intervals, and the distance from the outer wall of the pipeline is 3cm, so as to prevent the monitoring accuracy of the pipeline wall from being affected due to the vibration of the pipeline when being close to the pipeline.

8. The method of claim 7, wherein the method is based on monitoring the filling pipe for blockage by low frequency magnetic field. The probe is a cube structure with a height of 9.0cm; the probe transmits data through an optical fiber and has a shielding power supply inside, and is charged through a charging interface of the probe.

9. The method for monitoring blockage of a filling conduit based on low frequency magnetic field according to claim 1, characterized in that: The filling slurry includes coal gangue, cement, fly ash and water; the mass ratio of coal gangue to water is 4-6, the mass ratio of cement to fly ash is 0.4-0.6, and the mass ratio of water to fly ash is 0.2-0.5; the coal gangue, cement, fly ash and water are stirred according to the ratio to complete the preparation of the filling slurry; The magnetic admixture includes sodium sulfate, sodium chloride, calcium chloride or steel slag; the addition amount is: 80-120g of the magnetic admixture is added in each kilogram of prepared slurry.

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