A multi-channel flow velocity measurement system and method based on range gating

Abstract

The application discloses a multi-channel flow velocity measuring system and method based on distance gating, and belongs to the field of river and channel acoustic flow velocity monitoring. The system comprises a flow measuring instrument host, a flow measuring instrument auxiliary machine, a multi-channel switching device and an electro-acoustic unit. The host and the auxiliary machine are synchronized by means of GPS second pulse and exchange data through a wireless serial port. The multi-channel switching device is internally provided with a first single-chip microcomputer and a bus communication interface, and the electro-acoustic unit is internally provided with a second single-chip microcomputer for in-water detection. The signal processing module is loaded with distance gating timing logic, and the arrival of signals at the window is calculated according to the sound channel distance and the water sound velocity, and the receiving channels are turned on in time to filter out timing misalignment reflection interference. The method collects the forward and reverse flow propagation time by alternately switching the emission state of the host and the auxiliary machine, and calculates the cross-section flow velocity by the time difference method. The channel on time is adjustable, and the machine parameters can be started and stopped and the measuring points can be expanded in cascade. The application has the advantages of high anti-water clutter interference, high measurement efficiency, flexible channel configuration, and is suitable for long-term automatic monitoring of the layered flow velocity of the whole cross-section of a river or channel.

Description

Technical Field

[0001] This invention belongs to the field of acoustic velocity monitoring technology for river and canal fluids, specifically relating to a multi-channel velocity measurement system and method based on distance gating. Background Technology

[0002] The mainstream method for measuring river flow velocity currently used is the ultrasonic time-of-flight method. The basic principle is to calculate the fluid velocity by determining the time difference between upstream and downstream sound wave propagation. The direct time-of-flight method measurement principle is as follows: Figure 1 As shown, traditional single-depth time-of-flight measurement equipment can only obtain the flow velocity at a single point at a fixed depth in a water body. The flow velocity in natural rivers and channels is distributed in a gradient along the water depth. Single-point measurement cannot represent the average flow velocity of the entire cross-section, resulting in large measurement errors and making it difficult to meet the accuracy requirements of hydrological monitoring and water conservancy scheduling.

[0003] To achieve full-section layered velocity measurement, existing multi-channel flow measurement equipment generally uses hardware multiplexers to fix and switch channels, which has the following drawbacks: First, the number of channels is predetermined by the hardware circuit, making it impossible to flexibly add or remove measurement points according to river depth and monitoring needs. Expanding channels requires hardware modification, resulting in high construction costs. Second, hardware polling and channel switching takes a long time, and single-cycle measurement is time-consuming, making it difficult to support high-frequency, large-scale continuous monitoring. Third, the presence of silt, aquatic plants, and floating debris in the river causes sound waves to reflect multiple times between the riverbed and water impurities, creating noise interference. Fixed, normally open receiving channels simultaneously collect effective signals and interference reflections, causing distortion in propagation time calculations and poor velocity measurement stability. Summary of the Invention

[0004] The purpose of this invention is to provide a distance-gated multi-channel flow velocity measurement system and method to solve the problems of existing fixed hardware switching multi-channel flow measurement equipment, such as fixed channels, slow switching speed, severe water reflection interference, and insufficient cross-sectional measurement accuracy.

[0005] To solve the above problems, the technical solution of the present invention is as follows: A multi-channel flow velocity measurement system based on distance gating includes a flow meter main unit and a flow meter auxiliary unit. The flow meter main unit and the flow meter auxiliary unit are interconnected via a wireless serial communication link and configured with a GPS module to achieve time synchronization. Each of them is connected to a set of multi-channel switching devices, and each set of multi-channel switching devices is externally connected to several electroacoustic units. The multi-channel switching device is equipped with a bus communication interface and a first microcontroller, which is connected to a multi-channel analog switch chip. Both the flow meter main unit and the flow meter auxiliary unit are equipped with a signal processing module. The signal processing module has built-in distance gating timing calculation logic, which is used to calculate the theoretical arrival time of the acoustic signal of each channel based on the propagation distance of the sound channel and the sound velocity of the water body, and superimpose the channel transmission timing offset to generate the channel gating activation time. The corresponding receiving channel is activated only during the signal arrival window to filter out timing misalignment reflection interference signals.

[0006] Furthermore, both the main unit and auxiliary unit of the flow meter integrate a wireless serial port module and a receiving signal conditioning module, and the main unit of the flow meter is equipped with an external data output interface; the GPS module outputs a periodic second pulse synchronization signal, which serves as a unified timing reference for the main unit and auxiliary unit of the flow meter to transmit, select channels, and acquire signals.

[0007] Furthermore, the bus communication interface is used to transmit a transmit drive signal carrying a channel identifier and a receive gating control command carrying a channel identifier; the first microcontroller is used to parse the gating control command, control multiple analog switches through encoding logic to complete the target channel conduction, and supports setting the channel conduction duration through system configuration parameters, with the upper limit of the duration value constrained by the working interval of adjacent channels; multiple sets of multi-channel switching devices support cascading expansion, and the number of measurement channels is flexibly configured based on the local parameter encoding, and the shutdown or failure of a single channel does not affect the normal operation of the remaining channels.

[0008] Furthermore, the electroacoustic unit incorporates a second microcontroller, a water immersion status detection component, and a power amplifier tube; the water immersion status detection component is a water immersion switch or a water pressure sensor; the second microcontroller receives an coded signal with a channel identifier via a bus, and determines whether to initiate transmission based on the water immersion detection result; it only controls the power amplifier tube to emit an acoustic signal when its own channel identifier matches the command channel identifier and it detects complete water immersion.

[0009] Furthermore, the wireless serial port module transmits two types of data bidirectionally: one is the working mode switching control command issued by the host to the auxiliary machine, and the other is the arrival time measurement data of the acoustic signals of each channel transmitted back by the auxiliary machine to the host. The input terminal of the receiving signal conditioning module is connected to the output terminal of the multi-channel analog switch, which is used to amplify and filter the weak underwater acoustic signals received by each channel before transmitting them to the signal processing module to complete the propagation duration identification.

[0010] A multi-channel velocity measurement method based on distance gating includes the following steps: S1. The main unit and auxiliary unit of the flow meter rely on the second pulse synchronization signal output by the GPS module to complete the timing alignment. The system defaults to the main unit as the main transmitter and the auxiliary unit as the signal receiver. S2. After the synchronization pulse is triggered, the host sends out transmission commands with channel codes in the order of channel identifiers at fixed time intervals, driving the corresponding electroacoustic transducer to emit acoustic signals; at the same time, it sends a mode switching command to the auxiliary machine through the wireless communication link, notifying the auxiliary machine to switch to the transmission working mode in the next synchronization pulse cycle. S3, the auxiliary signal processing unit calculates the theoretical arrival time of each channel signal based on the channel distance and the sound speed in the water, and superimposes the channel transmission timing offset to obtain the selection start time of each channel; after reaching the corresponding time, it controls the multi-channel switching component to conduct the corresponding receiving channel, maintains the preset conduction time, and then turns off the channel, sequentially collects the effective acoustic signals of all channels and records the downstream propagation time of each channel, and wirelessly transmits the measurement data back to the host. S4. When the next set of synchronization pulses arrives, the auxiliary machine responds to the switching command issued by the host and switches to the transmitting end, driving its own electroacoustic transducer unit to emit acoustic signals in sequence according to the same time interval. S5. The host reuses the same distance gating timing operation logic as S3, and opens each receiving channel in time-division to collect the reverse acoustic signal and record the reverse propagation time of each channel. S6. The main unit calculates the stratified flow velocity at each water depth measuring point based on the propagation time of the same channel in the downstream and upstream directions using the time difference method. S7. Repeat S2 to S5 to complete multiple full measurement cycles, remove abnormal data through filtering algorithm, and output stable stratified flow velocity results; S8. The host transmits layered flow velocity, cross-sectional average flow velocity, and equipment operating status data to the outside through the external data output interface.

[0011] Furthermore, the channel conduction duration mentioned in step S3 can be modified online. The upper limit of the duration value is constrained by the working interval of adjacent channels. When the water body interference is strong, the conduction duration can be reduced to block clutter from entering. When the water body is clean and the interference is weak, the conduction duration can be increased to ensure the complete acquisition of effective signals.

[0012] Furthermore, any number of channel identifiers can be turned off through preset parameters on the machine. The transmission and reception timing will automatically skip the turned-off channels, while the remaining enabled channels will maintain a fixed timing interval and operate in an orderly manner.

[0013] Furthermore, before any electroacoustic transducer unit performs transmission, it determines the immersion status through a water immersion status detection component. If it is not immersed in water, the power amplifier drive circuit is locked to prevent the transmission of acoustic signals.

[0014] Furthermore, by cascading multiple sets of multi-channel switching components and updating the local channel coding configuration, the number of measurement channels can be expanded, and the newly added channels are synchronously adapted to the distance gating timing operation logic.

[0015] The beneficial effects of this invention are as follows: 1. Relying on the distance-gated timing mechanism, the receiving channel is only opened during the time period when the target underwater acoustic signal arrives. There is a time difference between the arrival time of the interference signal generated by water debris reflection and multiple sound wave reflections and the effective signal. When the interference signal arrives, the channel is in a closed state, which completely shields the noise from the timing level and greatly reduces the speed measurement jump error.

[0016] 2. All depth channels can complete two signal acquisitions, one downstream and one upstream, within one GPS second pulse cycle. The propagation time of all layered measurement points can be acquired in a single cycle, resulting in a high measurement rate and making it suitable for high-frequency continuous hydrological data acquisition and big data storage and analysis scenarios.

[0017] 3. The channel number and activation status are all configured by the system code, and idle measuring points can be turned off as needed; the multi-channel switching device supports hardware cascading, and only the channel configuration parameters of the local machine need to be adjusted to add measuring depth measuring points without replacing the main control hardware, which can be adapted to various working conditions such as shallow channels and deep rivers.

[0018] 4. The electroacoustic unit has a built-in water immersion detection function. When not submerged in water, it automatically shields the power amplifier's emission to prevent damage to the transducer from air vibration. A single channel failure or default shutdown does not affect the normal timing acquisition of other channels, making the equipment highly fault-tolerant.

[0019] 5. The use of GPS second pulses to unify the transmission and reception of the main and auxiliary units eliminates the propagation time measurement error caused by the clock offset at both ends, resulting in higher accuracy in time difference calculation.

[0020] 6. High versatility: The gate width, emission interval, and underwater sound velocity threshold can all be dynamically adjusted by the machine, making it suitable for different water quality environments such as clear water and turbid water with high sediment. Attached Figure Description

[0021] The invention will be further described below with reference to the accompanying drawings: Figure 1 Schematic diagram of the principle of single-point velocity measurement using the direct time difference method; Figure 2 : Schematic diagram of the overall composition of the 8-channel measurement system of the present invention; Figure 3 Block diagram of the internal hardware composition of the flow meter main unit and auxiliary unit; Figure 4 : Schematic diagram of distance gating multi-channel measurement timing based on GPS second pulse synchronization; Figure 5 Schematic diagram of the hardware circuit principle of the multi-channel switching device; Figure 6 Schematic diagram of the control circuit for the electroacoustic unit. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] A multi-channel flow velocity measurement system based on distance gating includes a flow meter main unit, a flow meter auxiliary unit, two sets of multi-channel switching devices, and several electroacoustic units. The overall system composition in 8-channel mode is as follows: Figure 2 As shown, a wireless serial communication link is established between the main galvanometer and the auxiliary galvanometer to achieve bidirectional data interaction. Both devices are equipped with GPS modules to achieve global timing consistency. The main galvanometer and the auxiliary galvanometer are each connected to a multi-channel switching device. Each multi-channel switching device is externally connected to multiple electroacoustic units, which are deployed at different water depths in the river to achieve layered measurement point deployment across the cross-section.

[0024] The multi-channel switching device is internally configured with a bus communication interface and a first microcontroller. The signal output terminal of the first microcontroller is connected to a multi-channel analog switch chip, which serves as the hardware execution unit for turning on and off the signals of each channel. In this embodiment, the multi-channel analog switch chip is preferably the ADG509 chip, and the bus communication interface is preferably the 485 communication interface.

[0025] Both the main unit and auxiliary unit of the current meter integrate signal processing modules. These modules carry the core distance gating timing logic of this invention, used to solve the problem of water reflection clutter interference. The timing control principle is as follows: Figure 4 As shown: the timing operation logic retrieves the propagation distance of the corresponding channel of each electroacoustic unit and the sound speed of the water body at the scene, and calculates the theoretical arrival time of the single-channel acoustic signal from the transmitter to the receiver; at the same time, it superimposes the fixed transmission timing offset of each channel to generate an independent gating and opening time for each channel; the system only controls the multi-channel analog switch to conduct the corresponding receiving channel within the calculated signal arrival window, and keeps the channel off during other periods.

[0026] The propagation path of the interference sound waves generated by the reflection of silt, aquatic plants, and riverbed in the water is different from that of the effective velocity measurement sound waves, and there is a significant deviation in the propagation time. The time when the interference signal arrives at the receiving end is not within the effective signal selection window. At this time, the receiving channel is in the off state, and the interference signal cannot enter the back-end signal acquisition circuit. The timing misaligned reflected interference signal is completely filtered out from the timing level, which solves the technical problems of clutter interference and poor velocity measurement accuracy of traditional equipment.

[0027] Furthermore, the internal hardware composition principles of the flow meter main unit and the flow meter auxiliary unit are as follows: Figure 3 As shown: In addition to the built-in signal processing module, the main unit of the flow meter also integrates a wireless serial port module, a receiving signal conditioning module, and an external data output interface; the auxiliary unit of the flow meter integrates a wireless serial port module and a receiving signal conditioning module. The hardware architecture of the main unit and the auxiliary unit of the flow meter is highly unified, with only the main unit adding an external data output interface, reducing equipment production and spare parts maintenance costs.

[0028] The system's GPS module continuously outputs a periodic second pulse synchronization signal. This second pulse serves as the unified timing reference for the entire system. All acoustic signal transmission actions, channel selection and conduction actions, and underwater acoustic signal acquisition actions are based on the rising edge of the second pulse as the timing start point. The local timers and delay calculation logic of the flowmeter main unit and auxiliary unit are synchronously reset, ensuring complete alignment of the transmission and reception timings at both ends and eliminating timing deviations caused by drift of the local crystal oscillators at both ends. During operation, each GPS second pulse triggers the downstream transmission process of the main unit, and the next GPS second pulse synchronously triggers the transmission process of the auxiliary unit. Relying on the unified second pulse ensures the matching of downstream and upstream propagation time acquisition timings, improving the accuracy of time-difference method flow velocity calculation from the hardware level.

[0029] Furthermore, the hardware circuit principle of the multi-channel switching device is as follows: Figure 5 As shown. The bus communication interface transmits two types of command signals bidirectionally: a transmit drive signal carrying the channel identifier and a receive gating control command carrying the channel identifier; the first microcontroller has a built-in encoding and parsing program, which receives the gating control command sent by the bus, identifies the target channel identifier, and outputs a level to control the multiplexer to complete the corresponding channel conduction; the first microcontroller supports setting the channel conduction duration through system configuration parameters, and the upper limit of the duration is constrained by the working interval of adjacent channels, adapting to different water quality conditions such as clear water and turbid water with high sediment.

[0030] Multiple sets of multi-channel switching devices reserve cascade communication interfaces, supporting hardware serial cascading to expand the number of measurement points; the number of system channels is flexibly configured based on local parameter encoding, and any channel identifier can be turned off individually, with the turned-off channel skipping the entire transmission and reception process; if a channel has a hardware failure and no signal return, the system automatically removes the measurement data of that channel, while the remaining channels are unaffected and maintain normal timing acquisition.

[0031] When the water body has high sediment content and strong clutter interference, the channel conduction time is reduced to compress the receiving window and block timing-misaligned interference signals. When the water body is clean and interference is weak, the channel conduction time is increased to ensure that effective acoustic signals can be completely acquired. When it is necessary to add water depth measurement points, a new multi-channel switching device can be cascaded. Only the channel configuration parameters of the instrument itself need to be adjusted to add measurement points, without modifying the main control hardware of the current meter host and auxiliary unit. This enables controllable channel parameters, cascaded hardware, and no system shutdown in case of single-channel failure, solving the problem that traditional fixed channels cannot flexibly adapt to different river depths.

[0032] Furthermore, the control circuit principle of the electroacoustic unit is as follows: Figure 6 As shown. Each electroacoustic unit has a built-in independent second microcontroller, a water immersion status detection component, and a power amplifier tube; the water immersion status detection component uses a water immersion switch or a water pressure sensor to collect the underwater immersion status of the electroacoustic unit in real time.

[0033] The second microcontroller receives the coded signal with channel identifier from the system via the bus communication interface, and synchronously reads the immersion signal collected by the water entry status detection component. It determines whether to start the acoustic signal transmission under two conditions: only when the channel identifier carried by the coded signal matches its own preset channel identifier, and the water entry detection component's judgment unit is completely immersed in the water, will the second microcontroller output a drive signal to turn on the power amplifier tube to transmit the acoustic signal; if either condition is not met, the second microcontroller directly locks the power amplifier tube drive circuit, prohibiting the transmission action.

[0034] When the electroacoustic unit is hoisted or inspected, it is exposed to the air. The water entry detection component provides a signal indicating that it has not entered the water. The second microcontroller shields the power amplifier tube drive to prevent the power amplifier tube from burning out due to idling. The unit only launches after the launch command corresponding to its own channel number arrives and the unit is fully submerged. This structure enables intelligent control of the electroacoustic unit's launch, protects the hardware from airborne launches, extends the service life of underwater equipment, and reduces the frequency of field maintenance.

[0035] Furthermore, the wireless serial port module establishes a bidirectional data transmission channel between the main unit and auxiliary unit of the current meter, carrying two types of core data interaction: the first type is downlink control data from the main unit, i.e., the working mode switching control command sent by the main unit to the auxiliary unit, used to notify the auxiliary unit to switch to the transmission working mode in the next second pulse cycle; the second type is uplink measurement data from the auxiliary unit, i.e., after the auxiliary unit completes a round of full-channel acquisition, it packages and sends back the arrival time of the acoustic signal of each channel and the corresponding channel identifier to the main unit for unified processing and storage. Wireless data transmission is completed only in the idle interval between two GPS second pulses, without occupying the transmission and gating acquisition sequence, avoiding wireless signal interference with underwater acoustic acquisition, eliminating the need to lay underwater wired synchronization cables, and simplifying on-site wiring construction in the river channel.

[0036] The input of the receiving signal conditioning module is directly connected to the output of the multiplexer analog switch, serving as a pre-processing unit for the underwater acoustic signal before it enters the signal processing module. When the channel selection window is open, the weak underwater acoustic signal is sent to the conditioning module via the multiplexer analog switch. The module integrates filtering circuits, signal amplification circuits, and analog-to-digital conversion circuits to filter out on-site power frequency electromagnetic interference, amplify weak underwater acoustic echoes, and convert the analog underwater acoustic signal into a standard digital signal before transmitting it to the signal processing module. The signal processing module identifies the signal peak value and accurately records the acoustic signal propagation time. This improves the signal-to-noise ratio of the underwater acoustic signal and reduces the measurement error of the propagation time.

[0037] A distance-gated multi-channel velocity measurement method completes a full-section layered velocity measurement in eight time-series steps. The specific process includes the following steps: S1. Global timing synchronization initialization: After the device is powered on and completes its self-test, the main unit and auxiliary unit of the flow meter rely on the second pulse synchronization signal output by the GPS module to complete global timing alignment. The system presets a basic working mode, in which the main unit acts as the main transmitter to perform the transmission and acquisition cycle, and the auxiliary unit continuously receives acoustic signals by default, waiting for the second pulse to trigger the formal measurement process.

[0038] S2. Host-based sequential acoustic signal transmission: The rising edge of the second pulse triggers a transmission process. The host generates coded transmission commands according to the channel identifier in ascending order at preset fixed time intervals. The commands are sent to the multi-channel switching device via the bus to drive the corresponding numbered electroacoustic unit to transmit acoustic signals. Simultaneously, the mode switching command is sent to the auxiliary unit via the wireless serial port module to inform the auxiliary unit to switch to the transmission working mode in the next second pulse cycle.

[0039] S3. The auxiliary unit performs downstream signal reception based on distance gating: The signal processing module inside the auxiliary unit calls the distance gating timing operation logic to calculate the theoretical arrival time of the acoustic signals of all channels respectively, and superimposes the channel transmission timing offset to obtain the gating start time of each channel; after reaching the corresponding start time, it controls the first microcontroller in the multi-channel switching device to turn on the corresponding receiving channel, maintains the standard gating gate width set by the device's built-in parameter control logic, and then automatically turns off the corresponding receiving channel; it traverses all measurement point signals in channel order to complete the acquisition, records the downstream propagation time of each channel, and transmits the packaged signal back to the host storage via the wireless serial port module.

[0040] S4. Auxiliary machine reverse current acoustic signal time division transmission: When the next set of GPS second pulses arrives, the auxiliary machine responds to the mode switching command issued by S2, switches to the transmitting end, and drives its own side electroacoustic unit to transmit reverse current water acoustic signals according to the same fixed time interval and the channel identifier sequence.

[0041] S5. Main unit receives reverse current signal based on distance gating: The main unit reuses the exact same distance gating timing operation logic as S3, and opens each receiving channel in time-division to collect the reverse current acoustic signal emitted by the auxiliary machine, and records the reverse current propagation time corresponding to all channels.

[0042] S6. Single-cycle stratified flow velocity solution: The main unit retrieves the downstream and upstream propagation times of the same channel, and uses the ultrasonic time difference method to calculate the stratified flow velocity at the water depth measuring point. The calculation is performed on all channels one by one to obtain the single-point flow velocity data of all depths of the cross section.

[0043] S7. Multi-cycle data smoothing: Repeat S2 to S5 in a loop to continuously collect data from multiple complete measurement cycles; The host has a built-in moving average filtering algorithm to automatically remove abnormal measurement values ​​with jumps, and outputs low-fluctuation and stable stratified flow velocity results after smoothing.

[0044] S8. External output of measurement data: The host computer outputs all measurement and equipment status data, such as the stratified flow velocity of each channel, the cross-sectional weighted average flow velocity, the equipment operating status, and the GPS second pulse time sequence status, to the upstream hydrological acquisition terminal and the host computer through its own configured external data output interface.

[0045] The above process forms a fully automated closed-loop velocity measurement process. It relies on the distance gating mechanism to achieve high-precision upstream and downstream data acquisition, and automatically completes the entire process of time synchronization, signal acquisition, velocity calculation, data smoothing, and external output. No manual operation is required, making it suitable for long-term hydrological monitoring scenarios in rivers.

[0046] Furthermore, during the distance selection process in step S3, the channel conduction duration is a parameter that can be modified online on the device itself. The upper limit of the duration value is constrained by the working interval of adjacent channels. After modifying the parameters, there is no need to restart the device, and the next round of GPS second pulse cycle will take effect directly.

[0047] On-site adaptation method: When the water has high sediment content, drastic sound velocity fluctuations, and a large amount of floating debris, the channel conduction time should be reduced to a smaller value to compress the receiving window and block noise interference; when the water is clear, has few impurities, and the sound velocity is stable, the conduction time can be increased to a larger value to ensure complete reception of effective acoustic signals. This design can flexibly balance signal reception integrity and equipment anti-interference capability, broadening the water quality adaptability range of the equipment.

[0048] Furthermore, in step S2, the host time-sharing transmission process has a channel opening and closing configuration item in the device's built-in parameter control logic. Operators can check any idle channel identifier in the device's parameter configuration area. When the device is running in sequence, the program automatically skips the transmission command corresponding to the closed channel and selects the reception sequence. The remaining enabled channels still work in an orderly manner according to the fixed time interval, and there will be no timing disorder or offset.

[0049] Exemplary operating condition: In an 8-channel deployment system, channels 2 and 5 are shut down via preset parameters. The device only executes the transmission and acquisition process for channels 1, 3, 4, 6, 7, and 8, with the transmission interval between each channel remaining uniform. This design can shut down useless measurement points in shallow water and shallow channel conditions, reducing the device's power consumption and data storage requirements. The timing operation remains stable and is unaffected by channel reduction.

[0050] Furthermore, before the entire acoustic signal transmission process is executed, the second microcontroller inside each electroacoustic unit reads the immersion signal output by the water immersion status detection component in real time. If the detection determines that the electroacoustic unit is not fully immersed in the water, the second microcontroller directly locks the power amplifier tube drive circuit, shields the transmission drive signal, and does not transmit acoustic signals. Only when full immersion is detected and the channel identifier matches will the system respond to the transmission command. This design relies on the second microcontroller to achieve hardware protection, prevents damage to the electroacoustic unit from no-load transmission, and reduces the probability of equipment failure and maintenance costs in the field.

[0051] Furthermore, if it is necessary to add more measuring points for river cross-section water depth measurement, multiple sets of multi-channel switching devices can be cascaded in hardware. After the hardware cascading is completed, only the local channel coding configuration parameters need to be updated to assign independent channel identifiers to the measuring points on the newly added multi-channel switching devices, thus completing the expansion of the number of measurement channels. There is no need to replace the main control hardware of the flowmeter host or auxiliary unit, nor to modify the original circuit structure. The newly added channels synchronously adapt to the distance gating timing operation logic and participate in the upstream and downstream acoustic signal acquisition and stratified flow velocity calculation process in unison with the original channels. This design can realize the expansion of measurement points without hardware modification, has low construction costs for river upgrades and renovations, and the equipment can be adapted to rivers of different water depths for long-term reuse.

[0052] The embodiments described in this specification are merely examples of implementations of the inventive concept. The scope of protection of this invention should not be considered as limited to the specific forms stated in the embodiments. The scope of protection of this invention also extends to equivalent technical means that can be conceived by those skilled in the art based on the inventive concept.

Claims

1. A multi-channel flow velocity measurement system based on distance gating, characterized in that, The device includes a main unit and an auxiliary unit for a flow meter. The main unit and the auxiliary unit are interconnected via a wireless serial communication link and configured with a GPS module to achieve time synchronization. The main unit and the auxiliary unit are each connected to a multi-channel switching device, which is externally connected to several electroacoustic units. The multi-channel switching device has a built-in bus communication interface and a first microcontroller, which is connected to a multi-channel analog switch chip. Both the main unit and the auxiliary unit have a signal processing module. The signal processing module has built-in distance gating timing calculation logic, which is used to calculate the theoretical arrival time of the acoustic signal of each channel based on the propagation distance of the sound channel and the sound speed of the water body, and to superimpose the channel transmission timing offset to generate the channel gating opening time. The corresponding receiving channel is turned on only during the signal arrival window to filter out timing misalignment reflection interference signals.

2. The multi-channel flow velocity measurement system based on distance gating according to claim 1, characterized in that, Both the main unit and auxiliary unit of the flow meter integrate a wireless serial port module and a receiving signal conditioning module. The main unit of the flow meter is equipped with an external data output interface. The GPS module outputs a periodic second pulse synchronization signal, which serves as a unified timing reference for the main unit and auxiliary unit of the flow meter to transmit, select channels, and acquire signals.

3. The multi-channel flow velocity measurement system based on distance gating according to claim 1, characterized in that, The bus communication interface is used to transmit transmit drive signals carrying channel identifiers and receive gating control commands carrying channel identifiers; the first microcontroller is used to parse the gating control commands.

4. The multi-channel flow velocity measurement system based on distance gating according to claim 1, characterized in that, The electroacoustic unit has a built-in second microcontroller, a water immersion status detection component, and a power amplifier tube. The water immersion status detection component is either a water immersion switch or a water pressure sensor. The second microcontroller receives coded signals with channel identifiers via a bus and determines whether to start transmission based on the water immersion detection results. It only controls the power amplifier tube to emit acoustic signals when its own channel identifier matches the command channel identifier and it detects that the device is fully submerged in water.

5. A multi-channel flow velocity measurement system based on distance gating according to claim 2, characterized in that, The wireless serial port module transmits two types of data bidirectionally: one is the working mode switching control command sent by the host to the auxiliary machine, and the other is the arrival time measurement data of the acoustic signals of each channel transmitted back by the auxiliary machine to the host. The input terminal of the receiving signal conditioning module is connected to the output terminal of the multi-channel analog switch, which is used to amplify, filter and preprocess the weak underwater acoustic signals received by each channel before transmitting them to the signal processing module to complete the propagation time identification.

6. A method applied to the distance-gated multi-channel flow velocity measurement system according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The main unit and auxiliary unit of the flow meter rely on the second pulse synchronization signal output by the GPS module to complete the timing alignment. The system defaults to the main unit as the main transmitter and the auxiliary unit as the signal receiver. S2. After the second pulse is triggered, the host sends out transmission commands with channel codes in the order of channel identifiers at fixed time intervals, driving the corresponding electroacoustic unit to emit acoustic signals; at the same time, it sends a mode switching command to the auxiliary machine through the wireless serial communication link, notifying the auxiliary machine to switch to the transmission working mode in the next second pulse cycle. S3, the auxiliary signal processing module calculates the theoretical arrival time of each channel signal based on the channel distance and the sound speed in the water, and superimposes the channel transmission timing offset to obtain the selection start time of each channel; after reaching the corresponding time, it controls the multi-channel switching device to conduct the corresponding receiving channel, maintains the preset conduction time, and then turns off the channel, sequentially collects the effective acoustic signals of all channels and records the downstream propagation time of each channel, and transmits the measurement data back to the host through the wireless serial port; S4. When the next set of second pulses arrives, the auxiliary machine responds to the switching command issued by the host and switches to the transmitting end, driving its own side electroacoustic unit to emit acoustic signals in sequence according to the same time interval. S5. The host reuses the same distance gating timing operation logic as S3, and opens each receiving channel in time-division to collect the reverse acoustic signal and record the reverse propagation time of each channel. S6. The main unit calculates the stratified flow velocity at each water depth measuring point based on the propagation time of the same channel in the downstream and upstream directions using the time difference method. S7. Repeat S2 to S5 to complete multiple full measurement cycles, remove abnormal data through filtering algorithm, and output stable stratified flow velocity results; S8. The host transmits layered flow velocity, cross-sectional average flow velocity, and equipment operating status data to the outside through the external data output interface.

7. The multi-channel flow velocity measurement method based on distance gating according to claim 6, characterized in that, The channel conduction duration mentioned in step S3 can be modified online. The upper limit of the duration value is constrained by the working interval of adjacent channels. When the water body interference is strong, the conduction duration can be reduced to block clutter from entering. When the water body is clean and the interference is weak, the conduction duration can be increased to ensure the complete acquisition of effective signals.

8. The multi-channel flow velocity measurement method based on distance gating according to claim 6, characterized in that, By disabling any number of channel identifiers using preset parameters, the transmit and receive timing will automatically skip the disabled channels, while the remaining enabled channels will maintain a fixed timing interval and operate in an orderly manner.

9. A multi-channel flow velocity measurement method based on distance gating according to claim 6, characterized in that, Before any electroacoustic unit can transmit, it determines the immersion status through a water immersion detection component. If the unit is not submerged in water, the power amplifier tube drive circuit is locked to prevent the transmission of acoustic signals.

10. A multi-channel flow velocity measurement method based on distance gating according to claim 6, characterized in that, By cascading multiple sets of multi-channel switching devices and updating the local channel coding configuration, the number of measurement channels can be expanded, and the newly added channels are synchronously adapted to the distance gating timing operation logic.

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