A high-speed acquisition system and acquisition method applied to laser interference fringe signals of an optical absolute gravimeter

Abstract

The application discloses a kind of high-speed acquisition system and acquisition method applied to optical absolute gravimeter laser interference fringe signal, the system includes analog signal conditioning unit, analog-digital conversion unit, system core control unit, data cache unit, data transmission unit and measurement and control terminal processing display unit.The application is directed to laser interference fringe signal frequency is high, voltage amplitude is low, acquisition rate is fast, and absolute gravity precision measurement requires signal integrity, measurement precision is high, and the high-speed acquisition system of laser interference fringe signal of optical free-fall absolute gravimeter based on FPGA is designed, the advantage of FPGA parallel computation processing is fully utilized, in combination with serial bus transmission technology (USB) and FIFO cache technology, the processing time of acquisition system in interference fringe signal acquisition, storage and transmission etc. is greatly shortened.The application effectively improves the acquisition speed of absolute gravity, and provides basic guarantee for realizing dynamic measurement and monitoring of absolute gravity.

Description

Technical Field

[0001] This invention relates to the field of rapid measurement and research technology of absolute gravity, and in particular to a high-speed acquisition system and method for laser interference fringe signals applied to optical absolute gravimeters. Background Technology

[0002] Gravitational acceleration is a variable parameter. On the Earth's surface, gravitational acceleration varies with altitude, latitude and longitude, and is constantly affected by factors such as tides, polar motion, and air pressure. Gravitational acceleration is of great significance in fields such as metrology, aerospace, geophysics, navigation aids, and resource exploration.

[0003] An optical absolute gravimeter is a device that utilizes the principle of laser interference and employs a classic free-fall method. Using the laser wavelength as the reference for length measurement, a free-falling body with a cornerstone prism mounted at the top of a vacuum cavity is allowed to fall freely within the cavity. A laser beam reaches a beam splitter; one path serves as the reference beam, while the other acts as the measurement beam, forming an interference pattern perpendicularly upwards. The interference signal is converted from optical to electrical by a photodetector. Through a data acquisition system, combined with a rubidium atomic clock providing high-precision time and frequency signals, the interference fringe signal of the freely falling body is obtained. A double-sample zero-crossing sampling method is used to perform a secondary fitting of the time-displacement sequence where the interference signal amplitude is zero, yielding the gravitational acceleration value at the measured point.

[0004] With technological advancements and the objective demands of scientific experiments, various gravity application fields are no longer satisfied with static measurements of absolute gravity under static laboratory conditions. The need for mobile gravity observations in the field and rapid dynamic measurements of absolute gravity in the deep ocean is increasing daily. Compared to absolute gravity measurements under static laboratory conditions, the conditions of mobile and deep-sea dynamic absolute gravity measurements place higher demands and standards on data acquisition systems. This requires acquisition systems to be not only small in size and mass for easy portability, but also to have fast signal acquisition and processing speeds. Furthermore, they must overcome the adverse environmental factors of complex and changing conditions in the field, meet the requirements for long-term rapid dynamic field measurements, and solve the problems of data loss, control terminal lag, and large size and mass that are difficult to carry in traditional static absolute gravity data acquisition systems under rapid measurement conditions. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a high-speed acquisition system and method for laser interference fringe signals applied to optical absolute gravimeters. Based on an FPGA microprocessor controller, it fully leverages the advantages of parallel processing computing to improve the overall system operating speed and the integrity and accuracy of signal acquisition, achieving high-speed signal acquisition and stable data transmission.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a high-speed acquisition system for laser interference fringe signals applied to an optical absolute gravimeter, characterized in that it comprises:

[0007] The analog signal conditioning unit, including the THS3091 operational amplifier, converts the optical signal generated by laser interference into an electrical signal and performs filtering to remove linear drift and suppress some high-frequency interference noise, and amplifies the original small signal to the range of the analog-to-digital converter.

[0008] The analog-to-digital conversion unit, including the AD9248 analog-to-digital converter chip and its peripheral circuits, converts continuous analog signals into discrete digital signals.

[0009] The external clock unit outputs a sine wave signal, providing a stable external clock and time reference.

[0010] The system's core control unit, including the XC7K160T series FPGA microcontroller, supports the USB 3.0 transmission protocol and has built-in FIFO logic, which processes and controls the acquisition, storage, and transmission of laser interference fringe signals.

[0011] Power conversion and supply unit to maintain the normal operation of the data acquisition system;

[0012] The data transmission unit includes an FT601 chip that acts as a bridge between USB 3.0 and FIFO. It uses a USB 3.0 micro-B interface to connect and communicate with the measurement and control terminal, transmitting the data processed by the microprocessor to the measurement and control terminal for display.

[0013] The measurement and control terminal processing and display unit reads information from the USB 3.0 acquisition device, stores the data in a local document, and uses a multi-threaded collaborative approach to process valid and invalid data separately. It then generates interference fringe signal waveforms on the measurement and control terminal display interface, continuously displaying the discretized interference fringe information obtained from the front-end data acquisition and processing onto the display.

[0014] A method for acquiring laser interferometric fringe signals in an optical absolute gravimeter, characterized by comprising the following steps:

[0015] S1: Set the number of buffer packets, the number of bytes per buffer packet, and the receiving threshold;

[0016] S2: Determine if a USB 3.0 data acquisition device is connected to the monitoring and control terminal. If it is, execute S3. If it is not, a dialog box will pop up to remind you that no device is connected.

[0017] S3: The USB 3.0 acquisition device that has been successfully connected is ready to communicate. If the connection is successful, proceed to S4. If it fails, a dialog box will pop up prompting you to reconnect and reporting the relevant error.

[0018] S4: Start the receiving thread, create a byte array with the same number of buffer packets as set in S1, and the array length is the same as the number of bytes per buffer packet set in S1. Store all byte arrays in a List.<byte[]> In the array;

[0019] S5: Reads the acquisition information from the USB 3.0 acquisition device in an infinite loop and sorts the acquisition information according to a List.<byte[]> The bytes in the array are received sequentially.

[0020] S6: Looping through the List<byte[]> The array is used to check if a start character exists in all the pre-received data in S5 using the array's Indexof() method. If a byte array exists, S7 is executed; otherwise, S5 is executed repeatedly.

[0021] S7: Receive the byte array containing the start character detected in S6 and all arrays following it, and check if there is an end character in the currently received array using the Indexof() method of the array. If there is an end character, execute S10; if there is no end character, repeat S8. If the amount of received data reaches the threshold set in S1 and no end character is detected, execute S9.

[0022] S8: Clear the byte array received in S7, and resubmit the cleared byte array to the List in S5.<byte[]> Data is received from an array;

[0023] S9: End this data collection and save all the data to a local text document (the document name is the current time, accurate to the second);

[0024] S10: End the current data collection and read, store the data in a local text document task in a task queue, use a multi-threaded approach to delete invalid data before the start symbol and after the end symbol of the current data collection, store the data in a local text document (the document name is named with the current time, accurate to the second), and then remove the task from the task queue.

[0025] S11: Generate a signal diagram from the data processed in S10, clear all arrays storing the received data to zero, and then start executing S4 until the acquisition is manually ended.

[0026] The beneficial effects of this invention are:

[0027] This invention fully utilizes the advantages of embedded systems, such as good customizability and strong stability. Based on an FPGA microprocessor controller, it fully leverages the advantages of parallel processing computing to improve the overall operating speed of the system and the integrity and accuracy of signal acquisition, achieving high-speed signal acquisition and stable data transmission.

[0028] This invention can automatically and reliably complete the storage and display of high-speed acquired signals, ensuring the reception of tens of millions of bytes within 0.3 seconds and the storage and display of signal data within 3 seconds. It features a data detection function to ensure that all acquired data is correct and valid. Threshold settings prevent unlimited storage due to acquisition device malfunctions, thereby enabling monitoring of the acquisition device's operational status.

[0029] This invention designs user-friendly and efficient measurement and control terminal software, further enhancing the overall interactivity, readability, and flexibility of the system. The system, characterized by its miniaturization and portability, combined with its advantages of fast signal acquisition and processing speed and high accuracy, achieves rapid and dynamic absolute gravity measurement. Attached Figure Description

[0030] Figure 1 This is a circuit diagram of the high-speed acquisition system of the present invention.

[0031] Figure 2 This is a flowchart of the high-speed acquisition system of the present invention.

[0032] Figure 3 This is a schematic diagram illustrating the data acquisition time of the high-speed acquisition system of the present invention.

[0033] Figure 4 This is a diagram of the display interface of the measurement and control terminal of the high-speed acquisition system of the present invention.

[0034] Figure 5 This is a diagram showing the software architecture of the high-speed acquisition system of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] This invention provides a high-speed acquisition system for laser interference fringe signals from an optical absolute gravimeter. The system includes an analog signal conditioning unit employing a THS3091 operational amplifier, which features a low signal-to-noise ratio, wide bandwidth, and low signal distortion. The design utilizes a cascaded amplifier with parallel filter connection to achieve front-end signal conditioning for acquisition. This analog signal conditioning unit filters the electrical signal obtained from the laser interference signal converted by a photodetector, removing linear drift and suppressing some high-frequency interference noise. It also amplifies the original small signal to within the optimal range of the analog-to-digital converter, preventing repeated zero-crossing and pseudo-zero-crossing phenomena.

[0037] The analog-to-digital conversion unit (ADC) includes the AD9248 analog-to-digital converter chip and its peripheral circuitry. The acquired interference fringe signal undergoes sampling, holding, quantization, and encoding to convert it into a digital signal that the controller can process. This chip boasts 14-bit sampling accuracy and a maximum sampling frequency of 65MHz, maximizing the system's acquisition resolution and minimizing the possibility of signal distortion. The ADC utilizes an A / D converter to convert continuous analog signals into discrete digital signals that the core controller can process.

[0038] The system's core control unit includes an XC7K160T series FPGA microcontroller, supporting USB 3.0 transmission protocol with a maximum transfer rate of 500MB / s. It features built-in FIFO logic for on-chip data buffering. It boasts a powerful clock management tile (CMT) and a phase-locked loop (PLL) to achieve high precision and low jitter. The entire process of acquiring, storing, and transmitting laser interference fringe signals is processed and controlled by the FPGA microcontroller.

[0039] The power conversion and supply unit refers to the unit that maintains the continuous and uninterrupted normal operation of each functional module of the system.

[0040] The data transmission unit includes the FT601 chip, which acts as a bridge between the USB 3.0 and FIFO interfaces. It is designed to connect to the monitoring and control terminal via a USB 3.0 micro-B interface, ensuring data quality and speed during transmission. This data transmission unit utilizes Universal Serial Bus (USB) technology to transmit data processed by the microprocessor to the monitoring and control terminal for display.

[0041] The measurement and control terminal's processing and display unit takes the discretized interference fringe information acquired and processed by the front end, uses a high-level programming language algorithm to make the signal continuous and present it on the display, achieving a human-computer interaction effect. Specifically, it uses C++ programming to read the acquisition information from the USB 3.0 acquisition device in a loop. When the received data volume reaches a set threshold and an end marker is detected, the reading of the acquisition information ends, and the data is stored in a document task queue. Simultaneously, a multi-threaded approach is used to delete invalid data before the start marker and after the end marker. Finally, the interference fringe signal waveform is generated on the measurement and control terminal's display interface.

[0042] The external clock unit utilizes a rubidium atomic clock to stably output a 10MHz sine wave signal, providing a stable external clock and time reference for the acquisition system.

[0043] This invention also provides a data acquisition method using the above-mentioned high-speed data acquisition system, comprising the following steps:

[0044] S1: Set the number of buffer packets, the number of bytes per buffer packet, and the receiving threshold;

[0045] S2: Determine if a USB 3.0 data acquisition device is connected to the monitoring and control terminal. If it is, execute S3. If it is not, a dialog box will pop up to remind you that no device is connected.

[0046] S3: The USB 3.0 acquisition device that has been successfully connected is ready to communicate. If the connection is successful, proceed to S4. If it fails, a dialog box will pop up prompting you to reconnect and reporting the relevant error.

[0047] S4: Start the receiving thread, create a byte array with the same number of buffer packets as set in S1, and the array length is the same as the number of bytes per buffer packet set in S1. Store all byte arrays in a List.<byte[]> In the array;

[0048] S5: Reads the acquisition information from the USB 3.0 acquisition device in an infinite loop and sorts the acquisition information according to a List.<byte[]> The bytes in the array are received sequentially.

[0049] S6: Looping through the List<byte[]> The array is used to check if a start character exists in all the pre-received data in S5 using the array's Indexof() method. If a byte array exists, S7 is executed; otherwise, S5 is executed repeatedly.

[0050] S7: Receive the byte array containing the start character detected in S6 and all arrays following it, and check if there is an end character in the currently received array using the Indexof() method of the array. If there is an end character, execute S10; if there is no end character, repeat S8. If the amount of received data reaches the threshold set in S1 and no end character is detected, execute S9.

[0051] S8: Clear the byte array received in S7, and resubmit the cleared byte array to the List in S5.<byte[]> Data is received from an array;

[0052] S9: End this data collection and save all the data to a local text document (the document name is the current time, accurate to the second);

[0053] S10: End the current data collection and read, store the data in a local text document task in a task queue, use a multi-threaded approach to delete invalid data before the start symbol and after the end symbol of the current data collection, store the data in a local text document (the document name is named with the current time, accurate to the second), and then remove the task from the task queue.

[0054] S11: Generate a signal diagram from the data processed in S10, clear all arrays storing the received data to zero, and then start executing S4 until the acquisition is manually ended.

[0055] Example

[0056] The present invention will now be described in detail with reference to the accompanying drawings:

[0057] Reference Figure 1-5 As shown, the optical absolute gravimeter laser interferometric fringe signal acquisition system is divided into a system control terminal and a front-end data acquisition unit. The system control terminal includes independently designed and developed laser interferometric fringe signal acquisition, control, and display software, whose function is to receive and process the acquired data. The front-end data acquisition unit includes the FPGA-based microprocessor-based main control system and other functional modules, primarily responsible for signal front-end processing, logic algorithms, and control transmission.

[0058] The above technical solution requires external interference fringe signals, an external clock signal, and an external trigger signal to complete high-speed data acquisition. The interference fringe signal is emitted by the laser interferometer of the absolute gravimeter and transmitted to the front-end conditioning circuit of the high-speed acquisition system using a coaxial cable with a BNC interface on one end and an SMA interface on the other. Simultaneously, a 10MHz high-precision sine wave signal is emitted using a rubidium atomic clock to provide a precise time reference for the high-speed acquisition system. Finally, the trigger signal output from the motor controlling the trailer's descent is connected to the trigger I / O of the high-speed acquisition system.

[0059] Through the above technical solution, the logical algorithm flow of the present invention is as follows: Figure 2 As shown. Specifically, when the FPGA receives an external trigger signal through the ADC acquisition module, after one clock cycle of the ADC register, it begins sending a start symbol to indicate the start of ADC synchronous sampling. The sampled data is then buffered in the FIFO. When the amount of data in the FIFO reaches the maximum threshold of 1024 bytes, the USB 3.0 reads the data buffered in the FIFO. When the amount of data transmitted through the USB 3.0 reaches the set amount, the program sends an end symbol. The measurement and control terminal reads the acquisition information from the USB 3.0 acquisition device in a loop. When the received data reaches the set threshold and the end symbol is detected, the reading of the acquisition information ends, and the data is stored in the document task queue. Simultaneously, a multi-threaded approach is used to delete invalid data before the start symbol and after the end symbol. Finally, an interference fringe signal waveform is generated on the measurement and control terminal display interface. The system waits for the arrival of a second external trigger and repeats the above acquisition process.

[0060] Taking the NIM-3A absolute gravimeter built in the laboratory as an example, the falling prism of the gravimeter falls freely in the vacuum chamber for 0.2 seconds, generating an interference signal with a maximum frequency of approximately 12MHz. Data transmission is performed via USB 3.0 with a transmission rate of up to 350MB / s. An asynchronous FIFO is used to match data between interfaces of different bit widths. DDR3 high-speed cache is used to buffer the data acquired by the ADC module. Through the design of the USB 3.0 interface circuit, device firmware, and the SLAVE FIFO mode and central control unit read / write operations in the interface devices, the data is transmitted to the PC. Test results show that the acquisition system can reliably transmit tens of millions of bytes of data within 0.1 seconds. A time consumption diagram is shown below. Figure 3 As shown.

[0061] The measurement and control terminal has functions such as two-dimensional, visual real-time data display, data saving, data querying, and data export, such as... Figure 4 As shown, these functions are used to analyze the absolute gravity value of the measured point.

[0062] Inventing software architecture, such as Figure 5As shown, Transform is a method class for numerical conversion, used for conversion between hexadecimal, decimal, binary, and string; Logger is a log class used to store runtime logs; SearchAndOpenDevice searches for and connects to devices; TaskQueue is a task queue class; TaskData is an entity class required by TaskQueue; HSAS is the interface function; ShowMsg is used for cross-thread calls to modify the UI; FTDIReadOrWriteAsync is used to implement asynchronous read and write with the device chip; TittinFunct is an algorithm class; Polyfit is a polynomial fitting function; ZeroCross is used to extract zero crossings; GetDisplacement is used to generate displacement; StandardDeviation is used to calculate standard deviation; AUncertainty is used to calculate Type A uncertainty; DeletSigma is used to implement 3sigma elimination; dashed and solid arrows indicate the reference relationships between each function.

[0063] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A high-speed acquisition method for laser interference fringe signals applied to optical absolute gravimeters, the method being implemented through a high-speed acquisition system, characterized in that... The high-speed acquisition system includes: The analog signal conditioning unit converts the optical signal generated by laser interference into an electrical signal and performs filtering to remove linear drift and suppress some high-frequency interference noise, and amplifies the original small signal to the range of the analog-to-digital converter. An analog-to-digital converter (ADC) converts continuous analog signals into discrete digital signals. The external clock unit outputs a sine wave signal, providing a stable external clock and time reference. The system's core control unit processes and controls the acquisition, storage, and transmission of laser interference fringe signals; Power conversion and supply unit to maintain the normal operation of the data acquisition system; The data transmission unit transmits the data processed by the microprocessor to the measurement and control terminal for display. The measurement and control terminal processing and display unit continuously displays the discrete interference fringe information obtained from the front-end data acquisition onto the display screen; The high-speed acquisition method includes the following steps: S1: Set the number of buffer packets, the number of bytes per buffer packet, and the receiving threshold; S2: Determine if a USB 3.0 data acquisition device is connected to the monitoring and control terminal. If it is, execute S3. If it is not, a dialog box will pop up to remind you that no device is connected. S3: The USB 3.0 acquisition device that has been successfully connected is ready to communicate. If the connection is successful, proceed to S4. If it fails, a dialog box will pop up prompting you to reconnect and reporting the relevant error. S4: Start the receiving thread, create a byte array with the same number of buffer packets as set in S1, and the array length is the same as the number of bytes per buffer packet set in S1. Store all byte arrays in a List.<byte[]> In the array; S5: Reads the acquisition information from the USB 3.0 acquisition device in an infinite loop and sorts the acquisition information according to a List.<byte[]> The bytes in the array are received sequentially. S6: Looping through the List<byte[]> The array is used to check if a start character exists in all the pre-received data in S5 using the array's Indexof() method. If a byte array exists, S7 is executed; otherwise, S5 is executed repeatedly. S7: Receive the byte array containing the start character detected in S6 and all arrays following it, and check if there is an end character in the currently received array using the Indexof() method of the array. If there is an end character, execute S10; otherwise, repeat S8. S8: Clear the byte array received in S7, and resubmit the cleared byte array to the List in S5.<byte[]> Data is received from an array; S9: End the current data collection and save all the collected data to a local text document; S10: End the current data collection and read information. Store the data in a local text document task queue. Use a multi-threaded approach to delete invalid data before the start symbol and after the end symbol of the current data collection, store the data in a local text document, and then remove the task from the task queue. S11: Generate a signal diagram from the data processed in S10, clear all arrays storing the received data to zero, and then start executing S4 until the acquisition is manually ended.

2. The high-speed acquisition method according to claim 1, characterized in that: The analog signal conditioning unit includes a THS3091 operational amplifier.

3. The high-speed acquisition method according to claim 1, characterized in that: The analog-to-digital conversion unit includes the AD9248 analog-to-digital converter chip and its peripheral circuitry.

4. The high-speed acquisition method according to claim 1, characterized in that: The core control unit of the system is an XC7K160T series FPGA microcontroller, which supports the USB 3.0 transmission protocol and has built-in FIFO logic.

5. The high-speed acquisition method according to claim 1, characterized in that: The data transmission unit includes an FT601 chip that acts as a bridge between USB 3.0 and FIFO, and uses a USB 3.0 micro-B interface to connect and communicate with the measurement and control terminal.

6. The high-speed acquisition method according to claim 1, characterized in that: The measurement and control terminal processing and display unit reads the information from the USB 3.0 acquisition device, stores the data in a local document, and uses a multi-threaded collaborative approach to process valid and invalid data separately, generating interference fringe signal waveforms on the measurement and control terminal display interface.

7. The high-speed acquisition method according to claim 1, characterized in that: In step S7, if the amount of received data reaches the threshold set in S1 and no end symbol is detected, then S9 is executed.

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