An automatic gain control method and circuit for ultrasonic flow metering devices

Abstract

The application provides an automatic gain control method and circuit of an ultrasonic flow metering device, aiming at improving the accuracy and stability of flow metering. The method automatically adjusts the gain by measuring the pulse width of the echo signal and comparing it with the expected value. The circuit includes a transmitting circuit, an ultrasonic transducer, a variable gain amplifier, a variable threshold comparator, a zero-crossing comparator, a time-of-flight measurement unit, a pulse width measurement unit, a time-to-digital converter, and a calculation and control unit. The scheme can realize independent gain configuration of uplink and downlink time-of-flight, and fine gain adjustment strategy based on echo amplitude change. In addition, by setting the maximum allowable pulse width change value, the application can automatically judge whether the measurement error is within a reasonable range and re-measure if necessary. This integrated design not only improves the flexibility and response speed of measurement, but also optimizes the signal processing process, providing an innovative solution for ultrasonic flow metering.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic metering devices, and more particularly to an automatic gain control method and circuit for ultrasonic flow metering devices. Background Technology

[0002] In the field of ultrasonic flow metering, traditional measurement techniques rely on measuring the time of flight (TOF) of ultrasonic signals to calculate fluid velocity and flow rate. These systems typically include a transmitting circuit, an ultrasonic transducer, a signal amplifier, and a signal processing unit. However, these traditional systems have limitations when handling measurements under varying environmental conditions. For example, changes in temperature, pressure, flow rate, or gas composition can cause fluctuations in the amplitude of the echo signal, leading to inaccurate measurement results. Furthermore, fixed gain settings cannot adapt to these variations, thus limiting the stability and accuracy of the measurement.

[0003] This invention proposes an automatic gain control method and circuit for an ultrasonic flow metering device. By precisely controlling the gain, it adapts to environmental changes, improves the accuracy and stability of measurements, accelerates the system response speed, and realizes a precise gain adjustment strategy. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an automatic gain control method and circuit for an ultrasonic flow metering device to solve one or more problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] An automatic gain control method for an ultrasonic flow metering device includes the following steps:

[0007] a. Measure the pulse width of one or more echoes at a comparator threshold during the ultrasonic time-of-flight process.

[0008] b. Compare the measured pulse width with the expected pulse width to obtain the deviation value.

[0009] c. Determine whether the echo signal amplitude is too large or too small based on the magnitude of the deviation value.

[0010] d. Design an automatic gain control strategy based on the deviation value quantification index, and adjust the gain of the echo signal amplifier.

[0011] e. After one or more gain adjustments, the echo signal with the expected amplitude is obtained.

[0012] In the above technical solution, the stability of the echo signal amplitude is ensured by measuring the pulse width of the echo signal and adjusting the gain according to the deviation value. This solution improves the measurement accuracy and stability of the ultrasonic flow metering device under different environmental conditions and reduces errors caused by signal amplitude fluctuations.

[0013] Furthermore, during the same time-of-flight measurement process, the first echo signal is detected, the time of flight is measured through zero-crossing detection, and the pulse width is measured through threshold detection. The time of flight can be measured before or after the pulse width measurement. The time of flight of one or more echo zero-crossing points, as well as the pulse width of one or more echoes, can be measured.

[0014] In the above technical solution, measurement efficiency is improved by completing the initial wave detection, zero-crossing detection, and pulse width measurement within the same time-of-flight measurement process. Simultaneously, allowing time-of-flight measurement to be performed before or after pulse width measurement increases measurement flexibility, enabling the system to respond more quickly to environmental changes, adjust gain promptly, and maintain measurement accuracy.

[0015] Furthermore, automatic gain control adjusts the gain of a variable gain amplifier based on the changes and magnitudes of one or more ultrasonic echoes.

[0016] If N pulse width signals are measured, and the amplitude of N1 echo signals is too large, and the absolute value of the pulse width deviation is greater than the set value M1, then the gain is reduced; if the absolute value of the pulse width deviation is greater than K1×M1, then the gain is reduced by level K1. If the amplitude of N2 echo signals is too small, and the absolute value of the pulse width deviation is less than the set value M2, then the gain is increased; if the absolute value of the pulse width deviation is less than K2×M2, then the gain is increased by level K2. The values ​​of N1, N2, M1, and M2 can all be configured independently.

[0017] In the above technical solution, more precise automatic gain control is achieved by adjusting the gain according to changes in the echo amplitude. This strategy can make personalized adjustments for amplitude changes in different echo signals, thereby optimizing the signal amplification effect and improving the accuracy of flow measurement.

[0018] Furthermore, automatic gain adjusts the gain of the variable gain amplifier based on the cumulative value of multiple echo pulse width deviations.

[0019] If the cumulative value of P1 echo pulse width deviations is greater than Q1, then the gain is reduced to level G1. If the cumulative value of P2 echo pulse width deviations is less than Q2, then the gain is increased to level G2. The values ​​of P1, P2, Q1, and Q2 can all be configured independently.

[0020] The above technical solution provides a gain adjustment method based on accumulated error by adjusting the gain by accumulating multiple echo pulse width deviation values. This method can reduce the influence of random errors, making the gain adjustment more robust and improving the system's adaptability and reliability in complex environments.

[0021] Specifically, when performing uplink time-of-flight measurements, the variable gain amplifier is configured to the uplink gain Gup. When performing downlink time-of-flight measurements, the variable gain amplifier is configured to the downlink gain Gdn. If a change in echo amplitude occurs between two uplink measurements, the uplink gain Gup is adjusted. If a change in echo amplitude occurs between two downlink measurements, the downlink gain Gdn is adjusted.

[0022] In the above technical solution, by distinguishing between uplink and downlink flight time measurements and configuring different gain values ​​for each, the system can be optimized for the different characteristics of downstream and upstream flows. This differentiated approach improves the adaptability of the measurement and ensures measurement accuracy under different flow directions.

[0023] Specifically, based on the changes and magnitudes of one or more ultrasonic echoes from uplink and downlink measurements, the flight time measurement error is determined to be within a reasonable range by using a set maximum permissible pulse width variation value Pmax.

[0024] If the actual pulse width change exceeds Pmax, the flight time measurement error is determined to be outside the reasonable range. The measurement result is then discarded, and the measurement is repeated promptly.

[0025] In the above technical solution, a preset threshold-based error judgment mechanism is provided by setting a maximum permissible pulse width variation value Pmax to determine whether the time-of-flight measurement error is within the allowable error range. This method enables the system to automatically determine the reliability of the measurement results and remeasure when necessary, thereby ensuring the accuracy and reliability of the measurement results.

[0026] To achieve the above-mentioned technical means, the present invention also provides an automatic gain control circuit for an ultrasonic flow metering device, comprising:

[0027] The transmitting circuit is used to control the transmission of electrical signals of a specific frequency to the transducer.

[0028] An ultrasonic transducer, comprising a pair of transducers, enables the transmission of ultrasonic signals and the reception of echo signals.

[0029] A variable gain amplifier used to amplify echo signals with configurable gain.

[0030] A variable threshold comparator is used to compare the echo signal output by the amplifier with a set threshold and output a comparison level.

[0031] The zero-crossing comparator is used to compare the amplified subsequent echo signal with the zero point after the first wave is detected by the variable threshold comparator, and output the comparison level when the echo signal crosses the zero point.

[0032] The time-of-flight measurement unit is used to measure the flight time of an ultrasonic wave from its emission to the zero-crossing point of the effective echo output by the zero-crossing comparator.

[0033] The pulse width measurement unit is used to measure the width of one or more pulse signals output by the variable threshold comparator to obtain the pulse width value.

[0034] A time-to-digital converter is used to convert the start time pulse signals of the time-of-flight measurement unit and the pulse width measurement unit into digital signals.

[0035] The computing and control unit is used to perform data processing, gain control strategy calculation, and overall hardware parameter control.

[0036] In the above technical solution, this circuit enables the automatic gain control method to be implemented, improves the system integration and practicality, and facilitates its application in actual ultrasonic flow metering devices.

[0037] Specifically, the variable gain amplifier has an uplink gain configuration Gup and a downlink gain configuration Gdn, and Gup and Gdn can be configured independently.

[0038] During a single measurement process, specifically a single uplink and downlink differential time-of-flight measurement, select Gup for uplink time-of-flight measurement and Gdn for downlink time-of-flight measurement.

[0039] The above technical solution provides a more flexible gain adjustment scheme by allowing independent configuration of the uplink gain configuration Gup and the downlink gain configuration Gdn of the variable gain amplifier. This design enables the system to automatically select the most suitable gain configuration based on the actual measurement conditions, optimizing the signal amplification effect and improving the flexibility and accuracy of the measurement.

[0040] Specifically, the variable threshold comparator has a first-wave threshold configuration value Vf and a pulse width detection threshold configuration value Vp. During a measurement process, the first-wave threshold configuration value Vf is configured first. After the first wave detection is completed, it switches to the pulse width detection threshold configuration value Vp to perform pulse width detection.

[0041] In the above technical solution, by enabling the variable threshold comparator to have a first-wave threshold configuration value Vf and a pulse width detection threshold configuration value Vp, and automatically switching between them during the measurement process, the degree of automation of the measurement is improved. This design allows the system to automatically adjust the threshold according to different measurement stages, improving the accuracy and efficiency of the measurement.

[0042] Specifically, the time-of-flight measurement unit measures and records the flight time from the ultrasonic wave emission to one or more zero-crossing points of the ultrasonic echo output by the zero-crossing comparator, and the number of these points is configurable.

[0043] The pulse width measurement unit measures and records the width of the pulse signal output by one or more variable threshold comparators. It can measure either the high-level width or the low-level width, and the number of measurements is configurable.

[0044] The above technical solution offers greater flexibility and adaptability by making the number of time-of-flight measurement units and pulse width measurement units configurable. This design allows the system to adjust the number of measurement units according to actual needs, optimizing resource allocation and improving measurement efficiency and accuracy.

[0045] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0046] (i) Measurement accuracy and stability: By measuring the pulse width of the echo signal and automatically adjusting the gain based on its deviation from the expected value, this invention ensures the consistency of the echo signal amplitude under various environmental conditions. This direct feedback control mechanism significantly improves the measurement accuracy of the ultrasonic flow metering device, reduces errors caused by signal amplitude fluctuations, and thus enhances the stability of the metering process.

[0047] (ii) Signal processing capability: This invention achieves accurate detection and amplitude comparison of echo signals by combining a zero-crossing comparator and a variable threshold comparator. This combination enables the system to accurately capture key signal characteristics, such as zero-crossing points and specific amplitude levels, thereby optimizing signal processing capabilities and improving the measurement accuracy of fluid velocity and flow rate.

[0048] (III) System Response: This invention can complete initial wave detection, zero-crossing detection, and pulse width measurement in a single flight time measurement. This integrated measurement process shortens the measurement cycle and improves the system's response speed to environmental changes. The rapid measurement and processing capabilities enable the system to promptly capture changes in fluid characteristics, thereby quickly adjusting the gain and maintaining the accuracy of the measurement data.

[0049] (iv) Gain Adjustment Strategy: This invention provides a precise gain adjustment strategy by accumulating multiple echo pulse width deviation values ​​or adjusting the gain based on changes in a single echo amplitude. This strategy enables the system to perform detailed gain adjustments based on actual measurement results, optimizing signal amplification and further improving the accuracy and reliability of flow measurement. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of an automatic gain control method for an ultrasonic flow metering device, as illustrated in the exemplary description of the present invention.

[0051] Figure 2 This is a schematic diagram of an automatic gain control circuit for an ultrasonic flow metering device according to the present invention.

[0052] Figure 3 This is a schematic diagram showing the relationship between the pulse width of the output signal of the variable threshold comparator and the amplitude of the echo signal in this invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0054] Application Overview

[0055] In the field of ultrasonic flow metering, the industry typically uses fixed-gain amplifiers to process echo signals to calculate fluid velocity and flow rate. While this method provides stable measurement results under ideal conditions, in practical applications, environmental factors such as temperature, pressure, flow rate variations, and differences in gas composition cause changes in the amplitude of the echo signal. This makes it difficult for fixed-gain amplifiers to adapt to these changes, thus affecting the accuracy and stability of the measurement. Furthermore, traditional measurement systems often require considerable time for initial wave detection, zero-crossing detection, and pulse width measurement, resulting in slow system response and an inability to promptly capture rapid changes in fluid characteristics. Moreover, existing gain adjustment strategies lack flexibility and precision, failing to provide fine-tuning based on actual measurement results, which limits the accuracy and reliability of flow metering.

[0056] Exemplary Description

[0057] The present invention relates to an automatic gain control method for an ultrasonic flow metering device and its corresponding circuit design. This method automatically adjusts the gain to adapt to environmental changes, ensuring the stability of the echo signal amplitude, thereby improving the accuracy and stability of flow metering.

[0058] Perform system calibration. Under zero-flow conditions, determine the initial gain values ​​for uplink and downlink measurements, denoted as Gup_init and Gdn_init, respectively. Simultaneously, determine the expected width of the output pulse signal of the variable threshold comparator, as well as the initial detection threshold Vf and the pulse width measurement threshold Vp.

[0059] Please refer to Figure 1 After calibration, the system enters normal operating mode. The transmitting circuit generates an electrical signal of a specific frequency, transmits the ultrasonic signal through the ultrasonic transducer, and receives the echo signal. The variable gain amplifier amplifies the echo signal, and its gain value is independently configured as Gup and Gdn depending on the uplink and downlink measurements.

[0060] During uplink measurement, the gain of the variable gain amplifier is set to Gup, and the detection threshold of the variable threshold comparator is initialized to the initial wave detection threshold Vf. When the amplitude of the echo signal exceeds Vf, the comparator's detection threshold automatically switches to the pulse width measurement threshold Vp. At this time, the time-of-flight measurement unit starts timing, measuring and recording the flight time from the starting point of the ultrasonic wave transmission to the effective zero-crossing point of the echo output by the zero-crossing comparator at multiple zero-crossing points. The pulse width measurement unit measures the pulse signal width output by the variable threshold comparator, including the high-level width or low-level width, and records these values.

[0061] Please refer to Figure 2 The downlink measurement process is similar to the uplink measurement, using the downlink gain value Gdn. By comparing the actual measured pulse width with the expected value, the system can determine whether the signal amplitude is too large or too small, and adjust the gain value accordingly. For example, if the measured pulse width is greater than the expected value, it indicates that the signal amplitude is too large, and the downlink measurement gain value Gdn needs to be decreased; conversely, Gdn needs to be increased.

[0062] To achieve more precise gain adjustment control, this invention proposes two control strategies. Control strategy 1 determines whether to increase or decrease the gain based on more than two echo pulse width values ​​that are too large or too small. Control strategy 2 adjusts the gain based on the cumulative value of four echo pulse width deviations. These strategies ensure that the system can perform fine-tuning of the gain based on actual measurement results, optimize signal amplification, and improve the accuracy and reliability of flow measurement.

[0063] Example

[0064] Let the desired pulse width values ​​P1e, P2e, P3e, and P4e be 500ns, 500ns, 450ns, and 200ns, respectively, and the maximum allowable pulse width variation Pmax be configured to 150ns. If the measured pulse width values ​​P1_up, P2_up, P3_up, and P4_up are 600ns, 600ns, 500ns, and 300ns, then according to control strategy 1, more than two echo pulse width values ​​are too large and greater than 40ns, requiring a reduction in gain Gup. Specifically, the values ​​of (P1_up-P1e), (P2_up-P2e), (P3_up-P3e), and (P4_up-P4e) are calculated to be 100ns, 100ns, 50ns, and 100ns, respectively. The measured three echo pulse widths are too large, exceeding twice 40ns, indicating that the echo signal amplitude is too high, requiring a reduction of the uplink measurement gain Gup by two levels.

[0065] Please refer to Figure 3 According to control strategy 2, if the pulse width values ​​of the four echoes are too large, and the sum of the deviations equals 350ns, which is greater than 4*80ns, then the gain Gup needs to be reduced by four levels. If the measured pulse width values ​​P1_up, P2_up, P3_up, and P4_up are 400ns, 400ns, 350ns, and 150ns respectively, it indicates that the echo signal is too small, and the gain Gup needs to be increased by two levels.

[0066] When the measured pulse width reached 655ns, the deviation was 155ns, which is greater than Pmax. This indicates that the signal amplitude variation is too large, and the flight time error of this measurement is significant. Therefore, the flight data of this measurement should be discarded. After adjusting the gain, the uplink measurement should be performed again.

[0067] After the gain calculation is completed, the new uplink gain value is updated to the uplink measurement gain value Gup. The data processing for downlink measurements is similar to that for uplink measurements. After gain adjustment, the new downlink gain value is updated to the downlink measurement gain value Gdn. For the next uplink measurement, the updated uplink measurement gain value Gup is used; for the next downlink measurement, the updated downlink measurement gain value Gdn is used.

[0068] Specific work process

[0069] System calibration is performed to determine the initial gain values ​​Gup_init and Gdn_init for uplink and downlink measurements, and to measure the desired width of the output pulse signal of the variable threshold comparator, as well as the first-wave detection threshold Vf and pulse width measurement threshold Vp. After calibration, the transmitting circuit generates an electrical signal at a specific frequency, which is transmitted and received via an ultrasonic transducer. The variable gain amplifier is independently configured as Gup and Gdn, depending on the uplink and downlink measurements, to amplify the echo signal.

[0070] In the uplink measurement, the gain value of the variable gain amplifier is set to Gup, and the detection threshold of the variable threshold comparator is initialized to the initial wave detection threshold Vf. Once the echo signal amplitude exceeds Vf, the comparator's detection threshold automatically switches to the pulse width measurement threshold Vp. The time-of-flight measurement unit times the echo signal from the start of the ultrasonic transmission until the valid echo zero-crossing point output by the zero-crossing comparator, measuring and recording the flight time at multiple zero-crossing points. The pulse width measurement unit measures the pulse signal width output by the variable threshold comparator and records these values.

[0071] The downlink measurement process is similar to the uplink measurement, using the downlink gain value Gdn. By comparing the actual measured pulse width value with the expected value, the system determines whether the signal amplitude is too large or too small, and adjusts the gain value accordingly. If the measured pulse width value is greater than the expected value, it indicates that the signal amplitude is too large, and the downlink measurement gain value Gdn is decreased; conversely, Gdn needs to be increased.

[0072] This invention proposes two control strategies for precise gain adjustment. Control strategy 1 determines whether to increase or decrease the gain based on more than two echo pulse width values ​​that are too large or too small. Control strategy 2 adjusts the gain based on the cumulative value of four echo pulse width deviations. These strategies ensure that the system can perform fine-tuning of the gain according to actual measurement results, optimize signal amplification, and improve the accuracy and reliability of flow measurement.

[0073] When the measured pulse width deviation exceeds the maximum permissible pulse width change Pmax, the system determines that the flight time error of this measurement is large, discards the flight data for this measurement, and re-measures after adjusting the gain. This ensures the accuracy and reliability of the measurement results. After completing the gain calculation, the new uplink gain value is updated to the uplink measurement gain value Gup. The data processing for downlink measurements is similar to that for uplink measurements; after gain adjustment, the new downlink gain value is updated to the downlink measurement gain value Gdn. The next uplink measurement uses the updated uplink measurement gain value Gup, and the next downlink measurement uses the updated downlink measurement gain value Gdn. In this way, each measurement adjusts the gain of the variable gain echo amplifier in a timely manner according to the changes in the echo signal amplitude, keeping the echo signal amplitude fluctuation within the required range to ensure measurement accuracy and stability.

[0074] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. An automatic gain control method for an ultrasonic flow metering device, characterized by, Includes the following steps: a. Measure the pulse width of one or more echoes at a comparator threshold during ultrasonic time-of-flight; b. Compare the measured pulse width with the expected pulse width to obtain the deviation value; c. Determine whether the echo signal amplitude is too large or too small based on the magnitude of the deviation value; d. Design an automatic gain control strategy based on the deviation value quantification index, and adjust the gain of the echo signal amplifier; e. After one or more gain adjustments, the echo signal with the expected amplitude is obtained; Automatic gain control adjusts the gain of a variable gain amplifier based on the changes and magnitudes of one or more ultrasonic echo amplitudes. If N pulse width signals are measured, and the amplitude of N1 echo signals is too large, and the absolute value of the pulse width deviation is greater than the set value M1, the gain is reduced; if the absolute value of the pulse width deviation is greater than K1×M1, the gain is reduced to level K1. If the amplitude of N2 echo signals is too small, and the absolute value of the pulse width deviation is less than the set value M2, the gain is increased; if the absolute value of the pulse width deviation is less than K2×M2, the gain is increased to level K2. The values ​​of N1, N2, M1, and M2 can all be configured independently. Alternatively, automatic gain adjusts the gain of a variable gain amplifier based on the sum of multiple echo pulse width deviation values; If the cumulative value of the P1 echo pulse width deviation values ​​is greater than Q1, then the gain G1 level is reduced; if the cumulative value of the P2 echo pulse width deviation values ​​is less than Q2, then the gain G2 level is increased. The values ​​of P1, P2, Q1, and Q2 can all be configured independently.

2. An automatic gain control method for an ultrasonic flow metering device as defined in claim 1, characterized in that: During the same time-of-flight measurement process, the first wave of the echo signal is detected, the time of flight is measured by zero-crossing detection, and the pulse width is measured by threshold detection. The time of flight measurement can be performed before or after the pulse width measurement. The time of flight of one or more echo zero-crossing points and the pulse width of one or more echoes can be measured.

3. An automatic gain control method for an ultrasonic flow metering device as recited in claim 1, wherein: When performing uplink flight time measurements, the variable gain amplifier is configured to the uplink gain Gup; when performing downlink flight time measurements, the variable gain amplifier is configured to the downlink gain Gdn; if the echo amplitude changes between two uplink measurements, adjust the uplink gain setting Gup; if the echo amplitude changes between two downlink measurements, adjust the downlink gain Gdn.

4. An automatic gain control method for an ultrasonic flow metering device as defined in claim 3, characterized in that: Based on the changes and magnitudes of one or more ultrasonic echoes from uplink and downlink measurements, the flight time measurement error is determined to be within a reasonable range by using the set maximum allowable pulse width variation value Pmax. If the actual pulse width change exceeds Pmax, the flight time measurement error is determined to be outside the reasonable range. The measurement result is then discarded, and the measurement is repeated promptly.

5. An automatic gain control circuit for an ultrasonic flow metering device, based on the automatic gain control method for an ultrasonic flow metering device according to any one of claims 1-4, characterized in that: Includes a transmitting circuit for controlling the transmission of electrical signals at a specific frequency to the transducer; An ultrasonic transducer, comprising a pair of transducers, enables the transmission of ultrasonic signals and the reception of echo signals. A variable gain amplifier for amplifying echo signals with configurable gain; A variable threshold comparator is used to compare the echo signal output by the amplifier with a set threshold and output a comparison level. The zero-crossing comparator is used to compare the amplified subsequent echo signal with the zero point after the first wave is detected by the variable threshold comparator, and output the comparison level when the echo signal crosses the zero point. The time-of-flight measurement unit is used to measure the flight time of an ultrasonic wave from its emission to the zero-crossing point of the effective echo output by the zero-crossing comparator. The pulse width measurement unit is used to measure the width of one or more pulse signals output by the variable threshold comparator to obtain the pulse width value. A time-to-digital converter is used to convert the start time pulse signals of the time-of-flight measurement unit and the pulse width measurement unit into digital signals; The computing and control unit is used to perform data processing, gain control strategy calculation, and overall hardware parameter control.

6. The automatic gain control circuit for an ultrasonic flow metering device as described in claim 5, characterized in that: The variable gain amplifier has an uplink gain configuration Gup and a downlink gain configuration Gdn, and Gup and Gdn can be configured independently; During a single measurement process, specifically a single uplink and downlink differential time-of-flight measurement, select Gup for uplink time-of-flight measurement and Gdn for downlink time-of-flight measurement.

7. The automatic gain control circuit for an ultrasonic flow metering device as described in claim 5, characterized in that: The variable threshold comparator has a first-wave threshold configuration value Vf and a pulse width detection threshold configuration value Vp. During a measurement, the first-wave threshold configuration value Vf is configured first. After the first wave detection is completed, it switches to the pulse width detection threshold configuration value Vp to perform pulse width detection.

8. The automatic gain control circuit for an ultrasonic flow metering device as described in claim 5, characterized in that: The time-of-flight measurement unit measures and records the flight time of the ultrasonic wave from its emission to the zero-crossing point of one or more ultrasonic echoes output by the zero-crossing comparator, and the number of such units is configurable. The pulse width measurement unit measures and records the width of the pulse signal output by one or more variable threshold comparators, and can measure either the high-level width or the low-level width, and the number of such units is configurable.

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