Automatic gain control method and circuit for ultrasonic flow metering device

Abstract

The invention provides an automatic gain control method and circuit of an ultrasonic flow metering device, and aims to improve the accuracy and stability of flow metering. According to the method, the gain is automatically adjusted by measuring the pulse width of an echo signal and comparing the pulse width with an expected value. The circuit comprises a transmitting circuit, an ultrasonic transducer, a variable gain amplifier, a variable threshold comparator, a zero-crossing comparator, a flight time measuring unit, a pulse width measuring unit, a time-to-digital converter and a calculation and control unit. According to the scheme, independent gain configuration of uplink and downlink flight time and a fine gain adjustment strategy based on echo amplitude change can be realized. In addition, by setting the allowable maximum pulse width change value, whether the measurement error is within a reasonable range can be automatically judged, and re-measurement can be carried out when necessary. According to the integrated design scheme, the flexibility and the response speed of measurement are improved, the signal processing flow is optimized, and an innovative solution is provided for ultrasonic flow metering.

Description

Technical Field

[0001] The invention relates to the field of ultrasonic metering devices, and in particular to an automatic gain control method and circuit for ultrasonic flow metering devices. Background Art

[0002] In the field of ultrasonic flow measurement, traditional measurement techniques rely on measuring the time of flight (TOF) of ultrasonic signals to calculate the flow rate and flow rate of the fluid. These systems usually include a transmitting circuit, an ultrasonic transducer, a signal amplifier, and a signal processing unit. However, these traditional systems have limitations when dealing with measurements under different environmental conditions. For example, the amplitude of the echo signal may fluctuate in the case of changes in temperature, pressure, flow rate, or changes in gas composition, resulting in inaccurate measurement results. In addition, fixed gain settings cannot adapt to these changes, which limits the stability and accuracy of the measurement.

[0003] The present invention proposes an automatic gain control method and circuit for an ultrasonic flow metering device, which adapts to environmental changes by accurately controlling the gain, improves measurement accuracy and stability, speeds up system response, and implements an accurate gain adjustment strategy. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, an object of the present 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 object, the technical solution of the present invention is as follows:

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

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

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

[0009] c. Determine whether the amplitude of the echo signal is too large or too small based on the size 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, an echo signal with the expected amplitude is obtained.

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

[0013] Furthermore, in the same flight time measurement process, the first wave detection of the echo signal is completed, the flight time measurement is realized by zero-crossing detection, and the pulse width measurement is realized by threshold detection, and the flight time measurement can be performed before or after the pulse width measurement. The flight time of one or more echo zero-crossing points and the pulse width of one or more echoes can be measured.

[0014] In the above technical solution, the measurement efficiency is improved by completing the first wave detection, zero-crossing detection and pulse width measurement in the same flight time measurement process. At the same time, the flight time measurement is allowed to be performed before or after the pulse width measurement, which increases the flexibility of the measurement and enables the system to respond to environmental changes more quickly, adjust the gain in time, and maintain the measurement accuracy.

[0015] Furthermore, the automatic gain is to adjust the gain of the variable gain amplifier according to the change and size of one or more ultrasonic echo amplitudes.

[0016] Set N measured pulse width signals. If the amplitude of N1 echo signal 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 by 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 by K2. The values ​​of N1, N2, M1, and M2 can be configured independently.

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

[0018] Furthermore, the automatic gain is to adjust the gain of the variable gain amplifier according to the accumulated value of a plurality of echo pulse width deviation values.

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

[0020] In the above technical solution, the gain is adjusted by accumulating multiple echo pulse width deviation values, providing a gain adjustment method based on cumulative error. This method can reduce the impact of accidental errors, make the gain adjustment more robust, and improve the adaptability and reliability of the system in complex environments.

[0021] Specifically, when performing uplink flight time measurement, the variable gain amplifier gain value is configured as the uplink amplifier gain Gup. When performing downlink flight time measurement, the variable gain amplifier gain value is configured as the downlink amplifier gain Gdn. If the echo amplitude changes between two uplink measurements, the uplink amplifier gain setting Gup is adjusted. If the echo amplitude changes between two downlink measurements, the downlink amplifier gain Gdn is adjusted.

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

[0023] Specifically, according to the change and size of the amplitude of one or more ultrasonic echoes in the uplink measurement and the downlink measurement, it is determined whether the flight time measurement error is within a reasonable range by setting the maximum allowable pulse width change value Pmax.

[0024] If the actual pulse width variation exceeds Pmax, it is determined that the flight time measurement error is not within a reasonable range, and the measurement result is discarded and re-measured in time.

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

[0026] In order to realize the above 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 an electrical signal of a specific frequency to the transducer.

[0028] The ultrasonic transducer includes a pair of transducers to realize the sending of ultrasonic signals and the receiving of echo signals.

[0029] A variable gain amplifier is used to amplify the echo signal with configurable gain.

[0030] The variable threshold comparator is used to compare the echo signal output by the amplifier with the 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 variable threshold comparator detects the first wave, and output a comparison level when the echo signal crosses the zero point.

[0032] The flight time measurement unit is used to measure the flight time from the emission of the ultrasonic wave 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 a pulse width value.

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

[0035] The calculation and control unit is used to realize 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 specifically, improves the integration and practicality of the system, and is easy to apply 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 measurement process, during an uplink and downlink differential flight time measurement, when measuring the uplink flight time, select Gup; when measuring the downlink flight time, select Gdn.

[0039] In the above technical solution, by allowing the uplink gain configuration Gup and the downlink gain configuration Gdn of the variable gain amplifier to be independently configured, a more flexible gain adjustment solution is provided. This design enables the system to automatically select the most appropriate gain configuration according to the actual measurement situation, optimizes the signal amplification effect, and improves 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 first configured. After the first wave detection is completed, it is switched to the pulse width detection threshold configuration value Vp to perform pulse width detection.

[0041] In the above technical solution, the variable threshold comparator is provided with a first wave threshold configuration value Vf and a pulse width detection threshold configuration value Vp, and automatically switches during the measurement process, thereby improving the degree of automation of the measurement. This design enables the system to automatically adjust the threshold according to different measurement stages, thereby improving the accuracy and efficiency of the measurement.

[0042] Specifically, the flight time measurement unit measures and records the flight time from the ultrasonic emission to the zero-crossing point of one or more ultrasonic echoes output by the zero-crossing comparator, and the number 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 the high level width or the low level width, and the number is configurable.

[0044] In the above technical solution, by making the number of flight time measurement units and pulse width measurement units configurable, higher flexibility and adaptability are provided. This design enables the system to adjust the number of measurement units according to actual needs, optimizes resource allocation, and improves 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 according to its deviation from the expected value, the present invention can ensure 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 the error caused by signal amplitude fluctuations, and thus improves the stability of the metering process.

[0047] (ii) Signal processing capability: The present invention realizes 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 features of the signal, such as the zero-crossing point and specific amplitude level, thereby optimizing the signal processing capability and improving the measurement accuracy of fluid velocity and flow rate.

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

[0049] (IV) Gain adjustment strategy: The present invention provides an accurate gain adjustment strategy by accumulating multiple echo pulse width deviation values ​​or adjusting the gain according to the change of a single echo amplitude. This strategy enables the system to make detailed gain adjustments based on actual measurement results, optimizes the signal amplification effect, and further improves the accuracy and reliability of flow measurement. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0052] Figure 3 It is a schematic diagram of the relationship between the pulse width of the output signal of the variable threshold comparator and the amplitude of the echo signal in the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and exemplary descriptions. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention.

[0054] Application Overview

[0055] In the field of ultrasonic flow measurement, the industry usually uses fixed gain amplifiers to process echo signals to calculate the flow rate and flow rate of the fluid. This method can provide stable measurement results under ideal conditions, but in actual applications, due to environmental factors such as changes in temperature, pressure, flow rate, and differences in gas composition, the amplitude of the echo signal will change, causing the fixed gain amplifier to be unable to adapt to these changes, thereby affecting the accuracy and stability of the measurement. In addition, traditional measurement systems usually take a long time to perform first wave detection, zero crossing detection, and pulse width measurement, resulting in slow system response and inability to capture rapid changes in fluid characteristics in a timely manner. Furthermore, the existing gain adjustment strategy lacks flexibility and accuracy, and cannot be fine-tuned according to actual measurement results, which limits the accuracy and reliability of flow measurement.

[0056] Example

[0057] The present invention relates to an automatic gain control method for an ultrasonic flow metering device and a corresponding circuit design thereof. The method automatically adjusts the gain to adapt to environmental changes, ensures the stability of the echo signal amplitude, and thus improves 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. At the same time, determine the expected width of the variable threshold comparator output pulse signal, as well as the first wave detection threshold Vf and pulse width measurement threshold Vp.

[0059] Please refer to Figure 1 After the calibration is completed, the system enters the normal working state. The transmitting circuit generates an electrical signal of a specific frequency, sends an 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 according to the difference between uplink and downlink measurements.

[0060] During the uplink measurement process, 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 first wave detection threshold Vf. When the amplitude of the echo signal exceeds Vf, the detection threshold of the comparator automatically switches to the pulse width measurement threshold Vp. At this time, the flight time measurement unit starts timing, from the ultrasonic transmission start point to the effective echo zero crossing point output by the zero crossing comparator, and measures and records the flight time of 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 the low level width, and records these values.

[0061] Please refer to Figure 2 The downlink measurement process is similar to the uplink measurement, and the downlink gain value Gdn is used for measurement. By comparing the actual measured pulse width value 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 value is greater than the expected value, it indicates that the signal amplitude has increased, and the downlink measurement gain value Gdn needs to be reduced; otherwise, Gdn needs to be increased.

[0062] In order to more accurately control the gain adjustment, the present invention proposes two control strategies. Control strategy 1 determines whether to reduce or increase the gain based on the situation that more than two echo pulse width values ​​are too large or too small. Control strategy 2 adjusts the gain based on the accumulated value of the four echo pulse width deviation values. These strategies ensure that the system can make detailed gain adjustments based on the actual measurement results, optimize the signal amplification effect, and improve the accuracy and reliability of flow measurement.

[0063] Example

[0064] Assume that the expected pulse width values ​​P1e, P2e, P3e, and P4e are 500ns, 500ns, 450ns, and 200ns, respectively, and the maximum allowable pulse width change Pmax is configured to be 150ns. If the pulse width values ​​P1_up, P2_up, P3_up, and P4_up measured this time are 600ns, 600ns, 500ns, and 300ns, respectively, then according to control strategy 1, more than two echo pulse width values ​​are too large and greater than 40ns, and the gain Gup needs to be reduced. 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 three echo pulse widths are measured to be too large and greater than twice of 40ns, indicating that the amplitude of the echo signal is too high, and the uplink measurement gain Gup needs to be reduced by two levels.

[0065] Please refer to Figure 3 According to control strategy 2, if the 4 echo pulse width values ​​are too large, and the accumulated deviation value is equal to 350ns, which is greater than 4*80ns, the gain Gup needs to be reduced by four levels. If the pulse width values ​​P1_up, P2_up, P3_up, and P4_up measured this time are 400ns, 400ns, 350ns, and 150ns respectively, it means that the echo signal becomes smaller and the gain Gup needs to be increased by two levels.

[0066] When the measured pulse width reaches 655ns, the deviation value is 155ns, which is greater than Pmax, indicating that the signal amplitude changes too much and the flight time error of this measurement is large. The flight data of this measurement should be abandoned. After adjusting the gain, re-perform the uplink measurement.

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

[0068] Specific working process

[0069] Perform system calibration to determine the initial gain values ​​Gup_init and Gdn_init for uplink and downlink measurements, and determine the expected width of the variable threshold comparator output pulse signal, as well as the first wave detection threshold Vf and pulse width measurement threshold Vp. After calibration, the transmitting circuit generates an electrical signal of a specific frequency, and sends and receives echo signals through the ultrasonic transducer. The variable gain amplifier is independently configured as Gup and Gdn according to the difference between 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 first wave detection threshold Vf. After the echo signal amplitude exceeds Vf, the detection threshold of the comparator automatically switches to the pulse width measurement threshold Vp. The flight time measurement unit counts from the start point of the ultrasonic transmission until the effective echo output of the zero-crossing comparator crosses the zero point, and measures and records the flight time of 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, and the downlink gain value Gdn is used for measurement. 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 has increased, and the downlink measurement gain value Gdn is reduced; otherwise, Gdn needs to be increased.

[0072] The present invention proposes two control strategies to accurately control the gain adjustment. Control strategy 1 determines whether to reduce or increase the gain based on the situation that more than two echo pulse width values ​​are too large or too small. Control strategy 2 adjusts the gain based on the accumulated value of the four echo pulse width deviation values. These strategies ensure that the system can make detailed gain adjustments based on the actual measurement results, optimize the signal amplification effect, and improve the accuracy and reliability of flow measurement.

[0073] When the measured pulse width value deviation exceeds the maximum allowable pulse width change Pmax, the system will determine that the flight time error of this measurement is large, abandon the flight data of this measurement, and re-measure after adjusting the gain. This can ensure 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 process of the downlink measurement is similar to that of the uplink. After completing the 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 will adjust the gain of the variable gain echo amplifier in time according to the change of the echo signal amplitude, so that the echo signal amplitude fluctuation is stable within the required range to ensure measurement accuracy and stability.

[0074] The various technical features described in the above exemplary embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the various technical features in the above exemplary embodiments 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 in that: The following steps are involved: a. measuring the pulse width of one or more echoes under the comparator threshold during the ultrasonic flight time; b. Compare the measured pulse width with the expected pulse width to obtain a deviation value; c. Determine whether the amplitude of the echo signal is too large or too small according to the size 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, an echo signal with the expected amplitude is obtained.

2. The automatic gain control method for an ultrasonic flow metering device according to claim 1, characterized in that: In the same flight time measurement process, the first wave detection of the echo signal is completed, the flight time measurement is realized through zero-crossing detection, and the pulse width measurement is realized through threshold detection. The flight time measurement can be before or after the pulse width measurement; the flight time of one or more echo zero-crossing points and the pulse width of one or more echoes can be measured.

3. The automatic gain control method for an ultrasonic flow metering device according to claim 2, characterized in that: Automatic gain is to adjust the gain of the variable gain amplifier according to the change and size of one or more ultrasonic echo amplitudes; Set N pulse width signals to be measured. If the amplitude of N1 echo signal 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 by K1. If the amplitude of N2 echo signal 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 by K2. The values ​​of N1, N2, M1, and M2 can be configured independently.

4. The automatic gain control method for an ultrasonic flow metering device according to claim 2, characterized in that: Automatic gain is to adjust the gain of the variable gain amplifier according to the accumulated value of multiple echo pulse width deviation values; If the cumulative value of the P1 echo pulse width deviation values ​​is greater than Q1, the gain G1 level is reduced; if the cumulative value of the P2 echo pulse width deviation values ​​is less than Q2, the gain G2 level is increased, and the values ​​of P1, P2, Q1, and Q2 can be configured independently.

5. The automatic gain control method for an ultrasonic flow metering device according to claim 1, characterized in that: When performing uplink flight time measurement, the variable gain amplifier gain value is configured as the uplink amplifier gain Gup; when performing downlink flight time measurement, the variable gain amplifier gain value is configured as the downlink amplifier gain Gdn; if the echo amplitude changes between two uplink measurements, the uplink amplifier gain setting Gup is adjusted; if the echo amplitude changes between two downlink measurements, the downlink amplifier gain Gdn is adjusted.

6. An automatic gain control method for an ultrasonic flow metering device as claimed in claim 5, characterized in that: According to the change and size of one or more ultrasonic echo amplitudes in uplink and downlink measurements, the maximum allowable pulse width change value Pmax is set to determine whether the flight time measurement error is within a reasonable range; If the actual pulse width variation exceeds Pmax, it is determined that the flight time measurement error is not within a reasonable range, and the measurement result is discarded and re-measured in time.

7. An automatic gain control circuit for an ultrasonic flow metering device, based on an automatic gain control method for an ultrasonic flow metering device according to any one of claims 1 to 6, characterized in that: It includes a transmitting circuit for controlling the transmission of an electrical signal of a specific frequency to the transducer; An ultrasonic transducer, comprising a pair of transducers, for transmitting ultrasonic signals and receiving echo signals; A variable gain amplifier for amplifying the echo signal with configurable gain; A variable threshold comparator, used for comparing the echo signal output by the amplifier with a set threshold and outputting a comparison level; A 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 a comparison level when the echo signal crosses the zero point; A flight time measurement unit, used to measure the flight time from the ultrasonic wave being emitted to the zero-crossing point of the effective echo output by the zero-crossing comparator; A pulse width measurement unit, used to measure the width of one or more pulse signals output by the variable threshold comparator to obtain a pulse width value; A time-to-digital converter, used for converting the start time pulse signals of the flight time measurement unit and the pulse width measurement unit into digital signals; The calculation and control unit is used to realize data processing, gain control strategy calculation and overall hardware parameter control.

8. An automatic gain control circuit for an ultrasonic flow metering device as claimed in claim 7, 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 measurement process, during an uplink and downlink differential flight time measurement, when measuring the uplink flight time, select Gup; when measuring the downlink flight time, select Gdn.

9. The automatic gain control circuit for an ultrasonic flow metering device according to claim 7, 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 process, the first wave threshold configuration value Vf is first configured. After completing the first wave detection, it is switched to the pulse width detection threshold configuration value Vp to perform pulse width detection.

10. The automatic gain control circuit for an ultrasonic flow metering device according to claim 7, characterized in that: The flight time measurement unit measures and records the flight time from the ultrasonic emission to the zero-crossing point of one or more ultrasonic echoes output by the zero-crossing comparator, and the number is configurable; 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 the high level width or the low level width, and the number is configurable.

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