Improved gas metering method based on tdc scheme

Abstract

The application discloses an improved gas metering method based on a TDC scheme, and specifically comprises the following steps: adopting a TDC metering test scheme, installing a transducer on a gas pipeline; setting a transducer driving waveform frequency and a signal sampling rate, performing wave sending and ADC sampling, obtaining downstream and upstream ultrasonic wave signal waveform data, dividing the ultrasonic wave signal waveform data into an ultrasonic wave signal waiting section and an ultrasonic wave signal arrival section, and obtaining the time used by the ultrasonic wave signal waiting section; after performing interpolation, waveform transformation, derivation and other processing on the data of the ultrasonic wave signal arrival section, obtaining a signal arrival key point, and acquiring the time used from starting to receive the ultrasonic wave signal to the signal arrival key point; after performing re-interpolation on the key point, obtaining a corrected time, thereby obtaining the total time of the ultrasonic wave signal from sending to receiving; calculating the time used by ultrasonic wave upstream flow in the gas pipeline, the time used by ultrasonic wave downstream flow, and the difference between the two, thereby calculating the gas flow rate and instantaneous flow in combination with the difference. The beneficial effect is that the waveform processing precision is high, and the ultrasonic wave metering is more accurate.

Description

Technical Field

[0001] This invention belongs to the technical field of ultrasonic gas metering, specifically relating to an improved gas metering method based on the TDC scheme. Background Technology

[0002] Currently, there are two main types of ultrasonic flow meters on the market for natural gas metering: the first is a metering scheme based on the correlation method; the other is the TDC metering method, also known as the TDC threshold method.

[0003] Among these methods, the correlation method involves a large amount of computation and a long measurement time, which is not conducive to rapid measurement, so it is generally used more in the civilian field; however, it has high accuracy, is less affected by temperature, and has lower performance requirements for ultrasonic transducers. The TDC threshold method is more common and mature, with integrated solutions, fast measurement speed, low power consumption, and is conducive to rapid measurement, and has a relatively wide measurement range, making it suitable for industrial and commercial fields; however, it is sensitive to temperature and medium, and has high requirements for sensors, so it was initially used more in the field of liquid measurement, and later gradually transitioned to the field of gas measurement.

[0004] Due to limitations in measurement integration solutions and ultrasonic sensors, domestic enterprises have made relatively few achievements in the field of industrial and commercial natural gas metering for medium and large diameters. When using the TDC threshold method, they are easily affected by gas composition and ambient temperature and pressure, or by the characteristics of ultrasonic sensors, which may lead to measurement errors in some cases.

[0005] Common TDC threshold method integrated metering chips include the GP2x series. Taking the GP22 as an example, its principle is as follows: The measurement process of TDC-GP22 is as follows... Figure 1 As shown, its main feature is finding the first hit level. By setting a threshold for first hit detection, the propagation time is determined based on the position of the first received waveform that is greater than or equal to the first hit threshold, which is crucial to measurement accuracy. To accurately locate the first hit position, the chip can be limited by setting many parameters, including adjusting the amplification of the received signal, setting the amplitude of the first hit detection, and the pulse width ratio of the first hit trigger comparison, etc., all to adjust according to the received signal in practice to ensure that the first hit position is consistently located in each measurement (e.g., always the third waveform). However, in long-term use, it has been found that the first hit position is often related to gas composition, detection temperature, pressure, and changes in transducer characteristics over a long period. In actual detection, any deviation in the first hit position detection due to any factor will lead to significant errors. In particular, almost all flow meter products are calibrated based on air; when measuring natural gas, the waveform characteristics change significantly, and if a recognition deviation occurs, unacceptable measurement errors will result. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the technical problem to be solved by this invention is: how to provide an improved gas metering method based on the TDC scheme, which accurately locates the actual arrival point of the ultrasonic wave in the received ultrasonic waveform, eliminates the influence of changes in the ultrasonic propagation medium and environment, improves the accuracy of ultrasonic wave propagation time measurement in gas pipelines, and thus improves the accuracy of gas metering.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] An improved gas metering method based on the TDC scheme, the key technology of which lies in the following steps:

[0009] Step 1: Using the TDC metering and testing scheme, install transducers on the gas pipeline;

[0010] Step 2: Set the transducer drive waveform frequency F and signal sampling rate Y, perform wave transmission and ADC sampling, and obtain N sets of ultrasonic signal waveform data; N is an integer greater than or equal to 2;

[0011] Step 3: Based on the characteristics of the ultrasonic signal before and after its arrival, the ultrasonic signal waveform data is divided into the ultrasonic signal waiting segment and the ultrasonic signal arrival segment, and the time T0 used for the ultrasonic signal waiting segment is obtained.

[0012] Step 4: After processing the data and waveform of the ultrasonic signal arrival segment, the signal arrival key point P is obtained, and the time T1 from the start of receiving the ultrasonic signal to the signal arriving at the key point P is obtained.

[0013] Step 5: Correct the signal arrival at key point P obtained in Step 4 to obtain the signal arrival at correction point Q and correction time T2, thereby obtaining the total time T of the ultrasonic signal from transmission to reception;

[0014] T = T0 + T1 + T2;

[0015] Step Six: Based on Steps Three to Five, obtain the time T required for ultrasonic backflow in the gas pipeline. NL The time T used for ultrasonic downstream flow SL ;

[0016] Step 7: Calculate the time difference ΔT = T for the forward and reverse flow of gas in the gas pipeline. NL -T SL ;

[0017] Step 8: Calculate the gas velocity V and instantaneous flow rate Q based on the time difference ΔT between upstream and downstream propagation. L .

[0018] Through the above design, the received waveform is analyzed and processed to find the point with the largest rate of change of waveform peak value, which is taken as the actual time when the ultrasonic wave arrives at the receiving transducer. In this invention, after waveform processing and data processing of the sampled data, the data accuracy is improved, key points are found, and then the key points are corrected in combination with the key points to obtain more accurate correction points. By combining the final correction points, the arrival time of the ultrasonic wave is confirmed, thereby calculating the gas velocity and instantaneous flow rate, resulting in high measurement accuracy.

[0019] A further solution is as follows: In step one, when installing the sampling equipment, a co-current transducer and a counter-current transducer are sequentially installed along the airflow direction on the gas pipeline. The co-current transducer and the counter-current transducer are respectively installed on both sides of the gas pipeline. The inner diameter of the gas pipeline is D, the straight-line distance between the co-current transducer and the counter-current transducer is L, and the angle between the line between the two and the wall of the gas pipeline is θ.

[0020] Using the above scheme, based on the co-current and counter-current transducers on both sides of the pipeline, the ultrasonic signal emitted by any one transducer can pass through the gas in the pipeline and be received by the other transducer. With the two transducers set one after the other, the ultrasonic waves generated will form co-current or counter-current ultrasonic waves when they pass through the gas in the pipeline.

[0021] A further technical solution, in order to achieve the calculation, includes at least one set of downstream ultrasonic signal waveform data and at least one set of upstream ultrasonic signal waveform data in the N sets of ultrasonic signal waveform data.

[0022] A further technical solution, step four, includes the following:

[0023] Step 41: Interpolate the arrival segment data of the ultrasonic signal and increase the signal sampling rate Y by a factor of M, that is, after the increase, the signal sampling rate is Y*M, and obtain the ultrasonic preprocessed waveform.

[0024] Step 42: Perform waveform transformation on the preprocessed ultrasonic waveform using the Hilbert algorithm to obtain the ultrasonic envelope;

[0025] Step 43: After obtaining the derivative data of the ultrasonic envelope by taking the derivative of the data, the position where the sign of the derivative data of the envelope changes is the position corresponding to the arrival of the signal at the key point P;

[0026] Step 44: Based on the location of the signal reaching the key point P within the ultrasonic envelope, obtain the time T1 taken from the start of receiving the ultrasonic signal to the signal reaching the key point P.

[0027] By employing the above steps, interpolation processing of the ultrasonic signal arrival segment data increases the data by a factor of M, thereby increasing the amount of ultrasonic data, making the waveform smoother, and improving its accuracy. Sampling accuracy determines envelope accuracy, which in turn determines the resolution of the measurement time. By calculating the point of change of the derivative sign of the envelope, i.e., the point of maximum rate of change of the original waveform peak value, the true arrival point of the ultrasonic wave is found, eliminating the influence of the ultrasonic propagation medium and ambient temperature.

[0028] A further technical solution, step five, details are as follows:

[0029] Step 51: Interpolate the signal to G points near key point P into a values ​​to obtain key point interpolation data. The accuracy after interpolation is [value missing].

[0030] Step 52: Find the new maximum value point from the key point interpolation data, which is the signal reaching the correction point Q;

[0031] Step 53: Based on the relative positions of the signal arrival at correction point Q and the signal arrival at key point P within the envelope, obtain the correction time T2;

[0032] If the signal reaches the critical point P before the signal reaches the correction point Q, then

[0033] If the signal reaches the critical point P after the signal reaches the correction point Q, then

[0034] By sampling the above method, after finding the key point, the location of the maximum rate of change can be determined to be near the key point. By selecting G points near the key point and interpolating again, the resolution of the envelope near the key point is improved. The maximum value point after interpolation is found, which is the final signal arrival correction point Q. After correcting the time in step four using the correction point location, the gas velocity and instantaneous flow rate are calculated.

[0035] In step eight, the formulas for calculating the gas velocity V and instantaneous flow rate Q are as follows:

[0036]

[0037] Q = K * π * D 2 *V / 4;

[0038] Wherein, K is the velocity distribution correction parameter; this velocity distribution correction parameter is related to the gas composition, temperature, pressure, Reynolds number and the surface morphology coefficient, and can be obtained by consulting the relevant documentation;

[0039] D is the inner diameter of the gas pipeline;

[0040] L is the straight-line distance between the co-current transducer and the counter-current transducer;

[0041] θ is the angle between the line from the downstream transducer to the upstream transducer and the wall of the gas pipeline.

[0042] Given the speed C of ultrasonic waves propagating in a stationary combustion gas and the gas flow velocity V, we can obtain:

[0043] Time required for ultrasonic backflow in gas pipeline

[0044] Then it exists:

[0045] Time taken for ultrasonic flow in gas pipeline

[0046] Then it exists:

[0047] C is the speed at which ultrasound propagates within a stationary gaseous atmosphere.

[0048] From formula (2)-(1), we get:

[0049]

[0050] Thus, the formulas for calculating the gas velocity V and instantaneous flow rate Q are obtained, namely:

[0051]

[0052] Q = K * π * D 2 *V / 4.

[0053] The beneficial effects of this invention are:

[0054] In real-world environments, changes in gas composition, ambient temperature, and pressure can cause variations in the received ultrasonic waveform, but its envelope shape remains almost unchanged, and its characteristics do not alter with environmental conditions. Therefore, the method employed in this invention analyzes and processes the received waveform and its envelope, combining transducer characteristics and specific algorithms to complete calculations. This completely avoids measurement errors caused by factors such as changes in the amplitude of the received waveform, ensuring the stability and reliability of the measurement. Attached Figure Description

[0055] Figure 1 A schematic diagram of the existing TDC measurement waveform;

[0056] Figure 2 This is a flowchart of the measurement steps of the present invention;

[0057] Figure 3 Waveform obtained from transducer sampling;

[0058] Figure 4 This is a diagram of the interpolated waveform and its corresponding envelope. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to the accompanying drawings.

[0060] In specific implementation, such as Figures 2 to 4 As shown:

[0061] An improved gas metering method based on the TDC scheme, see [link to relevant documentation]. Figure 2 Follow these steps:

[0062] Step 1: Using the TDC metering and testing scheme, install transducers on the gas pipeline;

[0063] When installing the sampling equipment, a co-current transducer and a counter-current transducer are sequentially installed along the airflow direction on the gas pipeline. The co-current transducer and the counter-current transducer are respectively installed on both sides of the gas pipeline. The inner diameter of the gas pipeline is D. The straight-line distance between the co-current transducer and the counter-current transducer is L. The angle between the line between the two and the wall of the gas pipeline is θ.

[0064] In this embodiment, the environment in which the gas pipeline is located is set to a room temperature of 25°C and the gas pressure is atmospheric pressure.

[0065] Step 2: Set the transducer drive waveform frequency F and signal sampling rate Y, perform wave transmission and ADC sampling, and obtain N sets of ultrasonic signal waveform data; N is an integer greater than or equal to 2;

[0066] In this embodiment, N=2; it includes a set of downstream ultrasonic signal waveform data and a set of upstream ultrasonic signal waveform data. The waveforms corresponding to the ultrasonic signal waveform data are detailed below. Figure 3 .

[0067] In this embodiment, the transducer drive waveform frequency F is 200KHz; the signal sampling rate Y is 4MHz;

[0068] Step 3: Based on the characteristics of the ultrasonic signal before and after its arrival, the ultrasonic signal waveform data is divided into the ultrasonic signal waiting segment and the ultrasonic signal arrival segment, and the time T0 used for the ultrasonic signal waiting segment is obtained.

[0069] Step 4: After processing the data and waveform of the ultrasonic signal arrival segment, the signal arrival key point P is obtained, and the time T1 from the start of receiving the ultrasonic signal to the signal arriving at the key point P is obtained.

[0070] The specific content is as follows:

[0071] Step 41: Interpolate the arrival segment data of the ultrasonic signal and increase the signal sampling rate from 4MHz by M=10 times. After the increase, the signal sampling rate is Y*M=4MHz*10=40MHz, and the ultrasonic preprocessed waveform is obtained.

[0072] Interpolation here can better preserve the shape of the original waveform and achieve a high sampling rate without improving hardware performance.

[0073] Step 42: Perform waveform transformation on the preprocessed ultrasonic waveform using the Hilbert algorithm to obtain the ultrasonic envelope; see details for the specific envelope. Figure 4 .

[0074] Step 43: After obtaining the derivative data of the ultrasonic envelope by taking the derivative of the data, the position where the sign of the derivative data of the envelope changes is the position corresponding to the arrival of the signal at the key point P;

[0075] Step 44: Based on the location of the signal reaching the key point P within the ultrasonic envelope, obtain the time T1 taken from the start of receiving the ultrasonic signal to the signal reaching the key point P.

[0076] In this embodiment

[0077] Step 5: Based on the signal obtained in Step 4, make corrections to the key point P, obtaining the signal arrival point Q and the correction time T2. Specifically:

[0078] Step 51: Interpolate the signal to G points near key point P into a values ​​to obtain key point interpolation data. The accuracy after interpolation is [value missing].

[0079] In this embodiment, let G = 5, then the 5 points have four periods;

[0080] In this embodiment, the interpolation has a = 1001 values, so the 1001 values ​​have 1000 cycles.

[0081] After interpolation, the precision is equal to

[0082] Step 52: Find the new maximum value point from the key point interpolation data, which is the signal reaching the correction point Q;

[0083] Step 53: Based on the relative positions of the signal arrival at correction point Q and the signal arrival at key point P within the envelope, obtain the correction time T2;

[0084] If the signal reaches the critical point P before the signal reaches the correction point Q, then:

[0085]

[0086] If the signal reaches the critical point P after the signal reaches the correction point Q, then:

[0087]

[0088] Thus, the total time T from the transmission of the ultrasonic signal to the reception is obtained;

[0089] Where T = T0 + T1 + T2;

[0090] Step Six: Based on Steps Three to Five, obtain the time T required for ultrasonic backflow in the gas pipeline. NL The time T used for ultrasonic downstream flow SL ;

[0091] Step 7: Calculate the time difference ΔT = T for the forward and reverse flow of gas in the gas pipeline. NL -T SL ;

[0092] Step 8: Calculate the gas velocity V and instantaneous flow rate Q based on the time difference ΔT between upstream and downstream propagation. L .

[0093] Gas velocity V and instantaneous flow rate Q L The calculation formula is:

[0094]

[0095] Q L =K*π*D 2 *V / 4;

[0096] Wherein, K is the velocity distribution correction parameter; this velocity distribution correction parameter is related to the gas composition, temperature, pressure, Reynolds number and the surface morphology coefficient, and can be obtained by consulting the relevant documentation;

[0097] D is the inner diameter of the gas pipeline;

[0098] L is the straight-line distance between the co-current transducer and the counter-current transducer;

[0099] θ is the angle between the line from the downstream transducer to the upstream transducer and the wall of the gas pipeline.

[0100] The working principle of this invention is as follows:

[0101] Compared to existing TDC metering, this method performs data analysis and waveform analysis on the waveform, continuously improving waveform accuracy to determine a more precise ultrasonic arrival time. This allows for accurate calculation of the airflow velocity and instantaneous flow rate within the pipe. The result is higher precision and more accurate metering.

[0102] The above are merely preferred embodiments of the present invention. It should be noted that any modifications and improvements made by those skilled in the art without departing from the present technical solution should also be considered to fall within the scope of protection claimed in this claim.

Claims

1. An improved gas metering method based on the TDC scheme, characterized in that... Follow these steps: Step 1: Using the TDC metering and testing scheme, install transducers on the gas pipeline; Step 2: Set the transducer drive waveform frequency F and signal sampling rate Y, perform wave transmission and ADC sampling, and obtain N sets of ultrasonic signal waveform data; N is an integer greater than or equal to 2; Step 3: Based on the characteristics of the ultrasonic signal before and after its arrival, divide the ultrasonic signal waveform data into an ultrasonic signal waiting period and an ultrasonic signal arrival period, and obtain the time taken for the ultrasonic signal waiting period. ; Step 4: After processing the data and waveforms of the ultrasonic signal arrival segment, the signal arrival key point P is obtained, and the time taken from the initial reception of the ultrasonic signal to its arrival at key point P is acquired. ; Step 5: Based on the signal obtained in Step 4, make corrections to the key point P, obtaining the signal arrival point Q and the correction time. Thus, the total time from the transmission of the ultrasonic signal to the reception is obtained. ; ； Step Six: Based on Steps Three to Five, obtain the time required for ultrasonic backflow in the gas pipeline. Time taken for ultrasonic downstream ; Step 7: Calculate the time difference between upstream and downstream gas propagation in the gas pipeline. ; Step 8: Based on the time difference between upstream and downstream propagation Calculate gas flow rate and instantaneous flow ; The specific content of step four is as follows: Step 41: Interpolate the arrival segment data of the ultrasonic signal, and increase the signal sampling rate Y by a factor of M. That is, after the increase, the signal sampling rate is... The ultrasonic preprocessed waveform is obtained; Step 42: Perform waveform transformation on the preprocessed ultrasonic waveform using the Hilbert algorithm to obtain the ultrasonic envelope; Step 43: After obtaining the derivative data of the ultrasonic envelope by taking the derivative of the data, the position where the sign of the derivative data of the envelope changes is the position corresponding to the arrival of the signal at the key point P; Step 44: Based on the location of the signal reaching key point P within the ultrasonic envelope, obtain the time taken from the initial reception of the ultrasonic signal to its arrival at key point P. ; ; The specific content of step five is as follows: Step 51: Interpolate the signal to G points near key point P into a values ​​to obtain key point interpolation data. The accuracy after interpolation is [value missing]. ; Step 52: Find the new maximum value point from the key point interpolation data, which is the signal reaching the correction point Q; Step 53: Based on the relative positions of the signal arrival at correction point Q and the signal arrival at key point P within the envelope, obtain the correction time. ; If the signal reaches the critical point P before the signal reaches the correction point Q, then ; If the signal reaches the critical point P after the signal reaches the correction point Q, then .

2. The improved gas metering method based on the TDC scheme according to claim 1, characterized in that: In step one, when installing the sampling equipment, a co-current transducer and a counter-current transducer are sequentially installed along the airflow direction on the gas pipeline. The co-current transducer and the counter-current transducer are respectively installed on both sides of the gas pipeline, and the inner diameter of the gas pipeline is [missing information]. The straight-line distance between the co-current transducer and the counter-current transducer is The angle between the two lines and the gas pipeline wall is .

3. The improved gas metering method based on the TDC scheme according to claim 2, characterized in that: In step two, among the N sets of ultrasonic signal waveform data, there is at least one set of downstream ultrasonic signal waveform data and at least one set of upstream ultrasonic signal waveform data.

4. The improved gas metering method based on the TDC scheme according to claim 2, characterized in that: In step eight, the gas flow rate and instantaneous flow The calculation formula is: ； ； Where K is the velocity distribution correction parameter; This refers to the inner diameter of the gas pipeline. The straight-line distance between the co-current transducer and the counter-current transducer; It is the angle between the line from the co-current transducer to the counter-current transducer and the wall of the gas pipeline.

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