A method for calculating the flow rate of a transient flow by a vortex flowmeter

Abstract

The present application relates to vortex flowmeter, specifically relates to a kind of vortex flowmeter measurement transient flow flow calculation method, complete vortex signal simulation to digital acquisition after spectrum analysis is carried out, to the original signal scanned to determine the effective starting point of effective signal, effective end point, and based on effective starting point and effective end point the transient flow flow corresponding to effective signal is calculated;The technical scheme provided by the present application can effectively overcome the defects that cannot be accurately measured in prior art for transient flow.

Description

Technical Field

[0001] This invention relates to vortex flow meters, and more specifically to a method for calculating the flow rate of transient flow measured by a vortex flow meter. Background Technology

[0002] Vortex flow meters are now widely used, especially in the flow detection of steam and medium- and low-pressure gases, due to their high accuracy, wide rangeability, good linearity, zero drift-free operation, simple and robust structure, and convenient installation and maintenance. As a velocity flow meter, it is commonly used for steady-state flow. However, in certain special applications, such as steam injection molding, the steam flow rate rapidly increases from 0 to a large flow rate, then quickly returns to 0 after a short period of time, with the entire process taking anywhere from 1 minute to 10 seconds.

[0003] The invention patent with authorization announcement number CN 101788313 B discloses a high-frequency response transient flow meter, which proposes to use two hot wire velocity probes to measure transient flow rate. Using hot wire velocity probes as sensors, the flow meter is obviously designed based on the principle of thermal diffusion. However, for gas media such as steam or gas media with unclear composition, the hot wire flow meter cannot work properly.

[0004] Existing vortex flow meters have three significant drawbacks when measuring transient flow. First, the presence of damping or filtering causes data smoothing, leading to distortion of results during the transient period. Second, when calculating transient flow using pulse counting, measurement anomalies occur when the flow signal contains noise. More importantly, when using traditional digital signal spectrum analysis methods, the frequencies calculated from the acquired signals over a period of time represent the entire time period, while only a portion of the transient flow may be effective, thus making accurate measurement of transient flow impossible. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a method for calculating the flow rate of transient flow using a vortex flow meter, which can effectively overcome the defect of the existing technology that cannot accurately measure transient flow.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for calculating the flow rate of transient flow measured by a vortex flowmeter involves performing spectrum analysis after the vortex signal is converted from analog to digital, and simultaneously scanning the acquired raw signal to determine the effective start point and effective end point of the effective signal. Based on the effective start point and effective end point, the transient flow rate corresponding to the effective signal is calculated.

[0010] Preferably, the step of traversing and scanning the acquired raw signal to determine the valid start point and valid end point corresponding to the valid signal includes:

[0011] S1. Determine the trend of change of the starting point by taking the difference. If the trend is downward, proceed to S2; otherwise, proceed to S4.

[0012] S2. Scan point by point, determine whether the amplitude of the scan point is greater than the high-level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan that is greater than the high-level threshold, update the current valid ending point; otherwise, proceed to S3.

[0013] S3. When the amplitude of the scan point is less than the low level threshold, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is less than the low level threshold in subsequent scans, update the current valid ending point.

[0014] S4. Scan point by point. Determine whether the amplitude of the scan point is less than the low level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan and is less than the low level threshold, update the current valid ending point. Otherwise, proceed to S5.

[0015] S5. When the amplitude of a scan point is greater than the high-level threshold, the scan point is taken as the valid starting point and a traversal scan is performed. When a point with an amplitude greater than the high-level threshold is scanned in a subsequent scan, the current valid ending point is updated.

[0016] Preferably, the step of calculating the transient flow rate corresponding to the valid signal based on the valid start point and valid end point includes:

[0017] Obtain the positions of the valid start point and valid end point among N sampling points, denoted as N. Start N End The acquired signal is then subjected to spectral analysis to obtain the digital frequency f. n The transient flow rate Q corresponding to the effective signal is calculated using the following formula:

[0018]

[0019] Among them, f s Where is the digital sampling rate, and K is the instrument coefficient of the vortex flowmeter.

[0020] Preferably, the setting of the high-level threshold and the low-level threshold includes:

[0021] Define a threshold level V that can be adjusted by a parameter. th V ref +V th V ref -V th These are respectively used as the high-level threshold and the low-level threshold. When the signal amplitude is greater than the high-level threshold V... ref +V th When the signal amplitude is less than the low-level threshold V, a valid high level is considered to have occurred. ref -V th When this occurs, a valid low level is considered to have occurred;

[0022] Among them, V ref This is the reference voltage.

[0023] Preferably, the vortex shear signal is simulated and then digitally acquired before being subjected to spectrum analysis, including:

[0024] Using the count value of the hardware counter as a reference, determine the current traffic range, and set an appropriate digital sampling rate based on the frequency calculated from the hardware counter to satisfy the sampling theorem.

[0025] Preferably, the step of determining the current traffic range based on the count value of the hardware counter, and setting an appropriate digital sampling rate according to the frequency calculated from the hardware counter to satisfy the sampling theorem, includes:

[0026] The hardware counter frequency is calculated with T0 as the time interval. When the count value C of the hardware counter is... hard When the value exceeds the preset threshold C0, the count value C of the hardware counter is used. hard Set a digital sampling rate f that satisfies the sampling theorem. s Otherwise, the digital sampling rate f s Keep the default sampling rate f sLow .

[0027] (III) Beneficial Effects

[0028] Compared with the prior art, the flow calculation method for transient flow measurement provided by the present invention can dynamically set the sampling rate according to the count value of the hardware counter in a timely manner, and can accurately find the effective start point and effective end point in the acquired signal, determine the precise time of the effective signal, and achieve accurate measurement of transient flow. This not only reduces the fluctuation of measurement error, but also ensures that the measurement error is within 2.5%. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0030] Figure 1 This is a flowchart illustrating the process of determining the valid start point and valid end point of a valid signal during the traversal scanning process in this invention.

[0031] Figure 2 This is a schematic diagram of a typical transient flow signal;

[0032] Figure 3 This is a graph comparing the errors of various algorithms. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] A method for calculating the flow rate of transient flow measured by a vortex flowmeter involves performing spectrum analysis after the vortex signal is converted from analog to digital, and simultaneously scanning the acquired raw signal to determine the effective start point and effective end point of the effective signal. Based on the effective start point and effective end point, the transient flow rate corresponding to the effective signal is calculated.

[0035] ① Before performing spectrum analysis after the vortex shear signal is converted from analog to digital acquisition, it includes:

[0036] Using the count value of the hardware counter as a reference, determine the current traffic range, and set an appropriate digital sampling rate based on the frequency calculated from the hardware counter to satisfy the sampling theorem.

[0037] Specifically, using the count value of the hardware counter as a reference, the current traffic range is determined, and an appropriate digital sampling rate is set according to the frequency calculated from the hardware counter to satisfy the sampling theorem, including:

[0038] The frequency of the hardware counter is calculated using a time interval of T0 (T0≤10ms). When the count value of the hardware counter is C... hard When the value exceeds the preset threshold C0, the count value C of the hardware counter is used. hard Set a digital sampling rate f that satisfies the sampling theorem.s Otherwise, the digital sampling rate f s Keep the default sampling rate f sLow .

[0039] ② Perform a traversal scan of the acquired raw signals to determine the valid start and end points corresponding to the valid signals, including:

[0040] S1. Determine the trend of change of the starting point by taking the difference. If the trend is downward, proceed to S2; otherwise, proceed to S4.

[0041] S2. Scan point by point, determine whether the amplitude of the scan point is greater than the high-level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan that is greater than the high-level threshold, update the current valid ending point; otherwise, proceed to S3.

[0042] S3. When the amplitude of the scan point is less than the low level threshold, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is less than the low level threshold in subsequent scans, update the current valid ending point.

[0043] S4. Scan point by point. Determine whether the amplitude of the scan point is less than the low level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan and is less than the low level threshold, update the current valid ending point. Otherwise, proceed to S5.

[0044] S5. When the amplitude of a scan point is greater than the high-level threshold, the scan point is taken as the valid starting point and a traversal scan is performed. When a point with an amplitude greater than the high-level threshold is scanned in a subsequent scan, the current valid ending point is updated.

[0045] In the technical solution of this application, the settings of the high-level threshold and the low-level threshold include:

[0046] Define a threshold level V that can be adjusted by a parameter. th V ref +V th V ref -V th These are respectively used as the high-level threshold and the low-level threshold. When the signal amplitude is greater than the high-level threshold V... ref +V th When the signal amplitude is less than the low-level threshold V, a valid high level is considered to have occurred. ref -V th When this occurs, a valid low level is considered to have occurred;

[0047] Among them, V ref This is the reference voltage.

[0048] ③ Calculate the transient flow rate corresponding to the valid signal based on the valid start point and valid end point, including:

[0049] Obtain the positions of the valid start point and valid end point among N sampling points, denoted as N. Start N End The acquired signal is then subjected to spectral analysis to obtain the digital frequency f. n The transient flow rate Q (in m³) corresponding to the effective signal is calculated using the following formula. 3 / s):

[0050]

[0051] Among them, f s The digital sampling rate is K, where K is the instrument coefficient of the vortex flow meter, and the unit is P / m. 3 .

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the flow rate of transient flow measured by a vortex flowmeter, characterized in that: After completing the vortex shear signal analog-to-digital acquisition, the spectrum analysis is performed while the acquired raw signal is scanned to determine the effective start point and effective end point of the effective signal, and the transient flow rate corresponding to the effective signal is calculated based on the effective start point and effective end point. The step of traversing and scanning the acquired raw signals to determine the valid start and end points corresponding to valid signals includes: S1. Determine the trend of change of the starting point by taking the difference. If the trend is downward, proceed to S2; otherwise, proceed to S4. S2. Scan point by point, determine whether the amplitude of the scan point is greater than the high-level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan that is greater than the high-level threshold, update the current valid ending point; otherwise, proceed to S3. S3. When the amplitude of the scan point is less than the low level threshold, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is less than the low level threshold in subsequent scans, update the current valid ending point. S4. Scan point by point. Determine whether the amplitude of the scan point is less than the low level threshold. If so, take the scan point as the valid starting point and perform traversal scanning. When the amplitude of a certain point is scanned in the subsequent scan and is less than the low level threshold, update the current valid ending point. Otherwise, proceed to S5. S5. When the amplitude of a scan point is greater than the high-level threshold, the scan point is taken as the valid starting point and a traversal scan is performed. When a point with an amplitude greater than the high-level threshold is scanned in a subsequent scan, the current valid ending point is updated. The calculation of the transient flow rate corresponding to the valid signal based on the valid start point and valid end point includes: Obtain the positions of the valid start point and valid end point among N sampling points, denoted as N. Start N End The acquired signals are then subjected to spectral analysis to obtain digital frequency data. The transient flow rate Q corresponding to the effective signal is calculated using the following formula: ， in, Where is the digital sampling rate, and K is the instrument coefficient of the vortex flowmeter.

2. The method for calculating the flow rate of transient flow measured by a vortex flowmeter according to claim 1, characterized in that: The setting of the high-level threshold and low-level threshold includes: Define a threshold level V that can be adjusted by a parameter. th ,Will , These are used as the high-level threshold and low-level threshold, respectively. When the signal amplitude is greater than the high-level threshold... When the signal amplitude is less than the low-level threshold, a valid high level is considered to have occurred. When this occurs, a valid low level is considered to have occurred; Among them, V ref This is the reference voltage.

3. The method for calculating the flow rate of transient flow measured by a vortex flowmeter according to claim 1, characterized in that: Before the vortex shear signal is simulated to digitally acquired and then subjected to spectrum analysis, the following are included: Using the count value of the hardware counter as a reference, determine the current traffic range, and set an appropriate digital sampling rate based on the frequency calculated from the hardware counter to satisfy the sampling theorem.

4. The method for calculating the flow rate of transient flow measured by a vortex flowmeter according to claim 3, characterized in that: The process of determining the current traffic range based on the hardware counter's count value, and setting an appropriate digital sampling rate according to the frequency calculated from the hardware counter to satisfy the sampling theorem, includes: The hardware counter frequency is calculated with T0 as the time interval. When the count value C of the hardware counter is... hard When the value exceeds the preset threshold C0, the count value C of the hardware counter is used. hard Set a digital sampling rate that satisfies the sampling theorem. Otherwise, digital sampling rate Keep the default sampling rate .

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