CN117804560A - Flow calculation method for measuring pulsating flow of vortex shedding flowmeter - Google Patents
Flow calculation method for measuring pulsating flow of vortex shedding flowmeter Download PDFInfo
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- 238000004364 calculation method Methods 0.000 title claims abstract description 11
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- 238000010586 diagram Methods 0.000 description 5
- 230000000541 pulsatile effect Effects 0.000 description 4
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Abstract
The invention relates to a vortex street flowmeter, in particular to a flow calculation method for measuring pulsating flow of the vortex street flowmeter, which comprises the steps of setting a high level threshold value and a low level threshold value, carrying out point-by-point scanning on collected vortex street digital signals according to the high level threshold value and the low level threshold value, counting the number of effective pulses in the point-by-point scanning process, and calculating the flow of the pulsating flow based on the number of the effective pulses; the technical scheme provided by the invention can effectively overcome the defect that the sparse change pulsating flow cannot be accurately metered in the prior art.
Description
Technical Field
The invention relates to a vortex shedding flowmeter, in particular to a flow calculation method for measuring pulsating flow by the vortex shedding flowmeter.
Background
Vortex shedding flowmeter is a flow meter based on fluid oscillation principle and is widely used in process measurement and control system. Currently, studies on vortex shedding flowmeters are established under a steady flow condition, and the corresponding volumetric flow is calculated by measuring the vortex shedding frequency over a period of time. However, in flow measurement in the industrial field, unsteady flow conditions are widely present, such as pulsating flow, which is a flow in which flow parameters periodically change over time. In industrial production, the fluids output by rotary, reciprocating, and various movable transfer devices are pulsating streams.
Metering pulsating flow using vortex shedding flowmeters is a difficult problem. Fang Min in its master graduation paper application study of HHT and wavelet transform in vortex street pulsating flow signal processing, it is proposed to use HHT (hilbert yellow transform) to denoise pulsating flow signals; huang Yunzhi and Xu Kejun in the paper of estimation of vortex street signal instantaneous frequency under pulsating flow condition utilize wavelet transform based on IIR filter bank to binary decompose signal, then to carry out Hilbert transform to the vortex street signal after decomposition to estimate instantaneous frequency.
In summary, the current disclosure still simulates the processing of the pulsatile flow signal, and assumes that there is a steady vortex street signal in the sampling period, but only adds some interference signals to the signal, and the purpose of the signal processing is to extract the steady vortex street signal. However, in real conditions, the vortex street signals generated by Du Erbeng of oil and gas recovery are not steady, as shown in FIG. 2, where the signals are seen to be sparsely varying, and for such signals the above method is not effective.
Disclosure of Invention
(one) solving the technical problems
Aiming at the defects existing in the prior art, the invention provides a flow calculation method for measuring pulsating flow by a vortex shedding flowmeter, which can effectively overcome the defect that the sparse variable pulsating flow cannot be accurately measured in the prior art.
(II) technical scheme
In order to achieve the above purpose, the invention is realized by the following technical scheme:
a flow calculating method for measuring pulsating flow of vortex street flowmeter sets high level threshold and low level threshold, scans collected vortex street digital signals point by point according to the high level threshold and the low level threshold, counts effective pulse number in the point by point scanning process, and calculates the flow of pulsating flow based on the effective pulse number.
Preferably, the method includes the steps of performing point-by-point scanning on the collected vortex street digital signals according to a high level threshold value and a low level threshold value, and counting the number of effective pulses in the point-by-point scanning process, including:
s1, judging whether the signal voltage value is smaller than a low level threshold, entering S2 when the signal voltage value is smaller than the low level threshold, otherwise entering S3;
s2, judging whether the high-low level flag bits are set or not, if the high-low level flag bits are set, carrying out validity check on the section of pulse, setting a section counter to 0, counting the number of valid pulses and returning to S1, otherwise, setting the low-level flag bits when the low-level flag bits are not set, accumulating the section counter and returning to S1;
s3, judging whether the signal voltage value is greater than a high level threshold, entering S4 when the signal voltage value is greater than the high level threshold, otherwise accumulating the interval counter, and returning to S1;
and S4, judging whether the high-level flag bit is set, if so, accumulating the interval counter and returning to S1, otherwise, setting the high-level flag bit, accumulating the interval counter and returning to S1.
Preferably, in S2, it is determined whether the high and low level flag bits are set, if the high and low level flag bits are set, validity checking is performed on the pulse segment, and meanwhile, the interval counter is set to 0, and the statistics of the number of valid pulses includes:
if the high and low level flag bits are set, judging that the section of pulse is a possible effective pulse, and calculating the frequency of the section of pulse based on the actual sampling rate and the effective point number of the section of pulse;
judging whether the frequency of the pulse is in a reasonable range, accumulating the pulse counter if the frequency of the pulse is in the reasonable range, returning to the step S1, and otherwise, directly returning to the step S1.
Preferably, the calculating the flow rate of the pulsating flow based on the effective pulse number includes:
recording the effective pulse number P obtained by m times of statistics 1 、P 2 、…、P m If the sampling rate and the sampling point number of each time are respectively kept at f s And N, calculating the average flow Q of m times by adopting the following formula:
wherein P is i For each stored effective pulse number, i=1, 2, …, m, K is the meter coefficient of the vortex shedding flowmeter.
Preferably, the setting a high level threshold and a low level threshold includes:
defining a parameter-adjustable threshold level V th V is set up ref +V th 、V ref -V th Respectively used as a high level threshold and a low level threshold, when the signal amplitude is larger than the high level threshold V ref +V th When the signal amplitude is less than the low level threshold V, an effective high level is considered to be present ref -V th When an active low level is considered to occur;
wherein V is ref Is the reference voltage.
Preferably, the method includes the steps of performing point-by-point scanning on the collected vortex street digital signals according to a high level threshold value and a low level threshold value, and counting the number of effective pulses in the point-by-point scanning process, including:
and after the data acquisition of the ping group is completed, carrying out point-to-point scanning on the acquired vortex street digital signals according to a high-level threshold value and a low-level threshold value, counting the effective pulse number in the point-to-point scanning process, and simultaneously carrying out data sampling on the pong group.
(III) beneficial effects
Compared with the prior art, the flow calculation method for measuring the pulsating flow of the vortex shedding flowmeter provided by the invention has more flexible threshold selection compared with a hardware counter, and pulse effectiveness check is added, so that the anti-interference capability is greatly improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It is evident that the drawings in the following description are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a diagram showing the number of effective pulses in a statistical point-by-point scanning process according to the present invention;
FIG. 2 is a schematic diagram of a typical sparsely populated pulsatile flow signal generated by Du Erbeng;
FIG. 3 is a schematic diagram of a pulsating flow signal with high frequency spurs;
FIG. 4 is a schematic diagram of a time domain waveform of a pulsatile flow signal superimposed with an interference signal detected in the field;
FIG. 5 is a schematic diagram of the frequency domain waveform obtained by Fourier transform of FIG. 4;
fig. 6 is a graph comparing errors between various algorithms.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
A flow calculating method for measuring pulsating flow of vortex street flowmeter sets high level threshold and low level threshold, scans collected vortex street digital signals point by point according to the high level threshold and the low level threshold, counts effective pulse number in the point by point scanning process, and calculates the flow of pulsating flow based on the effective pulse number.
(1) Setting a high level threshold and a low level threshold, comprising:
defining a parameter-adjustable threshold level V th V is set up ref +V th 、V ref -V th Respectively used as a high level threshold and a low level threshold, when the signal amplitude is larger than the high level threshold V ref +V th When the signal amplitude is less than the low level threshold V, an effective high level is considered to be present ref -V th When an active low level is considered to occur;
wherein V is ref Is the reference voltage.
(2) As shown in fig. 1, the method includes the steps of performing point-by-point scanning on the collected vortex street digital signals according to a high level threshold value and a low level threshold value, and counting the number of effective pulses in the point-by-point scanning process, including:
s1, judging whether the signal voltage value is smaller than a low level threshold, entering S2 when the signal voltage value is smaller than the low level threshold, otherwise entering S3;
s2, judging whether the high-low level flag bits are set or not, if the high-low level flag bits are set, carrying out validity check on the section of pulse, setting a section counter to 0, counting the number of valid pulses and returning to S1, otherwise, setting the low-level flag bits when the low-level flag bits are not set, accumulating the section counter and returning to S1;
s3, judging whether the signal voltage value is greater than a high level threshold, entering S4 when the signal voltage value is greater than the high level threshold, otherwise accumulating the interval counter, and returning to S1;
and S4, judging whether the high-level flag bit is set, if so, accumulating the interval counter and returning to S1, otherwise, setting the high-level flag bit, accumulating the interval counter and returning to S1.
Specifically, whether the high-low level flag bits are set is judged, if the high-low level flag bits are set, validity check is performed on the section of pulse, meanwhile, a section counter is set to 0, and the number of valid pulses is counted, including:
if the high and low level flag bits are set, judging that the section of pulse is a possible effective pulse, and calculating the frequency of the section of pulse based on the actual sampling rate and the effective point number of the section of pulse;
judging whether the frequency of the pulse is in a reasonable range, accumulating the pulse counter if the frequency of the pulse is in the reasonable range, returning to the step S1, and otherwise, directly returning to the step S1.
Meanwhile, in the technical scheme, in the process of carrying out point-by-point scanning on the collected vortex street digital signals according to the high-level threshold value and the low-level threshold value and counting the number of effective pulses, a ping-pong double-buffer mode is adopted, after the data collection of a ping group is completed, the collected vortex street digital signals are subjected to point-by-point scanning according to the high-level threshold value and the low-level threshold value, the number of effective pulses in the point-by-point scanning process is counted, and meanwhile the pong group carries out data sampling.
(3) Calculating a flow rate of the pulsatile flow based on the number of effective pulses, comprising:
recording the effective pulse number P obtained by m times of statistics 1 、P 2 、…、P m If the sampling rate and the sampling point number of each time are respectively kept at f s And N, calculating the average flow Q of m times by adopting the following formula:
wherein P is i For the effective pulse number stored each time, i=1, 2, …, m and K are the instrument coefficients of the vortex shedding flowmeter, and the unit is P/m 3 。
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (6)
1. A flow calculating method for measuring pulsating flow by vortex shedding flowmeter is characterized in that: setting a high level threshold and a low level threshold, carrying out point-to-point scanning on the collected vortex street digital signals according to the high level threshold and the low level threshold, counting the effective pulse number in the point-to-point scanning process, and calculating the flow of the pulsating flow based on the effective pulse number.
2. The flow rate calculation method for measuring pulsating flow by vortex shedding flowmeter according to claim 1, wherein: the method for carrying out point-to-point scanning on the collected vortex street digital signals according to the high level threshold and the low level threshold and counting the effective pulse number in the point-to-point scanning process comprises the following steps:
s1, judging whether the signal voltage value is smaller than a low level threshold, entering S2 when the signal voltage value is smaller than the low level threshold, otherwise entering S3;
s2, judging whether the high-low level flag bits are set or not, if the high-low level flag bits are set, carrying out validity check on the section of pulse, setting a section counter to 0, counting the number of valid pulses and returning to S1, otherwise, setting the low-level flag bits when the low-level flag bits are not set, accumulating the section counter and returning to S1;
s3, judging whether the signal voltage value is greater than a high level threshold, entering S4 when the signal voltage value is greater than the high level threshold, otherwise accumulating the interval counter, and returning to S1;
and S4, judging whether the high-level flag bit is set, if so, accumulating the interval counter and returning to S1, otherwise, setting the high-level flag bit, accumulating the interval counter and returning to S1.
3. The flow rate calculation method for measuring pulsating flow by vortex shedding flowmeter according to claim 2, characterized in that: s2, judging whether the high and low level flag bits are set, if yes, carrying out validity check on the section of pulse, setting a section counter to 0, and counting the number of valid pulses, wherein the method comprises the following steps:
if the high and low level flag bits are set, judging that the section of pulse is a possible effective pulse, and calculating the frequency of the section of pulse based on the actual sampling rate and the effective point number of the section of pulse;
judging whether the frequency of the pulse is in a reasonable range, accumulating the pulse counter if the frequency of the pulse is in the reasonable range, returning to the step S1, and otherwise, directly returning to the step S1.
4. A flow rate calculation method for measuring pulsating flow of vortex shedding flowmeter according to claim 3, characterized in that: the calculating the flow rate of the pulsating flow based on the effective pulse number comprises:
recording the effective pulse number P obtained by m times of statistics 1 、P 2 、…、P m If the sampling rate and the sampling point number of each time are respectively kept at f s And N, calculating the average flow Q of m times by adopting the following formula:
wherein P is i For the number of effective pulses per save, i=1, 2,..m, K is the meter coefficient of the vortex shedding flowmeter.
5. The flow rate calculation method for measuring pulsating flow by vortex shedding flowmeter according to claim 1, wherein: the setting of the high level threshold and the low level threshold includes:
defining a parameter-adjustable threshold level V th V is set up ref +V th 、V ref -V th Respectively used as a high level threshold and a low level threshold, when the signal amplitude is larger than the high level threshold V ref +V th When the signal amplitude is less than the low level threshold V, an effective high level is considered to be present ref -V th When an active low level is considered to occur;
wherein V is ref Is the reference voltage.
6. The flow rate calculation method for measuring pulsating flow by vortex shedding flowmeter according to claim 1, wherein: the method for carrying out point-to-point scanning on the collected vortex street digital signals according to the high level threshold and the low level threshold and counting the effective pulse number in the point-to-point scanning process comprises the following steps:
and after the data acquisition of the ping group is completed, carrying out point-to-point scanning on the acquired vortex street digital signals according to a high-level threshold value and a low-level threshold value, counting the effective pulse number in the point-to-point scanning process, and simultaneously carrying out data sampling on the pong group.
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