CN107478282B - Ultrasonic flow detection signal processing method and device and time difference method ultrasonic detection system - Google Patents
Ultrasonic flow detection signal processing method and device and time difference method ultrasonic detection system Download PDFInfo
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- CN107478282B CN107478282B CN201710706720.3A CN201710706720A CN107478282B CN 107478282 B CN107478282 B CN 107478282B CN 201710706720 A CN201710706720 A CN 201710706720A CN 107478282 B CN107478282 B CN 107478282B
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- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/66—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by measuring frequency, phase shift or propagation time of electromagnetic or other waves, e.g. using ultrasonic flowmeters
Abstract
The invention belongs to the field of signal processing, and discloses an ultrasonic flow detection signal processing method and device, and a time difference method ultrasonic detection system, wherein a band-pass amplifier with the same transmitting frequency is used for amplifying a coupling signal and eliminating most of out-of-band noise; carrying out automatic gain amplification on the coupled signal with the bandpass output, so that the output amplitude of the coupled signal subjected to automatic gain control is stabilized at a peak-to-peak value set by the chip; selecting a proper reference voltage, and converting the coupling signal subjected to automatic gain control into a square wave signal; and acquiring the time of the upper edge and the time of the lower edge of the square wave signal, solving the mean value of the time of the upper edge and the time of the lower edge of the square wave signal to obtain the peak value time of the sampling period of the coupling signal, and calculating the flow based on the same peak value time of the sampling period of the downstream coupling signal and the upstream coupling signal and the preset parameters such as the diameter of the pipeline. The invention is beneficial to adapting to the amplitude change of the coupling signal, so that the coupling signal has better adaptability in liquid/gas flow detection.
Description
Technical Field
The invention belongs to the field of signal processing, and particularly relates to an ultrasonic flow detection signal processing method and device and a time difference method ultrasonic detection system.
Background
In the existing time difference method ultrasonic detection system, because the coupling signal obtained by detection is often unstable, the coupling amplitude is sometimes large and sometimes small, the instantaneous change of the coupling signal is difficult to adapt no matter through an amplifier with fixed amplification factor or a method with adjustable amplification factor, the automatic adjustment function of an automatic gain amplification chip can be fully utilized in a mode of amplifying to a fixed peak-peak value (such as 2V), and the complexity and the hysteresis of software adjustment are avoided, so that the software processing process of the system is simplified; in the existing time difference method ultrasonic flow detection process, the forward/reverse flight time of the ultrasonic echo is usually obtained by adopting the modes of zero-crossing time point detection, single-edge time point detection and the like, and the detection methods are difficult to ensure better stability under the condition of coupling signal amplitude variation, and the existing technology is as follows: (1) amplifying the coupling signal by using an amplifier with a fixed amplification factor, and then acquiring the forward and reverse propagation time difference of the ultrasound; (2) the amplitude of the ultrasonic coupling signal obtained by detection is used for carrying out amplification factor modulation on the amplifier so as to adapt to the amplitude change of the ultrasonic signal, but the method has hysteresis of coupled signal processing.
In summary, the problems of the prior art are as follows: in the existing time difference method ultrasonic detection system, because the coupling signal is often unstable, the coupling amplitude is large and small, and the instantaneous change of the coupling signal is difficult to adapt no matter through an amplifier with fixed amplification factor or a method with adjustable amplification factor; in the existing time difference method ultrasonic flow detection process, the flight time of ultrasonic echoes is usually obtained by adopting the modes of zero-crossing detection, single-edge detection and the like, and the detection methods are difficult to ensure better stability under the condition of coupling signal amplitude variation; in the existing time-difference ultrasonic flow detection technology, the size of an echo signal needs to be considered, and an AGC (automatic gain amplification) chip or an automatic amplification function thereof is not adopted in an AGC chip amplification range to obtain a fixed peak-peak value (such as 2V) output signal; the method cannot be well adapted to liquid and gas flow detection, so that a stable time difference signal and a detection result cannot be obtained under the condition of the amplitude change of the coupling signal.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides an ultrasonic flow detection signal processing method and device and a time difference method ultrasonic detection system, which can obtain a stable time difference signal and a detection result under the condition of coupling signal amplitude change.
The ultrasonic flow detection signal processing method realized by the invention comprises the following steps:
amplifying the coupling signal by using a band-pass amplifier with the same transmission frequency and eliminating most of out-of-band noise;
carrying out automatic gain amplification on the coupled signal with the bandpass output, so that the output amplitude of the coupled signal subjected to automatic gain amplification is stabilized at a peak-to-peak value set by the chip;
selecting a proper reference voltage, and converting the coupling signal subjected to automatic gain amplification into a square wave signal;
and acquiring the time of the upper edge and the time of the lower edge of the square wave signal, solving the mean value of the time of the upper edge and the time of the lower edge of the square wave signal to obtain the peak value time of the sampling period of the coupling signal, and calculating the flow based on the same peak value time of the sampling period of the downstream coupling signal and the upstream coupling signal and the preset parameters such as the diameter of the pipeline.
Preferably, the signal amplitude of the coupling signal after the band-pass processing is within the signal amplitude input range of the automatic gain controller corresponding to the automatic gain amplification and is effectively and automatically adjusted by the amplification factor.
Preferably, the reference voltage range is set between the peak voltage of the first period and the peak voltage of the second period of the coupled signal after the automatic gain amplification.
Preferably, the reference voltage is an average value of a sum of the peak voltage of the first period and the peak voltage of the second period.
Another object of the present invention is to provide an ultrasonic flow rate detection signal processing apparatus, including: a band-pass amplifier, an automatic gain controller, a voltage comparator, a high-precision time measuring chip and a flow calculator, wherein,
the band-pass amplifier is consistent with the transmitting frequency and is used for carrying out fixed amplification factor and band-pass processing on the coupling signal;
the automatic gain controller is used for carrying out automatic gain control on the coupling signal subjected to the band-pass processing so as to enable the signal output amplitude of the coupling signal subjected to the automatic gain control to be stabilized at a preset peak-peak value;
the voltage comparator is used for converting the coupling signal subjected to automatic gain control into a square wave signal according to the acquired reference voltage;
the high-precision time measuring chip is used for detecting the upper/lower edge time points of the square wave signal output by the comparator and providing a high-precision time base for the subsequent forward/backward peak time;
and the flow calculator calculates the peak value time of the forward/backward propagation sampling period of the coupling signal through the upper/lower edge time points, and performs flow detection according to the peak value time of the forward/backward propagation coupling signal period and preset parameters such as the diameter of the pipeline. .
The signal processing scheme of the invention has stronger adaptability to the amplitude change of the coupling signal in the time difference method ultrasonic flow detection process, and meanwhile, the time information acquisition and processing method has better stability on the basis of the coupling signal processing of the method. Compared with a mode of adjusting the amplification factor through software processing, the method provided by the invention does not need to consider the size of an echo signal, and can obtain a fixed peak-peak value 2V output signal within the amplification range of an AGC (automatic gain amplification) chip, so that the method has better adaptability in liquid and gas flow detection.
The invention can improve the stability of the time difference measurement data; under different conditions (pressure, temperature, flow rate and other conditions) of the ultrasonic coupling signal, the amplitude of the coupling signal has certain change, and the difference of time points can be caused due to different signal intensities in a mode of sampling a fixed amplification factor or directly setting a comparison point to obtain the flight time, so that the measurement stability is reduced; under the condition of AGC function, the invention can better ensure the stability of signal output amplitude; under the condition of stable output amplitude, the time point obtained by the comparison point can also ensure higher stability.
Drawings
Fig. 1 is a flowchart of an ultrasonic flow detection signal processing method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a time-difference ultrasonic flowmeter according to an embodiment of the present invention.
Fig. 3 is a flowchart of an implementation of a method for processing an ultrasonic flow detection signal according to an embodiment of the present invention.
Fig. 4 is a diagram of a noisy ultrasound coupled signal provided by an embodiment of the present invention.
Fig. 5 is a signal diagram after bandpass amplification according to an embodiment of the present invention.
Fig. 6 is a diagram of an output signal of an AGC amplification circuit according to an embodiment of the present invention.
Fig. 7 is a graph of a square wave output from a fixed voltage comparator according to an embodiment of the present invention.
Fig. 8 is a diagram illustrating the upper and lower edge and peak detection processes according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The ultrasonic flow detection by time difference method is an ultrasonic flowmeter which determines the flow velocity of the measured fluid by measuring the time difference delta t of the upstream flow and the downstream flow which change along with the propagation velocity of the ultrasonic wave, wherein the time difference delta t and the flow velocity are in direct proportion, and the proportionality coefficient is called as the flow correction coefficient.
The application of the principles of the present invention will be further described with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, a method for processing an ultrasonic flow detection signal according to an embodiment of the present invention includes:
s101: performing fixed amplification factor and band-pass processing on the coupling signal by using a band-pass amplifier with the same transmission frequency;
in this step, the coupled signal is processed, that is, the bandpass amplifier with the same transmission frequency is used to perform signal amplification processing with fixed amplification factor and bandpass processing of frequency on the coupled signal, so as to eliminate the influence of various noises in the coupled signal on the detection, and to make the signal amplitude output from the bandpass amplifier within the amplitude input range of the AGC signal, so that the output signal meets the requirement of the AGC on the voltage amplitude range of the input signal.
S102: performing automatic gain control on the coupling signal subjected to the band-pass processing so as to enable the signal output amplitude of the coupling signal subjected to the automatic gain control to be stabilized at a fixed peak-peak value set by the chip;
in this step, the automatic gain control processing is performed on the coupled signal after the band-pass processing, so that the adaptability to the amplitude change of the coupled signal can be improved, the amplification factor of the coupled signal after the band-pass processing is automatically adjusted by using the AGC, so that the output amplitude of the coupled signal after the band-pass processing is stabilized at a preset peak-peak value, and the signal input to the AGC, namely the coupled signal after the band-pass processing, can output a stable amplitude (voltage) by using the automatic adjustment function of the AGC chip under the condition that the amplitude changes, thereby realizing the signal output of a fixed peak-peak value, so that the reference voltage selection of the comparator in the subsequent processing has better stability, and cannot correspondingly change along with the amplitude change of the coupled signal after the band-pass processing.
S103: converting the coupling signal subjected to automatic gain control into a square wave signal according to the obtained reference voltage;
in this step, a suitable reference voltage is selected, the coupling signal after the automatic gain amplification is converted into a square wave signal, and for example, the coupling signal after the automatic gain control is converted into a square wave signal by using a comparator.
In this step, as an optional embodiment, the reference voltage range is set between the peak voltage in the first period and the peak voltage in the second period of the coupled signal after performing the automatic gain control. In order to further improve the adaptability and stability, it is preferable that the reference voltage is set as an average value of a sum of a peak voltage in a first period and a peak voltage in a second period of the coupled signal after the automatic gain control. That is, the reference voltage may be selected as a value between a peak point (preset peak-to-peak value) and a highest voltage of a first period before the peak point (before full amplitude, first peak in fig. 6), for example, an average value of a sum of the peak point voltage and the highest voltage of the first period before the peak point, or a voltage value near the average value is selected as the reference voltage.
In this embodiment, the coupling signal after the automatic gain control is input to the comparator, and the square wave signal output with a stable pulse width is obtained through the comparison and conversion of the comparator.
In this embodiment, as shown in fig. 6, with the output signal waveform amplified by AGC,
so that the reference voltage selection of the comparator has better stability.
S104: acquiring the time of the upper edge and the time of the lower edge of the square wave signal, solving the mean value of the time of the upper edge and the time of the lower edge of the square wave signal, acquiring the peak value time of the sampling period of the forward-reverse coupled signal, and detecting the flow based on the same peak value time of the sampling period of the forward-flow coupled signal and the reverse-flow coupled signal, the preset diameter of the pipeline and other parameters.
In this step, on the basis of the obtained square wave signal, the upper and lower edge times are detected, and the average value is obtained to obtain the peak time of the coupled signal (the cycle peak time of the coupled signal).
In the step, the average value of the upper edge and the lower edge is obtained as the approximate time point of the peak value in the sampling period, and the time point is used as the forward flight time and the backward flight time, so that the discrete noise reduction of the averaging single edge is facilitated.
In this step, as an optional embodiment, the rising edge and falling edge time points (upper and lower edge times) of the pulse square wave may be detected by the time measurement chip, so as to obtain the crossing time point of the fixed voltage point in the half period of the coupling signal of the echo, and then the peak time point (the period peak time of the coupling signal) of the coupling signal in the sampling period is obtained by averaging the rising edge and falling edge time points, so that the flow rate detection may be performed based on the period peak time of the coupling signal in the forward flow and reverse flow and the preset parameters such as the pipe diameter.
In this embodiment, the average value of the upper and lower edge time points of the square wave signal is closer to the peak time of the coupled signal in the period, so that the peak time point of the current detection period can be approximated by using the more stable upper/lower edge time points.
In this embodiment, after the ultrasonic coupling signal is amplified, an AGC chip automatically amplifies an output signal to a peak-to-peak 2V signal, the signal is converted to a square wave signal by a comparator having a stable reference level, then an upper/lower edge time point of the square wave signal is detected by a time measurement chip, and after the upper/lower edge time is obtained, an average time of the two time points is calculated to obtain a peak point time of the coupling signal. The forward/reverse time measurement is completed through the method, and then the forward and reverse time difference is calculated, and the time difference is the original time difference of the ultrasonic flow detection by the time difference method.
In the embodiment of the invention, compared with a mode of adjusting the amplification factor through software processing, the method of the embodiment of the invention does not need to consider the size of the echo signal, and utilizes the automatic gain amplification function of an AGC chip, so long as a fixed peak-peak value (for example, 2V) output signal can be obtained within the amplification range of the AGC chip, thereby ensuring the stability of the output square wave of a subsequent comparator in class, the converted square wave signal can better ensure the stability of the upper edge and the lower edge, and the stability of the echo peak value point of the coupling signal can be better ensured by taking the time of the upper edge and the lower edge of the square wave signal and then obtaining the peak time point mode, so that the method has better adaptability in liquid and gas flow detection.
The invention is further described with reference to the following figures and specific embodiments.
The ultrasonic flow detection signal processing method provided by the embodiment of the invention comprises the following steps: (1) amplifying the ultrasonic coupling signal through a band pass amplifier; (2) stabilizing the output amplitude of the signal to a fixed peak-to-peak value by utilizing the fixed amplitude output amplification function of the AGC; (3) obtaining a square wave signal through a voltage comparator; (4) detecting the upper/lower edge time points of the square wave signal; (5) calculating the mean value of the upper/lower edge time points as the peak time of the coupled signal; (6) obtaining forward/backward peak time by the method and making difference to obtain propagation time difference; (7) the flow information is obtained by calculating parameters such as time difference, pipe diameter and the like. Wherein
Ultrasonic coupling signals: because the circuit and the ultrasonic coupling chip have certain noise, certain noise (including white noise, power frequency noise and other out-of-band noise in the circuit) exists in an ultrasonic signal obtained by coupling the ultrasonic coupling chip, and if the signal is directly used for time difference detection by the comparator, the detection result is easy to be unstable, so that the flow detection result is influenced; on the other hand, when ultrasound propagates in gas and liquid, the amplitude of the signal changes under the conditions of bubbles, fine particles, pressure, temperature, and the like, so that the directly obtained coupling signal has a certain change in amplitude, and the signal is as shown in fig. 4.
On the basis of the signals, in order to effectively eliminate various noises (such as white noise, power frequency noise and other out-of-band noises), designing and using a band-pass amplifier to effectively eliminate the influence of the signal noises on the detection result is a key step for improving the ultrasonic flow detection. In the processing of the algorithm, a bandpass amplifier having the same transmission frequency is used to perform bandpass amplification processing with fixed amplification factor and frequency on the coupled signal, thereby eliminating the influence of various noises on the detection stability, and the amplified output signal is as shown in fig. 5.
The AGC (automatic gain control) amplifying circuit mainly aims at adaptively processing the amplitude change of a coupling signal, because the amplitude change of the coupling signal is not effectively processed in the process after the coupling signal is processed by an amplifier with fixed amplification factor and passband, the signal output by the bandpass amplifier has certain change condition on the amplitude, particularly under the condition that bubbles, fine particles and the like exist in a pipeline. The automatic adjustment of the amplification factor of the AGC chip and the stabilization of the signal output amplitude at a fixed peak value and a peak value can be utilized to ensure that the input signal keeps stable voltage output under the condition of amplitude change. The output signal of the processing mode is combined with the band-pass amplification, so that the method has the advantages of stable signal amplitude, small out-of-band noise, high adaptability to the coupled signal and the like, and the input signal is shown in fig. 6.
The main purpose of the time-difference ultrasonic flow detection is to obtain a stable and high-precision forward and reverse time difference, the signal amplified and output by the band pass and the AGC has better adaptability and stability to signal noise, amplitude and the like to a certain extent, however, because the circuit has problems of certain time delay, jitter and the like, in order to obtain a high-precision time difference value, the peak value of an echo signal is a time difference detection point with the highest stability, in the design of a comparison circuit, the processing method selects the reference voltage range of a comparator between the peak voltage in a first period and the peak voltage in a second period, and a square wave output with a more stable pulse width is obtained through comparison, as shown in fig. 7.
The rise and fall time points of the pulse square wave are detected by a time measurement chip (as shown in fig. 8), the crossing time of the echo signal at a fixed voltage point in the half period can be obtained, and the peak time point of the coupling signal in the period can be obtained by averaging the two time points. By obtaining the forward and reverse ultrasonic flight time and calculating the time difference through the method, the ultrasonic flow detection signal with higher temperature and better adaptability can be obtained.
The present invention will be further described below with reference to the measurement principle of the ultrasonic flow meter by the time difference method and the main factors influencing the measurement.
Measurement principle of ultrasonic flowmeter by time difference method
The basic principle of the ultrasonic flowmeter is that the time difference exists when ultrasonic waves propagate in the fluid for the same distance in a forward flow and a backward flow mode, and the difference of the propagation time is related to the flow speed of the fluid to be measured, so that the flow speed of the fluid can be obtained by measuring the time difference, and the flow rate of the fluid can be calculated. The subject of the present invention is an ultrasonic flowmeter by a time difference method, and the measurement principle thereof will be described in detail below.
It can be seen from the measurement schematic diagram of the time-difference ultrasonic meter shown in fig. 2 that two ultrasonic transducers are respectively installed on two sides of the pipe diameter of the fluid to be measured, the propagation direction of the ultrasonic wave in the fluid can be changed in a certain manner, the flow velocity of the fluid can be indirectly measured by measuring the forward flow and reverse flow propagation time difference of the ultrasonic wave in the fluid, and further the flow value can be calculated.
The time difference method ultrasonic flowmeter measures the propagation time of ultrasonic waves in a fluid, and obtains the flow rate of the fluid by measuring the propagation time difference delta t of the ultrasonic waves in forward flow and reverse flow, and the specific principle is as follows:
setting the ultrasonic downstream propagation time t1Comprises the following steps:
ultrasonic wave counter-current propagation time t2Comprises the following steps:
wherein D is the diameter of the pipeline, v is the flow velocity of the measured fluid, c is the propagation velocity of the ultrasonic wave in the stationary fluid, and theta is the ultrasonic wave emission angle.
The following equation (2.1) is subtracted from equation (2.2): the propagation time difference Deltat of the forward and reverse ultrasonic waves is as follows:
the speed c of the ultrasonic wave propagating in the static fluid is far greater than the actual flow speed v of the measured fluid, namely c > > v. Thus, it is possible to obtain:
c2-v2cos2θ≈c2(2.4)
then (2.4) can be simplified to:
moving v in (2.6) to the left of the equation yields its calculation:
in the equation (2.7), the speed c of the ultrasonic wave in the stationary fluid is usually a constant, generally about 1500m/s, so the flow velocity v of the measured fluid is only related to the parameter D, the ultrasonic wave emission angle θ and the time difference Δ t, and D and θ are regarded as system parameters, so the flow velocity v and further the flow Q can be obtained by measuring the time difference Δ t. For a circular pipe, the flow calculation formula is:
wherein K is a fluid flow rate correction coefficient.
It can be seen from the above measurement principle that the flow value can be calculated by measuring the propagation time difference Δ t of the ultrasonic forward and backward flow, and therefore, the high-precision flow measurement value can be obtained only by obtaining the Δ t value with high precision.
Secondly, factors influencing the measurement accuracy of the time difference method ultrasonic flowmeter:
under the non-ideal condition, factors such as pipe wall propagation time, flow field distribution and the like can influence the measurement result, and the result obtained according to theoretical calculation is directly inaccurate. The factors influencing the measurement accuracy of the time-difference ultrasonic flowmeter can be summarized as follows:
(1) the influence of the law of refraction. The sound waves are refracted when incident on the surface of different media, and here, the sound wedge, the pipe wall and the fluid medium inside the pipeline are refracted differently, so that a certain time difference is generated.
(2) The difference in time caused by the emission drive. When pulse signals transmitted from the single chip microcomputer are transmitted to the transducers A and B respectively, the two transducers cannot be absolutely consistent in performance even if the types of the transducers A and B are the same because the transducers A and B are different, and time difference caused by signal transmission is caused.
(3) The time difference caused by the signal receiving process. The two transducers have two receive channels which are not necessarily perfectly symmetrical, which results in additional time differences being mixed in the received signals.
In addition to the above points, the factors that may influence the measurement accuracy of the transit time ultrasonic flow meter also include that in practical applications, the flow condition of the fluid in the industrial pipeline is very complex, the temperature inside and outside the pipeline may also have a large difference, and the factors that influence the measurement accuracy of the transit time ultrasonic flow meter can be summarized as many factors such as temperature variation, uneven flow velocity distribution, pipe wall thickness, acoustic path delay, and the like. Since most of the ultrasonic flow meters now use the clip-on probe in practice, the factor of the flow rate variation in the probe recess can be eliminated. If the circuit and the acoustic path are designed to be approximately symmetrical, the influence factor of the propagation delay of the circuit and the acoustic path can be eliminated.
Finally, the error of the flowmeter can be concentrated on the influence of temperature change, so the design should give emphasis to the factor in the aspect and take corresponding measures to avoid the influence. For the influence of the temperature on the flow velocity, it can be seen from the derived formula that the sound velocity c contained therein is relatively greatly influenced by the temperature change, and when the difference between the fluid temperature inside and outside the pipeline and the ambient temperature is relatively small, the influence can be ignored, but when the difference between the fluid temperature inside and outside the pipeline and the ambient temperature is relatively large, the parameter greatly influences the measurement result of the flow velocity. In order to solve the problem of influence of temperature factors on the flow rate c, the invention adopts an improved time difference method.
Third, improved time difference method ultrasonic flowmeter principle
The ultrasonic transducer mounting mode adopted by the invention is V-shaped mounting, and the principle of the improved time difference method is described below by taking V-shaped mounting as an example.
Under the condition of forward and reverse time measurement, the method can be used for detecting the flow of gas and liquid by a time difference method (in V-shaped installation, the ultrasonic wave propagation path is 2 times of Z-shaped installation with the same pipe diameter and the same half path), the forward and reverse propagation time of the ultrasonic wave is 2 times of that of Z-shaped installation, and the formula is as follows:
wherein t is1Is the propagation time at downstream, t2Propagation time in countercurrent
The two formulas are respectively transformed into the following forms:
the two formulas are subtracted to obtain
The formula obtained at this time theoretically eliminates C, and further theoretically avoids the influence of temperature on the flow velocity measurement of the fluid, namely, the influence on the flow measurement.
And (3) determining a scheme:
based on the theoretical analysis, the ultrasonic flowmeter designed by the invention uses a time difference method principle, is installed in a V shape, processes data according to an improved calculation method, avoids the influence of the key influence factor of temperature, and improves the measurement precision of the design as much as possible. The calculation formula of v deduced by the improved algorithm shows that after the pipeline and the ultrasonic probe are installed, two parameters D and theta are determined, and only the forward and backward flow propagation time t of the ultrasonic wave influencing v is the propagation time t of the forward and backward flow1And t2If the two time measurement accuracies are high, the accuracy of the final flow measurement is also high, so that the TDC-GP22 high-accuracy time measurement chip is selected for this factor when selecting the key device of the design, thereby improving the overall accuracy.
The following is a further description of the implementation of the ultrasonic flow detection signal processing method provided by the present invention.
Fig. 3 is a flowchart of an implementation of a method for processing an ultrasonic flow detection signal according to an embodiment of the present invention. The method specifically comprises the following steps:
(1) the time difference method ultrasonic flow detection method is mainly characterized in that the forward flight time and the reverse flight time of ultrasonic waves in a pipeline are measured, and then the flow velocity and the flow of gas/liquid in the pipeline in unit time are calculated through the forward/reverse time difference and the diameter of the pipeline; (2) in the process of detecting the forward flight time and the reverse flight time by the ultrasonic transducer, due to the changes of pressure, temperature, bubbles, particles and the like of gas/liquid in a pipeline, an original coupling signal has amplitude difference and certain out-of-band noise exists; (3) the band-pass amplifying circuit mainly aims at eliminating noise in the coupling signal, amplifying the coupling signal to a certain degree, improving the impedance characteristic of the coupling signal and facilitating subsequent signal processing and impedance matching; (4) because the band-pass amplifying circuit is set according to the ultrasonic frequency of different transmitting signals, the amplification factor and the output signal of the band-pass amplifying circuit have certain difference according to the amplitude of the coupling signal. Due to the automatic gain amplification function of the AGC chip, under the condition that the amplitude of an output signal changes, the output can be stabilized at a fixed output amplitude by automatically adjusting the amplification factor (1-100 times), and the characteristic is in the range of the amplification factor of the chip and has better adaptability to input signals with different amplitudes, so that the output signal amplified by the AGC chip has stable output when the amplitude of a coupling signal changes. (5) Compared with the mode that most of direct coupling signals are amplified and converted into square waves through a comparator, the signal output by the AGC has stable amplitude and can adapt to the coupling signals with different amplitudes, under the condition, the reference level of the input end of the comparator is more stable than the method of direct amplification and comparison, the selection of the reference level has better stability, and meanwhile, the output square waves of the scheme have stronger stability in width and time; (6) the time measuring chip is mainly used for measuring the total flight time of the output pulse of the comparator after the transmission pulse is processed by the coupling circuit, and the flight time obtained by detection has larger jump (especially under the condition of higher detection precision requirement, such as time difference precision reaching about 50 ps) due to the change of circuit noise and the amplitude of the coupling signal under the condition of not carrying out AGC amplification processing on the signal, so that the whole system can not meet the detection requirement. Because the peak point of the coupling signal is a relatively stable time point, on the basis of processing the signal in the front sequence and comparing and outputting the signal, a sampling time measuring chip (such as GP22 or a high-speed counter and the like) simultaneously detects the rising and falling edge time of the square wave signal output by the comparator, calculates the mean value of the two time points, uses the mean value as the approximate value of the peak point of the coupling signal, obtains the forward and reverse flight time by using the method, and calculates the current time difference and the instantaneous flow. The time difference method ultrasonic flow signal processing method improves the detection precision and stability of one-way flight time and two-way time difference in the aspects of signal amplitude change, time difference detection stability and the like.
An embodiment of the present invention further provides an ultrasonic flow detection signal processing apparatus, including: a band-pass amplifier, an automatic gain controller, a voltage comparator, a high-precision time measuring chip and a flow calculator, wherein,
the band-pass amplifier is consistent with the transmitting frequency and is used for carrying out fixed amplification factor and band-pass processing on the coupling signal;
the automatic gain controller is used for carrying out automatic gain control on the coupling signal subjected to the band-pass processing so as to enable the signal output amplitude of the coupling signal subjected to the automatic gain control to be stabilized at a preset peak-peak value;
the voltage comparator is used for converting the coupling signal subjected to automatic gain control into a square wave signal according to the acquired reference voltage;
the high-precision time measuring chip is used for detecting the upper/lower edge time points of the square wave signal output by the comparator and providing a high-precision time base for the subsequent forward/backward peak time;
and the flow calculator calculates the peak value time of the forward/backward propagation sampling period of the coupling signal through the upper/lower edge time points, and performs flow detection according to the peak value time of the forward/backward propagation coupling signal period and preset parameters such as the diameter of the pipeline.
In this embodiment, the signal amplitude of the coupling signal after the band-pass processing is within the signal amplitude input range of the automatic gain controller corresponding to the automatic gain amplification, and the effective automatic adjustment of the amplification factor is obtained.
In this embodiment, the reference voltage range is set between the peak voltage of the first period and the peak voltage of the second period of the coupled signal after the automatic gain control is performed.
In this embodiment, the reference voltage is an average value of a sum of the peak voltage of the first period and the peak voltage of the second period.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (4)
1. An ultrasonic flow detection signal processing method, characterized in that the ultrasonic flow detection signal processing method comprises:
amplifying the coupling signal by using a band-pass amplifier with the same transmission frequency and eliminating most of out-of-band noise;
carrying out automatic gain amplification on the coupled signal with the bandpass output, so that the output amplitude of the coupled signal subjected to automatic gain amplification is stabilized at a peak-to-peak value set by the chip;
selecting a proper reference voltage, and converting the coupling signal subjected to automatic gain amplification into a square wave signal;
acquiring the upper and lower edge time of the square wave signal, solving the mean value of the upper and lower edge time of the square wave signal to obtain the peak value time of the sampling period of the coupling signal, and calculating the flow based on the peak value time of the same sampling period of the downstream and upstream coupling signals and the preset diameter parameter of the pipeline;
the signal amplitude of the coupling signal after the band-pass processing is within the signal amplitude input range of the automatic gain controller corresponding to the automatic gain amplification and the effective automatic adjustment of the amplification factor is obtained;
the reference voltage range is set between the peak voltage of the first period and the peak voltage of the second period of the coupled signal after the automatic gain amplification.
2. The ultrasonic flow test signal processing method of claim 1, wherein the reference voltage is an average of a sum of the peak voltage of the first period and the peak voltage of the second period.
3. An ultrasonic flow rate detection signal processing device of the ultrasonic flow rate detection signal processing method according to claim 1, characterized in that the ultrasonic flow rate detection signal processing device comprises: band-pass amplifier, automatic gain controller, voltage comparator, high accuracy time measurement chip and flow calculator, wherein:
the band-pass amplifier is consistent with the transmitting frequency and is used for carrying out fixed amplification factor and band-pass processing on the coupling signal;
the automatic gain controller is used for carrying out automatic gain control on the coupling signal subjected to the band-pass processing so as to enable the signal output amplitude of the coupling signal subjected to the automatic gain control to be stabilized at a preset peak-peak value;
the voltage comparator is used for converting the coupling signal subjected to automatic gain control into a square wave signal according to the acquired reference voltage;
the high-precision time measuring chip is used for detecting the upper/lower edge time points of the square wave signal output by the comparator and providing a high-precision time base for the subsequent forward/backward peak time;
and the flow calculator calculates the peak value time of the forward/backward propagation sampling period of the coupling signal through the upper/lower edge time points, and performs flow detection according to the peak value time of the forward/backward propagation coupling signal period and preset parameters such as the diameter of the pipeline.
4. A time difference method ultrasonic detection system using the ultrasonic flow detection signal processing method according to any one of claims 1 to 2.
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| CN111351958B (en) * | 2018-12-21 | 2021-11-02 | 上海华虹计通智能系统股份有限公司 | Time delay detection method and device, and fluid speed measurement method and system |
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