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CN108548578B - Ultrasonic echo signal characteristic peak identification method based on self-adaptive threshold - Google Patents

Ultrasonic echo signal characteristic peak identification method based on self-adaptive threshold Download PDF

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CN108548578B
CN108548578B CN201810270004.XA CN201810270004A CN108548578B CN 108548578 B CN108548578 B CN 108548578B CN 201810270004 A CN201810270004 A CN 201810270004A CN 108548578 B CN108548578 B CN 108548578B
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赵伟国
卜勤超
章涛
虞结勇
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China Jiliang University
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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
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Abstract

本发明提出了一种基于自适应阈值的超声波回波信号特征峰识别方法。现有的识别方法有盲目性和不适应性，容易出现跳波现象。本发明首先将换能器接收到的回波信号进行滤波放大，利用峰值检测电路得到回波信号的峰值电压信号。然后进行回波峰值信号的台阶识别，同时选定阈值。最后通过判断取峰值台阶的中值作为阈值，并不断更新存储回波信号数组，使得阈值能够根据实际的回波信号进行自适应调整以得到实时阈值的最优值。本发明不仅可以根据回波信号幅值的变化进行调整，而且当当前回波信号特征峰出现变化，自适应阈值也可以实时调整，这使得自适应阈值相比固定阈值法有着更强的适应性。

Figure 201810270004

The invention proposes a method for identifying characteristic peaks of ultrasonic echo signals based on adaptive thresholds. Existing identification methods are blind and unsuitable, and are prone to wave-hopping phenomenon. The invention firstly filters and amplifies the echo signal received by the transducer, and obtains the peak voltage signal of the echo signal by using a peak detection circuit. Then the step identification of the echo peak signal is carried out, and the threshold is selected at the same time. Finally, by judging and taking the median value of the peak step as the threshold, and continuously updating the stored echo signal array, the threshold can be adaptively adjusted according to the actual echo signal to obtain the optimal value of the real-time threshold. The invention can not only adjust according to the change of the echo signal amplitude, but also adjust the adaptive threshold in real time when the characteristic peak of the current echo signal changes, which makes the adaptive threshold more adaptable than the fixed threshold method.

Figure 201810270004

Description

Ultrasonic echo signal characteristic peak identification method based on self-adaptive threshold
Technical Field
The invention belongs to the technical field of flow detection, and relates to a method for identifying characteristic peaks of echo signals of an ultrasonic flowmeter.
Background
Compared with other types of flow meters, the ultrasonic flow meter has the advantages of high precision, low pressure loss, bidirectional measurement and the like. While signal processing is the core technology of ultrasonic flow meters. Domestic ultrasonic flow meters mainly measure the flight time of ultrasonic echo signals by a threshold level method. And when the ultrasonic echo signal exceeds the set threshold voltage, carrying out zero-crossing detection on the ultrasonic echo signal so as to measure the flight time of the ultrasonic signal. The set threshold level is called a threshold value, the first peak exceeding the threshold value is called a characteristic peak, and the time of a certain fixed zero crossing point after the characteristic peak is measured is used as the flight time of the echo signal, so that the accuracy of each measurement is ensured.
The threshold level method has poor anti-interference capability, when the echo signal changes greatly, the amplitude of the characteristic peak changes, which causes the identification error of the system characteristic peak, so that the zero crossing point of the measurement is different, and the accuracy of the measurement is influenced, and the phenomenon is called 'wave jump'. The traditional threshold level method generally fixes a threshold value, and then judges characteristic waves according to the position of the threshold value, and the identification method has certain limitation and is easy to generate wave hopping phenomenon.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an ultrasonic echo signal characteristic peak identification method based on an adaptive threshold.
The invention mainly comprises the following steps:
the method comprises the following steps: and filtering and amplifying the echo signal received by the transducer, and then obtaining a peak voltage signal of the echo signal by using a peak detection circuit. And selecting m pieces of echo data with the maximum peak value closest to the set target amplitude as a reference for processing the echo signal data. Setting an initial threshold Th according to the m echo signals0。
Step two: and identifying the steps of the echo peak signals. The maximum value of the echo peak signal is selected, and then the voltage of each peak step is determined. And setting a resolution D, namely considering that two sampling points are on the same peak step when the difference between the amplitudes of two adjacent sampling points is less than the resolution D, and considering that the next peak step appears when the difference between the amplitudes of two adjacent sampling points is greater than the resolution. Obtaining a step array A ═ A from the peak step identification result1,A2…Ak]. Where k represents the corresponding peak step total, where A1Is the first peak step, AkThe peak step maximum. By dividing each element in array A by AkObtaining a ratio array R ═ R1,R2…1]。
On one hand, the threshold selection selects two peak steps with the largest amplitude difference from all the peak steps and takes the midpoint of the voltage values of the peak steps as a threshold, so that the fault tolerance of the threshold selection is improved; on the other hand, the threshold value is close to the reference zero crossing point of the echo as much as possible, and the influence of overall amplitude fluctuation is reduced.
Step three: storing N echo signals according to the first-in first-out principle to obtain N step arrays Ai＝[A1i,A2i,…,Aki]，i∈[1,N]K is the total number of peak steps of the echo signal; obtaining N proportional arrays R simultaneouslyi＝[R1i,R2i,…,1]，i∈[1,N]Wherein R is1i、R2i、R3iAre respectively the ithThe ratio of the first peak step to the maximum peak value, the ratio of the second peak step to the maximum peak value and the ratio of the third peak step to the maximum peak value of the echo. Thereby obtaining the voltage average value of the peak stepj∈[1,k]：
Figure BDA0001612314770000022
Simultaneously obtaining the proportional average value of each peak step
Figure BDA0001612314770000023
Figure BDA0001612314770000024
Comparing the step arrays of the currently acquired echoes according to the sequence to obtain a first element A larger than a threshold valuep，p∈[1,k]。
When p is 1 and judged to obtain
Figure BDA0001612314770000025
If the first peak step is lost, getAs the first peak step.
When p is 2, the first peak step is considered to be successfully identified.
Taking the median of the first peak step and the second peak step of the collected echo as a threshold, and obtaining the self-adaptive threshold as follows:
and continuously updating and storing the echo signal array by a first-in first-out principle, so that the threshold can be adaptively adjusted according to the actual echo signal to obtain the optimal value of the real-time threshold.
Furthermore, the method also comprises the steps of carrying out wave hopping identification on the echo data after the first peak step identification and compensation, and setting R1(N+1)、R2(N+1)、R3(N+1)Respectively representing the ratio of the first, second and third peak steps of the currently measured echo signal to the maximum peak step.
When in use
Figure BDA0001612314770000028
And when the current threshold value is between the first peak value step and the second peak value step, no wave jump exists.
When in use
Figure BDA0001612314770000031
And then, if the current threshold value is between the first peak step and the reference step, the zero crossing point is moved forward by one period, and the zero crossing point is delayed backward by one period to be used as the real echo reaching time.
When in use
Figure BDA0001612314770000032
And when the current threshold value is between the second peak value step and the third peak value step, the zero crossing point is delayed by one period as a whole, and the previous period of the zero crossing point is taken as the real echo arrival time.
Compared with the prior art, the invention adopts an ultrasonic echo signal characteristic peak identification method of self-adaptive threshold value, and sets the threshold value according to the identified characteristic wave peak value. The self-adaptive threshold value can be adjusted according to the change of the amplitude of the echo signal, and can be adjusted in real time when the characteristic peak of the current echo signal changes, so that the self-adaptive threshold value has stronger adaptability compared with a fixed threshold value method.
Drawings
FIG. 1 is a schematic diagram of an ultrasonic flow meter circuit used in an embodiment of the present invention;
FIG. 2 is a flow chart of a method for identifying characteristic peaks of an ultrasonic echo signal based on adaptive threshold;
FIG. 3 illustrates an original echo signal and a peak step in an embodiment of the present invention;
FIG. 4 is a graph of peak voltage magnitudes in an embodiment of the present invention;
fig. 5 is a schematic diagram of echo signal hopping data processing in the present invention.
Detailed Description
The present invention is described in further detail below with reference to the attached drawing figures.
The circuit principle of the ultrasonic flowmeter used in the present embodiment is shown in fig. 1, and is mainly composed of 8 parts: the device comprises a singlechip, a switch switching circuit, a transducer (A, B), an echo signal preprocessing circuit, a zero-crossing detection circuit, a peak detection circuit and a signal acquisition module. The echo signal processing circuit plays a role in filtering and amplifying the ultrasonic echo signal.
Fig. 2 is a flow chart of a method for identifying a characteristic peak of an ultrasonic echo signal based on an adaptive threshold, and the method comprises the following steps:
the method comprises the following steps: the echo signal received by the transducer is filtered and amplified, and then a peak voltage signal of the echo signal is obtained by using a peak detection circuit, as shown in fig. 3, the original echo signal and the peak step in this embodiment are obtained. And selecting m pieces of echo data with the maximum peak value closest to the set target amplitude as a reference for processing the echo signal data. In this embodiment, the number m of echo signal data stored is 100, and the initial threshold Th is set through experimental observation0＝1.65V。
Step two: and step identification of the echo peak signal, namely selecting the maximum value of the echo peak signal, and determining the voltage of each peak step according to the voltage value of the peak step. The resolution D is set, as can be seen from the peak voltage amplitude diagram in fig. 4, the fluctuation range of the peak voltage amplitude in this embodiment is 0.02V, and therefore the resolution D is set to 0.03V, that is, when the difference between the amplitudes of two adjacent sampling points is smaller than the resolution D, two sampling points are considered to be on the same peak step, otherwise, when the difference between the amplitudes of two adjacent sampling points is larger than the resolution, the next peak step is considered to occur.
Obtaining a step array A ═ A from the peak step identification result1,A2…Ak]. Where k represents the corresponding peak step total number, whichIn A1Is the first peak step, AkThe peak step maximum. By dividing each element in array A by AkObtaining a ratio array R ═ R1,R2…1]。
On one hand, the threshold selection selects two peak steps with the largest amplitude difference from all the peak steps and takes the midpoint of the voltage values of the peak steps as a threshold, so that the fault tolerance of the threshold selection is improved; on the other hand, the threshold value is close to the reference zero crossing point of the echo as much as possible, and the influence of overall amplitude fluctuation is reduced.
Step three: storing N echo signals according to the first-in first-out principle, in this embodiment, taking N to 10, and obtaining 10 step arrays Ai＝[A1i,A2i,…,Aki]，i∈[1,10]K is the total number of peak steps of the echo signal; obtain 10 proportional arrays R simultaneouslyi＝[R1i,R2i,…,1]，i∈[1,10]Wherein R is1i、R2i、R3iThe ratio of the first peak step to the maximum peak value, the ratio of the second peak step to the maximum peak value and the ratio of the third peak step to the maximum peak value of the ith echo are respectively. Thereby obtaining the average voltage value of each peak stepj∈[1,k]：
Figure BDA0001612314770000042
Simultaneously obtaining the proportional average value of each peak step
Figure BDA0001612314770000043
Figure BDA0001612314770000044
Comparing the step arrays of the currently acquired echoes according to the sequence to obtain a first element A larger than a threshold valuep，p∈[1,k]。
When p is 1 and judged to obtainIf the first peak step is lost, get
Figure BDA0001612314770000046
As the first peak step.
When p is 2, the first peak step is considered to be successfully identified.
Taking the median of the first peak step and the second peak step of the collected echo as a threshold, and obtaining the self-adaptive threshold as follows:
and continuously updating and storing the echo signal array by a first-in first-out principle, so that the threshold can be adaptively adjusted according to the actual echo signal to obtain the optimal value of the real-time threshold.
Step four: performing wave hopping identification on the echo data subjected to first peak step identification and compensation, and setting R1(N+1)、R2(N+1)、R3(N+1)Respectively representing the ratio of the first, second and third peak steps of the currently measured echo signal to the maximum peak step.
When in use
Figure BDA0001612314770000051
And when the current threshold value is between the first peak value step and the second peak value step, no wave jump exists.
When in use
Figure BDA0001612314770000052
And then, if the current threshold value is between the first peak step and the reference step, the zero crossing point is moved forward by one period, and the zero crossing point is delayed backward by one period to be used as the real echo reaching time.
When in use
Figure BDA0001612314770000053
Then the current threshold value is between the second peak value step and the third peak value step, and the zero crossing point can be integrally delayedAnd in the latter period, taking the previous period from the zero-crossing point as the real echo arrival time.
The time measuring module in the embodiment adopts DTC-GP22, and can simultaneously measure 3 continuous echo periods in the process of calculating the arrival time of the ultrasonic echo signal; three zero-crossing points t can be obtained according to the hopping data processing schematic diagram of FIG. 51、t2、t3When there is no beat, i.e., when the threshold value is 2, t is2For echo arrival time, t0＝(t1+t2+t3) (iii)/3 as echo arrival time to improve the stability of the measurement;
when the threshold 1 condition occurs, t is set3As the true echo arrival time;
when the threshold 3 condition occurs, then t will be1As the true echo arrival time.

Claims (1)

1.一种基于自适应阈值的超声波回波信号特征峰识别方法，其特征包括以下步骤：1. a method for identifying characteristic peaks of ultrasonic echo signals based on self-adaptive threshold, it is characterized in that comprising the following steps: 步骤一：将换能器接收到的回波信号进行滤波放大，然后利用峰值检测电路得到回波信号的峰值电压信号；选择最大峰值与所设定目标幅值最接近的m个回波数据作为回波信号数据处理的参照；根据比较记录的m个回波信号，设定初始阈值Th0；Step 1: Filter and amplify the echo signal received by the transducer, and then use the peak detection circuit to obtain the peak voltage signal of the echo signal; select m echo data whose maximum peak value is closest to the set target amplitude as The reference of echo signal data processing; according to the m echo signals recorded by comparison, set the initial threshold Th 0 ; 步骤二：回波峰值信号的台阶识别：首先选取峰值信号的最大值，再通过各个峰值台阶的电压值确定各个峰值台阶电压大小；由峰值台阶识别结果，得到台阶数组A＝[A1，A2...Ak]；其中k代表对应的峰值台阶总数，A1为第一峰值台阶，Ak为峰值台阶最大值；通过数组A中的各个元素除以Ak，得到比例数组R＝[R1，R2...1]；Step 2: Step identification of the echo peak signal: first select the maximum value of the peak signal, and then determine the voltage value of each peak step by the voltage value of each peak step; obtain the step array A=[A 1 , A from the peak step identification result 2 ...A k ]; where k represents the total number of corresponding peak steps, A 1 is the first peak step, and A k is the maximum value of the peak step; by dividing each element in the array A by A k , the proportional array R = [R 1 , R 2 ... 1]; 阈值选取：从各个峰值台阶中选择幅值差最大的两个峰值台阶并将峰值台阶的中点作为阈值；同时要尽量靠近回波的参考过零点，减小整体幅值波动的影响；Threshold selection: select the two peak steps with the largest amplitude difference from each peak step and use the midpoint of the peak steps as the threshold; at the same time, try to be as close to the reference zero-crossing point of the echo as possible to reduce the influence of the overall amplitude fluctuation; 步骤三：按先进先出原则存储N个回波信号，得到N个台阶数组Ai＝[A1i，A2i，...，Aki]，i∈[1，N]，同时得到N个比例数组Ri＝[R1i，R2i，...，1]，其中R1i、R2i、R3i分别为第i个回波的第一峰值台阶与最大峰值的比值、第二峰值台阶与最大峰值的比值、第三峰值台阶与最大峰值的比值；由此得到峰值台阶的电压平均值
Figure FDA0002254186370000011
Step 3: Store N echo signals according to the FIFO principle, and obtain N step arrays A i =[A 1i , A 2i ,..., A ki ], i∈[1, N], and simultaneously obtain N Ratio array R i =[R 1i , R 2i , . Ratio to the maximum peak value, ratio of the third peak step to the maximum peak value; from this, the voltage average value of the peak step is obtained
Figure FDA0002254186370000011
 同时得到各峰值台阶的比例平均值
Figure FDA0002254186370000013
At the same time, the proportional average value of each peak step is obtained.
Figure FDA0002254186370000013
Figure FDA0002254186370000014
Figure FDA0002254186370000014
 针对当前采集回波的台阶数组，按先后顺序比较得到首个大于阈值的元素Ap，p∈[1，k]；For the step array of the currently collected echoes, compare in order to obtain the first element A p greater than the threshold, p∈[1, k]; 当p＝1且判断得到
Figure FDA0002254186370000015
第一峰值台阶丢失，则取
Figure FDA0002254186370000016
作为第一峰值台阶；When p=1 and it is judged that
Figure FDA0002254186370000015
If the first peak step is lost, take
Figure FDA0002254186370000016
as the first peak step; 当p＝2时，则认为成功识别第一峰值台阶；When p=2, it is considered that the first peak step is successfully identified; 取采集回波的第一峰值台阶和第二峰值台阶的中值作为阈值，则由此可得自适应阈值为：Taking the median value of the first peak step and the second peak step of the collected echo as the threshold, the adaptive threshold can be obtained as:
Figure FDA0002254186370000021
Figure FDA0002254186370000021
 以先进先出的原则不断更新存储回波信号数组，使得阈值能够根据实际的回波信号进行自适应调整以得到实时阈值的最优值；Continuously update the stored echo signal array according to the principle of first-in, first-out, so that the threshold value can be adaptively adjusted according to the actual echo signal to obtain the optimal value of the real-time threshold value; 所述的回波数据还进行跳波识别，来防止测量中信号跳波引起的误差，具体是：The echo data is also identified by wave hopping to prevent errors caused by signal hopping in the measurement, specifically: 针对第一峰值台阶识别及补偿后的回波数据进行跳波识别，设R1(N+1)、R2(N+1)、R3(N+1)分别表示当前测得的回波信号的第一、第二、第三峰值台阶与最大峰值台阶的比值；The first peak step identification and the compensated echo data are used for wave hopping identification. Let R 1(N+1) , R 2(N+1) and R 3(N+1) represent the currently measured echoes respectively. The ratio of the first, second, and third peak steps of the signal to the largest peak step; 当时，则当前阈值在第一、第二峰值台阶之间，无跳波；when , the current threshold is between the first and second peak steps, and there is no jumping wave; 当
Figure FDA0002254186370000023
时，则当前阈值在第一峰值台阶与参考台阶之间，过零点前移一个周期，则将过零点往后延迟一个周期作为真实的回波达到时间；when
Figure FDA0002254186370000023
When the current threshold is between the first peak step and the reference step, the zero-crossing point is moved forward by one cycle, and the zero-crossing point is delayed by one cycle as the real echo arrival time; 当
Figure FDA0002254186370000024
时，则当前阈值在第二、第三峰值台阶之间，过零点会整体延后一个周期，则将过零点往前一个周期作为真实的回波到达时间。when
Figure FDA0002254186370000024
When the current threshold is between the second and third peak steps, the zero-crossing point will be delayed by one cycle as a whole, and the zero-crossing point is one cycle before the real echo arrival time.
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