CN115727907A - Method for judging characteristic time reference wave of sound wave signal of ultrasonic flowmeter - Google Patents
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Abstract
A method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter, the ultrasonic flow meter including a first acoustic transceiver unit for transmitting a first acoustic signal and receiving a second acoustic signal, and a second acoustic transceiver unit for transmitting the second acoustic signal and receiving the first acoustic signal, the method comprising: (a) Receiving a first waveform corresponding to the first sound wave signal and a second waveform corresponding to the second sound wave signal; (b) Sampling a plurality of peak values of the first waveform and the second waveform; (c) setting a search range according to the plurality of peak values; (d) Setting the first peak value in the search range as a characteristic peak value; (e) Recording a first time between a zero point and a pre-zero point after the characteristic peak value and a second time between the zero point and a post-zero point, and calculating an average time of the first time and the second time; and (f) calculating the total flight time according to the average time.
Description
Technical Field
The present invention relates to a method for determining a sound wave signal of an ultrasonic flowmeter, and more particularly, to a method for determining a characteristic time reference wave of a sound wave signal of an ultrasonic flowmeter.
Background
The flow meter is one of the important instruments in industrial measurement, has close relation in various industrial applications and scientific research, and has higher and higher requirements on measurement accuracy, and the flow meter is widely applied in various fields, such as semiconductor manufacturing processes: the measurement technique using a flow meter is used in the manufacturing process of the coating apparatus, the etching apparatus, the cleaning apparatus, and the drying apparatus.
Ultrasonic technology has been used for military, medical and other purposes, and has been developed for many industrial applications in recent years, and although ultrasonic flow meters are measuring instruments that appear later, they have characteristics of no resistance to fluid, an extended sensor life, and avoidance of contamination by being in non-contact with a measuring body, and have gained much attention and use in recent years.
The measuring method of the ultrasonic flowmeter is that after the ultrasonic propagation time difference algorithm is adopted to measure the flow velocity in the pipeline, the flow is converted by the flow velocity. When the ultrasonic wave moves in the same direction as the fluid, the faster the flow velocity, the larger the propagation time difference. The fluid state can change the speed of ultrasonic wave, and the time difference obtained by the front sensor and the rear sensor is used for estimating the flow speed and the flow.
However, when the sound wave (ultrasonic wave) waveforms received by the corresponding front and rear sensors are not consistent, that is, the sound wave characteristic time reference waves obtained by the front sensor and the rear sensor are not consistent, the estimation of the flow velocity and the flow rate will have a great error, and the function of precise measurement cannot be achieved.
Therefore, how to design a method for determining a characteristic time reference wave of a sound wave signal of an ultrasonic flowmeter, which performs pre (pre) processing on the sound wave and determining the sound wave signal to realize precise measurement of the ultrasonic flowmeter, is a major subject to be studied by the inventors of the present invention.
Disclosure of Invention
The invention aims to provide a method for judging characteristic time reference waves of sound wave signals of an ultrasonic flowmeter, and solves the problems in the prior art.
In order to achieve the above object, the present invention provides a method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter, wherein the ultrasonic flow meter includes a first acoustic transceiver unit for transmitting a first acoustic signal and receiving a second acoustic signal, and a second acoustic transceiver unit for transmitting the second acoustic signal and receiving the first acoustic signal. The method comprises the following steps: (a) Receiving a first waveform corresponding to the first sound wave signal and a second waveform corresponding to the second sound wave signal; (b) Sampling a plurality of peak values of the first waveform and the second waveform; (c) setting a search range according to the plurality of peak values; (d) Setting the first peak value in the search range as a characteristic peak value; (e) Recording a first time between the zero point and the pre-zero point after the characteristic peak value and a second time between the zero point and the post-zero point, and calculating an average time of the first time and the second time; and (f) calculating a total time of flight from the average time.
In one embodiment, before step (b), the method further comprises: (f) And setting a lower standard deviation threshold and an upper standard deviation threshold. The step (d) further comprises: (d1) When the first peak value is larger than the upper threshold of the standard deviation, setting the first peak value as a characteristic peak value; (d2) When the first peak value is smaller than the lower limit threshold of the standard deviation, the first peak value is excluded as a characteristic peak value; and (d 3) setting the characteristic peak value when the continuous peak value is judged to be larger than the standard deviation upper limit threshold value.
In one embodiment, before step (b), the method further comprises: (f) And setting a standard deviation lower limit threshold and a standard deviation upper limit threshold. The step (d) further comprises: (d1) When the first peak value is larger than the standard deviation upper limit threshold value, the characteristic peak value is set; (d2) When the first peak value is smaller than the lower limit threshold of the standard deviation, the first peak value is excluded as a characteristic peak value; and (d 3) when the continuous peak value is judged to be greater than or equal to the lower threshold value of the standard deviation and less than or equal to the upper threshold value of the standard deviation, judging whether the next peak value is greater than the previous peak value, and if so, setting the next peak value as the characteristic peak value.
In one embodiment, step (d 3) comprises: (d4) And when the latter peak value is larger than the former peak value and exceeds a variable quantity by more than one, setting the peak value as a characteristic peak value.
In one embodiment, the variation is a ratio of a maximum slope variation of any two adjacent peaks.
In an embodiment, the method for determining a characteristic time reference wave further includes: (e1) Obtaining a first peak value and a second peak value of the first sound wave signal; (e2) Obtaining a first peak value and a second peak value of the second acoustic signal; (e3) Comparing the first peak value of the first sound wave signal and the second peak value of the second sound wave signal with the second peak value of the first sound wave signal and the second peak value of the second sound wave signal to judge whether the first sound wave signal and the second sound wave signal are aligned; and (e 4) if the first acoustic signal is not aligned with the second acoustic signal, replacing the corresponding first peak and second peak, so that the first acoustic signal is aligned with the second acoustic signal.
In one embodiment, step (e 4) comprises: when the first sound wave signal is ahead of the second sound wave signal, replacing the second peak value of the first sound wave signal with the first peak value of the first sound wave signal; when the second acoustic signal is ahead of the first acoustic signal, the second peak of the second acoustic signal is replaced with the first peak of the second acoustic signal.
In one embodiment, the upper threshold of the standard deviation is that the signal-to-noise ratio is equal to 10, and the lower threshold of the standard deviation is that the signal-to-noise ratio is equal to 5.
In one embodiment, peaks other than the proximity of the first acoustic signal frequency to the second acoustic signal frequency are deleted.
The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.
Drawings
FIG. 1: is a schematic diagram of the operation of an ultrasonic flow meter of the present invention.
FIG. 2: is a waveform schematic diagram of the acoustic signal of the ultrasonic flowmeter of the invention.
FIG. 3: the flow calculation diagram of the ultrasonic flowmeter in the prior art is shown.
FIG. 4 is a schematic view of: is a waveform diagram of the sound wave signal received by the sound wave transceiving unit of the present invention.
FIG. 5: the invention is a waveform schematic diagram for optimizing the judgment of the characteristic time reference wave of the sound wave signal.
FIG. 6: the waveform schematic diagram is another optimized waveform schematic diagram for judging the characteristic time reference wave of the sound wave signal.
FIG. 7: the invention is a flow chart of a method for judging characteristic time reference waves of sound wave signals of an ultrasonic flowmeter.
Wherein, the reference numbers:
100 ultrasonic flowmeter
11 first acoustic transceiver unit
12 second acoustic wave transceiving unit
S1 first Acoustic Signal
S2 second Acoustic Signal
S11 to S16 step
Tup1, tup2, tdn1, tdn2: peak value
Detailed Description
The invention will be described in detail with reference to the following drawings, which are provided for illustration purposes and the like:
as shown in fig. 1, which is a schematic diagram of the operation of an ultrasonic flow meter of the present invention, illustrated in longitudinal section. The ultrasonic flowmeter 100 of the present invention includes a first sound wave transmitting/receiving unit 11 and a second sound wave transmitting/receiving unit 12. In the present embodiment, the first acoustic transceiver unit 11 and the second acoustic transceiver unit 12 are provided in pairs at positions opposing the outer surface of the flow pipe. However, the paired arrangement of the two transceiving units is not limited to the one shown in fig. 1, which means that in other embodiments, the first acoustic transceiving unit 11 and the second acoustic transceiving unit 12 may be arranged on the same line of the outer surface of the circulation pipe. The first acoustic transceiver unit 11 is configured to transmit a first acoustic signal S1 and receive a second acoustic signal S2; the second acoustic transceiver unit 12 is used for transmitting a second acoustic signal S2 and receiving a first acoustic signal S1. The first acoustic signal S1 and the second acoustic signal S2 are ultrasonic signals (ultrasonic signals).
The first acoustic transceiver unit 11 transmits the ultrasonic signal obliquely to the flowing direction of the fluid in the flow pipe and the second acoustic transceiver unit 12 receives the ultrasonic signal, at this time, the transmission and reception of the first acoustic transceiver unit 11 and the second acoustic transceiver unit 12 are switched, the second acoustic transceiver unit 12 transmits the ultrasonic signal obliquely to the opposite flowing direction of the fluid in the flow pipe and the first acoustic transceiver unit 11 receives the ultrasonic signal, so that the flow rate can be measured from the transmission time difference of the ultrasonic signal in the fluid, which will be described in detail later.
Fig. 2 is a schematic diagram showing a waveform of an acoustic wave signal of the ultrasonic flowmeter according to the present invention. The acoustic waveform includes a first acoustic signal S1 transmitted by the first acoustic transceiver unit 11 to the second acoustic transceiver unit 12 for receiving, and a second acoustic signal S2 transmitted by the second acoustic transceiver unit 12 to the first acoustic transceiver unit 11 for receiving. Although there is a time difference between the two sound wave signals, the two sound wave signals can be compared in a flush manner by setting time offset so as to accurately judge the characteristic time reference wave position of the sound wave signal.
Fig. 3 is a schematic diagram illustrating a flow calculation of a prior art ultrasonic flowmeter. Wherein,
Δ t ＝T down -T up \823080type (3)
Wherein M is a sound wave path, D is an inner radius of the pipeline, theta is an incident angle of the ultrasonic wave, and C 0 Speed of sound in the medium, V mean speed (flow rate) of fluid, T up Time required for upstream, T down Time required for downstream, Δ t Is the time difference between the two sound wave transceiving units. Therefore, the flow rate in the flow passage can be calculated (estimated) by the equations (1) to (4).
The main technical feature of the present invention is to perform pre-processing (pre-) processing and sound wave signal determination on sound wave signals received by the sound wave transceiver (for example, the first sound wave signal S1 received by the second sound wave transceiver 12 and the second sound wave signal S2 received by the first sound wave transceiver 11).
Fig. 4 is a schematic waveform diagram of an acoustic wave signal received by the acoustic wave transceiver unit. In order to accurately determine (detect) the characteristic time reference wave (i.e., the first start wave of the acoustic wave used for flow rate calculation) of the acoustic wave signal of the ultrasonic flow meter, the technical means proposed by the present invention is described below.
The ideal ultrasound signal is a complete envelope shape, but due to factors of the measured position or the measured conditions, the ultrasound signal cannot so assume a complete envelope shape. Therefore, the method for judging the characteristic time reference wave of the acoustic wave signal provided by the invention mainly comprises the following key steps:
step 1: the timing at which the sound wave is received is set. For example, since the time delay from the first sound wave transceiving unit 11 to the second sound wave transceiving unit 12 when the first sound wave signal S1 approaches the second sound wave transceiving unit 12 is, for example, set the timing for receiving the sound wave according to the speed of the sound wave and the type of the medium \8230;, etc., the receiver of the second sound wave transceiving unit 12 is turned on (enabled) to start receiving the required sound wave signal, for example, at the time t1 shown in fig. 4.
And 2, step: the standard deviation of the noise is calculated. Since the frequency of the transmitted sound wave is known (for example, 1 MHz), it is possible to judge whether or not it is noise from the frequency of the received sound wave signal, and further calculate the standard deviation of the noise (magnitude). Therefore, the threshold size for subsequent determinations can be dynamically designed based on a reasonable standard deviation of noise size.
And step 3: a peak of the sound wave is established. By sampling the peak value (including the valley value) of the received sound wave, the peak value of the sound wave, that is, the waveform characteristic of the sound wave is obtained (established). In practice, since the frequency of the transmitted sound wave is known, unreasonable noise or glitches (glitchings) which may or may not belong to the correct waveform can be filtered out by means of secondary filtering to be regarded as the desired sound wave signal, i.e. to leave only peaks at the desired frequency.
And 4, step 4: a search window is established. When determining the acoustic signal and the noise and sampled peak of the acoustic wave, a search window may be opened before approaching the estimated characteristic time reference wave position. Through the established search window, only the data in the search window is calculated, and the calculation time and the calculated data amount can be saved. For example, the number of data acquired (sampled) is typically 4000, and if the entire 4000 is calculated, the data amount calculation is burdened. The range of the search window is designed to cover the characteristic time reference wave data, for example, the search window is opened at time t2 and is closed at time t3 shown in fig. 4.
And 5: the first peak in the search window is obtained. Based on the search window and the sampled peaks, a first peak within the search window is obtained. Such as the peak at time t2 shown in fig. 4. And judging whether the first peak value in the search window is a characteristic time reference wave of the sound wave, if not, judging the next peak value. The method for judging whether the characteristic time reference wave is adopted is as follows:
(1) And taking the signal-to-noise ratio (SNR) less than 5 as judgment: and if the peak value is smaller than SNR =5, directly judging the peak value non-characteristic time reference wave.
(2) And judging that the signal-to-noise ratio (SNR) is more than 10: if the peak value is greater than SNR =10, the peak value is directly determined as the characteristic time reference wave, and as shown in fig. 4, the peak value at time t4 is greater than SNR =10, so the peak value is determined as the characteristic time reference wave.
(3) And if the signal-to-noise ratio (SNR) is between 5 and 10, further determining whether the peak is a characteristic time reference wave, as described below.
The signal-to-noise ratio is not limited to the above values (SNR =5, SNR = 10), and is intended to describe whether the peak is a characteristic time reference wave directly determined by the magnitude relationship between the two values or to perform a more detailed determination when the peak is between the two values.
Step 6: calculating the zero crossing time: when the signal-to-noise ratio of the peak value is greater than 10 and it is determined that the peak value is after the characteristic time reference wave (for example, time t4 in fig. 4), an arithmetic mean calculation is performed through a time difference between the zero point and the front of the zero point and a time difference between the zero point and the rear of the zero-crossing point, and the obtained time difference can overcome an error caused by an offset (offset) of the acoustic waveform.
And 7: the total time of flight (TOF) is calculated. The total flight time is calculated according to the average time, and then the calculation (estimation) of the flow is achieved.
In the manner of determining the characteristic time reference wave, it is worth mentioning if the signal to noise ratio is between 5 and 10 in (3). When the sampled peak is in the vicinity of signal-to-noise ratio SNR =5 or signal-to-noise ratio SNR =10, it is easy to erroneously determine whether the peak is a characteristic time reference wave. The following description is made with reference to the drawings.
Fig. 5 is a schematic waveform diagram illustrating the optimization of the characteristic time reference wave determination of the acoustic wave signal according to the present invention. It is to be noted that the peak value is obtained in the search window on the premise that the above step 3 (establishing the peak value of the sound wave) and step 4 (establishing the search window) are performed. As shown in fig. 5, at time t1, a possible characteristic time reference wave is obtained (because the peak is between the snr 5 and 10), and therefore, it is determined again later whether the sampled peak is larger than the peak obtained at time t 1. If not, the peak value obtained at the time t1 is judged not to be the characteristic time reference wave. And, judge again afterwards whether the new peak value is the characteristic time reference wave, until finding the correct characteristic time reference wave.
As shown in fig. 5, another peak is found at time t2 after (say) 90 sampling points have elapsed. At this time, it is determined whether the second peak value (Tup 2) is greater than the first peak value (Tup 1). Further, if the second peak value (Tup 2) is greater than the first peak value (Tup 1), it is determined whether the second peak value (Tup 2) is sufficiently greater than the first peak value (Tup 1). The judgment basis is that the maximum slope of two adjacent peak values is used as the judgment basis, for example, the maximum slope of two peak values is Smax, if the difference between the second peak value (Tup 2) and the first peak value (Tup 1) is greater than 20 percent (i.e. 0.2 x Smax) of the maximum slope, but not limited thereto, the second peak value (Tup 2) is greater than the first peak value (Tup 1). Therefore, the second peak (Tup 2) is identified (set) as a new (possible) characteristic time reference wave. Then, the same judgment is carried out on the sampling peak value, and the real characteristic time reference wave when the peak value is between the signal-to- noise ratio 5 and 10 can be judged.
Referring to fig. 6, another waveform diagram for optimizing the characteristic time reference wave determination of the acoustic wave signal is shown. As mentioned above, since the ultrasonic flowmeter includes the first acoustic transceiver 11 for transmitting the first acoustic signal S1 and receiving the second acoustic signal S2, and the second acoustic transceiver 12 for transmitting the second acoustic signal S2 and receiving the first acoustic signal S1, the acoustic signals are similar in two sets, and thus, the aforementioned determining step is performed twice, that is, the first acoustic transceiver 11 is a first peak (Tup 1) and the second peak (Tup 2), the second acoustic transceiver 12 is a first peak (Tdn 1) and a second peak (Tdn 2), and the same determining step is performed once for the first acoustic signal S1 and once for the second acoustic signal S2.
More optimally, the sound wave transmitted by the upstream transceiving unit is compared with the sound wave transmitted by the downstream transceiving unit. First, the first peak value (Tup 1) and the second peak value (Tup 2) of the first acoustic transceiver unit 11 and the first peak value (Tdn 1) and the second peak value (Tdn 2) of the second acoustic transceiver unit 12 are obtained according to the above steps and compared two by two to determine whether the peak values are "close in size". That is, when Tup1 is compared with Tdn1 (by (Tdn 1-Tup 1)/Tup 1), tup1 is compared with Tdn2 (by (Tdn 2-Tup 1)/Tup 1), tup2 is compared with Tdn1 (by (Tdn 1-Tup 2)/Tup 2), and Tup2 is compared with Tdn2 (by (Tdn 2-Tup 2)/Tup 2), the first comparison value Cmp1, the second comparison value Cmp2, the third comparison value Cmp3, and the fourth comparison value Cmp4 are obtained, respectively.
When Tup1 is close to Tdn1 and Tup2 is also close to Tdn2, it is determined that the first acoustic signal S1 and the second acoustic signal S2 are aligned. Conversely, when Tup2 is closer to Tdn1, it indicates that the first acoustic signal S1 is not aligned with the second acoustic signal S2, and the first acoustic signal S1 is before (precedes) the second acoustic signal S2. Similarly, when Tup1 is closer to Tdn2, it means that the first acoustic signal S1 is not aligned with the second acoustic signal S2, and the second acoustic signal S2 is before (before) the first acoustic signal S1.
Once the condition that the two sound waves are not aligned is judged, the order of the peak values is adjusted. That is, when the first acoustic signal S1 is ahead (before) the second acoustic signal S2, tup2 is replaced with Tup1; conversely, when the second acoustic signal S2 is ahead (before) the first acoustic signal S1, tdn2 is replaced with Tdn1. This allows the calculation of Tup1 and Tdn1 and the calculation of Tup2 and Tdn2 to be matched (matched), i.e., tup1 is calculated for Tdn1 and Tup2 is calculated for Tdn 2. By adjusting the alignment signal (i.e. changing the characteristic time reference wave to the correct position), the condition that the characteristic time reference wave shifts (cancel) due to disappearance (into noise) when signal transmission occurs can be eliminated (offset).
Preferably, in order to avoid the false determination of the characteristic time reference wave due to the tiny waveform variation, the peak value can be replaced to ensure that the determined characteristic time reference wave is not changed any more. For example, when it is determined to be Tup1 of the characteristic time reference wave or Tdn1 of the characteristic time reference wave, if the variation is not large, the characteristic time reference wave is maintained as Tup1 and Tdn1, thereby reducing the frequent variation of the characteristic time reference wave. Unless, tup1 determined as the characteristic time reference wave or Tdn1 of the characteristic time reference wave varies greatly, the characteristic time reference wave is replaced with a new characteristic time reference wave.
Therefore, the position of the characteristic time reference wave can be roughly judged through the basic steps (step 1-step 7), and the total flight time is calculated, thereby achieving the calculation (estimation) of the flow. Furthermore, the position of the characteristic time reference wave can be found more accurately through optimized judgment and adjustment, so that the measurement result of the ultrasonic flowmeter is improved, and the technical effect of the invention is realized.
Fig. 7 is a flowchart of a method for determining a characteristic time reference wave of a sound wave signal of an ultrasonic flowmeter according to the present invention. Referring to fig. 1, the ultrasonic flowmeter includes a first acoustic transceiver unit 11 that transmits a first acoustic signal S1 and receives a second acoustic signal S2, and a second acoustic transceiver unit 12 that transmits a second acoustic signal S2 and receives the first acoustic signal S1. The method comprises the following steps: first, a first waveform corresponding to a first acoustic signal and a second waveform corresponding to a second acoustic signal are received (S11). Then, a plurality of peaks of the first waveform and the second waveform are sampled (S12). Then, a search range (search window) is set based on the plurality of peaks (S13). Then, the first peak in the search range is set as a characteristic peak (S14). Then, a first time before and after the zero-crossing point and a second time after and after the zero-crossing point after the characteristic peak are recorded, and an average time of the first time and the second time is calculated (S15). Finally, the total time of flight (TOF) is calculated from the average time (S16).
Before the step (S12), the method further includes: and setting a standard deviation lower threshold and a standard deviation upper threshold, wherein the standard deviation lower threshold and the standard deviation upper threshold are signal-to-noise ratio (SNR).
The step (S14) further includes: when the first peak is larger than the upper threshold of standard deviation (for example, SNR = 10), the characteristic peak is set. When the first peak is smaller than the lower threshold of standard deviation (e.g., SNR = 5), the first peak is excluded as the characteristic peak. Or when the continuous peak value is judged to be larger than the standard deviation upper limit threshold value, the characteristic peak value is set.
The step (S14) further includes: when the first peak value is larger than the standard deviation upper limit threshold value, the characteristic peak value is set. When the first peak value is smaller than the standard deviation lower limit threshold value, the first peak value is excluded as the characteristic peak value. Or when the continuous peak value is judged to be greater than or equal to the lower limit threshold of the standard deviation and less than or equal to the upper limit threshold of the standard deviation, judging whether the next peak value is greater than the previous peak value or not, and if so, setting the peak value as the characteristic peak value. When the latter peak value is larger than the former peak value and the latter peak value is larger than the former peak value by more than a variable amount, the characteristic peak value is set. In one embodiment, the variation is a ratio of a maximum slope variation of any two adjacent peaks.
The method for determining the characteristic time reference wave further comprises: a first peak and a second peak of the first acoustic signal are obtained. A first peak and a second peak of the second acoustic signal are obtained. Comparing the first plurality of peak values with the second plurality of peak values to determine whether the first acoustic signal and the second acoustic signal are aligned. And if the first sound wave signal is not aligned with the second sound wave signal, replacing the corresponding first peak value and second peak value, so that the first sound wave signal is aligned with the second sound wave signal. When the first sound wave signal is ahead of the second sound wave signal, the second peak value of the first sound wave signal is replaced by the first peak value of the first sound wave signal. When the second acoustic signal is ahead of the first acoustic signal, the second peak of the second acoustic signal is replaced with the first peak of the second acoustic signal.
Therefore, by the method for judging the characteristic time reference wave of the sound wave signal of the ultrasonic flowmeter, the position of the characteristic time reference wave can be roughly judged through basic steps (step 1-step 7), the total flight time is calculated, and the calculation (estimation) of the flow is further achieved. Moreover, the position of the characteristic time reference wave can be found more accurately through optimized judgment and adjustment, so that the measurement result of the ultrasonic flowmeter is improved, and the technical effect of the invention is realized.
The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter, the ultrasonic flow meter comprising a first acoustic transceiver unit for transmitting a first acoustic signal and receiving a second acoustic signal, and a second acoustic transceiver unit for transmitting the second acoustic signal and receiving the first acoustic signal, the method comprising:
(a) Receiving a first waveform corresponding to the first sound wave signal and a second waveform corresponding to the second sound wave signal;
(b) Sampling a plurality of peak values of the first waveform and the second waveform;
(c) Setting a searching range according to the peak values;
(d) Setting the first peak value in the searching range as a characteristic peak value;
(e) Recording a first time between zero and before the zero crossing point after the characteristic peak value and a second time between zero and after the zero crossing point, and calculating an average time of the first time and the second time; and
(f) And calculating a total flight time according to the average time.
2. A method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter according to claim 1, further comprising, before step (b):
(f) Setting a standard deviation lower limit threshold and a standard deviation upper limit threshold;
wherein step (d) further comprises:
(d1) When the first peak value is larger than the standard deviation upper limit threshold value, the characteristic peak value is set;
(d2) When the first peak value is smaller than the lower limit threshold of the standard deviation, the first peak value is excluded as the characteristic peak value; and
(d3) And when the continuous peak value is judged to be larger than the standard deviation upper limit threshold value, setting the characteristic peak value.
3. A method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter according to claim 1, further comprising, before step (b):
(f) Setting a standard deviation lower limit threshold and a standard deviation upper limit threshold;
wherein step (d) further comprises:
(d1) When the first peak value is larger than the upper threshold value of the standard deviation, the first peak value is set as the characteristic peak value;
(d2) When the first peak value is smaller than the lower limit threshold of the standard deviation, the first peak value is excluded as the characteristic peak value; and
(d3) And when the continuous peak value is judged to be greater than or equal to the lower limit threshold of the standard deviation and less than or equal to the upper limit threshold of the standard deviation, judging whether the next peak value is greater than the previous peak value or not, and if so, setting the next peak value as the characteristic peak value.
4. The method for determining a characteristic time reference wave of a sonic signal of an ultrasonic flowmeter according to claim 3, comprising in step (d 3):
(d4) And when the latter peak value is larger than the former peak value and exceeds a variable quantity, setting the characteristic peak value.
5. The method of claim 4, wherein the variance is a ratio of a maximum slope variance of any two adjacent peaks.
6. The method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter according to claim 4, further comprising:
(e1) Obtaining a first peak value and a second peak value of the first sound wave signal;
(e2) Obtaining a first peak value and a second peak value of the second acoustic signal;
(e3) Comparing the first peak value of the first sound wave signal and the second peak value of the second sound wave signal with the second peak value of the first sound wave signal and the second peak value of the second sound wave signal to judge whether the first sound wave signal and the second sound wave signal are aligned; and
(e4) And if the first sound wave signal is not aligned with the second sound wave signal, replacing the corresponding first peak value and the second peak value so as to align the first sound wave signal with the second sound wave signal.
7. An ultrasonic flow meter acoustic signal characteristic time reference wave determination method as defined in claim 6, comprising in step (e 4):
replacing the second peak value of the first sound wave signal with the first peak value of the first sound wave signal when the first sound wave signal is ahead of the second sound wave signal;
when the second acoustic signal is ahead of the first acoustic signal, the second peak of the second acoustic signal is replaced with the first peak of the second acoustic signal.
8. The method for determining a characteristic time reference wave of an acoustic signal of an ultrasonic flow meter according to claim 2 or 3, wherein the upper threshold value of the standard deviation is a signal to noise ratio equal to 10, and the lower threshold value of the standard deviation is a signal to noise ratio equal to 5.
9. A method of determining a characteristic time reference wave of a sonic signal of an ultrasonic flow meter as claimed in claim 1, characterised in that in step (b) peaks outside the vicinity of the first sonic signal frequency and the second sonic signal frequency are deleted.
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