JP4825367B2 - Ultrasonic flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic flow meter.
[0002]
[Prior art]
As shown in FIG. 15, ultrasonic waves are transmitted from one transducer 1 to the other transducer 2 of a set of ultrasonic transducers that are disposed upstream and downstream of the flow tube 3 at a distance L in the fluid. The flow velocity V of the fluid is calculated by calculating the flow velocity V of the fluid from the forward propagation time when transmitting the ultrasonic wave and the backward propagation time when transmitting the ultrasonic wave from the transducer 2 to the transducer 1.
[0003]
In the above-described measurement principle, there is a method of detecting a zero-cross point of a specific wave as a reception detection method for specifying the time when the ultrasonic wave reaches the transmitter / receiver on the receiving side, that is, the arrival time. FIG. 16 shows a transmission drive signal and a reception wave indicating the timing of transmission. The actual received wave is very small and is first amplified. The received wave in the figure shows the waveform after amplification.
[0004]
When a reaches, the amplitude gradually increases. After that, it becomes maximum amplitude and gradually decreases. However, the arrival point a is hidden behind noise and cannot be detected. Therefore, the following method is performed.
[0005]
A threshold voltage V _TH is determined as a reference voltage level (also referred to simply as a reference level) sufficiently larger than noise, and the first wave reaching this level, for example, the third wave in FIG. This is a method of detecting reception by detecting a zero cross point c that passes through the rear zero level.
[0006]
The threshold value V _TH is determined so as to always detect the zero cross point of some specific wave (for example, the third wave), and the actual propagation time t is the time τ from point a to point c. Obtained in advance and stored, and obtained by subtracting the time τ from the value corresponding to the measured time t + τ.
[0007]
As a method for determining the specific wave at the time of reception detection (that is, the specific wave), in addition to the method in which the wave that first exceeds a certain reference level is the specific wave as described above, Two reference levels are prepared, and when the first wave that exceeds the first reference level immediately exceeds the other reference level, it is determined that the wave is the specific wave. Methods are also known (Japanese Patent Laid-Open Nos. 10-332452 and 2000-283812).
[0008]
In order to obtain the forward propagation time and the backward propagation time from transmission to reception, instead of simply subtracting the time τ from the measured arrival time t + τ, in order to improve the accuracy of the propagation time measurement, By repeating the transmission in the same direction a plurality of times (n-1 times), transmission / reception in one direction, for example, the forward direction is repeated continuously n times, and the first (first) forward transmission to the last The time until the (n-th) reception, i.e., n times the arrival time, is measured collectively, and then transmission and reception in the other direction, for example, the reverse direction is repeated n times in a similar manner to obtain the first reverse direction. The time from transmission to the last reception, that is, n times the arrival time is measured together, nτ is subtracted from the measured values obtained by multiple transmissions in each direction, the propagation time in each direction is calculated, and the flow velocity In addition, an ultrasonic flow meter for determining flow rate is also public It is.
[0009]
[Problems to be solved by the invention]
By the way, the actual received wave is not as clean as shown in FIG. 16, but as shown in FIG. A reception wave for transmission (transmission) with an ultrasonic pulse appears greatly in a form that suddenly rises after a lapse of time determined mainly by the distance between the transmitter and the receiver and the speed of sound from the time of transmission, and gradually decreases. The first large portion is the original signal portion circled and labeled A, and the subsequent portion of gradually decreasing amplitude is the reverberation circled and labeled B (also called tailing). Then, when about three times the time interval from the transmission time point to the signal point A has elapsed from the transmission time point, the ultrasonic wave reflected by the reception-side transducer is reflected again by the transmission-side transducer. Then, a small received wave appears again at the receiving transducer. This small received wave is called a 1.5 round-trip wave in the part circled and marked with the symbol C.
[0010]
The above is a case where transmission is performed only once. In order to improve the accuracy of arrival time measurement, repeat the next transmission with reception several times, and when measuring multiple times of arrival time collectively, these become noise (reverberation noise, 1.5 round trips) Affects the measurement).
[0011]
That is, since the reverberation noise is not sufficiently small, 1.5 round-trip noise has an adverse effect on the next reception (zero cross point). In particular, in a small flowmeter with a small distance L between the transducers, these noises cannot be ignored as compared with signals (received waves), which is a major obstacle.
[0012]
FIG. 2 is an enlarged view of the vicinity of the zero cross point of the targeted specific wave. Since the received wave is larger than the noise, it can be represented as shown in the figure. In the actual received wave with noise, the zero cross point shifts from the true time point (zero cross point) and an error occurs. In this figure, noise is on the plus side, but of course there can be a minus side.
[0013]
When transmission / reception is repeated continuously as described above, since there is neither reverberation noise nor 1.5 round-trip noise at the time of the first reception, the true received wave itself can be received, and the true zero cross point can be detected. . However, after the second reception, reverberation noise and 1.5 round-trip noise after the third reception are received together with the true received wave. Moreover, since these noises are synchronized with the transmission, they are also synchronized with the true received wave, and always appear in the same phase relationship with the true received wave.
[0014]
In FIG. 2, these two noises are combined and represented as noise. Eventually, a true received wave + noise is received by the transmitter / receiver due to this noise, and the zero cross point deviates from the true zero cross point. This error is a large flow error especially at a minute flow rate, and has been a major obstacle to improving the accuracy of the ultrasonic flowmeter. If the noise polarity is opposite to that of FIG. 2 (that is, the phase angle is 180 degrees different), the error of the zero cross point also reverses the error polarity of FIG. 2 as shown in FIG. Value.
[0015]
The description will be continued with reference to FIG. This schematically represents a received wave for one transmission, and noise that is not synchronized with the transmission is omitted. The shapes of the signal part A, the reverberation B and the 1.5 reciprocating wave C appear almost the same every time for a short time when the temperature or the like does not change, and further, only the polarity of the transmission drive without changing the voltage and pulse width. Inversely, it has been confirmed through experiments and the like that not only the signal portion A but also the reverberation B and the 1.5 reciprocating wave C have different phase angles of 180 ° C. (the peak values are the same and only the polarity is reversed).
[0016]
Therefore, an object of the present invention is to provide an ultrasonic flowmeter that can eliminate the above-described obstacles due to reverberation and noise caused by 1.5 reciprocating waves.
[0017]
[Means for Solving the Problems]
If the polarity of only the true received wave in FIGS. 2 and 3 is reversed, the targeted specific wave appears on the minus side, as shown in FIGS. 4 and 5, and the absolute value of the error is the same and only the polarity is reversed. In the present invention, such a phenomenon is utilized to cancel an error due to noise.
[0018]
If the transmitter on the transmitting side is driven so that the aimed wave appears on the positive side, the drive is positive, and if the transmitter on the transmitting side is driven so that the targeted wave appears on the negative side, it is negative. The following can be said when driving.
[0019]
If the influence (error) of the reverberation noise by the positive drive on the reception point by the positive drive is + α (FIG. 2), the influence of the reverberation noise by the negative drive on the reception point by the positive drive is −α (FIG. 3). ), The influence of reverberation noise due to positive driving on the reception point due to negative driving is −α (FIG. 4), and the influence of reverberation noise due to negative driving upon the reception point due to negative driving is + α (FIG. 5). .
[0020]
Further, if the influence (error) of 1.5 reciprocating noise due to positive driving given to the receiving point due to positive driving is + β (FIG. 2), 1.5 reciprocating noise due to negative driving given to the receiving point due to positive driving. The influence of -β (FIG. 3) is 1.5, and the influence of 1.5 round-trip noise due to the positive drive on the reception point by negative drive is -β (FIG. 4), 1 by the negative drive given to the reception point by negative drive. The effect of .5 round trip noise is + β (FIG. 5).
[0021]
First, consider only the effects of reverberant noise. Reverberation noise affects the next reception. If the positive drive is repeated continuously, reception of the positive drive is affected by the reverberation noise of the previous positive drive, resulting in an error of + α every time. If negative driving is performed once while positive driving continues, reception of the negative driving is affected by the reverberation noise of the previous positive driving and becomes an error of -α, and the negative driving is further performed. Reception by the positive drive next to the drive becomes an error of −α due to the influence of reverberation noise of the negative drive. That is, by mixing negative driving once, -α error is generated twice at the time of reception and the next time of reception. Therefore, if the negative driving is performed once out of the four times, two of the four errors are offset by + α and the other two are canceled by −α.
[0022]
The same applies to 1.5 round-trip noise, and this affects the next reception. When the positive drive is continuously repeated, reception of the positive drive is affected by 1.5 round-trip noise of the previous positive drive, resulting in an error of + β every time. If negative driving is performed once while positive driving continues, reception of the negative driving is affected by the reverberation noise of the previous positive driving, resulting in an error of -β. The reception by the positive drive next to the drive causes an error of + β due to the influence of 1.5 round-trip noise of the positive drive immediately before the negative drive, but the reception by the next positive drive is the negative drive. Under the influence of 1.5 noise of driving, an error of -β is obtained. In other words, by mixing (pinch) negative driving once, two times of reception and the next reception become −β error. Therefore, if negative driving is performed once out of four times, an error due to 1.5 round-trip noise is canceled out by two of four times being + α and the other two being −α.
[0023]
In this way, in order to cancel by two times of + β and two times of −β, the two times of driving before the negative driving are positive driving, and the two drivings following the negative driving are also positive. It is necessary to drive.
[0024]
FIG. 6 is a diagram showing the relationship of the above [0021] to [0023].
[0025]
Therefore, 1/4 of the transmission that is repeated a certain number of times is set as transmission with the opposite polarity, and after transmission with the opposite polarity, transmission with non-reverse polarity is performed at least twice, thereby reverberating noise and 1.5 reciprocations. The adverse effects of both noises can be minimized.
[0026]
In the above description, positive driving and negative driving positive / negative do not indicate the actual driving polarity, but two driving patterns shown in FIGS. 7A and 7B in which only the polarity is reversed. One of these is expressed as positive and the other is expressed as negative. The drive pattern in FIG. 7 is a waveform (pattern) of a drive pulse applied to the transmitter / receiver (ultrasonic transducer) on the transmission side. The drive pattern in FIG. 7A is called “positive drive”. In this case, the driving pattern in FIG. 5B is “negative driving”. The error α due to the effect of reverberation noise and the error β due to the effect of 1.5 round-trip noise can be both positive and negative.
[0027]
Therefore, in order to achieve the above object, the invention of claim 1 is provided with at least one pair of ultrasonic transducers that act both as a transmission side and a reception side, and in the forward and downstream directions in the fluid flow from upstream to downstream. in the opposite direction from the downstream of the upstream to transmit and receive ultrasonic waves, an ultrasonic flow meter obtains the flow rate from the arrival time of the respective direction and transmit a first one of the transducer in each direction as a sender, When the received wave detector that receives the signal of the other receiving-side transmitter / receiver detects the received wave, the transmitting-side transmitter / receiver is driven again and transmitted, and this is repeated a plurality of times, and each direction in the ultrasonic flowmeter of the time from the transmission of the first to receive a certain number of eyes it is measured to determine the arrival time from the results for each,
The received wave detection unit has a point at which a wave that first exceeds a certain reference level first crosses zero as a reaching point,
Only the polarity of the drive pattern of transmission can be reversed, and a reverse reference level in which only the polarity of the reference level is reversed is prepared,
When the polarity of the transmission drive pattern is reversed, the reception corresponding to the transmission is the arrival point at which the wave that first crossed the reverse reference level in the reverse direction then crosses zero,
When the driving pattern of the first transmission is positive and the opposite polarity is negative, the transmission is performed by repeating positive, positive, negative, and positive from the first transmission. It is the ultrasonic flowmeter which is characterized.
[0028]
In the present invention, by preparing two reference levels (reference voltages) having the same voltage but different polarities in the received wave detection unit, by using the reference level on the positive or negative side where the targeted specific wave appears, A specific wave can be captured corresponding to the polarity of the drive (ie, the polarity of the drive pattern). FIG. 8 shows the relationship between the reference level and the received wave when the solid line has the reference level on the positive side, and the relationship between the reference level and the received wave when the dotted line has the reference level on the negative side.
[0029]
Usually, the point of arrival cannot be specified only by comparison with a simple zero level. First, it is necessary to capture the targeted wave. Therefore, in the invention of claim 1, the reference level is prepared on both the plus side and the minus side.
[0030]
Further, the invention of claim 2 is provided with at least one pair of ultrasonic transducers that act both as a transmitting side and a receiving side, and in the fluid flow, it is superfluous from upstream to downstream in the forward direction and from downstream to upstream in the reverse direction. send and receive sound waves in the ultrasonic flow meter obtains the flow rate from the arrival time of the respective direction and transmit a first one of the transducer in each direction as a sender, the other of the receiving transducer When the received wave detector that receives the signal detects the received wave, the transmitter side transmitter / receiver is driven and transmitted again, and this is repeated a plurality of times, and from the first transmission for each direction. measuring the time until the reception of a certain number of eyes, in the ultrasonic flow meter for determining the arrival time from the result,
The reception wave detection unit, the first receiving receiving a first round of reception is the arrival point to point wave is determined that the specific-th among the group of the received wave due to one transmission zero-crosses,
For the second and subsequent receptions, the first zero cross point after the time when a certain amount of time has been subtracted from the time from the previous transmission to the arrival point has elapsed since that time transmission is made the arrival point,
Transmission can only reverse the polarity of the drive pattern,
When the driving pattern of the first transmission is positive and the opposite polarity is negative, the transmission is performed by repeating positive, positive, negative, and positive from the first transmission. It is the ultrasonic flowmeter which is characterized.
[0032]
In the second aspect of the invention, if the wave targeted by the first reception can be captured (as a capturing method, it is often performed that the wave first exceeds a voltage of a certain reference level), the second After the second reception, the reception time is predicted from the arrival time in the previous transmission / reception, and the zero cross point closest to the prediction point is set as the reception point, that is, the arrival point. Specifically, the second and subsequent receptions arrive at the first zero cross point after the time obtained by subtracting a certain time from the time from the previous transmission to the arrival point (that is, the arrival time) has elapsed since that transmission. I tried to make it a point.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described with reference to examples of the drawings.
[0034]
[Example 1]
FIG. 9 shows the overall configuration of the first embodiment. The received wave detection unit will be described in detail with reference to the drawings .
The transducers 1 and 2 are ultrasonic transducers that can be used for both transmission and reception. Both transducers transmit and receive ultrasonic waves in the fluid in the forward direction from upstream to downstream or in the reverse direction from downstream to upstream.
[0035]
The reception wave detection unit 4 outputs a reception wave detection signal when a reception-side transducer, for example, 2 is connected and a reception wave is detected. When receiving the first transmission command signal from the control unit 6, the transmitter driving unit 5 first drives the transmitting-side transmitter / receiver, for example, 1, and then drives whenever a received wave detection signal is received from the received wave detection unit 4. To do. However, when the nth received wave detection signal is received from the first counter 7, the drive is stopped thereafter until the first transmission command signal is newly received. In this embodiment, meaningless (n + 1) th driving is performed, but there is no problem because it is ignored on the receiving side.
[0036]
The first counter 7 counts the received wave detection signal from the received wave detection unit 4 and outputs the nth received wave detection signal (nth received wave detection signal). The counter 7 is reset by a first transmission command signal from the control unit 6. The second counter 8 measures a time n (t ₁ + τ) from the first transmission command signal to the nth received wave detection signal. The control unit 6 reads the time (count value). In the embodiment, the count value is cleared to zero by the first transmission command signal, and the count is started.
[0037]
The control unit 6 switches the roles of the two transducers 1 and 2 by inverting the transmission / reception switching signal at regular intervals and switching the switches 9 and 10.
After each switching, the first transmission command signal is output after a time when noise or the like due to the switching is stopped each time. When the n-th received wave detection signal is input, the measurement value (count value) of the counter 8, for example, n (t ₂ + τ) is read, and the measurement value in the opposite direction performed immediately before is used. The flow rate is further calculated.
[0038]
In addition, a reverse polarity drive instruction signal is further output from the received wave detection unit 4 to the transmitter drive unit, and when this signal is “High”, the transmitter drive unit has a reverse drive pattern. The transmission drive is performed at
[0039]
In the embodiment, the drive in which the third wave appears on the plus side is a normal drive pattern, and the zero cross point of the third wave is a reception point (arrival point). Therefore, the transmission reception point (arrival point) when the reverse polarity drive signal is “High” is the zero cross point of the third wave appearing on the minus side.
[0040]
FIG. 10 is a diagram showing a part of the transmitter driver 5 and a transmitter / receiver, for example, 1 on the transmitting side. The two switches S1 and S2 are switched by the reverse polarity drive signal. By setting the reverse polarity drive signal to “High”, the pattern of the drive pulse applied to the transducer, for example, 1 is reversed. The polarity can be In the state where the switches S1 and S2 are shown, when the drive pulse of the positive drive pattern supplied to the line 11 is applied to the transducer 1 and the reverse polarity drive signal becomes “Low”, the switches S1 and S2 are shown. In this state, an inverted driving pulse, that is, a driving pulse having a negative driving pattern is applied to the transducer 1.
[0041]
FIG. 11 is an electric circuit diagram of the received wave detection unit. A signal Vin input from a receiving side transmitter / receiver, for example, 2 via the changeover switch 10 is amplified by an amplifying unit 11 (not shown), and is amplified. The received wave is inputted to the + input of the comparator 12, the − input of the − input and zero cross detection comparator 14 of the comparator 13, and the + input of the comparator 15 of zero cross detection.
[0042]
The counter 16 has outputs of Q0, Q1, Q2, and Q3 and sequentially becomes “High”. The timing around this is shown in FIG. 12 together with the first transmission command signal and the received wave detection signal. The first transmission command signal is “High” when measurement is not being performed, and the fall is regarded as the first transmission timing. When the first transmission command signal becomes “Low” and the reset is released, the counter 16 starts counting the signal obtained by delaying the reception wave detection signal by the delay circuit 17. This delay time is set to be slightly longer than the transmission drive time performed by the transmitter driver at the same time that the reception wave detection signal is output, and is counted up after transmission performed simultaneously with reception is completed. It has become. Here, the Q1 output is output to the transmitter driver as a reverse polarity drive instruction signal. Further, as shown in FIG. 11, when the Q2 output is a switching signal of the switches S3 and S4 and the Q2 output is "Low", the zero cross point of the wave exceeding the reference level 350 mV for the first time, "High" In this case, the zero cross point of the wave exceeding the negative reference level of −350 mV for the first time is selected.
[0043]
Therefore, when the Q1 output is “High”, the transmitter / receiver is driven with a drive pulse of reverse polarity, and when the received wave arrives, the counter 16 counts up, and the Q2 output becomes “High” to drive reverse polarity. Corresponding reception is performed.
[0044]
Thus, if the first transmission is positive, the polarity of transmission will be positive, positive, negative, positive repetition from the first transmission, and the number of quarters of a fixed number of transmissions will be One of the two driving patterns is transmitted, and after the transmission in this pattern, the other pattern is transmitted at least twice, and the object is realized.
[0045]
Reference numeral 18 is an RSFF, and 19 is a rising edge detection circuit. Further, the Q0 output and Q3 output of the counter 16 are not used.
[0046]
[Example 2]
This second embodiment, since only the Example 1 reception wave detection unit 4 in comparison with different, is a diagram illustrating the overall configuration instead in FIG. 9, FIG. 10, described in accordance with the electrical circuit of Figure 13 is here To do.
[0047]
FIG. 13 illustrates a main part of the received wave detection unit according to the second embodiment. A reference level of 350 mV is prepared, and the amplification degree of an amplifier (not shown) is adjusted so that the wave that first reaches this voltage becomes the target wave. Further, when the first transmission command signal is input from the control unit 6 and this signal is not measured, it is “High”, and the first transmission is performed at the falling point to “Low”. Is. This signal is a reset signal for the RSFF 20, the counter 21, and the counter 23. Therefore, when the first transmission command signal becomes “Low”, the output Q of the RSFF 20 is “Low”, the switch S3 selects the reference level of 350 mV, and the switch S4 selects the output of the comparator 24. The counter 16 has the same function as the counter 16 of the first embodiment (FIG. 11). Similarly, when the measurement is started, the output Q2 is “Low”, so that the switch S5 is changed from “High” to “Low”. The output of the comparator 25 for detecting the zero cross to is selected.
[0048]
Further, the delay of the delay circuit 17 is the same as that in FIG. 11, and the timing in FIG. 12 can be similarly applied.
When a wave with a received wave reaches the reference level of 350 mV, the Q output of RSFF 18A once becomes “Low”, and when the zero cross is detected by the comparator 25, it again becomes “High”. Is output as a received wave detection signal.
[0049]
At the same time, this signal is inputted to the input S of the RSFF 20, where the output of the RSFF 20 is Q "High", the switch S3 switches to select the zero level, and the comparator 24 changes from "Low" to "High". The function switches to zero cross detection. Further, the switch S4 is also switched, and the A = B output of the comparator 26 is selected, and this signal becomes “High” when the time has elapsed from the previous transmission (previous arrival time−Δt) time, and at that time, the Q of the RSFF 18A The output is “Low”, and becomes “High” when the comparator 25 selected by the switch S5 detects zero crossing.
[0050]
The reception wave detection signal is a latch signal of the storage device 27 and a reset signal of the counter 23, and is configured to store the value of the counter 23 at the reception point and reset the counter 23 at the next moment. Note that Δt is set to the number of clocks corresponding to ½ period of the ultrasonic wave.
[0051]
The counter 23 counts the arrival time of the ultrasonic wave, and stores the counter value (arrival time) at this moment in the storage device 27 by the latch input (that is, the received wave detection signal) of the storage device 27. When the storage device 27 stores the arrival time, the counter 23 is reset, and the next arrival time is measured.
[0052]
The subtracter 28 receives the count value of the counter 23 stored in the memory 27, that is, the previous arrival time is input as C input, and the other is a numerical value of the number of clocks corresponding to the time of 1/2 cycle of the ultrasonic wave. Δt is input. C−Δt, that is, a value obtained by subtracting a constant value Δt from the previous arrival time is input to the B input of the digital comparator 26.
[0053]
Further, if the output of the counter 23 is input to the digital comparator 26 as the A input, and the A and B inputs are equal, the A = B output becomes “High”. When the count of the counter 23 advances and becomes equal to C−Δt, the output A = B becomes “High”, the output Q of the RSFF 18A becomes “Low”, and the next zero cross is awaited.
[0054]
As described above, the counter 16 counts a signal obtained by delaying the reception wave detection signal, and becomes “High” in order of Q0, Q1, Q2, Q3, Q0, Q1,. Q1 is output to the transmitter drive unit as a reverse polarity drive instruction signal, and the function is the same as in the first embodiment. Q2 is a switching signal for the switch S5, and when Q2 becomes “High” following Q1, a reverse zero cross of the received wave by the reverse polarity drive pattern is captured.
[0055]
As a result, if the first transmission is positive, the transmission polarity becomes positive, positive, negative, and positive in order from the first transmission. It is possible to transmit one of the two types of drive patterns and perform transmission using the other drive pattern at least twice after transmission using this pattern, and thus the object can be realized.
[0056]
Example 3
FIG. 14 illustrates a main part of the received wave detection unit according to the third embodiment. The overall configuration of the flow meter is the same as in the first and second embodiments as shown in the block diagram of FIG. In FIG. 14, elements having the same functions as those in FIG. Combining the comparator 24B with both edge detectors 30 that detect both rising and falling edges and output signals, zero crossings from both “High” to “Low” and “Low” to “High”. Is input to the S input of RSFF 18A. Thus, a correct reception point can be detected regardless of the polarity of the drive pattern, and the circuit configuration is simple. In this embodiment, Δt ′ is distinguished from Δt in the second embodiment, with Δt ′ being the number of clocks corresponding to a quarter period of the ultrasonic wave.
[0057]
Example 4
In FIG. 14, the output of Q1, Q2 and Q3 of the counter 16 is ORed, and this OR is used as a reverse polarity drive instruction signal .
[0058]
In each of the above embodiments, when the number of continuous repeated transmissions and receptions performed in one of the ultrasonic propagation directions is not a multiple of 4, the ratio of the number (number of times) of one drive pattern to the other drive pattern is 1: Although it cannot be 3, the error due to the influence of noise can be minimized by approaching this value (ratio), and such a value is also included in the scope of the present invention.
[0059]
【The invention's effect】
Since the ultrasonic flowmeter of the present invention is configured as described above, the measurement error of the propagation time (or arrival time) of ultrasonic waves due to reverberation and 1.5 reciprocating waves is canceled or almost canceled to minimize. Therefore, the accuracy of the flow meter can be increased.
[0060]
Further, in the invention of claim 2, since the arrival point can be specified only by the zero cross, it is only necessary to catch the specific wave only on one side, and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a received waveform of an ultrasonic flowmeter.
FIG. 2 is a diagram illustrating an error of a zero cross point according to the present invention.
FIG. 3 is a diagram illustrating an error of a zero cross point according to the present invention.
FIG. 4 is a diagram illustrating an error of a zero cross point according to the present invention.
FIG. 5 is a diagram for explaining an error of a zero cross point according to the present invention.
FIG. 6 is a diagram illustrating a received wave according to the present invention.
FIGS. 7A and 7B are diagrams of drive pulses according to the present invention, and FIGS. 7A and 7B show different drive patterns.
FIG. 8 is a diagram illustrating received waves and reception points according to the present invention.
FIG. 9 is a block diagram of the overall configuration of an embodiment of the present invention.
FIG. 10 is an electric circuit diagram for switching drive patterns in the embodiment of the present invention.
FIG. 11 is an electrical circuit diagram of a main part of a received wave detection unit according to the first embodiment of the present invention.
FIG. 12 is a timing chart according to the first embodiment of the present invention.
FIG. 13 is an electric circuit part of a main part of a received wave detection unit according to the second embodiment of the present invention.
FIG. 14 is a main circuit section of a received wave detector according to a third embodiment of the present invention.
FIG. 15 is a schematic diagram illustrating the principle of an ultrasonic flow meter.
FIG. 16 is a diagram for explaining a zero cross point detection method in the prior art.
[Explanation of symbols]
1, 2 Ultrasonic transducer 4 Received wave detection unit 5 Transmitter drive unit A Signal unit B Reverberation C 1.5 reciprocating wave

Claims (2)

Provide at least one pair of ultrasonic transducers that act as both transmitter and receiver, and transmit and receive ultrasonic waves in the fluid flow from upstream to downstream in the forward direction and from downstream to upstream in the reverse direction. in the determining the flow amount from the arrival time ultrasonic flow meter, and transmits a first one of the transducer in each direction as a sender, the received wave detection section that receives the signal of the other receiving-side transducer There transmitted to drive again sender transducer When detecting reception wave, which was configured to repeat a plurality of predetermined number of times, the time from transmission of the first round for each direction to receive a certain number of eyes In an ultrasonic flowmeter that measures and calculates the arrival time from the result,
The received wave detection unit has a point at which a wave that first exceeds a certain reference level first crosses zero as a reaching point,
Only the polarity of the drive pattern of transmission can be reversed, and a reverse reference level in which only the polarity of the reference level is reversed is prepared,
When the polarity of the transmission drive pattern is reversed, the reception corresponding to the transmission is the arrival point at which the wave that first crossed the reverse reference level in the reverse direction then crosses zero,
When the driving pattern of the first transmission is positive and the opposite polarity is negative, the transmission is performed by repeating positive, positive, negative, and positive from the first transmission. The characteristic ultrasonic flowmeter. Provide at least one pair of ultrasonic transducers that act as both transmitter and receiver, and transmit and receive ultrasonic waves in the fluid flow from upstream to downstream in the forward direction and from downstream to upstream in the reverse direction. in the determining the flow amount from the arrival time ultrasonic flow meter, and transmits a first one of the transducer in each direction as a sender, the received wave detection section that receives the signal of the other receiving-side transducer There transmitted to drive again sender transducer When detecting reception wave, which was configured to repeat a plurality of predetermined number of times, the time from transmission of the first round for each direction to receive a certain number of eyes In an ultrasonic flowmeter that measures and calculates the arrival time from the result,
The reception wave detection unit, the first receiving receiving a first round of reception is the arrival point to point wave is determined that the specific-th among the group of the received wave due to one transmission zero-crosses,
For the second and subsequent receptions, the first zero cross point after the time when a certain amount of time has been subtracted from the time from the previous transmission to the arrival point has elapsed since that time transmission is made the arrival point,
Transmission can only reverse the polarity of the drive pattern,
When the driving pattern of the first transmission is positive and the opposite polarity is negative, the transmission is performed by repeating positive, positive, negative, and positive from the first transmission. The characteristic ultrasonic flowmeter.

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