JP2006220583A - Ultrasonic flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an accurate flow meter. <P>SOLUTION: A signal received by ultrasonic transducers 3 and 4 is reshaped into a packet form to find a reception point from the reshaped packet-formed reception wave and propagation time of an ultrasonic wave is measured to operate the amount of a flowing fluid. This allows the propagation time of the ultrasonic wave to be stably measured with the form of the reshaped packet-formed reception wave is hardly affected even if the form of the reception wave is somewhat deformed owing to a change in the state of the fluid, making it possible to obtain a high-accuracy ultrasonic flow meter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid.

  Conventionally, as this type of flow meter, there is an ultrasonic flow meter 101 as shown in FIG. FIG. 12 is a cross-sectional view, and a pair of ultrasonic transducers 103 and 104 are installed facing each other through the fluid on the upstream side and the downstream side of the flow path 102 through which the fluid flows, and between the pair of ultrasonic transducers. The flow rate of the fluid is measured from the propagation time of the ultrasonic wave, and the flow rate is calculated to obtain a flow meter (see, for example, Patent Document 1).

In the figure, a single arrow 105 (solid line) indicates the direction in which the fluid flows, and a double arrow 106 (broken line) indicates the direction in which the ultrasonic wave propagates. Note that the direction in which the fluid flows and the direction in which the ultrasonic waves propagate intersect at an angle θ.
JP 2002-13958 A

  However, in the conventional flow meter 101, an ultrasonic wave is propagated from the upstream ultrasonic transducer 103 to the downstream ultrasonic transducer 104, and the ultrasonic propagation time Tud and the downstream ultrasonic transducer are also transmitted. The ultrasonic wave is propagated from 104 to the ultrasonic transducer 103 on the upstream side, the ultrasonic wave propagation time Tdu is measured alternately, the time difference is calculated using the measured ultrasonic wave propagation times Tud, Tdu, and the flow rate is calculated. It was. At this time, a predetermined reference level was set as a trigger level, and the propagation time was measured. For this reason, since the trigger level may fluctuate due to changes in the fluid state or the fluid temperature, etc., the received waveform of the ultrasonic wave may undergo very complex processing. The received waveform was identical. In addition, since complicated calculation processing is performed, there is a problem of causing an error.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object thereof is to provide a high-accuracy ultrasonic flowmeter with a simple configuration by shaping a received ultrasonic waveform into a packet shape.

  In order to solve the conventional problem, an ultrasonic flowmeter of the present invention includes a pair of ultrasonic transducers that transmit and receive ultrasonic waves, transmits ultrasonic waves from the one ultrasonic transducer, and transmits the other ultrasonic flowmeter. A shaping unit that receives the ultrasonic wave and cuts a high-frequency component of the received ultrasonic signal and shapes the received waveform in a packet shape; and a reception point detection unit that detects a reception point from the received waveform shaped in the packet shape; And a propagation time measuring unit that measures the propagation time of the ultrasonic wave from the transmission of the ultrasonic wave to the reception point, and the flow rate is calculated from the propagation time of the ultrasonic wave.

  With this configuration, the propagation time of the ultrasonic wave propagating between the upstream ultrasonic transducer and the downstream ultrasonic transducer, that is, the propagation time from the upstream side to the downstream side and from the downstream side to the upstream side is simultaneously measured. Therefore, a highly accurate ultrasonic flowmeter can be realized.

  In addition, the ultrasonic flowmeter of the present invention receives the received waveform as one large received waveform in the form of a packet, so that even if the received waveform is slightly deformed, it can be received stably and with a simple configuration and high accuracy An ultrasonic flowmeter can be realized.

  The ultrasonic flowmeter of the present invention includes an ultrasonic propagation time from an upstream ultrasonic transducer to a downstream ultrasonic transducer and an ultrasonic wave from the downstream ultrasonic transducer to the upstream ultrasonic transducer. The propagation time can be accurately measured even if the received waveform is slightly deformed. Therefore, even if the received waveform is deformed due to fluctuations in the fluid state or changes in the temperature of the fluid during measurement, the ultrasonic propagation time can be measured accurately, and a highly accurate ultrasonic flow meter can be realized. it can.

  The first invention comprises an ultrasonic flowmeter comprising a pair of ultrasonic transducers that transmit and receive ultrasonic waves, transmitting ultrasonic waves from the one ultrasonic transducer, and receiving by the other ultrasonic transducer, A shaping unit that cuts a high-frequency component of a received ultrasonic signal and shapes a reception waveform in a packet shape, a reception point detection unit that detects a reception point from the reception waveform shaped in the packet shape, and the transmission of ultrasonic waves A propagation time measuring unit for measuring the propagation time of the ultrasonic wave to the reception point, and calculating the flow rate from the propagation time of the ultrasonic wave. With this configuration, even if the received waveform is slightly deformed depending on the fluid state, there is almost no effect on the packet-shaped waveform, and the ultrasonic propagation time can be accurately measured, and the ultrasonic flow rate is highly accurate. The total can be realized.

  In the second invention, in particular, the received waveform shaping section of the first invention is constituted by a low-pass filter. As a result, a simple circuit can be used, and the received waveform can be stably shaped into a packet. For this reason, a highly accurate ultrasonic flowmeter can be realized.

  In the third aspect of the invention, in particular, the received waveform shaping portion of the second aspect of the invention is configured so as to be shaped into a packet after the received waveform is fully wave shaped. Therefore, a more stable packet-like received waveform can be obtained, and a highly accurate ultrasonic flow meter can be realized.

  According to the fourth aspect of the invention, in particular, the reception waveform shaping unit of the first aspect of the invention is configured to shape the reception waveform in a packet form from each peak value of the reception waveform after the reception waveform is subjected to full wave shaping. With this configuration, even if the received waveform is slightly deformed, the packet-shaped received waveform is hardly deformed, and a highly accurate ultrasonic flowmeter can be realized.

  In the fifth aspect of the invention, the reception point of the first aspect of the invention is particularly detected from the peak of the reception waveform shaped into a packet. With this configuration, even if the received waveform is somewhat deformed, the received waveform shaped into a packet hardly changes, so a highly accurate ultrasonic flowmeter can be realized.

  In the sixth aspect of the invention, the reception point of the first aspect of the invention is particularly configured to detect the reception point from the average value of two points where the reception waveform shaped in a packet crosses a predetermined reference level. With this configuration, even if the received waveform is somewhat deformed, the received waveform shaped into a packet hardly changes, so a highly accurate ultrasonic flowmeter can be realized.

  In the seventh aspect of the invention, in particular, the reception point of the first aspect of the invention is configured such that the reception waveform shaped into a packet is differentiated and the reception point is detected from the zero-cross point of the differential waveform. With this configuration, even if the received waveform is slightly deformed, the S / N of the received waveform shaped into a packet is greatly improved. Therefore, even if the received waveform is slightly deformed, the reception point is stable, so high accuracy An ultrasonic flowmeter can be realized.

  In an eighth aspect of the invention, in particular, in any one of the first to seventh aspects of the invention, the drive circuit of the ultrasonic transducer and the receiving circuit are configured as symmetrical circuits having the same impedance. With this configuration, the symmetry of the received waveform received on the upstream side and the downstream side is improved, and a highly accurate ultrasonic flowmeter can be realized.

  In the ninth aspect of the invention, in particular, the impedance of the eighth aspect of the invention is configured to be a symmetrical circuit that matches the impedance of the ultrasonic transducer. With this configuration, the received waveform is large and the S / N is large, and a highly accurate ultrasonic flowmeter can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 shows a block diagram of an ultrasonic flow meter 1 according to the first embodiment of the present invention.

  In FIG. 1, an upstream ultrasonic transducer 3 and a downstream ultrasonic transducer 4 are installed in the flow path 2 so as to face each other through a fluid. In addition, the single arrow 5 (solid line) in a figure shows the direction through which a fluid flows, and the double arrow 6 (broken line) has shown the direction through which an ultrasonic wave propagates. Note that the direction in which the fluid flows and the direction in which the ultrasonic waves propagate intersect at an angle θ. 7 is a transmitter for generating a burst signal for driving the transmitter ultrasonic transducer, and 8 is a switching unit for switching the signal from the transmitter 7 to the upstream ultrasonic transducer 3 or the downstream ultrasonic transducer 4. Show.

  The switching unit switches the transmission signal, and also performs an operation of switching the reception signal from the upstream ultrasonic transducer 3 or the downstream ultrasonic transducer 4 to the receiving unit 9 constituted by an amplifier or the like. 10 is a received waveform shaping unit that shapes the received waveform into a packet, 11 is a time measuring unit that measures the propagation time of ultrasonic waves using a signal from the transmitting unit and a signal from the received waveform shaping unit, and 12 is an ultrasonic wave. The flow rate calculation part which calculates the flow volume of the fluid from the propagation time of is shown.

  In this configuration, in the conventional ultrasonic flowmeter, for example, ultrasonic waves are transmitted from the upstream ultrasonic transducer 3 and received by the downstream ultrasonic transducer 4. FIG. 2 shows voltage waveforms of the transmission wave and the reception wave at this time. Reference numeral 13 denotes a transmission wave from the transmission unit 7, which is composed of three rectangular waves. Reference numeral 14 denotes a received wave, which is sinusoidal. 15 indicates a zero point of the received wave, and 16 indicates a reference voltage of a predetermined level.

  The zero cross point 18 that comes next to the point 17 where the received wave crosses the reference level is the reception time point, and the time from the start point 19 of the transmission wave to the zero cross point is the ultrasonic wave propagation time Tud. Similarly, the switching unit 8 is operated to measure the ultrasonic propagation time Tdu from the downstream ultrasonic transducer 4 to the upstream ultrasonic transducer 3. Using the ultrasonic propagation times Tud and Tdu thus obtained, the flow rate of the fluid was calculated by the flow rate calculation unit 12 as follows.

The propagation time of the ultrasonic wave from the upstream ultrasonic transducer 3 to the downstream ultrasonic transducer 4 is Tud, and the ultrasonic wave propagation from the downstream ultrasonic transducer 4 to the upstream ultrasonic transducer 3 is Tud. If the time is Tdu, the propagation velocity of ultrasonic waves in the fluid is Vs, and the fluid flow velocity is Vf,
Tud = Ld / [Vs + Vf · cos (θ)],
Tdu = Ld / [Vs−Vf · cos (θ)]
It becomes. Ld indicates the distance between the ultrasonic transducers.

From these,
Vs + Vf · cos (θ) = Ld / Tud,
Vs−Vf · cos (θ) = Ld / Tdu
And subtracting both sides,
2 * Vf · cos (θ) = (Ld / Tud) − (Ld / Tdu)
= Ld * [(1 / Tud)-(1 / Tdu)]
It becomes.

Therefore,
Vf = {Ld / [2 · cos (θ)]} * [(1 / Tud) − (1 / Tdu)]
Thus, the fluid flow velocity Vf can be obtained. Further, the flow rate Qm is obtained by multiplying the cross-sectional area Sr of the flow path 2. That is, Qm = Sr * Vf is the measured flow rate value.

  In this case, if the magnitude of the received wave 14 changes or the shape changes due to the state of the fluid flow, interference with the reflected wave from the wall of the flow path, or the temperature change of the fluid, for example, In the case of FIG. 2, the reference level is set between the second and third peaks, but between the first and second, or between the third and fourth. It may be set to. In this case, the ultrasonic wave propagation time Tud may become inaccurate.

  FIG. 3 is a waveform diagram showing a packet-like received wave 19 of the ultrasonic flowmeter according to the first embodiment of the present invention. In FIG. 3, a conventional received wave is indicated by a broken line 14.

  In this case, since the received wave is shaped by the shaping unit 10 as a lump or packet of waves having a large voltage, even if the size or shape of the received wave 14 is slightly deformed, a packet-like received wave having a large voltage is formed. 19, for example, the reference level 16 can be set at a slightly higher position from the zero point, that is, with a margin, and the intersection with the reference level can be set as the ultrasonic propagation time Tud. it can. Therefore, even if the received wave 14 fluctuates somewhat, the shaping unit 10 shapes the packet as a received packet 19 that is stable, so that the propagation time is stable, and the propagation time measuring unit 11 can perform highly accurate propagation time measurement. It becomes possible.

  As described above, according to the present invention, the received waveform of the ultrasonic wave from upstream to downstream or from downstream to upstream is shaped by the received waveform shaping unit 10 into a packet having a large amplitude, and the shaped received wave is used. Since the propagation time of the ultrasonic wave is measured by the propagation time measuring unit 11, the measurement time does not change depending on the state of the fluid as in the conventional case, and a highly accurate ultrasonic flow meter can be realized.

(Embodiment 2)
FIG. 4 is a block diagram illustrating the function of the shaping unit 10 that shapes the received waveform into a packet shape according to the second embodiment of the present invention. Reference numeral 20 denotes a received waveform, 21 denotes a low-pass filter composed of L (coil) and C (capacitance), and 22 denotes a packet-like waveform shaped by cutting high-frequency components.

  The received waveform can be shaped into a stable packet by simply passing through a low-pass filter having a simple circuit configuration. Therefore, a stable and highly accurate ultrasonic flowmeter can be realized.

(Embodiment 3)
FIG. 5 is a block diagram illustrating the function of the shaping unit 10 that shapes the received waveform into a packet shape according to Embodiment 3 of the present invention. Reference numeral 20 denotes a received waveform, reference numeral 23 denotes a full wave rectification unit, and reference numeral 24 denotes a full wave rectified received wave. That is, the received wave 20 was first subjected to full-wave rectification and then passed through the low-pass filter shown in Embodiment 2 and shaped into a packet shape. Note that a solid line 25 of the received wave 24 subjected to full-wave rectification indicates a received wave that has passed as it is, and 25 indicates a received wave that has been positively and negatively inverted. By performing full wave rectification on the received wave in this way, a more stable and smooth packet-like received wave can be obtained by the low-pass filter. Therefore, a stable and highly accurate ultrasonic flowmeter can be realized.

(Embodiment 4)
FIG. 6A shows a shaping unit 10 that shapes a received waveform in a packet form according to the fourth embodiment of the present invention. A solid line 27 and a broken line 28 indicate a reception wave subjected to full-wave rectification. In FIG. 6B, the full-wave rectified waveform is phase-inverted and added to synthesize a packet-like received waveform 29 having peaks in the positive and negative directions.

  A sine wave-like reception waveform was shaped using each peak of the synthesized packet-like reception waveform 29 to obtain a packet-like reception wave 30. Thus, a smoother packet-like received waveform can be synthesized by full-wave rectifying the received waveform and superimposing it after inversion. Thereby, an inexpensive and highly accurate ultrasonic flowmeter can be realized.

  In this case, assuming that the packet-like received wave is sinusoidal and fitting the approximate curve, a smoother and more stable packet-like received wave is obtained.

(Embodiment 5)
Hereinafter, the ultrasonic propagation time measuring unit 11 will be described.

  FIG. 7 shows a reception point detection unit that detects reception points in the time measurement unit 11. Reference numeral 31 denotes a received wave shaped into a packet, and 32 denotes a peak point of the received wave 31 shaped into a packet. The time to the peak point 32 is detected as the ultrasonic wave propagation time Tud.

  As a result, even if the received waveform is slightly deformed due to the fluid state or the like, the reception point, that is, the propagation time of the ultrasonic wave is measured from the stable packet-like received waveform 31. A flow meter can be realized.

(Embodiment 6)
FIG. 8 shows a reception point detector for detecting a reception point in the sixth embodiment.

  31 is a received wave shaped into a packet, and 33 is a reference level set to a predetermined level. Reference numerals 34 and 35 denote two intersections between the received wave 31 shaped into a packet and the reference level 33. An average value 36 is obtained from these two intersections and used as a reception point, and is detected as an ultrasonic wave propagation time Tud.

  As a result, even if the received waveform is slightly deformed due to the fluid state or the like, the reception point 36 obtained from the average value of the two points of the stable packet-like received waveform, that is, the propagation time of the ultrasonic wave is further stabilized. Therefore, a stable and highly accurate ultrasonic flowmeter can be realized.

(Embodiment 7)
In FIG. 9, the receiving point detection part which detects the receiving point in Embodiment 7 is shown. Reference numeral 31 denotes a received wave shaped into a packet, and 37 denotes a differentiated waveform obtained by differentiating the received wave 31. The ultrasonic wave propagation time Tud is measured using the zero-cross point 38 of the differential waveform 37 as a reception point.

  Thereby, the stability of the propagation time Tud is further improved, and a stable and highly accurate ultrasonic flowmeter can be realized.

(Embodiment 8)
10, the ultrasonic transducer drive circuit unit 39 in the transmission unit 7 and the reception circuit unit 40 in the reception unit 9 according to Embodiment 8 of the present invention are shown.

  The transmission side ultrasonic transducer 41 is connected to a signal source 42 via an output resistor 43. The ultrasonic transducer 44 on the receiving side is connected to the receiving circuit 46 via the input resistor 45. An arrow 47 indicates that the ultrasonic wave is propagating from the transmission side ultrasonic transducer 41 to the reception side ultrasonic transducer 44. In such a transmission / reception system, when the output resistance 43 and the input resistance 44 are variously changed and an experiment is performed over, for example, several ohms to several hundred kilohms, When the ultrasonic transducer on the side is 41 and the ultrasonic transducer on the reception side is 44, and when the ultrasonic transducer on the transmission side is 44 and the ultrasonic transducer on the reception side is 41, respectively. It was found that the received waveform was very similar.

  It was also found that the degree of coincidence of waveforms greatly decreased as the ratio of the values of the output resistance 45 and the input resistance 43 differed. Therefore, in an ultrasonic flowmeter such as the present invention that requires waveform similarity, it is necessary to match the values of the output resistance 43 and the input resistance 45 in order to accurately measure the ultrasonic propagation time. It is. In this way, the output resistance 43 on the ultrasonic transmission side and the input resistance 45 on the reception side are matched to improve the similarity of the received wave and the ultrasonic propagation time is measured. Therefore, the ultrasonic propagation time is more accurate. And a highly accurate ultrasonic flow meter can be realized.

(Embodiment 9)
FIG. 11 shows the relationship between the output resistance value of the ultrasonic transducer drive circuit and the receiving circuit and the input resistance value and the reception voltage when the ultrasonic wave is received in the ninth embodiment of the present invention. The output resistance value 43 and the input resistance value 45 are the same resistance value. In FIG. 11, the horizontal axis represents the logarithm of the resistance value, and the vertical axis represents the reception voltage 48. Here, when the resistance value is sequentially increased from a small value, the reception voltage 48 increases with the resistance value, and when the maximum value is passed, the reception voltage 48 decreases with the resistance value.

  The resistance value of this maximum value (indicated by the broken line 49) coincided with the internal impedance of the ultrasonic transducer used. That is, when the output resistance value and the input resistance value in the ultrasonic transmission circuit unit 39 and the reception circuit unit 40 of the present invention are matched with the internal impedance of the ultrasonic transducer to be used, a relatively large reception voltage is obtained. It is done. For this reason, ultrasonic propagation time can be measured with good S / N.

  As described above, according to the present invention, the received voltage is compared by matching the output resistance 43 on the ultrasonic transmission side and the input resistance 45 on the reception side with the internal resistance of the ultrasonic transducer. Since the ultrasonic propagation time can be measured with a good S / N ratio, a more accurate ultrasonic propagation time can be obtained and a highly accurate ultrasonic flowmeter can be realized.

  As described above, the ultrasonic flowmeter according to the present invention shapes the packet into a stable packet and measures the propagation time of the ultrasonic wave from the shaped received waveform even if the received waveform varies somewhat depending on the fluid state. It can be applied to a fluid flow meter for home use or industrial use.

Block diagram of ultrasonic flowmeter in embodiment 1 of the present invention Ultrasonic waveform diagram according to Embodiment 1 of the present invention Ultrasonic packet waveform diagram in Embodiment 1 of the present invention The block diagram which showed the function of the shaping part in Embodiment 2 of this invention The block diagram which showed the function of the shaping part in Embodiment 3 of this invention (A) Full-wave rectified waveform diagram according to the fourth embodiment of the present invention (b) Packet waveform diagram according to the fourth embodiment of the present invention Waveform diagram of reception point detector in embodiment 5 of the present invention Waveform diagram of reception point detection unit in Embodiment 6 of the present invention Differential waveform diagram of packet-like received waveform in the seventh embodiment of the present invention Circuit diagram of ultrasonic flowmeter according to embodiment 8 of the present invention Relationship diagram between resistance and voltage in the ninth embodiment of the present invention Cross section of conventional ultrasonic flowmeter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic flow meter 2 Flow path 3 Upstream ultrasonic transmitter / converter 4 Downstream ultrasonic transmitter / receiver 7 Transmitted wave 8 Received wave 10 Shaping unit 11 Time measuring unit 12 Flow rate calculating unit 13 Transmitted wave 14 Received wave 16 Reference level 19 Packet-shaped reception wave 21 Low-pass filter 23 Full-wave rectification 39 Drive circuit section 40 Reception circuit section

Claims (9)

It has a pair of ultrasonic transducers that transmit and receive ultrasonic waves, transmits ultrasonic waves from the one ultrasonic transducer, receives them by the other ultrasonic transducer, and cuts the high-frequency component of the received ultrasonic signal A shaping unit that shapes a received waveform in a packet shape, a reception point detection unit that detects a reception point from the received waveform shaped in a packet shape, and measures the propagation time of ultrasonic waves from transmission of ultrasonic waves to the reception point An ultrasonic flowmeter that calculates a flow rate from the propagation time of the ultrasonic wave. The ultrasonic flowmeter according to claim 1, wherein the received waveform is shaped using a low-pass filter. The ultrasonic flowmeter according to claim 2, wherein the received waveform is shaped after full wave shaping. The ultrasonic flowmeter according to claim 1, wherein the received waveform is shaped into a packet shape from each peak value of the received waveform after the received waveform is fully wave-shaped. The ultrasonic flowmeter according to claim 1, wherein a reception point is detected from a peak of a reception waveform shaped into a packet. The ultrasonic flowmeter according to claim 1, wherein a reception point is detected from two points where a reception waveform shaped in a packet shape intersects a predetermined reference level. The ultrasonic flowmeter according to claim 1, wherein a received waveform shaped into a packet is differentiated, and a received point is detected from a zero cross point of the differentiated waveform. 8. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic transducer drive circuit and the receiving circuit are symmetrical circuits with equal impedance. 9. The ultrasonic flowmeter according to claim 8, wherein the impedance is a symmetric circuit in which the impedance is matched with the impedance of the ultrasonic transducer.

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