JP5867708B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flowmeter that includes a pair of ultrasonic transducers that are attached to the outer surface of a tubular body through which a fluid flows and that are disposed obliquely opposite to an upstream side and a downstream side.

  In order to measure the flow rate of a tubular body through which a fluid flows, an ultrasonic flow meter is widely used. The ultrasonic flowmeter has a propagation time difference formula in which ultrasonic waves are alternately injected from a pair of ultrasonic transducers arranged obliquely facing the upstream side and the downstream side, and the flow velocity is determined from the propagation time difference, and bubbles in the fluid. In addition, there is a Doppler method in which an ultrasonic wave is reflected on a solid material and a flow velocity is obtained from a frequency difference caused by the Doppler effect. In the propagation time difference equation and the Doppler method, the propagation time difference equation can usually ensure higher accuracy.

  In the propagation time difference formula, an ultrasonic propagation time difference is calculated from the reception waveform of the upstream ultrasonic transducer and the reception waveform of the downstream ultrasonic transducer by the trigger method or the correlation method. In the trigger method, a constant trigger level is set for a received waveform, and a propagation time difference is obtained based on the time when the trigger level is exceeded a certain number of times. On the other hand, in the correlation method, the propagation time difference is obtained by correlating the entire waveform existing in a certain time width. In the trigger method, if the reception waveform is disturbed by disturbance such as bubbles, the trigger position is shifted, which may cause a large error. On the other hand, in the correlation method, since the entire waveform is correlated, a large error does not occur even if the reception waveform is temporarily disturbed.

  However, when there is a joint, elbow, or branch near the position where the pair of ultrasonic transducers is attached, or when there is a large amount of deposits or deposits on the scale, the received waveform reflects the ultrasonic waves inside the tube. As a result, a large amount of multiple wave components are included, the degree of correlation is lowered, and an error may occur in the propagation time (reliability is reduced). In Patent Document 1, a plurality of one-shot circuits and OR circuits are combined, and an ultrasonic transducer is driven with a waveform (voltage) having a constant period followed by a waveform having a phase opposite to that of this waveform. Technology is disclosed. According to Patent Document 1, by applying an anti-phase waveform to an ultrasonic transducer, it is possible to forcibly stop vibration and reduce reverberation (multiple wave component).

JP-A-10-253413

  However, in the technique of Patent Document 1, an anti-phase waveform is always applied after the ultrasonic transducer is driven with a waveform having a constant period, regardless of whether or not the received waveform contains many multiwave components. To do. This is a factor that makes it difficult to obtain a high degree of correlation because the received waveform is shortened even when multiple waves are not generated (is not affected). That is, there is a problem that the measurement accuracy is always lowered instead of the wide application range.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic flowmeter that improves measurement accuracy by taking appropriate measures against multiple wave components included in a received waveform.

  In order to solve the above-mentioned problems, a typical configuration of an ultrasonic flowmeter according to the present invention is a pair attached to the outer surface of a tubular body through which a fluid flows, and each of which is disposed diagonally opposite to an upstream side and a downstream side. An ultrasonic transducer, a transmission circuit for generating a first transmission wave that drives one of the ultrasonic transducers, and the other of the ultrasonic transducers when one of the ultrasonic transducers is driven by the first transmission wave A received waveform determination unit that determines whether or not a received waveform to be received includes a predetermined number or more of multiple wave components, and a received waveform determination unit that determines that the received waveform includes a predetermined number or more of multiple wave components And a control unit that causes the transmission circuit to generate a second transmission wave delayed by a half cycle from a predetermined timing after the second period, and to drive one of the ultrasonic transducers again with the second transmission wave. It is characterized by that.

  According to the above configuration, appropriate measures can be taken depending on whether or not the received waveform includes a predetermined number or more of multiple wave components. That is, when the received waveform does not contain a predetermined number or more of multiple wave components, nothing is done, and only when the received waveform contains a predetermined number or more of multiple wave components, the phase is delayed by a half cycle. 2 Outputs the transmission wave and regains the reception waveform used for the calculation of the correlation method. Thereby, improvement of measurement accuracy can be aimed at.

  The received waveform determination unit includes a multiple-wave component greater than or equal to a predetermined value in the received waveform when an amplitude greater than or equal to a predetermined ratio with respect to the amplitude at the peak is detected after a predetermined time from the peak of the amplitude of the received waveform. It is good to determine that According to this configuration, the above case classification can be appropriately executed.

  The control unit may set the predetermined timing after the center of the second transmission wave. According to such a configuration, since the range in which vibration is forcibly suppressed becomes relatively short, the received waveform can be prevented from being shortened (suppressed) more than necessary, and higher measurement accuracy can be realized. it can.

  The control unit shifts the predetermined timing in order and applies the second transmission wave a plurality of times, and the reception waveform determination unit determines the multiplexed wave component of the reception waveform corresponding to each second transmission wave, so that the control unit It is preferable to detect the wave component that is within the allowable range and has the latest predetermined timing. According to such a configuration, it is possible to detect the optimum received waveform used for the calculation of the correlation method, and this can be used for the calculation of the correlation method. Therefore, higher measurement accuracy can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic flowmeter which improves a measurement precision can be provided by taking an appropriate measure with respect to the multiwave component contained in a received waveform.

It is a block diagram which shows schematic structure of the ultrasonic flowmeter concerning this embodiment. It is a figure which illustrates the 1st transmission wave and the 2nd transmission wave. It is a figure which illustrates the received waveform which does not contain many multiwave components. It is a figure which illustrates the received waveform in which many multiwave components are contained. It is a flowchart explaining the operation | movement of the ultrasonic flowmeter shown in FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic flowmeter 100 according to the present embodiment. As shown in FIG. 1, the ultrasonic flow meter 100 includes a detector 102 and a converter 104. The detector 102 includes a pair of ultrasonic transducers 112 and 114 that are attached to the outer surface of the tube 110 through which a fluid flows, and are disposed diagonally opposite to the upstream side and the downstream side, respectively. Here, it is assumed that the ultrasonic transducer 112 is disposed on the upstream side and the ultrasonic transducer 114 is disposed on the downstream side.

  The converter 104 includes a control unit 120, a storage unit 122, a transmission circuit 124, a changeover switch 126, an amplifier 128, an A / D converter 130, a calculation unit 132, a received waveform determination unit 134, a display unit 136, and an output unit 138. Consists of. Hereinafter, the operation of each part of the ultrasonic flow meter 100 will be described first, and then the operation of the ultrasonic flow meter 100 will be described.

  The control unit 120 includes a central processing unit, a so-called CPU, and controls the ultrasonic flowmeter 100 as a whole. The storage unit 122 includes a ROM, a RAM, a flash memory, and the like, and stores programs executed by the control unit 120 and various types of information.

  FIG. 2 is a diagram illustrating the first transmission wave 140 and the second transmission wave 142. FIG. 2A illustrates the first transmission wave 140, and FIG. 2B illustrates the second transmission wave 142. . In FIG. 2B, the first transmission wave 140 is indicated by a dotted line for easy understanding. The transmission circuit 124 generates a first transmission wave 140 illustrated in FIG. The first transmission wave 140 is a waveform (voltage) with a constant period that drives one of the ultrasonic transducers 112 and 114. The changeover switch 126 switches between the transmission side and the reception side of the ultrasonic transducers 112 and 114. That is, the side connected to the transmission circuit 124 and the side connected to the amplifier 128 are switched.

  When the flow rate of the tube 110 is measured, the ultrasonic flow meter 100 switches the changeover switch 126 and alternately applies the first transmission wave 140 generated by the transmission circuit 124 to the ultrasonic transducers 112 and 114. By applying the first transmission wave 140 to one of the ultrasonic transducers 112 and 114, the ultrasonic wave generated from one is crossed in the fluid and received by the other of the ultrasonic transducers 112 and 114. Therefore, when the upstream ultrasonic transducer 112 is driven by the first transmission wave 140, the received waveform received by the downstream ultrasonic transducer 114 and the downstream ultrasonic transducer 114 are transmitted by the first transmission wave. The received waveforms received by the ultrasonic transducer 112 on the upstream side when driven at 140 can be obtained.

  FIG. 3 is a diagram illustrating a received waveform that does not contain many multiwave components. FIG. 4 is a diagram illustrating a received waveform containing a large number of multiple wave components. As illustrated in FIG. 3 and FIG. 4, the received waveform received by the other of the ultrasonic transducers 112 and 114 is large due to the influence of the multiwave component generated by the reflection of the ultrasonic wave in the tube body 110. Change. If the received waveform contains many multiwave components, a large amplitude is likely to appear not only at the front part but also at the rear side of the front part.

  The received waveform received by the other of the ultrasonic transducers 112 and 114 is amplified by the amplifier 128 and A / D converted by the A / D converter 130. And the calculating part 132 detects a waveform with a correlation method from a received waveform, calculates | requires the reception time of an ultrasonic wave, and calculates | requires each propagation time from the difference of transmission time and reception time. The speed of sound of the ultrasonic wave increases with the flow velocity when moving from upstream to downstream, and decreases with the flow velocity when moving from downstream to upstream. Therefore, since a difference occurs in the propagation time, the flow velocity and the flow rate can be obtained from the propagation time difference in consideration of the components of the ultrasonic direction and the flow direction.

  When a received waveform that does not contain many multiwave components as illustrated in FIG. 3 is obtained, the propagation time difference can be accurately calculated by the correlation method when the received waveform is long (the number of waves is large). it can. Here, as in the technique of Patent Document 1, if a waveform having an antiphase is applied in the middle to forcibly suppress vibration, the received waveform is shortened, and it is rather difficult to obtain a high degree of correlation. On the other hand, when a received waveform containing a large amount of multiple wave components as illustrated in FIG. 4 is obtained, the longer the received waveform, the greater the influence of the multiple wave components, and the propagation time difference is accurately calculated by the correlation method. Can not do it. Therefore, in this case, it is necessary to suppress the multiwave component.

  Therefore, the transducer 104 of the ultrasonic flowmeter 100 includes a reception waveform determination unit 134, and whether or not the reception waveform received by the other of the ultrasonic transducers 112 and 114 includes a multiple wave component greater than or equal to a predetermined value. Take appropriate measures for each case. The reception waveform determination unit 134, when a predetermined time t from the time when the amplitude of the reception waveform reaches a peak, detects an amplitude H2 of a predetermined ratio or more with respect to the amplitude H1 at the peak time, It is determined that the component is contained. That is, the predetermined time t and the predetermined ratio determine the “permissible range of influence due to multiple wave components”. Here, the predetermined time t is 10 μs and the predetermined ratio is 1/2. Note that the predetermined time and the value of the predetermined ratio can be determined as appropriate and stored in the storage unit 122 in advance.

  The display unit 136 displays the received waveform received by the other of the ultrasonic transducers 112 and 114, the signal intensity thereof, the flow velocity and the flow rate calculated by the calculation unit 132 on the screen, and transmits them to the user. The output unit 138 outputs the received waveform received by the other of the ultrasonic transducers 112 and 114, the signal intensity thereof, the flow velocity and the flow rate calculated by the calculation unit 132, and the like.

  FIG. 5 is a flowchart for explaining the operation of the ultrasonic flowmeter 100. As shown in FIG. 5, in the ultrasonic flowmeter 100, the control unit 120 controls the transmission circuit 124 to alternately apply the first transmission wave 140 to the ultrasonic transducers 112 and 114 (step S200). Thereby, the reception waveform received by each ultrasonic transducer 112, 114 is obtained (step S202).

  The reception waveform determination unit 134 determines whether or not the obtained reception waveform contains a predetermined number or more of multiple wave components (step S204). When the received waveform determining unit 134 determines that a predetermined number or more of multiple wave components are not included (step S204 NO), the calculating unit 132 calculates a propagation time difference from the received waveform by the correlation method (step S206). A flow velocity and a flow rate are calculated (step S208).

  When the reception waveform determination unit 134 determines that a multiple wave component greater than or equal to the predetermined value is included (YES in step S204), the control unit 120 follows the predetermined timing after the second cycle illustrated in FIG. The transmission circuit 124 generates a second transmission wave 142 that is delayed by a half period. The second transmission wave 142 forcibly suppresses vibration with a waveform having an opposite phase from a predetermined timing after the second period. The predetermined timing is set in units of half cycles. In FIG. 2B, the third cycle is delayed by a half cycle, but the present invention is not limited to this, and the second cycle or the like may be delayed.

  The control unit 120 may set the predetermined timing after the center of the second transmission wave 142. As a result, the range in which vibration is forcibly suppressed becomes relatively short, so that the received waveform can be prevented from being shortened (suppressed) more than necessary, and higher measurement accuracy can be realized. In addition, it is possible to prevent the ultrasonic wave due to the waveform having the opposite phase from becoming strong.

  The transmission circuit 124 alternately applies the generated second transmission wave 142 to the ultrasonic transducers 112 and 114 (step S210), and drives the upstream ultrasonic transducer 112 again with the second transmission wave 142. When the downstream ultrasonic transducer 114 is driven again by the second transmission wave 142, the received waveform is received by the upstream ultrasonic transducer 112. Received waveforms are obtained (step S202). As a result, as a received waveform used for the calculation of the correlation method, a received waveform in which the influence of the multiple wave component is within an allowable range can be read again, and the measurement accuracy can be improved.

  The control unit 120 shifts the predetermined timing in order to apply the second transmission wave 142 a plurality of times, and the reception waveform determination unit 134 determines the multiple wave component of the reception waveform corresponding to each second transmission wave 142. The control unit 120 may detect the influence of the multiple wave component within the allowable range and the latest predetermined timing. As a result, it is possible to detect the optimum received waveform used for the calculation of the correlation method, and this can be used for the calculation of the correlation method. Therefore, higher measurement accuracy can be realized. Note that shifting the predetermined timing in sequence means shifting the predetermined timing, for example, in the second cycle, the third cycle, and so on.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention is applicable to an ultrasonic flowmeter that includes a pair of ultrasonic transducers that are attached to the outer surface of a tubular body through which a fluid flows and that are disposed obliquely facing the upstream side and the downstream side.

DESCRIPTION OF SYMBOLS 100 ... Ultrasonic flowmeter, 102 ... Detector, 104 ... Converter, 110 ... Tube, 112, 114 ... Ultrasonic vibrator, 120 ... Control part, 122 ... Memory | storage part, 124 ... Transmission circuit, 126 ... Changeover switch , 128, amplifier, 130, A / D converter, 132, calculation unit, 134, reception waveform determination unit, 136, display unit, 138, output unit, 140, first transmission wave, 142, second transmission wave.

Claims (4)

A pair of ultrasonic transducers attached to the outer surface of the tube through which the fluid flows, each disposed diagonally opposite the upstream side and the downstream side;
A transmission circuit for generating a first transmission wave for driving one of the ultrasonic transducers;
Received waveform determination for determining whether a received waveform received by the other of the ultrasonic transducers includes one or more multiwave components when one of the ultrasonic transducers is driven by the first transmitted wave And
When the received waveform determination unit determines that the received waveform contains a multiple-wave component greater than or equal to a predetermined value, a second transmission wave is generated by delaying the phase after a predetermined period from the second period by a half period. A control unit that generates a circuit and drives one of the ultrasonic transducers again with the second transmission wave;
An ultrasonic flowmeter comprising:   The received waveform determination unit, when a predetermined ratio or more of amplitude relative to the amplitude at the peak is detected after a predetermined time from the peak of the amplitude of the received waveform, The ultrasonic flowmeter according to claim 1, wherein it is determined that a component is contained.   The ultrasonic flowmeter according to claim 1, wherein the control unit sets the predetermined timing after the center of the second transmission wave. The control unit shifts the predetermined timing in order to apply the second transmission wave a plurality of times, and the reception waveform determination unit determines a multiple wave component of a reception waveform corresponding to each of the second transmission waves,
The ultrasonic flowmeter according to any one of claims 1 to 3, wherein the control unit detects an influence of a multiwave component within an allowable range and the predetermined timing is the slowest. .

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