JP2005181268A - Ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which can measure a flow rate always in stable condition, by measuring a flow rate on the basis of the reflective correlation method when there are many air bubbles and/or particles and by measuring a flow rate on the basis of the differential propagation time method when there are a few air bubbles and/or particles in the measured fluid flowing the inside of a measuring tube. <P>SOLUTION: The ultrasonic flowmeter comprises: at least two flow rate measuring means of a first and a second one measuring flow rate by the correlation method as a method of detection of differential time; an ultrasonic transceiver means for transmitting and receiving ultrasonic wave signals from a first transducer to a second transducer via specified path; and a reception identifying means for identifying reception device on the basis of the intensity of received signals or correlation values at the aforementioned ultrasonic transceiver means, and the aforementioned first and second flow rate measuring means are changed over by the aforementioned reception identifyinmg means on the basis of the identified signals. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flowmeter, and more particularly to improve the stability (environment resistance) of signal detection. Specifically, even if bubbles are generated, the flow rate is accurately adjusted corresponding to the bubbles. The present invention relates to an ultrasonic flowmeter that can be measured.

  The ultrasonic flowmeter in the prior art has two methods of measuring the flow rate by the propagation time difference method and measuring the flow rate by the reflection type correlation method.

As shown in FIG. 3, the configuration of the ultrasonic flowmeter based on the propagation time difference method is such that the first transducer 112 is disposed on the upstream side of the pipe 111 and on the upstream side, and is opposed to the first transducer 112. A measurement unit 114 which is provided with a second transducer 113 at the downstream side, transmits and receives ultrasonic waves from the first and second transducers 112 and 113, calculates a time difference thereof, and measures a flow velocity; It is roughly composed of
In the ultrasonic flowmeter having such a configuration, the ultrasonic wave is emitted from the first transducer 112 on one side, received by the second transducer 113 at a position different from the transmission, and conversely, the ultrasonic wave is transmitted from the second transducer 113. And the first transducer 112 receives the signal, calculates the discretized correlation value by A / D conversion of the received signal on the upstream side and the received signal on the downstream side, and obtains the time difference corresponding to the flow velocity.

As shown in FIG. 4, the configuration of the ultrasonic flowmeter based on the reflection type correlation method is the same as that of the first transducer 112A for emitting ultrasonic waves to the pipe 111 in the flow direction, and the first transducer 112A. The second transducer 113A is disposed at a position, and receives the reflected ultrasonic waves reflected from the bubbles 115 by the ultrasonic waves emitted from the first transducer 112A.
The positions of the first and second transducers 112 </ b> A and 113 </ b> A can be changed as appropriate so that the reflected ultrasonic waves from the measurement fluid flowing in the pipe 111 can be received.
In the ultrasonic flowmeter having such a configuration, first, ultrasonic waves are blown from the first transducer 112A, and reflected waves scattered from the bubbles 115 and particles are measured. At that time, ultrasonic waves are transmitted twice or more at a certain time interval, and the flow rate is measured from the correlation of received signals obtained from the plurality of reflected waves.
As described above, when bubbles 115 and particles increase in the measurement fluid flowing in the pipe 111, the ultrasonic wave propagating in the pipe 111 is scattered. Therefore, the scattered wave is received and the flow velocity is obtained from the correlation.

JP-A-2002-243514 (pages 4-5, Fig. 1)

  However, the ultrasonic flowmeter based on the propagation time difference method described in the prior art has the feature that the flow velocity can be measured even if bubbles or particles do not exist in the measurement fluid in the pipe, but on the other hand, if the number of bubbles and particles increases, There is a problem that measurement is impossible because the sound wave does not reach.

  In addition, the ultrasonic flowmeter based on the reflection-type correlation method has the feature that the flow velocity can be measured even if bubbles or particles increase in the measurement fluid in the pipe. There is a problem that it becomes impossible to measure because of the decrease.

  Therefore, there is a problem that must be solved in an ultrasonic flowmeter that can obtain a flow rate in a stable state without being influenced by the amount of bubbles or particles present in the measurement fluid flowing in the pipe, and can obtain the flow rate. .

  In order to solve the above problems, the ultrasonic flowmeter of the present invention is configured as follows.

(1) An ultrasonic flowmeter is an ultrasonic flowmeter that obtains a flow rate based on an ultrasonic signal that passes through a measurement fluid in a measurement tube, and detects a time difference corresponding to a flow velocity from the propagation state of the two ultrasonic signals. At least two first and second flow velocity measuring means for detecting a flow velocity using a correlation method as means for performing, a transmission / reception means for transmitting and receiving ultrasonic waves from one transducer to another transducer via a predetermined path, and Determination means for determining switching between the two first and second flow velocity measuring means from the intensity or correlation value of the received signal obtained by the transmission / reception means, and the two first and second based on the determination means Switching means for automatically switching the flow velocity measuring means.
(2) The first flow velocity measuring means measures the time by propagating ultrasonic waves from the upstream transducer to the downstream transducer, and measures the time by propagating the ultrasonic waves from the downstream transducer to the upstream transducer. The second flow velocity measuring means measures the reflected signal of fine particles such as bubbles and particles in the fluid of the transmitted ultrasonic signal a plurality of times and receives the received signal. The ultrasonic flowmeter according to (1), which is a reflection correlation method for obtaining a flow velocity from the correlation of
(3) The ultrasonic flowmeter according to (2), wherein the second flow velocity measuring means uses either an upstream transducer or a downstream transducer.

  As is clear from the above description, according to the present invention, by combining both the propagation time difference method and the reflection type correlation method, it is possible to stabilize from the state where bubbles and particles are present to the state where they are not present. The flow rate can be measured.

  Hereinafter, embodiments of the ultrasonic flowmeter of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the ultrasonic flowmeter of the present invention is provided on the outer periphery of the measuring tube 11, and emits ultrasonic waves and also has a function of receiving a transducer A (12), which is a first transducer. A transducer B (13), which is a second transducer provided on the downstream side of the transducer A (12) and has a function of receiving and receiving ultrasonic waves from the transducer A (12), and a transducer A (12) or Transmitter circuit 14 for emitting ultrasonic waves from transducer B (13), receiver circuit 15 for receiving ultrasonic waves from transducer A (12) or transducer B (13), transducer A (12) and transducer B The supersonic sound received by the switch 16 for switching the connection to (13) and the receiving circuit 15 An A / D converter 17 that converts a signal into a digital signal, a correlation calculator 18 that calculates a discretized correlation value based on the digital signal generated by the A / D converter 17 and obtains a time difference, and a correlation calculator 18 And a digital signal processor DSP (19) that obtains the flow velocity from the time difference calculated in step (1), controls the timing of ultrasonic transmission from the transmission circuit 14, and controls the switching of the switching device 16.
Among these, the control of the switching unit 16 by the digital signal processor DSP (19) is performed by setting the switching unit 16 to the AS side so that the transducer A (12) and the transducer B (13) are used, and the transmission circuit 14 and the transducer A (12). ) And on the BR side, the transducer B (13) and the receiving circuit 15 are connected, and on the contrary, on the BS side, the transmitting circuit 14 and the transducer B (13) are connected and on the AR side, the receiving circuit 15 and the transducer are connected. The first flow rate measuring means controls to connect A (12).
Further, the transmitter 16 is connected to the AS side so that only the transducer A (12) is used, the transmitter circuit 14 and the transducer A (12) are connected, and the AR circuit is connected to the receiver circuit 15 and the transducer A (12). It is the second flow velocity measuring means that controls so as to.

The correlation calculator 18 calculates a discrete correlation value of the digitized signal. At that time, the ultrasonic wave emitted from the upstream transducer A (12) is received by the downstream transducer B (13), and the ultrasonic wave emitted from the downstream transducer B (13) is received by the upstream transducer A (12). The correlation calculation is performed on the basis of the signal received in step (b).
As a result of the correlation calculation, the time difference at which the correlation value becomes maximum is obtained, and the flow velocity is calculated. At the same time, the correlation value is calculated and sent to the digital signal processor DSP (19).

  The switch 16 is so-called switching means, and is controlled by a signal from the digital signal processor DSP (19). This switching is configured so that the transmission circuit 14 and the reception circuit 15 can be controlled independently.

When the correlation value is sufficiently large, the digital signal processor DSP (19) determines to use the time difference propagation mode (propagation time difference method) that is the first flow velocity measuring means. By this determination, a transmission start signal is sent to the transmission circuit 14 at a certain interval, and at the same time, a command is issued to the switcher 16 to switch the role of the transmission / reception transducer after a certain time interval from transmission to reception. In this case, the transmission / reception pair is AS / BR or BS / AR in the figure. In the case of the embodiment, one transducer A (12) and another transducer B (13) are used.
On the other hand, when the correlation value is smaller than a certain value, it is determined that the reflection correlation method as the second flow velocity measuring means is used. In this case, at least two ultrasonic waves are sent to the same transducer at a short time interval. In the case of the embodiment, it is sent to the transducer A (12). Further, a command is sent to the switcher 16 so that the transmission / reception pair is AS / AR.

  In the propagation time difference method selected when the correlation value is large, as shown in FIG. 2 (A), an ultrasonic wave is emitted from the upstream transducer A (12), and the ultrasonic wave passing through the predetermined path is converted into the transducer B ( 13). Similarly, transmission and reception are switched to emit ultrasonic waves from the downstream transducer B (13), and the emitted ultrasonic waves are received by the upstream transducer A (12) through a predetermined path. Each of these received signals is converted by an A / D converter, a correlation value discretized by a correlation calculator is calculated, a time difference corresponding to the flow rate is obtained, and the flow velocity is calculated.

  In the reflection correlation method selected when the correlation value is small, as shown in FIG. 2B, transmission / reception is performed by the upstream only transducer or the downstream only transducer. In the embodiment, transmission / reception is performed only by the transducer A (12). At that time, a correlation is calculated from a pair of a signal waveform received at a specific time after transmitting a signal and a signal transmitted and received at a predetermined time from the transducer A (12), and the correlation is calculated from the correlation. Calculate the flow rate.

As a result, when there are few bubbles and particles, the ultrasonic wave is transmitted to the transducer on the opposite side (downstream when transmitted from upstream, upstream when transmitted from downstream), and the signal is transmitted with little disturbance of the waveform. Therefore, the maximum value of the correlation when the correlation is obtained is large (the waveforms of the two received waves are similar).
On the other hand, when the number of bubbles and particles increases, the correlation value of the signal detected by the opposite transducer decreases, and the reflected wave increases. In that case, the flow velocity is calculated by correlation due to reflection.

In this way, it is determined by the judgment that the correlation value is sufficiently large that there are few bubbles and particles, and the flow velocity is measured based on the propagation time difference method using the transducer A (12) and the transducer B (13). Judging that there are many bubbles and particles by judging that the correlation value is small enough, and measuring the flow velocity based on the reflection correlation method using only the transducer A (12), both defects are replenished. The flow velocity of the measurement fluid can be accurately measured.
Here, although it is determined that the propagation time difference method or the reflection correlation method is used based on the magnitude of the correlation value, this may be determined based on the strength of the ultrasonic reception signal. When measuring by the propagation time difference method, if there are many bubbles or the like, the received signal becomes weak. Therefore, it can be controlled to switch to the reflection correlation method based on the magnitude of the signal.

  With the same circuit configuration, the flow rate is measured based on the propagation time difference method when there are few bubbles or particles in the measurement fluid flowing in the measuring tube, and the flow rate is measured based on the reflection correlation method when there are many bubbles or particles. By doing so, an ultrasonic flowmeter capable of measuring a stable flow rate even when the state of the measurement fluid changes is provided.

It is the block diagram which showed schematically the structure of the ultrasonic flowmeter of this invention. It is explanatory drawing which showed the waveform of the ultrasonic wave based on a propagation time difference method and the waveform of the ultrasonic wave based on a reflection correlation method. It is explanatory drawing which showed the method of measuring the flow velocity based on the propagation time difference method in a prior art. It is explanatory drawing which showed the method of measuring the flow velocity based on the reflection correlation method in a prior art.

Explanation of symbols

11 Measuring tube 12 Transducer A
13 Transducer B
14 Transmission Circuit 15 Reception Circuit 16 Switch 17 A / D Converter 18 Correlation Calculator 19 Digital Signal Processor DSP

Claims (3)

An ultrasonic flowmeter for obtaining a flow rate based on an ultrasonic signal passing through a measurement fluid in a measurement tube,
At least two first and second flow velocity measuring means for detecting a flow velocity using a correlation method as a means for detecting a time difference corresponding to the flow velocity from the propagation state of two ultrasonic signals;
Transmitting and receiving means for transmitting and receiving ultrasonic waves from one transducer to another via a predetermined path;
Determining means for determining switching between the two first and second flow velocity measuring means from the intensity or correlation value of the received signal obtained by the transmitting / receiving means;
An ultrasonic flowmeter comprising: switching means for automatically switching the two first and second flow velocity measuring means based on the determination means.   The first flow velocity measuring means measures the time by propagating the ultrasonic wave from the upstream transducer to the downstream transducer, and measures the time by propagating the ultrasonic wave from the downstream transducer to the upstream transducer. A propagation time difference method for obtaining a flow velocity from a time difference, wherein the second flow velocity measuring means measures a reflected signal of a fine particle such as a bubble or a particle in a fluid of a transmitted ultrasonic signal a plurality of times, and correlates the received signal 2. The ultrasonic flowmeter according to claim 1, which is a reflection correlation method for obtaining a flow velocity. 3. The ultrasonic flowmeter according to claim 2, wherein the second flow velocity measuring means uses either an upstream transducer or a downstream transducer.

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