JP2016156665A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an ultrasonic flowmeter with which, of a simple configuration though, it is possible to measure the propagation velocity of an ultrasonic signal with high accuracy without being affected by variations in the characteristics of electronic components.SOLUTION: Provided is an ultrasonic flowmeter equipped with an ultrasonic conversion element for transmitting/receiving an ultrasonic signal on the upstream and downstream sides of the outer wall of a measurement tube in which a fluid to be measured flows, wherein the ultrasonic flowmeter is characterized in being provided with: an ultrasonic signal transmission unit; a first switching unit for switching the connection of this transmission unit and an ultrasonic conversion element; an ultrasonic signal reception unit; a second switching unit for complementarily switching the connection of this reception unit and the ultrasonic conversion element; a capacitor for differentiating the rise portion of a transmission waveform inputted to the ultrasonic conversion element via the first switching unit and inputting the resultant signal to the reception unit; a data processing unit for calculating a propagation time difference between upstream and downstream and the flow rate of the fluid to be measured on the basis of the ultrasonic signal inputted to the reception unit and received by the ultrasonic conversion element; and a control unit for collectively controlling the operations of these transmission unit, first switching unit, reception unit, second switching unit, and data processing unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic flowmeter, and more particularly, to removal of influence on delay time measurement due to variations in electronic component characteristics of a transmission / reception circuit in a transmission method.

  FIG. 4 is a configuration explanatory view showing an example of an ultrasonic flowmeter based on a conventionally used transmission method. In FIG. 4, the control unit 1 comprehensively controls the operations of the data processing unit 2, the transmission unit 3, the reception unit 4, the first switching unit 5 and the second switching unit 6 according to a predetermined program, In addition to these controls, transmission waveform data is generated and output to the transmission unit 3, an appropriate gain setting signal is generated and output to the reception unit 4, and the data processing unit 2 starts the operation of the transmission unit 3. Notify that

  The data processing unit 2 receives the operation start signal of the transmission unit 3 from the control unit 1 as a starting point for the propagation time measurement, and determines the propagation time based on the measurement signal that has reached the reception unit 4 through the propagation paths A and B. While calculating, holding parameters necessary for the flow rate measurement, the flow velocity is calculated from the measured propagation time and finally the flow rate is calculated.

  The transmission unit 3 is enabled by the control signal input from the control unit 1 and generates and outputs an ultrasonic transmission waveform according to the transmission waveform data input from the control unit 1. The ultrasonic transmission waveform is transmitted to the ultrasonic transducers 9 and 10 via the switching units 5 and 6 and the signal lines 7 and 8 made of, for example, coaxial cables.

  The receiving unit 4 sets a gain by a gain setting signal input from the control unit 1 and amplifies signals converted and output from the ultrasonic transducers 9 and 10.

  The switching units 5 and 6 are switched and driven in conjunction with each other to alternately and alternately switch the signal lines 7 and 8 that connect the transmission unit 3 and the reception unit 4 and the ultrasonic transducers 9 and 10.

  One end of the signal line 7 is connected to one fixed contact a of the switching unit 5, the other end is connected to the ultrasonic transducer 9, and one end of the signal line 8 is connected to one fixed contact e of the switching unit 6. The other end is connected to the ultrasonic transducer 10. The signal line 7 is also connected to the other fixed contact b of the switching unit 5, and the signal line 8 is also connected to the other fixed contact f of the switching unit 6.

  The ultrasonic transducers 9 and 10 are constituted by piezoelectric elements, for example, and propagation paths A and B of the respective ultrasonic signals are formed on the outer wall of the measurement tube 11 so as to sandwich the measurement tube 11 through which the fluid to be measured flows. They are arranged opposite to the upstream side and the downstream side in a positional relationship that intersects with the tube axis of the measurement tube 11 at a predetermined angle in an oblique direction.

  These control unit 1, data processing unit 2, transmission unit 3, reception unit 4, first switching unit 5 and second switching unit 6 constitute a signal conversion unit 12.

  When one of the ultrasonic transducers 9 and 10 (for example, the ultrasonic transducer 9) functions as an ultrasonic generator due to the piezoelectric effect, the other (for example, the ultrasonic transducer 10) functions as an ultrasonic detector due to the piezoelectric effect. As such, their functions switch alternately and complementarily.

  For example, when an ultrasonic transmission waveform generated and output from the transmission unit 3 is input to the ultrasonic transducer 9, the ultrasonic transducer 9 generates an ultrasonic signal. The ultrasonic signal generated by the ultrasonic transducer 9 is received by the ultrasonic transducer 10 through the propagation path A inside the measurement tube 11, converted into an electrical signal, and output to the receiver 4.

  FIG. 5 is a circuit diagram showing an example of the transmission unit 3, and the same reference numerals are given to portions common to FIG. 4. The transmission unit 3 is basically configured as a half bridge circuit that generates a rectangular wave. In FIG. 5, the waveform generator 3 a generates an original waveform (pulse waveform) signal of transmission waveform data to be transmitted to the ultrasonic transducers 9 and 10 based on the control of the controller 1.

  The driver 3b is connected to the gates of the two MOSFETs 3e and 3f, and drives the MOSFETs 3e and 3f according to the original waveform (pulse waveform) signal of the transmission waveform data input from the waveform generator 3a.

  The source of MOSFET 3e is connected to the positive terminal of variable DC power supply 3c that supplies a transmission waveform voltage of positive voltage + V1, and the negative terminal of variable DC power supply 3d that supplies the transmission waveform voltage of negative voltage -V2 is connected to the source of MOSFET 3f. It is connected. The negative terminal of the variable DC power source 3c and the positive terminal of the variable DC power source 3d are connected to a common potential point.

  The anode of the protection diode 3g is connected to the drain of the MOSFET 3e, and the cathode of the protection diode 3h is connected to the drain of the MOSFET 3f.

  The cathode of the diode 3g and the anode of the diode 3h are connected in common and connected to the movable contact a of the switching unit 5 and are used for damping to discharge the electric charge accumulated in the piezoelectric elements of the ultrasonic transducers 9 and 10. It is connected to one end of a resistance 3i for protection.

  The other end of the protective resistor 3i is connected to a common potential point via a damping switch 3j.

  FIG. 6 is a circuit diagram showing an example of the receiving unit 4, and parts common to FIG. 4 are given the same reference numerals. In FIG. 6, the receiving unit 4 includes a capacitor 4a, a bandpass filter 4b, a variable gain amplifier (VGA) 4c, a D / A converter 4d, and an A / D converter 4e.

  The input terminal of the variable gain amplifier 4c is connected to the movable contact d of the switching unit 6 through a series circuit of a capacitor 4a and a band pass filter 4b.

  The gain of the variable gain amplifier 4c is set to a desired value according to the voltage set from the control unit 1 via the D / A converter 4d.

  The output signal of the variable gain amplifier 4c is converted into a digital signal by the A / D converter 4e and then input to the data processing unit 2.

  The operation of FIG. 4 will be described. In measuring the flow rate, a parameter τ (described later) related to the propagation time of the ultrasonic signals such as the signal lines 7 and 8, the pipe material, and the lining in a state where the ultrasonic transducers 9 and 10 are attached to the outer wall of the measurement tube 11 is used. Set in the signal converter 12.

  In the initial state, the movable contact a of the switching unit 5 is connected to the fixed contact b, and the movable contact d of the switching unit 6 is connected to the fixed contact e.

<Measurement of propagation time “td”>
The propagation time “td” is the propagation time along the flow direction from the ultrasonic transducer 9 through the propagation path A to the ultrasonic transducer 10.

  The control unit 1 sets the output voltage of the variable DC power sources 3c and 3d of the transmission unit 3 to an appropriate value, and sends the transmission waveform data of the ultrasonic waveform to the waveform generation unit 3a. Further, a setting value for setting the gain of the variable gain amplifier 4c to an appropriate desired value is sent to the D / A converter 4d of the receiving unit 4, and the gain of the variable gain amplifier 4c is set to a desired value.

  The control unit 1 outputs an ultrasonic wave generation start signal to the transmission unit 3 and the data processing unit 2. The waveform voltage for transmitting the ultrasonic wave is transmitted from the transmission unit 3 to the ultrasonic transducer 9 via the switching unit 5.

  The ultrasonic signal generated by the ultrasonic transducer 9 is received by the ultrasonic transducer 10 through the propagation path A inside the measurement tube 11 and converted into an electrical signal, and is sent to the receiver 4 via the switching unit 6. After being input and amplified to an appropriate value, it is converted into a digital signal and input to the data processing unit 2.

  The data processing unit 2 holds the propagation time “td” of the ultrasonic signal from the transmission unit 3 to the reception unit 4. The starting point of this propagation time “td” is based on the start signal of ultrasonic generation sent from the control unit 1 to the data processing unit 2 as described above.

  Inside the transmission unit 3, the waveform generation unit 3a converts the transmission waveform data into an appropriate drive waveform signal, and according to the start signal input from the control unit 1, the MOSFETs 3e and 3f are driven via the driver 3b to generate a rectangular wave. And output to the movable contact a of the switching unit 5 via the diodes 3g and 3h. The operation of the transmitter 3 is the same in the measurement of the propagation time “tu” described below.

<Measurement of propagation time “tu”>
The propagation time “tu” is a propagation time in the direction opposite to the flow direction from the ultrasonic transducer 10 through the propagation path B to the ultrasonic transducer 9.

  In measuring the propagation time “tu”, the control unit 1 outputs a control signal for switching the movable contact a of the switching unit 5 to the fixed contact c side and switching the movable contact d of the switching unit 6 to the fixed contact f side. To do. In the state where the movable contact a of the switching unit 5 and the movable contact d of the switching unit 6 are switched, the same operation as the measurement of the propagation time “td” is performed.

  The control unit 1 outputs an ultrasonic generation start signal to the transmission unit 3 and the data processing unit 2, and the ultrasonic signal travels in the direction opposite to the propagation path when measuring the propagation time “td”, that is, from the transmission unit 3. It reaches the ultrasonic transducer 10 through the fixed contact c of the switching unit 5, is received by the ultrasonic transducer 9 through the propagation path B inside the measuring tube 11, is converted into an electrical signal, and is converted via the switching unit 6. After being input to the receiving unit 4 and amplified to an appropriate value, it is converted into a digital signal and input to the data processing unit 2. The data processing unit 2 holds the propagation time “tu” of the ultrasonic signal from the transmission unit 3 to the reception unit 4.

The propagation time “td” can be expressed by equation (1),
td = {L / (C + V × cosθ)} + τ1 (1)

The propagation time “tu” can be expressed by equation (2).
tu = {L / (CV × cosθ)} + τ2 (2)

In the expressions (1) and (2),
L: Distance to propagate in the pipe
C: speed of sound
V: Flow velocity in the tube θ: Angle between the flow velocity in the tube and the propagation direction of ultrasonic waves τ1, τ2: Delay from the start signal of the transmission unit 3 (mainly variation in rise time due to semiconductors in the transmission unit 3).
Among these, L, C, and θ are numerical values that can be determined and set when the flow meter is installed.

When the difference in propagation time between td and tu is calculated as Δt = tu-td, the flow velocity V is obtained by equation (3). Thereby, since the cross-sectional area through which the flow rate of the measuring tube 11 flows is known, the flow rate is obtained.
V = C ² × (Δt-Δτ) / (2 × L × cosθ) (3)
However, Δt = tu-td, Δτ = τ2-τ1

  Δτ can be ignored when explaining the principle operation. However, as a practical problem, Δτ is generated about several tens of nsec and becomes a measurement error of the flow velocity V.

  Non-Patent Document 1 describes the measurement principle and configuration of an ultrasonic flowmeter of a propagation time difference method based on the transmission method similar to the present invention.

Satoshi Fukuhara, 3 others, “Ultrasonic Flowmeter US350”, Yokogawa Technical Report, Yokogawa Electric Corporation, January 20, 2004, Vol. 48 No. 1 (2004) p. 29-32

  τ1 and τ2 are the delays mainly caused by the transmitter 3, but they are composed of drivers, MOSFETs, diodes, etc., and the semiconductor elements used are relatively slow, medium and high withstand voltage products. It has several tens of nsec, and the total delay is several hundred nsec or more.

  When a transmission waveform is actually generated, these delays occur as variations of 10% or more each time, so that τ1 = τ2 is not satisfied, and the value of Δτ becomes a level that affects the measurement of the flow velocity V.

  In addition, in the configuration example of FIG. 4, there is only one transmission unit 3, but when using in multi-channel, at least two transmission units 3 are necessary, and the delay is reduced due to the influence of the variation of electronic components between them. The variation is even greater.

  In order to eliminate the influence of this delay, for example, a transmission waveform is generated multiple times and corrected by the average value, or the actual rising waveform is fed back by appropriate resistance division from the signal line of the transmission waveform and propagated there It can be considered as the starting point of time measurement.

  Although the correction by the average value can correct the delay of the entire typ value, the variation Δτ at the time of waveform generation that affects the flow velocity V cannot be completely removed, and the accuracy of the flow velocity V cannot be increased. Also, the feedback method requires a mechanism to make the level of the feedback signal constant because the peak value of the transmission waveform changes greatly depending on the material and size of the tube to be measured, the type of fluid inside, etc. .

  As a circuit example of the feedback mechanism, a mechanism that makes feedback constant uses a variable gain amplifier that is always provided in an ultrasonic flowmeter and feeds back a transmission waveform signal. The signal line is a transmission / reception signal line that is also used as a reception signal, and the addition of a resistor needs to be appropriately selected so that the influence of impedance mismatch is small.

  In addition, adding a resistor to the transmission / reception signal line increases the possibility of picking up high-frequency noise signals during reception, necessitating a design that takes into account the effects of noise resistance degradation, etc. Become.

  Even if such a correction circuit can be added, since it is attached to each transmission signal line in the case of a multi-channel having a plurality of transmission units as described above, the influence on each signal line is considered. And a design that reduces the circuit scale is required.

  The present invention solves these problems. The purpose of the present invention is to simply connect a simple capacitor to the transducer of the ultrasonic flowmeter, and to detect the ultrasonic signal without being affected by variations in the characteristics of the electronic components. The object is to realize an ultrasonic flowmeter capable of measuring the propagation velocity with high accuracy.

In order to achieve such an object, the invention described in claim 1 of the present invention is
In an ultrasonic flowmeter in which ultrasonic transducers for transmitting and receiving ultrasonic signals are attached to the upstream side and the downstream side of the outer wall of the measurement pipe through which the fluid to be measured flows,
An ultrasonic signal transmitter;
A first switching unit that switches and connects the transmission unit and the ultrasonic transducer;
An ultrasonic signal receiver;
A second switching unit that complementarily switches and connects the receiving unit and the ultrasonic transducer;
A capacitor that differentiates a rising portion of a transmission waveform input to the ultrasonic transducer through the first switching unit and inputs the differentiated portion to the reception unit;
A data processing unit that calculates an upstream and downstream propagation time difference and flow rate of the fluid to be measured based on an ultrasonic signal received by the ultrasonic transducer input to the receiving unit;
A control unit that comprehensively controls operations of the transmission unit, the first switching unit, the receiving unit, the second switching unit, and the data processing unit,
Is provided.

The invention according to claim 2 is the ultrasonic flowmeter according to claim 1,
The receiving unit amplifies a signal input through the capacitor to a logic level.

The invention according to claim 3 is the ultrasonic flowmeter according to claim 2,
Latch means for latching the logic signal and outputting it to a data processing unit for calculating the flow rate of the fluid to be measured based on the received signal of the ultrasonic transducer is provided.

The invention according to claim 4 is the ultrasonic flowmeter according to claim 3,
The data processing unit calculates transmission waveform start time information based on an output signal of the latch means.

The invention according to claim 5 is the ultrasonic flowmeter according to claim 3 or claim 4,
The control unit calculates and holds the start time information of the transmission waveform, and then outputs a reset signal for releasing the latch of the latch unit.

  Accordingly, it is possible to reduce the influence of offset due to variations in electric circuit elements and cables, and to realize an ultrasonic flowmeter capable of performing highly accurate measurement.

It is a configuration explanatory view showing an embodiment of the present invention. It is composition explanatory drawing which shows the other Example of this invention. It is composition explanatory drawing which shows an example of the conventional ultrasonic flowmeter. It is composition explanatory drawing which shows an example of the ultrasonic flowmeter based on the transmission method used conventionally. FIG. 5 is a circuit diagram illustrating an example of a transmission unit 3 in FIG. 4. FIG. 5 is a circuit diagram illustrating an example of a receiving unit 4 in FIG. 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of an embodiment of the present invention, and the same reference numerals are given to portions common to FIG. 1 differs from FIG. 4 in that a capacitor 13 is connected between the receiver 4 and the signal line 7 and a capacitor 14 is connected between the receiver 4 and the signal line 8.

  FIG. 2 is a circuit diagram showing a specific example of the receiving unit 4 in FIG. 1, and the same reference numerals are given to portions common to FIG. 2 is different from FIG. 6 in that a latch circuit 15 is provided between the data processing unit 2 and the variable gain amplifier 4c of the receiving unit 4. FIG.

  The operation of FIG. 1 will be described. The basic measurement operation is the same as that of the conventional configuration shown in FIG. 4, but when the transmission waveform of the propagation path A is generated, a part of the waveform is input to the capacitor 13 and is received as a rising differential waveform. The difference is that it is input to the variable gain amplifier 4c.

At this time, the gain of the variable gain amplifier 4c is set so that the output reaches a logic level voltage, and the output waveform of the variable gain amplifier 4c is held by the latch circuit 15.

  The data processing unit 2 can grasp the start time information without the semiconductor delay of the transmission unit 3 from the output of the latch circuit 15 and can measure the propagation time from this time information.

  When the data processing unit 2 knows the start time information, it sends a reset signal to the latch circuit 15 to release the data hold of the latch circuit 15. The gain of the variable gain amplifier 4c is set to an appropriate gain by a gain setting signal from the control unit 1 in preparation for the received signal.

  Also for the propagation path B, by generating a transmission waveform in the same manner as the propagation path A, the starting point of the transmission waveform can be found. In this way, the starting point of the propagation waveform can be a signal from which the delay of the semiconductor element of the transmission unit 3 is removed, not from the conventional control unit 1.

  The capacitors 13 and 14 in FIG. 1 are sufficiently attenuated even when the transmission waveform is high voltage by making it sufficiently smaller than the capacitance of the piezoelectric elements constituting the ultrasonic transducers 9 and 10 that become the load of the transmitter 3. The obtained peak value can be safely input to the variable gain amplifier 4c.

  Further, since only the frequency component of the rise time of the transmission waveform is necessary, the high frequency component that does not affect the frequency band of the transmission and reception waveforms of the ultrasonic transducers 9 and 10 can be passed.

  Further, the gain setting value of the variable gain amplifier 4c at this time corresponds to the peak value of the transmission wave that changes corresponding to the material of the measurement tube 11, the contamination by the internal deposits, the influence of the coating, the change depending on the fluid to be measured, and the like. However, since the peak value can be grasped in advance, it can be easily calculated and set in advance from circuit constants such as the capacitors 13 and 14, and the change can be automatically handled.

  In the configuration of the conventional ultrasonic flowmeter, simple capacitors 13 and 14 are added by utilizing existing functions to account for variations in the propagation measurement time caused by variations in the characteristics and operating conditions of the electronic components of the transmitter 3. Just remove it.

  Specifically, as shown in FIG. 1, the connection destination of the capacitors 13 and 14 is devised, and the delay time is simply provided by connecting the latch circuit 15 to a part of the data processing unit 2 created by an FPGA or the like. The starting point of the transmission waveform, which is the starting point of measurement, can be measured without being affected by variations in the electronic components of the waveform generating unit.

According to such a configuration, the following effects can be expected.
The starting point of the propagation time that does not affect the variation due to electronic components can be measured. In other words, parts can be selected without worrying about the delay time of each semiconductor element. spread.

  In the case of multi-channel, it becomes unnecessary to make correction by switching the route due to delay time shift, and if a switching function is provided only for this correction, it can be removed.

  This can be realized by adding simple parts and functions to an existing ultrasonic flow meter, and its design is easy, so that an ultrasonic flow meter with high design freedom and high accuracy can be provided.

  In the above embodiment, the transmission type ultrasonic flowmeter has been described. However, the present invention is not limited to the transmission type, and can be applied to a transmission / reflection type ultrasonic flowmeter as shown in FIG.

  In FIG. 3, one transmitter 17 is used to measure the propagation time in the propagation path A, and the other transmitter 18 is used to measure the propagation time in the propagation path B. However, in the case of FIG. 3, the transmission unit 3 is not common as in FIG. 1, and there is a possibility that the variation of the parts of the transmission units 17 and 18 may be further increased, which affects the starting point of the propagation time measurement.

  In order to reduce this influence, for example, after measuring the propagation time of the propagation path A using one transmission unit 17, the switching units 21 and 22 are switched and the propagation time of the propagation path B is measured by the same transmission unit 17, Similarly, the propagation time of the propagation path A and the propagation time of the propagation path B are measured using the other transmission unit 18, and the transmission units 17 and 18 are calculated by calculating the difference and the average from the measurement data of these four propagation times. The influence of the delay variation of can be reduced.

  In such a case as well, the capacitors 23 and 24 are connected between the signal lines 7 and 8 and one of the receiving units 19 and 20 as in FIG. 1, and the data processing unit 16 and the capacitors 23 and 24 are connected. If a latch circuit 15 similar to that shown in FIG. 2 is provided between either of the receiving units 19 and 20, and a function for measuring the starting point of the start is added, measurement without affecting the variation of the electronic components of the transmitting units 17 and 18 can be performed. it can.

  As described above, according to the present invention, it is possible to realize an ultrasonic flowmeter capable of measuring the propagation speed of an ultrasonic signal with high accuracy without being affected by variations in characteristics of electronic components.

DESCRIPTION OF SYMBOLS 1 Control part 2 Data processing part 3 Transmission part 4 Reception part 5 1st switching part 6 2nd switching part 7, 8 Signal line 9,10 Ultrasonic transducer 11 Measuring tube 12 Signal conversion part 13, 14 Capacitor 15 Latch circuit

Claims (5)

In an ultrasonic flowmeter in which ultrasonic transducers for transmitting and receiving ultrasonic signals are attached to the upstream side and the downstream side of the outer wall of the measurement pipe through which the fluid to be measured flows
An ultrasonic signal transmitter;
A first switching unit that switches and connects the transmission unit and the ultrasonic transducer;
An ultrasonic signal receiver;
A second switching unit that complementarily switches and connects the receiving unit and the ultrasonic transducer;
A capacitor that differentiates a rising portion of a transmission waveform input to the ultrasonic transducer through the first switching unit and inputs the differentiated portion to the reception unit;
A data processing unit that calculates an upstream and downstream propagation time difference and flow rate of the fluid to be measured based on an ultrasonic signal received by the ultrasonic transducer input to the receiving unit;
A control unit that comprehensively controls operations of the transmission unit, the first switching unit, the receiving unit, the second switching unit, and the data processing unit,
An ultrasonic flowmeter characterized by comprising: The ultrasonic flowmeter according to claim 1, wherein the receiving unit amplifies a signal input through the capacitor to a logic level.   3. The ultrasonic wave according to claim 2, further comprising latch means for latching the logic signal and outputting the latched signal to a data processing unit for calculating a flow rate of the fluid to be measured based on a reception signal of the ultrasonic transducer. Flowmeter.   The ultrasonic flowmeter according to claim 3, wherein the data processing unit calculates start time information of a transmission waveform based on an output signal of the latch means.   5. The ultrasonic flowmeter according to claim 3, wherein the control unit outputs a reset signal for releasing the latch of the latch means after calculating and holding the start time information of the transmission waveform.

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