JP3498628B2 - Ultrasonic transducer and ultrasonic flow meter using it - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring the flow rate and flow velocity of gas or liquid by ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic flowmeter of this type is known, for example, from Japanese Patent Application Laid-Open No. 9-133561. The temperature (T0) of a standard non-measurement fluid and the temperature of a non-measurement fluid in use are known. From the information (Tsv), T0 / Tsv is used as the correction coefficient to improve the flow rate measurement accuracy.

[0003]

However, in the above-mentioned conventional ultrasonic flowmeter, when the measurement result in the state of no flow (hereinafter referred to as zero point) becomes a value other than 0 due to temperature change, the operation compensation temperature range is set. There is a problem that it is difficult to set the whole value to 0 only by the correction coefficient, and the stability of the zero point due to temperature change cannot be obtained.

The present invention has been made to solve the above problems, and an object of the present invention is to improve the stability of the zero point due to temperature changes by the structure of an ultrasonic transducer.

[0005]

In order to solve the above problems, the present invention is configured so that the unnecessary vibration mode of the piezoelectric body and the resonance frequency of the case are different frequencies.

According to the above invention, it is possible to prevent the piezoelectric body and the case from resonating, and it is possible to reduce the influence of unnecessary vibration on the ultrasonic pulse transmitted and received by the pair of ultrasonic transducers. Therefore, the stability of the zero point due to temperature change can be improved.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Ultrasonic vibration according to the first embodiment of the present invention
The child is a piezoelectric body that mutually converts electrical signals and mechanical vibrations.
And a case and a matching layer on the outside of the piezoelectric body.
The piezoelectric body is fixed to the inner wall side of the top of the case,
The matching layer is fixed to the outer wall side of the case,
Resonance frequency of unwanted vibration mode and resonance frequency of the case
The ultrasonic transducer was configured so that the
Therefore, the influence of the unnecessary vibration mode can improve the stability of the zero point due to the temperature change.

The ultrasonic transducer according to the second aspect of the present invention is
In the ultrasonic transducer of the first aspect, the piezoelectric body is
It is configured to spread and vibrate, and the resonance frequency or
The resonance frequency of the vibration is the frequency of the unnecessary vibration mode.
Since the configuration is adopted, the stability of the zero point due to the temperature change can be improved.

An ultrasonic transducer according to a third aspect of the present invention is
In the ultrasonic flowmeter of the first aspect, the inner wall side surface of the case or
Has a vibration damper fixed to the side of the outer wall,
It is possible to improve the stability of the zero point due to the temperature change.

An ultrasonic transducer according to a fourth aspect of the present invention is
In the ultrasonic flowmeter of the form No. 3, the damping body is not a rigid body.
Since it is configured as described above, it is possible to reduce the influence of the unnecessary vibration mode and improve the stability of the zero point due to the temperature change.

An ultrasonic transducer according to a fifth aspect of the present invention is the ultrasonic transducer.
In the ultrasonic flowmeter of the form 3 above, the damping body is made of an elastic body.
So as order to the arrangement, it is possible to improve the stability of the zero point due to the reduction can changes in temperature effect of unwanted vibration modes.

An ultrasonic transducer according to a sixth aspect of the present invention is
In the ultrasonic flowmeter of the first embodiment, fold it on the side wall of the case.
Since the bent portion is provided, the influence of the unnecessary vibration mode can be reduced and the stability of the zero point due to the temperature change can be improved.

An ultrasonic flowmeter according to a seventh aspect of the present invention is
In the ultrasonic flowmeter of the first aspect, the top of the case is piezoelectric.
Since the shape is similar to that of the body, the direction of the piezoelectric body is
This makes it easy to attach to the ultrasonic flowmeter.

[0014] Ultrasonic flowmeter of the eighth embodiment of the present invention, the
Provided in the flow rate measurement section where the measurement fluid flows and this flow rate measurement section
Any of the first to seventh modes for transmitting and receiving ultrasonic waves
A pair of ultrasonic transducers and one of the ultrasonic transducers.
Connected to the ultrasonic transducer
A reception detection circuit that detects ultrasonic pulses and the ultrasonic pulse
A timer for measuring the propagation time of the
The control unit that controls the timer and the flow from the output of the timer
Ultrasonic flowmeter with a calculation unit for calculating the amount by calculation
Therefore, the influence of unnecessary vibration mode can be reduced and the temperature change
It is possible to improve the stability of the zero point.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. It is to be noted that components having the same reference numerals in the drawings are the same and detailed description thereof will be omitted.

(Embodiment 1) FIG. 1 is a block diagram showing an ultrasonic flowmeter according to Embodiment 1 of the present invention. In FIG. 1, 1 is a flow rate measuring unit through which a fluid to be measured flows, 2 and 3 are ultrasonic transducers arranged diagonally opposite to the flow direction of the flow rate measuring unit 1, 4 is an ultrasonic transducer 2, 3, an oscillator circuit for transmitting the operating frequency of 3 is connected to the oscillator circuit 4, and a drive circuit for driving the ultrasonic transducers 2, 3.
6 is a switching circuit for switching ultrasonic transducers to be transmitted and received, 7
Is a reception detection circuit for detecting the ultrasonic pulse, 8 is a timer for measuring the propagation time of the ultrasonic pulse, 9 is a calculation unit for calculating the flow rate from the output of the timer 8, and 10 is a control signal for the drive circuit 5 and the timer 8. It is a control unit that outputs.

First, the operation and action will be described. For example, air is used as the non-measuring fluid, and about 500 kHz is selected as the operating frequency of the ultrasonic transducers 2 and 3. The oscillator circuit 4 is composed of, for example, a capacitor and a resistor, and transmits a square wave of about 500 kHz.
Since the drive circuit 7 drives the ultrasonic transducer 2 from the signal of the oscillation circuit 4, it can output a drive signal composed of a burst signal of three square waves. In order to improve the resolution of the measured flow rate, for example, the sing-around method is used for the measuring means.

The control unit 10 outputs a transmission start signal to the drive circuit 5 and, at the same time, starts the time measurement of the timer 8. When the drive circuit 5 receives the transmission start signal, it drives the ultrasonic transducer 2 to transmit an ultrasonic pulse. The transmitted ultrasonic pulse propagates in the flow rate measurement 1 and is received by the ultrasonic transducer 3. The received ultrasonic pulse is converted into an electric signal by the ultrasonic transducer 3 and output to the reception detection circuit 7. The reception detection circuit 7 determines the reception timing of the reception signal and outputs the reception detection signal to the control unit 10. When the control unit 10 receives the reception detection signal, the delay time t is set in advance.
After the elapse of d, the transmission start signal is output to the drive circuit 5 again, and 2
Perform the second measurement. After repeating this operation N times, the timer 8 is stopped. The calculation unit 10 divides the time measured by the timer 8 by the number N of times of measurement, subtracts the delay time td, and calculates the propagation time t1.

Subsequently, the switching circuit 6 switches the ultrasonic transducers connected to the drive circuit 5 and the receiving circuit 7, and the control unit 1 is restarted.
At 0, at the same time as outputting the transmission start signal to the drive circuit 5,
The time measurement of the timer 8 is started. Contrary to the measurement of the propagation time t1, the ultrasonic pulse is transmitted by the ultrasonic transducer 3 and the measurement received by the ultrasonic transducer 2 is repeated N times, and the calculation unit 9 calculates the propagation time t2.

Here, the ultrasonic transducer 2 and the ultrasonic transducer 3
L is the distance connecting the centers of the points, C is the speed of sound in the airless state,
When the flow velocity in the flow rate measuring unit 1 is V and the angle between the direction of the flow of the non-measurement fluid and the line connecting the centers of the ultrasonic transducers 2 and 3 is θ, the propagation times t1 and t2 are t1 = L / (C + Vcosθ) (1) t2 = L / (C-Vcosθ) (2) When the sound velocity C is deleted from the equations (1) and (2) and the flow velocity V is obtained, V = L / 2cosθ (1 / t1-1 / t2) (3) is obtained. Since L and θ are known, the flow velocity V can be obtained by measuring t1 and t2. This flow velocity V and flow rate measuring unit 1
The flow rate Q can be calculated by Q = KSV (4) where S is the area of S and the correction coefficient is K.

Next, consider the influence of the unnecessary vibration mode in the flow rate measurement in the absence of flow. Generally, in the sing-around method, the reverberation time of the ultrasonic pulse transmitted from the ultrasonic transducer 2 and the ultrasonic transducer 3 that has received the ultrasonic pulse.
If the vibration time of is longer than the propagation time t1, it is affected by these vibrations in the time measurement. Therefore, assuming that these vibrations include frequency components other than the used frequency,
Calculate the variation of the zero point with temperature. The frequency used is f1, the frequency of unnecessary vibration is f2, f1 and f2 are continuous sine waves, and the amplitude of unnecessary vibration is A for simplification of calculation. Note that there is a frequency shift in f2, and the frequency difference is df2. Also, because there is no air flow,
When the temperature is T, the propagation time Pt between the ultrasonic transducers is Pt.
Is represented by Pt = L / (331 + 0.6 · T) (5).

Here, when transmitting with the ultrasonic transducer 2, R1 = sin {2π · f1 · (t−Pt)} + A sin (2π · f2 · t) (6) When transmitting with the ultrasonic transducer 3 Let R2 = sin {2π · f1 · (t−Pt)} + Asin {2π · (f2 + df2) · t} (7). R when the temperature T is changed from the equations (6) and (7)
The times t1 and t2 at which 1 and R2 cross zero at the fifth time are obtained, and the flow rate is calculated using the equation (3). f1 is 500kH
2 to 4 show the calculation results when z and f2 are 200 kHz and A is -60 dB and df2 is 0 kHz, 1 kHz and 5 kHz.

As shown in FIG. 2, when there is no deviation in f2,
There is no change in the zero point due to temperature. On the other hand, df2 is 1
In FIGS. 3 and 4 where the frequency is 5 kHz, the zero point periodically fluctuates depending on the temperature. Also, depending on the size of df2,
A change in amplitude is seen. From the above calculation results, it can be estimated that the zero point periodically changes due to temperature due to the influence of the unnecessary vibration mode.

Therefore, the configuration of the ultrasonic transducer and the operating frequency,
The relationship between unnecessary vibration frequencies is shown. An example of the configuration of the ultrasonic oscillator 11 is shown in FIG. 5, and a piezoelectric body used in this ultrasonic oscillator 11 is shown in FIGS. The ultrasonic transducer 11 includes a piezoelectric body 12, a case 13, a matching layer 14, and a back lid 15. Case 13
Is made of stainless steel with a thickness of 0.2 mm, and is molded to a depth of about 3 mm. When the vibration analysis of the shape in which only the back lid 15 is attached to the case 13 is performed using the finite element method, a resonance mode exists near about 200 kHz. The piezoelectric body 12 used for the ultrasonic transducer 11 is a square having one side of the electrode surface of about 8 mm and a height of about 2.7 mm. Since the piezoelectric body 12 having this shape cannot vertically vibrate, the piezoelectric body 16 is provided with three vertical grooves 17 as shown in FIG. 6, and the piezoelectric body 18 is provided with three vertical and horizontal grooves 19 as shown in FIG. Make it possible. The impedance characteristics of the piezoelectric body 16 and the piezoelectric body 18 having these configurations are shown in FIGS. In the impedance characteristic of FIG. 8, resonance of an unnecessary vibration mode is seen near 200 kHz. On the other hand, in the impedance characteristic of FIG. 9, almost no resonance of the unwanted vibration mode near 200 kHz is seen.

10 and 11 show the results of an experiment in which an ultrasonic transducer using the piezoelectric body 16 and the piezoelectric body 18 was constructed and the fluctuation of the zero point due to the temperature change was measured. In FIG. 10, the zero point shows periodical fluctuation due to temperature change. On the other hand, in FIG. 11, no periodic phenomenon is seen in the fluctuation of the zero point due to the temperature change.

From the above results, when the resonance frequency of the unnecessary vibration mode of the piezoelectric body 12 and the resonance frequency of the case 13 are close to each other, the zero point periodically fluctuates due to temperature change, and the piezoelectric body 12
It can be seen that when the piezoelectric body 12 is configured so that the resonance frequency of the unnecessary vibration mode and the resonance frequency of the case 13 are different from each other, the zero point is stable without depending on the temperature change.

Although the sing-around method is used for measuring the flow rate in the first embodiment, the present invention is not limited to the above condition, and even if the measurement is performed only once, the periodic measurement is performed N times and the average value is measured. You may use for the method. Although the non-measuring fluid is air, it may be a gas such as LP gas or city gas other than air, or a liquid such as water or gasoline.

Further, although the pair of ultrasonic transducers are arranged so as to be diagonally opposed to the flow, they may be arranged in parallel to the flow, and the reflection on the inner wall surface of the flow rate measuring portion is used. You may arrange | position in such a position. Also, the frequency used for the ultrasonic transducer is 500 kHz, and the frequency for unwanted vibration is 2
Although it is set to 00 kHz, it is not limited to the above condition,
The frequency used is generally 10 kHz to 1 MHz for gas and 100 kHz to 10 MHz for liquid. Moreover, the electrode surface of the piezoelectric body is a square with one side of 8 mm and the height is 2.7 mm.
However, a rectangular parallelepiped other than the above size, a thin disk, a cylinder, or a polygonal pillar may be used.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 12 is a sectional view of the ultrasonic transducer of the second embodiment. Reference numeral 20 is an ultrasonic transducer, 22 is a case, 23 is a matching layer, and 24 is a back cover. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 5 is that the piezoelectric body 12 has a cylindrical shape. The operation principle is the same as that of the first embodiment, and therefore will be omitted.

For example, nine cylindrical piezoelectric bodies 21 having a diameter of 1.5 mm and a height of 2.7 mm and a matching layer 23 are adhesively fixed to the top of the case 22, and the back lid 24 is electrically welded to the case 22. To do. In the piezoelectric body 21, the resonance frequency of spreading vibration is higher than the resonance frequency of longitudinal vibration. Therefore, if the spreading vibration is an unnecessary vibration, the resonance frequency of the unnecessary vibration mode of the piezoelectric body 21 and the resonance frequency of the case 22 are different from each other, so that the influence of the unnecessary vibration mode can be reduced and the temperature change as in the first embodiment. The zero point is stable without depending on.

In the second embodiment, the longitudinal vibration of the columnar piezoelectric body is used, but the longitudinal vibration of the polygonal columnar piezoelectric body or the spreading vibration of a thin disk may be used. Further, nine piezoelectric bodies 21 are provided, but the required number may be used, and any number may be used as long as it is one or more.

(Embodiment 3) Embodiment 3 of the present invention will be described below with reference to the drawings. FIG. 13 is a sectional view of the ultrasonic transducer of the third embodiment. Reference numeral 25 is an ultrasonic transducer, 26 is a piezoelectric body, 27 is a case, 29 is a matching layer, and 30 is a back cover. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 5 is that the damping body 27 is provided on the side surface of the inner wall of the case 27. The operation principle is the same as that of the first embodiment, and therefore will be omitted.

For example, a damping body 27 made of a stainless steel ring having a thickness of 0.3 mm and a width of 2.5 mm is adhered and fixed to the side surface of the inner wall of the case 28. Since the characteristics of the piezoelectric body 26 deteriorate when it comes into contact with the vibration damper 28, the piezoelectric body 26 and the vibration damper 27 are configured so as not to contact each other. The matching layer 23 and the back lid 30 are attached to form the ultrasonic transducer 25. Piezoelectric body 26
The resonance frequency of the unnecessary vibration mode is about 2 as shown in Fig. 8.
It is 00 kHz. Since the damping body 27 is adhered to the case 28, the mass increases, and the resonance frequency shifts to a lower frequency side than 200 kHz. Further, since the rigidity is improved, it becomes difficult to vibrate.

In the experiment in which the fluctuation of the zero point due to the temperature change was measured by the ultrasonic flowmeter using the ultrasonic transducer 25 having the above-mentioned structure, the result substantially equal to that of FIG. 11 of the first embodiment was obtained.
As described above, even if the piezoelectric body 26 has an unnecessary vibration mode of 200 kHz, the case 28 is provided with the vibration damping body 27 made of a rigid body so that the resonance frequency is different from the frequency of the unnecessary vibration mode of the piezoelectric body 26. For example, it can be seen that the zero point is stable regardless of temperature changes. Furthermore, since the vibration damper 27 is contained in the case 28, it hardly touches the non-measuring fluid directly, so that corrosion due to the non-measuring fluid can be prevented and long-term reliability can be improved.

In the third embodiment, the damping body 27 has a thickness of 0.
Although the ring made of stainless steel has a width of 3 mm and a width of 2.5 mm, the size, material and shape may be changed, and a plurality of rods or plates may be used. Further, although the damping body 27 is fixed to the side surface of the inner wall of the case 28 by adhesion, it may be fixed by means other than adhesion,
It may be provided on the side surface of the outer wall.

(Embodiment 4) Hereinafter, Embodiment 4 of the present invention will be described with reference to the drawings. FIG. 14 is a sectional view of the ultrasonic transducer of the fourth embodiment. Reference numeral 31 is an ultrasonic transducer, 32 is a piezoelectric body, 34 is a case, 35 is a matching layer, and 36 is a back cover. The above is the same as the configuration of FIG. The difference from the configuration of FIG. 5 is that the damping body 33 is provided on the side surface of the outer wall of the case 34. The operation principle is the same as that of the first embodiment, and therefore will be omitted.

For example, polyimide having a thickness of 50 μm and 25
A Kapton tape made of a silicon-based adhesive having a thickness of μm is used as the vibration damper 33. Since the silicone-based adhesive hardly changes in hardness even at a low temperature, it can be used as an elastic body in a wide temperature range. In addition, the polyimide has a function of increasing the mass of the vibration damper 33 and increasing the vibration damping effect. The piezoelectric body 32 and the matching layer 35 are adhered to the case 34, and the back cover 3
After the 6 is electrically welded, a Kapton tape is wound around the outer wall side surface of the case 34 several times to form the damping body 33. It was confirmed that the resonance of the ultrasonic oscillator 31 near 200 kHz was slightly weakened by providing the vibration damper 33. It is considered that this is because the vibration damping body 33, which is an elastic body, absorbs and loses the vibration energy of the case 34 to reduce the mechanical Q.

In the experiment in which the variation of the zero point due to the temperature change was measured by the ultrasonic flowmeter using the ultrasonic transducer 31 having the above-mentioned configuration, the result almost equal to that of FIG. 11 of Example 1 was obtained.
As described above, even if the piezoelectric body 32 and the case 34 have an unnecessary vibration mode of 200 kHz, if the vibration damping body 33 made of an elastic body is provided in the case 34 to weaken the resonance of the ultrasonic vibrator 31, the temperature change can be suppressed. It can be seen that the zero point is stable without dependence. Further, since the vibration control body 33 is very thin, the stability of the zero point can be improved without making the ultrasonic transducer 31 too large.

In the fourth embodiment, the damping body 33 is a Kapton tape made of polyimide and a silicone adhesive for the case 3
The tape is not limited to the Kapton tape, but a tubular or ring-shaped rubber molded product may be fitted into the outer wall or inner wall of the case 33, or the outer wall or inner wall of the case 34 may be covered with rubber. Alternatively, it may be configured by applying a damping paint or the like.

(Fifth Embodiment) A fifth embodiment of the present invention will be described below with reference to the drawings. FIG. 15 is a sectional view of the ultrasonic transducer of the fifth embodiment. 37 is an ultrasonic oscillator, 38 is a piezoelectric body, 39 is a case, 41 is a matching layer, and 42 is a back cover. The above is the same as the configuration of FIG. 5 is different from the configuration in FIG. 5 in that a bent portion 40 concentric with the top portion is provided on the side wall of the case 39 to enhance the rigidity of the case 39. The operation principle is the same as that of the first embodiment, and therefore will be omitted.

A case 39 having a top portion is molded from a stainless plate having a thickness of 0.2 mm. At this time, the side wall is heavenly
Simultaneously molding the parts and concentric bent portion 40.
The ultrasonic body 37 is assembled by adhesively fixing the piezoelectric body 38 on the inner wall side of the top portion and the matching layer 41 on the outer wall side and electrically welding the back lid 42. The case 39 has almost the same structure as the case 13 of the first embodiment, but since the bent portion 40 is provided, the rigidity is increased and the side wall portion is less likely to vibrate. Further, the resonance frequency of the case 39 shifts to a higher frequency side than 200 kHz, and becomes a frequency different from the frequency of the unnecessary vibration mode of the piezoelectric body 38. As described above, even if the piezoelectric body 38 has an unnecessary vibration mode of 200 kHz, if the bending portion 40 is provided to increase the rigidity of the case 39, parts such as a vibration suppressor can be attached to the case 39 or the size thereof can be increased. Even if it is not changed, a stable zero point that does not depend on temperature change can be easily obtained.

In the fifth embodiment, the bent portion 40 is concentrically formed with the top portion, but the bent portion 40 may be provided in two or more places. For example, as shown in FIG.
A bead 43 or a bent portion 44 may be provided in the vertical direction as shown in FIG. Further, when the piezoelectric body is, for example, a quadrangle, the direction of the piezoelectric body contained in the case can be understood by performing a molding process so that the top portion 45 has a shape similar to a quadrangle as shown in FIG. Easy to install. Needless to say, when the piezoelectric body is a polygon other than a quadrangle, at least the shape of the top part may be changed according to the shape of the piezoelectric body.

Although the case is made of stainless steel in Examples 1, 3 and 5, any material that can be used in the non-measuring fluid may be used. Although the case has a thickness of 0.2 mm, it may be thicker or thinner than this thickness, and it is not necessary to make the thickness of the entire case the same. Also, the operating frequency of the piezoelectric body was set to 500 kHz and the unnecessary vibration frequency was set to 200 kHz,
It goes without saying that the used frequency and the unnecessary vibration frequency change depending on the shape of the piezoelectric body used and the vibration mode.

As described above, according to each embodiment, the following effects are obtained.
Is obtained.

The first ultrasonic transducer has an electrical signal and a mechanical
A piezoelectric body that converts vibrations to each other and a case on the outside of the piezoelectric body.
And a matching layer, wherein the piezoelectric body is the ceiling of the case.
Is fixed to the inner wall side of the case, and the matching layer is the outer wall of the case.
Is fixed to the side and the resonance frequency of the unwanted vibration mode of the piezoelectric body
The number and the resonance frequency of the case are different.
The effect of unnecessary vibration mode is due to the ultrasonic transducer
It is possible to improve the stability of the zero point due to temperature changes.
Wear.

The second ultrasonic transducer is the ultrasonic wave of the first form.
In a wave oscillator, the piezoelectric body vibrates longitudinally and spreads
Resonance frequency of longitudinal vibration or resonance of spreading vibration
The frequency is set to the frequency of the unnecessary vibration mode.
Therefore, it is possible to improve the stability of the zero point due to temperature changes.
it can.

The ultrasonic transducer of the third form is the same as that of the first form.
In the case of the ultrasonic flowmeter, the inner wall side or outer wall side of the case
Since the vibration damper is fixed to the surface, the effect of unnecessary vibration modes is warmed.
It is possible to improve the stability of the zero point due to
It

The fourth ultrasonic transducer is the ultrasonic wave of the third form.
In the wave flow meter, the damping body is configured to consist of a rigid body.
Therefore, the effect of unwanted vibration mode can be reduced and
The stability of the zero point can be improved.

The fifth ultrasonic transducer is the ultrasonic wave of the third form.
In the wave flowmeter, the damping body is configured to be an elastic body.
Therefore, the effect of unwanted vibration mode can be reduced and
The stability of the zero point can be improved.

The sixth ultrasonic transducer is the ultrasonic wave of the first form.
The wave flow meter has a bent part on the side wall of the case.
Therefore, the effect of unwanted vibration mode can be reduced and
The stability of the zero point can be improved.

The seventh ultrasonic flowmeter is the ultrasonic wave of the first form.
In wave flow meters, the top of the case resembles the shape of a piezoelectric body
The shape makes it possible to see the direction of the piezoelectric body.
Easy installation to ultrasonic flowmeter.

In the eighth ultrasonic flowmeter, the fluid to be measured flows.
Flow rate measuring unit and the ultrasonic wave installed in this flow rate measuring unit.
Any one of the first to seventh ultrasonic transducers for receiving
And a drive circuit for driving one of the ultrasonic transducers, and
One of the above ultrasonic transducers is connected to detect ultrasonic pulses.
The reception detection circuit and the propagation time of the ultrasonic pulse
Timer for controlling the drive circuit and the timer for controlling the timer.
The flow rate is calculated from the control unit and the output of the timer.
Since it is an ultrasonic flowmeter equipped with a calculation unit that
The influence of modes can be reduced and the stability of the zero point due to temperature changes
Can be improved.

[0053]

As is apparent from the above description, the ultrasonic transducer of the present invention has the following advantages.

The first ultrasonic transducer has an electrical signal and a mechanical signal.
A piezoelectric body that converts vibrations to each other and a case on the outside of the piezoelectric body.
And a matching layer, wherein the piezoelectric body is the ceiling of the case.
Is fixed to the inner wall side of the case, and the matching layer is the outer wall of the case.
Is fixed to the side and the resonance frequency of the unwanted vibration mode of the piezoelectric body
The number and the resonance frequency of the case are different.
The effect of unnecessary vibration mode is due to the ultrasonic transducer
The stability of the zero point due to temperature changes can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic flowmeter according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram calculated when the frequency difference df2 is 0 kHz in the same flowmeter.

FIG. 3 is a characteristic diagram calculated for the same flowmeter when the frequency difference df2 is 1 kHz.

FIG. 4 is a characteristic diagram calculated when the frequency difference df2 is 5 kHz in the same flowmeter.

FIG. 5 is a sectional view of an ultrasonic transducer in the same flow meter.

FIG. 6 is a sectional view of an ultrasonic transducer in the same flow meter.

FIG. 7 is an external perspective view of a piezoelectric body (vertical and horizontal grooves) in the same flow meter.

FIG. 8 is an impedance characteristic diagram of a piezoelectric body (vertical groove) in the same flowmeter.

FIG. 9 is an impedance characteristic diagram of a piezoelectric body (longitudinal groove) in the same flowmeter.

FIG. 10 is a characteristic diagram of the same flowmeter measured by using a piezoelectric material having vertical grooves.

FIG. 11 is a characteristic diagram measured using a piezoelectric body having vertical and horizontal grooves in the same flow meter.

FIG. 12 is a sectional view of an ultrasonic transducer according to a second embodiment of the present invention.

FIG. 13 is a sectional view of an ultrasonic transducer according to a third embodiment of the present invention.

FIG. 14 is a sectional view of an ultrasonic transducer according to a fourth embodiment of the present invention.

FIG. 15 is a sectional view of an ultrasonic transducer according to a fifth embodiment of the present invention.

FIG. 16 is a sectional view of Modification 1 of the ultrasonic transducer.

FIG. 17 is a side view of Modification 2 of the ultrasonic transducer.

FIG. 18 is an external view of Modification 3 of the ultrasonic transducer.

[Explanation of symbols]

1 Flow rate measurement unit 2, 3, 20, 25, 31, 37 Ultrasonic transducer 5 drive circuit 7 Reception detection circuit 8 timer 9 Operation part 10 Control unit 12, 21, 26, 32, 38 Piezoelectric body 13, 22, 28, 34, 39 cases 27, 33 damping body

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04R 17/00 330 H04R 17/00 330Y (72) Inventor Toshiharu Sato 1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (56) References Japanese National Publication No. 9-511570 (JP, A) International Publication 97/21985 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01F 1 / 00-9 / 02 H04R 1/44 H04R 17/00

Claims (8)

(57) [Claims] 1. A case having a top and a side wall, and the top.
Fixed to the inner wall side of the machine to convert electrical signals and mechanical vibrations to each other
And a matching layer fixed to the outer wall side of the top part
The resonance frequency of the unnecessary vibration mode of the piezoelectric body and
Ultrasonic vibration with different resonance frequencies
Child. 2. A resonance frequency or a longitudinal vibration of longitudinal vibration of a piezoelectric body.
Claim the moving resonance frequency as the frequency of the unwanted vibration mode
Item 2. The ultrasonic transducer according to item 1. 3. A damping body is provided on the inner wall side surface or the outer wall side surface of the case.
The ultrasonic transducer according to claim 1, which is fixed. 4. The ultrasonic sound as claimed in claim 3, wherein the damping body is a rigid body.
Wave flow meter. 5. The super according to claim 3, wherein the vibration damping body is made of an elastic body.
Sonic flow meter. 6. A case in which a bent portion is provided on a side wall portion of the case.
Item 2. The ultrasonic flowmeter according to item 1. 7. The top of the case has a shape similar to that of a piezoelectric body.
The ultrasonic transducer according to claim 1, which has a shape of a circle. 8. A flow rate measuring section through which a fluid to be measured flows and this flow
An ultrasonic wave is transmitted and received in the quantity measuring unit.
7. A pair of ultrasonic transducers according to any one of 7 and one of
A drive circuit for driving the ultrasonic transducer, and the other ultrasonic transducer
Reception detection that is connected to an ultrasonic transducer and detects ultrasonic pulses
Circuit and timer for measuring the propagation time of the ultrasonic pulse
A control unit for controlling the drive circuit and the timer; and an operation unit for calculating the flow rate from the output of the timer.
Ultrasonic flowmeter with and .