JP4385597B2 - Ultrasonic transducer and ultrasonic flowmeter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer that transmits and receives an ultrasonic pulse, and an ultrasonic flowmeter that measures a flow rate of a gas or a liquid using the ultrasonic transducer.
[0002]
[Prior art]
A conventional ultrasonic transducer has a configuration as shown in FIG. That is, a piezoelectric body 22 is provided in the cap-shaped conductive case 21.
[0003]
The upper electrode surface of the piezoelectric body 22 is electrically fixed to the lower surface of the top wall of the case 21 by means such as adhesion, while the acoustic matching layer 23 is attached to the upper surface of the top wall.
[0004]
The lower open portion of the cap-shaped case 21 is closed by a terminal plate 25 fixed to the flange 24 by means such as welding, and the first and second external electrode terminal portions 26 and 27 are connected to the terminal plate 25. Has been deployed.
[0005]
The first external electrode terminal portion 26 is electrically connected to the terminal plate 25. On the other hand, the second external electrode terminal portion 27 includes a large-diameter portion 29 held on the terminal plate 25 via an electrical insulating material 28, and a conductor 30 having elasticity.
[0006]
That is, the second external electrode terminal portion 27 is sandwiched between the lower electrode surface of the piezoelectric body 22 and the terminal plate 25 (see, for example, Patent Document 1).
[0007]
[Patent Document 1]
JP 2001-50785 (page 3-6, FIG. 8)
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional one, the clamping force between the second external electrode terminal portion 27 and the piezoelectric body 22, in other words, the pressure contact force of the second external electrode terminal portion 27 against the piezoelectric body 22 is the same as that of the case 21 and the terminal plate. It was uniquely determined by the size of 25.
[0009]
Therefore, the pressure contact force of the second external electrode terminal portion 27 with respect to the piezoelectric body 22, that is, the contact resistance is likely to vary, and there is a problem that an unstable element is generated in the performance as the ultrasonic transducer.
[0010]
An object of the present invention is to solve such a conventional problem, and to stabilize the performance as an ultrasonic transducer and to provide an ultrasonic flowmeter with high measurement accuracy.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a cap-like conductive case in which one electrode surface side of the piezoelectric body is fixed to the inner surface of the top portion and the lower surface of the acoustic matching layer is fixed to the outer surface of the top portion with an adhesive. A terminal plate fixed to a flange portion formed on the lower open side of the case, a first external electrode terminal provided directly on the terminal plate, and an insulating through hole in the terminal plate. A second external electrode terminal connected to the other electrode surface side of the piezoelectric body, and the second external electrode terminal has a back portion held by an electrical insulating material that closes the hole of the terminal plate. An electrode terminal, and a conductor interposed between the electrode terminal and the other electrode surface of the piezoelectric body, and sandwiched between the electric insulating material and the other electrode surface of the piezoelectric body. Furthermore, it is paired with the inner peripheral side base of the flange in the case On the upper surface portion of the terminal plate to form a clearance space to allow deformation of the inner peripheral side base of the flange, the deformation amount of the inner peripheral side base of the flange relative to the clearance space, the other of the piezoelectric The contact pressure between the electrode surface and the conductor of the second external electrode terminal is adjusted , and the electrical connection between the second external electrode terminal portion and the piezoelectric body can be ensured.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a cap-like conductive case in which one electrode surface side of the piezoelectric body is fixed to the inner surface of the top portion and the lower surface of the acoustic matching layer is fixed to the outer surface of the top portion with an adhesive, and a lower portion of the case. A terminal plate fixed to a flange formed on the open side, a first external electrode terminal provided directly on the terminal plate, and an insulating penetrating hole provided in the terminal plate; A second external electrode terminal connected to the electrode surface side, the second external electrode terminal having an electrode terminal whose back is held by an electrical insulating material that closes the hole of the terminal plate; and It is composed of a conductor interposed between the electrode terminal and the other electrode surface of the piezoelectric body, and is configured to be sandwiched between the electrical insulating material and the other electrode surface of the piezoelectric body, Upper surface part of terminal board corresponding to inner peripheral side base of flange in case Forms a clearance space to allow deformation of the inner peripheral side base of the flange, the deformation amount of the inner peripheral side base of the flange relative to the clearance space, the other electrode surface and the second of the piezoelectric The contact pressure of the external electrode terminal with the conductor is adjusted , and the electrical connection between the second external electrode terminal portion and the piezoelectric body can be ensured .
[0013]
And by arranging such an ultrasonic transducer on the downstream side of the fluid passage and calculating the flow rate based on the ultrasonic propagation time, it is possible to measure the fluid flow rate with high accuracy.
[0014]
【Example】
Embodiments will be described below with reference to the accompanying drawings.
[0015]
In FIG. 1, a flow rate measuring unit 1 is a flow rate measuring unit that measures the flow rate of an object to be measured flowing through a fluid flow path 2, and a pair of ultrasonic transducers 3 and 4 are arranged.
[0016]
The ultrasonic wave propagation time during which the ultrasonic wave propagates between the ultrasonic transducers 3 and 4 is measured by the measurement circuit 5 and is output to the flow rate calculation circuit 6 as a signal. The flow rate calculation unit 6 obtains a flow rate based on the signal.
[0017]
The temporary operation of the ultrasonic flowmeter will be described. Let L be the distance of a straight line connecting the centers of the ultrasonic transducers 3 and 4, and let θ be the angle between this straight line and the longitudinal direction of the flow path 1 that is the direction in which the object to be measured flows.
[0018]
Let C be the velocity at which ultrasonic waves are transmitted through a stationary fluid, and V be the flow velocity of the fluid flowing through the flow path 1.
[0019]
The flow rate of the fluid flowing through the flow path 2 is measured by the ultrasonic transducer 3 disposed on the upstream side with respect to the flow path 2 and the ultrasonic transducer 4 disposed on the downstream side.
[0020]
First, ultrasonic waves are transmitted from the ultrasonic transducer 3. The transmitted ultrasonic wave is obliquely cut through the flow path 2 and received by the ultrasonic transducer 4. The ultrasonic propagation time t1 at that time is
t1 = L / (C + V cos θ)
Indicated by Next, an ultrasonic wave is transmitted from the ultrasonic transducer 4. The transmitted ultrasonic wave is obliquely cut through the flow path 2 and received by the ultrasonic transducer 3. The ultrasonic propagation time t2 at that time is
t2 = L / (C−Vcos θ)
Indicated by Since the sound speed C of the fluid changes depending on the measurement environment such as temperature, if the sound speed C of the fluid is deleted from the equations t1 and t2,
V = (1 / t1-1 / t2) L / 2 cos θ
The following equation is obtained. From this equation, the flow velocity V of the fluid is required since L and θ are known. In order to accurately obtain V, it is necessary to accurately measure t1 and t2, so it is necessary to equalize the directivity of the ultrasonic waves. Further, when the flow rate is Q, the cross-sectional area of the flow path 1 is S, and the correction coefficient is K, the flow rate Q can be obtained by an arithmetic expression of Q = KSV.
[0021]
In the ultrasonic flow meter, the flow rate is calculated from the calculation formula by the flow rate calculation circuit 6 based on the signal related to the ultrasonic propagation time output from the measurement circuit 5.
[0022]
Details of the ultrasonic transducers 3 and 4 will be described in detail below with reference to FIGS.
[0023]
In the figure, the acoustic matching layer 8 is fixed to the upper surface of the top wall of the case 7 and the upper electrode surface of the piezoelectric body 9 is fixed to the lower surface of the top wall with an adhesive.
[0024]
The case 7 is made of a conductive material, has a cap shape as a whole, and a flange 10 extends outward from the lower opening.
[0025]
The conductive terminal board 11 is disposed so as to close the lower open portion of the case 7 and is integrated with the case 7 by fixing its peripheral edge to the flange 10 by means such as welding.
[0026]
The terminal plate 11 is provided with first and second external electrode terminal portions 12 and 13.
[0027]
The first external electrode terminal portion 12 is directly connected to the outer peripheral portion of the terminal plate 11, and the second external electrode terminal portion 13 is connected to the lower electrode surface of the piezoelectric body 9 through the conductor 14. .
[0028]
That is, the second external electrode terminal portion 13 is composed of an electrode terminal 15 and a conductor 14, and the conductor 14 is arranged at the center of an elastic material 16 such as silicon rubber. is doing.
[0029]
The second external electrode terminal portion 13 passes through a hole 18 formed in the terminal plate 11, and the back portion is closed with an electrical insulating material 19 such as glass.
[0030]
In other words, the second external electrode terminal portion 13 is sandwiched between the piezoelectric body 9 and the terminal plate 11 by an electric insulating material 19, and the connection with the piezoelectric body 9 is the clamping force, in other words. It depends on the pressure contact force in a unified manner.
[0031]
An inert gas such as nitrogen gas is sealed in the sealed space 20 in the case 7 closed by the terminal plate 11 or the like.
[0032]
And between the upper surface of the outer peripheral portion of the terminal plate 11 and the base end portion of the flange 10 of the case 7, the pressure contact force of the second external electrode terminal portion 13 against the piezoelectric body 9 (by the piezoelectric body 9 and the terminal plate 11). A play space S as an adjusting means for adjusting the clamping force of the second external electrode terminal portion 13 is formed by a thinning.
[0033]
In the above configuration, the pressure contact force of the second external electrode terminal portion 13 with respect to the piezoelectric body 9 can be adjusted by the positional relationship between the upper surface of the outer peripheral portion of the terminal plate 11 and the flange 10 of the case 7.
[0034]
That is, compared with the thing of FIG. 2, the direction which deform | transformed and faced the base end of the flange 10 in the case 7 in the part of the play space S like FIG.
[0035]
That is, the substantial height of the case 7 is lowered by the deformation, and the pressure contact force is increased accordingly.
[0036]
Therefore, in practice, if the pressure contact force is adjusted while measuring the electrical resistance between the first and second external electrode terminal portions 12 and 13, an ultrasonic transducer with no variation in performance is obtained. An ultrasonic flowmeter capable of accurate flow measurement can be obtained.
[0037]
The adjusting means is not limited to the play space S. In short, any adjustment is possible as long as the substantial height of the case 7 can be adjusted. It is also possible to adjust the position of the terminal board 11 by adjusting the position of the terminal board 11 by changing the degree of bending, or by attaching the electrical insulating material 19 to the terminal board 11 using a screw system.
[0038]
Thus, according to the structure of an Example, it becomes possible to adjust, measuring a resistance value so that the conduction resistance of an ultrasonic transducer may become fixed, and a stable resistance value can be ensured. Therefore, it is possible to provide a highly reliable ultrasonic transducer and an ultrasonic flowmeter capable of measuring a flow rate with higher accuracy by eliminating variations in the transmission sensitivity of ultrasonic waves and preventing a decrease in transmission / reception sensitivity.
[0039]
Since the adjustment means is configured to change a part of the case, the resistance value can be adjusted after the assembly is completed, and the performance can be guaranteed as a final finished product.
[0040]
【The invention's effect】
As described above, according to the present invention, there is no variation in performance, and an ultrasonic transducer with high accuracy can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an ultrasonic flowmeter in an embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing an ultrasonic transducer in the same embodiment. Longitudinal sectional view showing an ultrasonic transducer [Fig. 4] Cross sectional view showing a conventional ultrasonic transducer [Explanation of symbols]
2 Fluid passage 3, 4 Ultrasonic transducer 7 Case 9 Piezoelectric body 11 Terminal plate 12, 13 External electrode terminal section 14 Conductor 15 Electrode terminal 19 Electrical insulation material S Play space

Claims (2)

One electrode surface side of the piezoelectric body is attached to the inner surface of the top part, and the lower surface of the acoustic matching layer is fixed to the outer surface of the top part with an adhesive, and the lower open part side of this case A terminal plate fixed to the formed outward flange portion , a first external electrode terminal provided directly on the terminal plate, and an insulating penetrating hole provided in the terminal plate; A second external electrode terminal connected to the electrode surface side, the second external electrode terminal having an electrode terminal whose back is held by an electrical insulating material that closes the hole of the terminal plate; and It is composed of a conductor interposed between the electrode terminal and the other electrode surface of the piezoelectric body, and is configured to be sandwiched between the electrical insulating material and the other electrode surface of the piezoelectric body, On the upper surface part of the terminal board corresponding to the inner peripheral side base of the flange in the case , To form a clearance space to allow deformation of the inner peripheral side base of the flange, said by deformation of the inner peripheral side base of the flange against the play space, the second outer and the other electrode surface of the piezoelectric An ultrasonic transducer that adjusts the contact pressure of the electrode terminal with the conductor .   An ultrasonic flowmeter in which the ultrasonic transducer according to claim 1 is disposed above and downstream of a fluid passage so as to calculate a flow rate based on an ultrasonic propagation time.

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