JPH0350207B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention measures the velocity, volume, etc. of a liquid by emitting or receiving ultrasonic waves to or from a liquid flowing from one side to the other in a pipe or container. This relates to piezoelectric transducers used in

[Prior art] In an ultrasonic flowmeter, in order to reduce measurement errors due to changes in liquid temperature, etc., ultrasonic waves are emitted obliquely at a predetermined angle using a piezoelectric transducer attached to the top wall of a pipe or container, and the ultrasonic waves are It is configured to receive ultrasonic waves traveling through the liquid by piezoelectric transducers attached to the lower wall surface corresponding to the sound wave emission direction. By the way, since conventional general piezoelectric transducers have used ultrasonic transducers exhibiting thickness vibration or longitudinal vibration, they have been used as "wedges" with slopes that allow ultrasonic waves from such transducers to be emitted or received obliquely. The disadvantage was that it had to be used in combination with Furthermore, due to Poisson's ratio, such an ultrasonic transducer generates radial vibration or transverse vibration at the same time as thickness or longitudinal vibration, and this unnecessary vibration is transmitted through the wall surface of the tube or container and is received by the receiving transducer. , it acted as a nozzle for regular ultrasonic waves propagating in the liquid, worsening the S/N ratio.

[Problems to be Solved by the Invention] In order to solve the above problems, as disclosed in Japanese Patent Application No. 55-60513, which was proposed earlier than the present application, a single blind on the surface of a piezoelectric substrate is proposed. There is one in which a shaped electrode is formed and ultrasonic waves are emitted obliquely from this electrode.

This configuration will be explained with reference to FIGS. 1 and 2.

As shown in Figure 1, this elastic surface ultrasonic element has a structure in which interdigital electrodes y are formed by vapor deposition on the surface of a piezoelectric substrate x made in a rectangular shape using zirconate titanate, lithium niobate, etc. When a drive signal of a desired frequency is applied to the interdigital electrode y, surface acoustic waves f are generated that propagate on the surface of the piezoelectric substrate x from both sides of the electrode y.

Furthermore, when such an elastic surface ultrasound element is placed in a liquid W such as water as shown in FIG. 2, and a drive signal is applied to the interdigital electrode y, the surface acoustic wave is converted into a longitudinal wave, Ultrasonic wave s and piezoelectric substrate x
Proceeds through the liquid W obliquely to the horizontal line. The radiation angle θ of this ultrasonic wave is θ=cos ^-1 (V _c /f・
d) Expressed by the formula. In the formula, V _c is the speed of sound in the liquid,
f is the surface wave center frequency, and d is the electrode period.

The elastic surface ultrasound element including this interdigital electrode y has a wave transmitting function and also a wave receiving function for receiving the emitted ultrasonic wave. Therefore, in the case of a piezoelectric transducer for an ultrasonic flowmeter using this elastic surface ultrasonic element, two elastic surface ultrasonic elements for wave transmission and wave reception are connected to the upper wall surface of a pipe or container via a liquid. , and the lower wall surface so as to be oblique to each other in accordance with the emission angle of the ultrasonic waves, so as to measure the velocity, amount, etc. of the liquid.

However, in the case of a piezoelectric transducer using an elastic surface ultrasonic element with interdigital electrodes, it is necessary to use two elastic surface ultrasonic elements, one for transmitting waves and one for receiving waves, and the number of parts is large. However, there are disadvantages such as the electrical connection tends to become complicated and the application is limited.

The present invention aims to eliminate such drawbacks.

[Means for Solving the Problems] The present invention forms a plurality of interdigital electrodes at a certain distance on the surface of a piezoelectric substrate, one of the interdigital electrodes is used for wave transmission, and the other interdigital electrodes are used for wave transmission. for receiving waves, comprising an elastic surface ultrasonic element arranged so as to be in contact with a liquid in a pipe or a container, and a reflecting plate placed opposite to the elastic surface ultrasonic element with the liquid interposed therebetween. This is a piezoelectric transducer for an ultrasonic flowmeter, which is characterized by:

[Function] In the above configuration, the ultrasonic waves emitted in an oblique direction from the interdigital transducer are reflected on the inner wall of the tube or container or on the reflecting plate disposed on the inner wall, and are reflected on the piezoelectric substrate. It is captured by another wave-receiving interdigital electrode.
Then, the speed, amount, etc. of the liquid are detected. At this time, since the ultrasonic waves were captured using a reflector, tubes such as circular tubes that do not have a plate surface horizontal to the piezoelectric substrate,
This method can also be applied to tubes with rough surfaces and can be detected as accurately as possible.

[Example] Next, an example of the present invention will be described with reference to FIGS. 3 to 6.

3 and 4 show an elastic surface ultrasonic element 1, in which two interdigital electrodes 3a each consisting of a plurality of pairs of parallel arc-shaped conductors are mounted on the surface of a single rectangular piezoelectric substrate 2 made of lead zirconate titanate or the like. , 3b are formed at a certain distance apart.

When the interdigital electrodes 3a and 3b are constructed of parallel arc-shaped conductors, surface acoustic waves f (ultrasonic waves s) can be emitted in only one direction, as shown in an enlarged view in FIG. Therefore, the interdigital electrodes 3a, 3b
are arranged with the center of the arc inward so that the waves are transmitted and received inwardly.

This piezoelectric substrate 2 has input/output terminals 5a, 5
The electrodes 3a and 3b are attached to the outer surface of the closed end of a cylindrical holder 6 with a bottom extending through the holder 6 using an adhesive or the like, with the interdigital electrodes 3a and 3b facing outside. A flange 7 is provided around the rim of the open end of the holder 6 to be attached to a liquid feeding pipe or a liquid feeding container. The one interdigital electrode 3a is connected to the input terminal 5a for wave transmission via a thin metal wire 4b, and the other interdigital electrode 3
b is used for wave reception and is connected to the output terminal 5b via a thin metal wire 4b, and then the outer surface of the surface ultrasonic element 1 is coated with a protective layer 8, and is used as a wave transmitter/receiver.

The input terminal 5a is connected to an external high frequency oscillator O.
(see FIG. 6), and its drive signal is applied to the interdigital electrode 3a. Also, output terminal 5b
is connected to an external measuring circuit device M (see FIG. 6), and the electrical signal generated at the interdigital electrode 3b is taken out from the terminal 5b. The protective layer 8 electrically insulates and waterproofs the outer surface of the ultrasonic element 1, the exposed portions of the terminals 5, and the thin metal wires 4a and 4b, and serves to protect the ultrasonic waves from being emitted by the interdigital electrodes 3a and 3b. It is made of a material that has approximately the same acoustic impedance as the liquid so as not to interfere with reception.

As shown in FIG. 6, the piezoelectric transducer has an elastic surface ultrasonic element 1 attached to an opening S provided in the upper wall surface of a tube C or container carrying a liquid W so as to be in contact with the liquid, and A reflecting plate R is placed below the ultrasonic element 1 by immersing it in a liquid.

It can be said that this reflector R can be omitted by using the bottom surface of the tube C or the container, but there are various mounting options such as when the tube surface is not a plane parallel to the piezoelectric substrate 2, such as a circular tube, or when the surface is rough. Therefore, by placing this reflector R opposite to the surface ultrasonic element 1 via a liquid, the reflected waves can be reflected as described below without being affected by the shape of the tube, surface roughness, etc. It becomes possible to capture the image.

The operation of this embodiment will be explained.

As mentioned above, the high frequency oscillator O is connected to the output terminal 5a.
When the measurement circuits M are connected to the input terminals 5b and a drive signal of the desired frequency is applied by the oscillator O to the interdigital electrodes 3a of the ultrasonic element 11 via the input terminals 5a, the surface acoustic waves f become longitudinal waves. It is converted into an ultrasonic wave s and radiated inward at a required radiation angle θ. This ultrasonic wave s propagates diagonally across the liquid W, and is reflected by a reflection plate R disposed at a position facing the intermediate position between the interdigital electrodes 3a and 3b.
According to the law of reflection, the wave is refracted diagonally upward and returned to the piezoelectric substrate 2, and an electric signal is generated at the receiving interdigital electrode 3b, which is transmitted to the measuring circuit device M via the input terminal 5b.
The velocity, volume, etc. of the liquid are measured from the ultrasonic transmission time or frequency phase difference (Doppler frequency).

7 to 9 show a piezoelectric transducer according to a second embodiment of the present invention.

Here, as shown in FIGS. 7 and 8, on the surface of a rectangular piezoelectric substrate 12 as an elastic ultrasonic element 11,
One interdigital electrode 13a made up of a plurality of parallel conductors at the center, and two interdigital electrodes 13b made of a plurality of pairs of parallel arc-shaped conductors on both sides.
are formed at a certain distance from each other. Then, input terminal 15a and output terminal 15
b, 15b are pasted on the outer surface of the closed end of the holder 16, and the central interdigital electrode 13a is connected to the input terminal 15a for wave transmission via a thin metal wire 14a, and the interdigital electrodes 13b on both sides are attached to the outer surface of the closed end of the holder 16. , 13b for receiving waves, and the thin metal wire 1 is connected to the output terminals 15b, 15b.
4b and 14b and then covered with a protective layer 18.

Even in this configuration, as shown in FIG. 9, as in the first embodiment, the elastic surface ultrasonic element 11 is attached at the flange 17 so as to be in contact with the liquid, and a reflecting plate R is placed below the ultrasonic element 1 by immersing it in the liquid.

In this embodiment, the ultrasonic waves s emitted obliquely downward in two directions from the transmitting interdigital transducer 13a of the surface ultrasonic element 11 are respectively refracted obliquely upward by the reflecting plate R, and are refracted obliquely upward by the two receiving interdigital transducers. shaped electrode 13
b, 13b, the ultrasonic wave transmission time in the forward direction and the ultrasonic wave transmission time in the reverse direction relative to the flow of the liquid W are determined, and the velocity, amount, etc. of the liquid can be measured from these time relationships.

[Effects of the Invention] As described above, the present invention forms a plurality of interdigital electrodes at a certain distance on the surface of a piezoelectric substrate, one of which is used for wave transmission, and the other interdigital electrodes are used for wave transmission. For wave reception, an elastic surface ultrasonic element is configured using a common piezoelectric substrate, and the ultrasonic wave s is captured and reflected by a reflecting plate placed opposite to the elastic surface ultrasonic element via a liquid. has the following effects.

(a) It is economical because it only requires the application of a single elastic surface ultrasonic element.

(b) Since only a single elastic surface ultrasonic element needs to be wired, installation is simple, and it can be easily installed even in places where it was previously considered difficult to apply.

(c) Since interdigital electrodes are formed on the same piezoelectric substrate, an elastic surface ultrasonic element with wave transmitting and wave receiving functions can be manufactured extremely easily by using methods such as screen printing. .

(d) Ultrasonic waves can be captured by the reflector regardless of the shape of the tube, improving detection accuracy.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the action of the interdigital electrode y;
FIG. 2 is a longitudinal sectional side view showing the action of the interdigital electrode y in water. 3 to 6 show a first embodiment of the present invention, FIG. 3 is a plan view, FIG. 4 is a longitudinal side view, and FIG. 5 is an enlarged plan view of a comb-shaped electrode 3a made of parallel arc-shaped conductors. , FIG. 6 is a longitudinal sectional side view of the installed state. Furthermore, FIGS. 7 to 9 show a second embodiment of the present invention, in which FIG. 7 is a plan view, FIG. 8 is a vertical side view, and FIG. 9 is a vertical side view in an installed state. 1, 11: surface ultrasound element, 2, 21: piezoelectric substrate, 3a, 3b, 13a, 13b: interdigital electrode.

Claims (1)

[Claims] 1. A piezoelectric transducer that measures the velocity, volume, etc. of a liquid by emitting or receiving ultrasonic waves into a liquid flowing from one side to the other in a pipe or container, comprising: a piezoelectric substrate; A plurality of interdigital electrodes are formed on the surface at a certain distance apart, one of which is used for transmitting waves, and the other interdigital electrode is for receiving waves, so that it comes into contact with the liquid in the pipe or container. 1. A piezoelectric transducer for an ultrasonic flowmeter, comprising: an elastic surface ultrasonic element disposed in the elastic surface ultrasonic element; and a reflecting plate opposed to the elastic surface ultrasonic element with a liquid interposed therebetween. 2. An elastic surface ultrasonic element in which two interdigital electrodes are formed at a certain distance on the surface of a piezoelectric substrate, one of which is used for transmitting waves, and the other interdigital electrode is used for receiving waves. A piezoelectric transducer for an ultrasonic flowmeter according to claim 1, further comprising: 3. An elastic surface ultrasonic element in which three interdigital electrodes are formed at a certain distance on the surface of a piezoelectric substrate, the central interdigital electrode is used for transmitting waves, and the interdigital electrodes on both sides are used for receiving waves. A piezoelectric transducer for an ultrasonic flowmeter according to claim 1, further comprising: