JP4106499B2 - Ultrasonic detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic detector used for a flow meter and the like.
[0002]
[Prior art]
For example, an ultrasonic detector used as a flowmeter is generally a disk-shaped ultrasonic transducer (piezoelectric element) in a hole bottom 2a of a bottomed cylindrical holder 2 as shown by reference numeral 1 in FIG. 3), and if necessary, an acoustic bonding agent 4 is interposed between the ultrasonic transducer 3 and the hole bottom 2a of the holder 2, and the holding plate 5 and the opening of the holder 2 that are placed on the ultrasonic transducer 3 are disposed. A spring member (here, a disc spring) 7 is interposed between the lid body 6 fitted and fixed thereto, and the ultrasonic vibrator 3 is pressed against the hole bottom 2 a of the holder 2 by the spring force of the spring member 7. The structure is fixed (see, for example, JP-A-5-231888).
[0003]
Such ultrasonic detectors 1 are usually press-fitted and fixed in through-holes 8a that are provided so as to face the tube wall of the flow meter body (tube body) 8, and one of the ultrasonic detectors 1 A transmission circuit 10 is connected to one ultrasonic transducer 3 via a lead wire 9, and a reception circuit is connected to the ultrasonic transducer of the other ultrasonic detector (not shown here) via a lead wire. They are connected and put into practical use. In this case, when the end face of the holder 2, that is, the bottom plate 11 is exposed in the flow path of the flow meter main body 8 interposed in the pipe (illustrated), and the ultrasonic vibrator 3 vibrates by energization from the oscillation circuit 9. The vibration is transmitted to the fluid flowing in the flow meter main body 8 via the acoustic bonding agent 4 and the bottom plate 11 of the holder 2, and therefore the bottom plate 11 of the holder 2 functions as a vibration plate.
[0004]
[Problems to be solved by the invention]
By the way, recently, as the holder 2, since it is light in weight and low in manufacturing cost, for example, a holder made of a resin such as tetrafluoroethylene / perfluoroalkoxyethylene (PFA) has been widely used. .
However, such a resin holder 2 generally has a slight gas permeability due to the resin characteristics. Therefore, when the fluid to be measured is a gas or a liquid that is easily vaporized. The gas penetrates between the bottom plate (vibrating plate) 11 of the holder 2 and the ultrasonic transducer 3, and bubbles are generated in the ultrasonic bonding agent 4 to deteriorate the ultrasonic transmission characteristics. Is a corrosive fluid, the corrosive gas penetrates into the holder and the ultrasonic vibrator 3 is corroded, and in either case, the detection accuracy is greatly deteriorated.
[0005]
As a countermeasure against this, there is an idea of reducing the gas permeation by forming the bottom plate 11 of the holder 2 to be thick, but in this case, since the load applied to the ultrasonic transducer 3 becomes large, sufficient vibration ( In order to generate (ultrasonic), a large electric power must be applied, resulting in a low-efficiency detector. In addition, there is a way of thinking that a non-gas permeable shielding plate is interposed between the vibration plate 11 and the ultrasonic vibrator 3, but in this case, both the processing accuracy and assembly accuracy, deformation of the vibration plate 11, etc. Insufficient adhesion is likely to be insufficient, and deterioration of ultrasonic transmission characteristics is unavoidable.
[0006]
The present invention has been made in view of the above-described problems. The object of the present invention is to make gas intrusion into the holder without forming a thick diaphragm of the holder or using a special shielding plate. It is an object of the present invention to provide an ultrasonic detector that reliably prevents the occurrence of defects and contributes greatly to the improvement of durability and reliability.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention is made of a bottomed cylindrical resin made of ethylene tetrafluoride / perfluoroalkoxyethylene, which is respectively fixed in a through-hole formed so as to face the tube wall of the flowmeter body . In an ultrasonic detector in which an ultrasonic vibrator is closely fixed to the hole bottom of the holder and the bottom plate of the holder is used as a vibration plate, a non-gas permeable metal vapor deposition film is laminated on the surface of the holder. To do.
In the ultrasonic detector configured as described above, the non-gas permeable metal vapor deposited film formed on the surface of the holder prevents gas from entering the resin holder.
In the present invention, the surface of the holder on which the metal vapor-deposited film is laminated can be formed on at least the inner bottom surface or end surface of the holder and further on the inner and outer peripheral surfaces of the holder holes.
[0008]
In the present invention, the metal deposited film, particularly but not ask the material, as much as possible ultrasound absorption capacity little material, such as zirconium, not to want to choose a metal such as gold.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0010]
FIG. 1 and FIG. 2 show the main structure of a flow meter including an ultrasonic detector as a first embodiment of the present invention. Since the basic structure of the ultrasonic detector and the flowmeter is the same as that shown in FIG. 4, the same parts as those shown in FIG. A duplicate description will be omitted. A feature of the first embodiment is that a thin film 12 is previously formed in a predetermined thickness on the surface (inner bottom surface) of the hole bottom 2a of the holder 2, and the acoustic bonding is performed on the thin film 12. The ultrasonic transducer 3 is pressed and fixed via the agent 4.
[0011]
In the first embodiment, the holder 2 is made of a resin excellent in chemical resistance, for example, tetrafluoroethylene / perfluoroalkoxyethylene resin (PFA). Like other general-purpose plastics, It has a slight gas permeability. On the other hand, the thin film 12 is made of a metal vapor-deposited film such as zirconium (Zr) or gold (Au), and is completely impermeable to gas.
[0012]
In the ultrasonic detector 1 configured as described above, when the ultrasonic vibrator 3 vibrates by energization from the oscillation circuit 9, the vibration is transmitted through the acoustic bonding agent 4 and the bottom plate 11 of the holder 2 as in the conventional case. Is transmitted to the fluid flowing in the flow meter main body 8, the propagation signal is received by an ultrasonic detector (not shown) on the receiving side and taken into the receiving circuit, and the flow rate is calculated by an arithmetic circuit (not shown). . At this time, if the fluid flowing in the flow meter main body 8 is a gas or a liquid that is easily gasified, the gas or vaporized gas tends to enter the holder 2 through the bottom plate (vibration plate) 11 of the holder 2 having permeability. However, in the first embodiment, since the non-gas permeable thin film 12 is formed on the inner bottom surface of the holder 2, the gas to enter the holder 2 is penetrated by the thin film 12. As a result, the gas does not stay between the bottom plate 11 of the holder 2 and the ultrasonic transducer 3, and the ultrasonic transmission characteristics are maintained well. In addition, since the gas intrusion into the holder 2 is prevented in this way, the ultrasonic vibrator 3 contacts the corrosive gas even if the fluid flowing in the flow meter body 8 is highly corrosive. The corrosion is also prevented.
[0013]
In the first embodiment, the thin film 12 is formed on the inner bottom surface of the holder 2, but instead, the thin film 12 is formed on the end surface (outer bottom surface) 2c of the holder 2. Anyway. Also in this case, since the thin film 12 prevents the gas from entering the holder 2, the same effects as those of the first embodiment can be obtained.
[0014]
FIG. 3 shows an ultrasonic detector as a second embodiment of the present invention. The feature of the second embodiment is that the range in which the non-gas permeable thin film 12 is formed is added to the surface (inner bottom surface) of the hole bottom 2a of the holder 2 in the first embodiment. The inner peripheral surface 2b is also enlarged.
That is, in the second embodiment, since the impermeable thin film 12 exists on the entire surface in the hole of the holder 2, the gas that tries to enter the inside through the peripheral wall of the holder 2 is also prevented from entering, The ultrasonic transducer 3 can be more reliably prevented from being corroded as well as the above-described good maintenance of the ultrasonic transmission characteristics.
[0015]
In the above-described embodiment, the thin film 12 is laminated on the inner sides 2a and 2b of the holder 2. However, the present invention is not limited to this, and a thin film is laminated on the outer side of the holder 2, that is, the end surface 2c and the outer peripheral surface 2d. Also good.
[0016]
【The invention's effect】
As described above, according to the ultrasonic detector of the present invention, the non-gas permeable metal vapor deposited film formed on the surface of the tetrafluoroethylene / perfluoroalkoxyethylene holder prevents gas intrusion into the holder. Therefore, measures such as forming a thick diaphragm for the holder or using a special shielding plate are not required, and it is possible to prevent a decrease in the efficiency of ultrasonic generation and a decrease in the transmission capability of ultrasonic waves. And durability reliability is remarkably improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the main structure of a flow meter including an ultrasonic detector according to a first embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view showing the ultrasonic detector as the first embodiment.
FIG. 3 is a cross-sectional view showing a structure of an ultrasonic detector as a second embodiment of the present invention.
FIG. 4 is a cross-sectional view showing the structure of a conventional ultrasonic detector.
[Explanation of symbols]
1 Ultrasonic detector 2 Holder 2a Holder bottom (inner bottom)
2b Holder inner peripheral surface 2c Holder end surface 2d Holder outer peripheral surface 3 Ultrasonic vibrator 4 Acoustic bonding agent 6 Lid 5 Press plate 7 Spring member 8 Flow meter body 11 Bottom plate of the holder (vibrating plate)
12 Thin film

Claims (1)

Ultrasonic transducers are attached to the bottom of a bottomed cylindrical resin holder made of ethylene tetrafluoride and perfluoroalkoxyethylene, fixed in through-holes that face the tube wall of the flow meter body. An ultrasonic detector which is fixed and uses a bottom plate of the holder as a vibration plate, wherein a non-gas permeable metal vapor deposition film is laminated on the surface of the holder.

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