JPS599518A - Ultrasonic wave current and flow meter - Google Patents

Abstract

PURPOSE:To make the leakage of an ultrasonic wave signal small and to perform highly accurate measurement even though fluid to be measured is a gas, by providing a gap between the side surface of an ultrasonic wave vibrator and the ultrasonic wave transducer-mounting surface of a measuring pipe. CONSTITUTION:An ultrasonic wave vibrator 11 is embedded and bonded in the tip of a packing material 12. The inner diameter of a case 14 is made to be larger than the outer diameter of the packing material 12 by about 1mm.. The base part side of the packing material 12 is bonded to the center of the bottom surface of the case 14. Therefore, a gap 17 is fomed between the side surface of the vibrator 11 and a transducer mounting surface and an element housing 2. Even though lateral vibration occurs in the vibrator 11, the lateral vibration is stopped by the gap 17, and only the small amount of it is propagated to the outside. The ultrasonic wave, which leaks to the housing 2 and a measuring pipe 1, is reduced to almost zero. Even though fluid to be measured is a gas, highly accurate measurement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a flowmeter using ultrasonic waves, and particularly to an ultrasonic flowmeter suitable for measuring the flow velocity and flow rate of gas.

[Technical background of the invention and its melting point]

2. Description of the Related Art Ultrasonic flowmeters that use fluid as a propagation medium for ultrasonic waves and measure the flow rate and flow rate of the fluid based on the propagation time have been widely used. The transducer section of such an ultrasonic flowmeter usually has a configuration as shown in FIG.

That is, an ultrasonic transducer 364 is disposed at two points in the measurement tube 1, and one ultrasonic transducer 364 passes through the measurement tube 1 as shown by the arrow 6. An ultrasonic signal is emitted into the flowing fluid as indicated by the arrow 6, and is received by the other opposing ultrasonic transducer 4.

The ultrasonic transducer 3.4 is as shown in FIG.
It is made of crystals and ceramics such as quartz, niobium oxide, lead zirconate, etc. that have an electrostrictive piezoelectric effect.
It is mainly composed of an ultrasonic transducer 11 with electrodes attached to both sides of the transponder.

The ultrasonic transducer 11 is embedded in a backing material 12 so that the ultrasonic waves radiated to the back surface are absorbed by the backing material 12. Additionally, a coating is provided on the ultrasonic transducer 11 for the purpose of acoustic matching to efficiently radiate ultrasonic waves into the fluid and to protect its surface from corrosive substances contained in the fluid. Material 13
is covered. The entire transformer 7'h user t:j is housed in a case 14 and fixed within the element housing 2 with screws 15.

Incidentally, the ultrasonic vibrator 11 uses vibration in the thickness direction, but in reality, it also vibrates in a direction perpendicular to y (ridge direction) at the same time as this thickness vibration. The degree of this lateral vibration is
Although it varies depending on the material used for the vibrator, it is about 10% to 1% of the thickness vibration. The reason why the vibrator 11 is embedded in the backing material 12 in FIG.
This is to reduce the leakage of ultrasonic signals to the measuring tube 1 through the tube 4. Such measures are important in measuring longevity. When the ultrasonic signal leaks, the leaked component repeats the propagation and reflection inside the transducer 2 and the measuring tube 1, and the ultrasonic signal is transmitted to one ultrasonic transducer 3 and propagated in the fluid. together with the other ultrasonic transducer 4
This is because the signal is received through the Niremento Uzing 2 and becomes noise when measuring the flow velocity and flow rate.

Conventionally, the fluid to be measured by such an ultrasonic flowmeter is mainly a liquid, and the acoustic impedance of the fluid to be measured is 3 to 1,5XlO', 9/8-m2, and that of ceramic or wood. (approximately 9/8-m to 3X10')/
It is 101a degrees. Furthermore, the amount of ultrasonic attenuation within the fluid to be measured is approximately 0.5 dB/crn, and the level of the ultrasonic signal radiated from the transducer is high, so the ultrasonic wave is transmitted to the element housing 2 through the case 14. It was sufficient to suppress the leakage of the sound wave signal to about -40 dB.

However, when the fluid to be measured is a gas such as breathing gas, the acoustic impedance of the gas is approximately 2×102 kg/S-m!
As you can see, as the acoustic matching between the ultrasonic transducer and the gas deteriorates, the amount of ultrasonic attenuation in the gas also decreases by 10 d.
Since the ultrasonic wave is as large as B/gn, the level of ultrasonic radiation in gas is significantly reduced compared to that in liquid, and is about −40 dB or less than that in liquid. Therefore, when the ultrasonic transducer 11 is embedded in the backing material 12 as shown in FIG. 2, the level of the leaked ultrasonic signal will increase unless the portion of the backing material 1B surrounding the side 5 of the transducer 11 is made large. The SA of the received ultrasonic signal becomes relatively large.
decreases significantly, making measurement difficult. Therefore, the ultrasonic transducer 3゜4 and the element housing 2
This will lead to an increase in the size of the 0 caliber. However, especially in small-diameter measuring tubes, as the diameter of the element housing 20 increases, the opening 7 of the element housing 20 also becomes larger, which causes turbulence in the fluid flow within the measuring tube 1 and causes measurement errors. . As described above, with conventional ultrasonic flowmeters, it is difficult to measure accurately when the fluid to be measured is gas.

[Purpose of the invention]

The purpose of this invention is to reduce the leakage of ultrasonic signals to other than the fluid to be measured, without increasing the size of the ultrasonic transducer, and to perform highly accurate measurements even when the fluid to be measured is gas. By providing a flow needle capable of ultrasonic flow rate.

[Summary of the invention]

This invention prevents the leakage of transverse vibrations that occur simultaneously with thickness vibrations of the ultrasonic vibrator by providing a gap between the side surface of the ultrasonic vibrator and the ultrasonic transducer mounting surface of the measuring tube. The ultrasonic vibrator emits only the ultrasonic signals necessary for measuring flow velocity and flow rate. That is, since the acoustic impedance of a gas is about 10-4 to 101 compared to that of a solid, if the side surfaces of the vibrator are made of gas, the impedance of the solid is the same.

The lateral vibration is 10% compared to when the king material is around the sides.
The transverse vibration of the vibrator is reduced by about -4 to 10-5, and the transverse vibration of the vibrator no longer leaks to the element housing or measurement tube.

〔Effect of the invention〕

According to this invention, leakage of ultrasonic signals that do not contribute to measurement into the element housing or measurement tube is effectively suppressed, so that only the ultrasonic signals necessary for measurement are emitted directly from the ultrasonic transducer into the fluid. can be propagated into the fluid S/1'J
It is possible to improve the This is particularly effective when the fluid to be measured is gas. Furthermore, according to the present invention, leakage of the transverse vibration of the ultrasonic transducer is prevented by providing only a small gap, so that the dimensions of the ultrasonic transducer and the diameter of the element housing do not become large. Therefore, the flow of fluid is not disturbed and measurement accuracy is improved.

[Embodiments of the invention]

FIG. 3 shows the configuration of an ultrasonic transducer section according to an embodiment of the present invention. In this example, the ultrasonic transducer 11 is not embedded in the backing 12, but simply has its back surface adhered onto the front end surface of the backing material 12. This vibrator 11
A coating material 13 is adhered or molded onto the surface other than the surface in contact with the backing material 12 . The coating 13 is typically 1/4 wavelength thick for acoustic matching purposes--so that the outer diameter of the coating 13 is equal to or slightly smaller than the outer diameter of the backing material 12. The inner diameter of the case 14 is slightly larger (about is) than the outer diameter of the measuring material 12.
A backing material 120 base side (vibrator 1
The end face (on the opposite side to 1) is fixed with adhesive.

Therefore, there is a gap 17 between the side surface of the coating material 13 and the case 14, in other words, between the side surface of the transducer 1 and the inner surface of the element housing 2, which is the ultrasonic transducer mounting surface of the measuring tube 1. is formed, and even if transverse vibration occurs simultaneously when the vibrator 11 performs thickness vibration, this transverse vibration is blocked by the gap 11 and propagates only 10 to 108 degrees. Measuring tube 1
Ultrasonic waves leaking to tl almost disappear. In addition, if not only the ultrasonic transducer 3 for transmission but also the ultrasonic transducer 4 has a similar structure, the ultrasonic vibrations propagating from the oscillator 2 to the transducer 1 will also be reduced. . Therefore, in the end, the ultrasonic signal received by the transducer of the receiving ultrasonic transducer 4 is radiated by the thickness vibration from the surface of the transducer of the transmitting ultrasonic transducer S, and the fluid to be measured is A signal with good I consisting only of the ultrasonic signal 9- propagated as a medium can be received.

FIG. 4 shows another embodiment of the invention. In this embodiment, unlike the embodiment shown in FIG. 3, the gap 17 is not formed down to the bottom of the case 14, but the base 12a of the backing material 12 is formed into a flange shape having an outer diameter equal to the inner diameter of the case 14. A gap 17 is formed between the case 14 and the circumferential surface of the backing material 12 excluding the flanged base 12m.

In this case, the backing material 12 near the bottom of the case 14
Since the ultrasonic vibrations radiated inside are sufficiently attenuated, even if the side surface of the backing material 12 (the surface of the flanged base 12a) is adhered to the case 14, the vibration of the vibrator 1 passes through the case 14 and is transmitted to the element housing 2. It will not be communicated to. According to this embodiment, the flanged base 12a of the backing material 12
By holding the vibrator 17 in the case 14, the vibrator 11 is correctly positioned at the center of the case 14, so that a gap 17 with a uniform thickness is formed around the vibrator 11, and a gap 1710- Therefore, the effect of inhibiting transverse vibration of the vibrator 1 can be further increased.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an outline of an ultrasonic flow rate needle, Fig. 2 is a cross-sectional view showing the configuration of the ultrasonic transducer 9 section in a conventional ultrasonic flow rate needle, and Figures 3 and 4 are FIG. 2 is a sectional view of an ultrasonic transducer section showing an embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Measuring tube, 2... Element housing (ultrasonic transducer installation part), 3e4... Ultrasonic transducer, 11... Ultrasonic vibrator, 12... Backing material, 13 ...Coating material, 14...Case, 17...Hollow gap. Applicant's agent Patent attorney Takehiko Suzue 11- Figure 1 Figure 2 Figure 6

Claims (4)

[Claims] (1) A pair of ultrasonic transducers including an ultrasonic transducer and a backing material that supports the back surface of the transducer are mounted facing each other in the measurement tube, and ultrasonic signals are transmitted between these transducers. A device for measuring the flow velocity or flow rate of a fluid flowing through a measuring tube by transmitting and receiving, characterized in that a gap is provided between a side surface of the ultrasonic vibrator and an ultrasonic transducer mounting surface of the measuring tube. Ultrasonic flow meter. (2) The dimension of the ultrasonic transducer in the direction perpendicular to the thickness direction is smaller than the dimension of the ultrasonic transducer support surface of the backing material, and the backing material is attached only to the ultrasonic transducer mounting surface of the measurement tube on the base side. The ultrasonic flow rate meter according to claim 1, wherein the ultrasonic flow rate meter is held. (3) The ultrasonic flow meter according to claim 2, wherein the backing material is held only on the end surface of the base side on the ultrasonic transducer mounting surface of the measuring tube. (4) The base side of each backing material is formed into a brim shape,
3. The ultrasonic flowmeter according to claim 2, wherein the end surface and peripheral surface of the flanged base are held on the ultrasonic transducer mounting surface of the measuring tube.