JPH04301724A - Sound lens and detecting device for liquid within pipe by means of sound lens - Google Patents

Abstract

PURPOSE:To detect liquid within a pipe by means of ultrasonic waves even if the pipe with a small bore is thick in wall thickness. CONSTITUTION:There is provided a sound lens 10 made up of two sections 10A and 10B which are joined with a curved surface furnished with a specified curvature, and are different in sound velocity. The sound lens 10 is interposed between an ultrasonic wave probe 12 and a measured pipe 14, and useless energy propagated in the circumferential direction of a pipe wall is relatively lessened with ultrasonic waves converged in the center of the pipe, so that liquid can thereby be efficiently detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic lens and a method for detecting liquid in a pipe using the same. In particular, the present invention relates to an acoustic lens suitable for detecting the presence or absence of liquid in a pipe using ultrasonic waves, and the above method using the same.

0002

BACKGROUND OF THE INVENTION Various methods and devices are known for detecting the presence or absence of liquid in a pipe. Among these methods, there is a method using ultrasound. Until now, when using ultrasonic waves (hereinafter referred to as sound waves) to detect the presence or absence of liquid in a metal pipe and measure the liquid level, the method used was to directly radiate sound waves from the outside of the pipe wall to the inside and detect the reflected waves. is often used. That is, by utilizing the fact that the amount of reflection of emitted sound waves differs depending on the presence or absence of liquid, the reflected waves are received and predetermined signal processing is performed.

0003

[Problems to be Solved by the Invention] When the diameter of the pipe is relatively large and the wall thickness of the pipe is not very large, the conventional method described above can be detected well, but as the pipe diameter is small and the wall thickness is large, The amount of sound waves radiated into the tube is small,
Moreover, the amount of sound waves leaking and propagating in the circumferential direction within the tube wall increases, making it difficult to detect the liquid level. In particular, when the pipe diameter is 25 mm or less or the wall thickness is 3 mm or more,
As the attenuation of the reflected waves increases, it is difficult to distinguish between the reflected waves and the waves that propagate in the circumferential direction within the pipe wall and return, resulting in a problem that accurate detection and measurement cannot be performed.

[0004] Therefore, the present invention provides an acoustic lens that makes it possible to accurately detect liquid in a pipe even when the pipe diameter is small or thick, and a method for detecting liquid in a pipe using the same. The purpose is to provide a detection method.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention injects sound waves in a direction perpendicular to the tangent to the pipe wall (towards the center of the pipe), focuses them on the center of the pipe, and reduces the amount of sound waves passing through the liquid. In addition to providing an acoustic lens for increasing the number of liquids, the present invention also provides a method for detecting liquid in a pipe using this acoustic lens.

That is, according to the present invention, the ultrasonic probe is fixed to one surface of a first member, and the other surface of the first member is formed by a predetermined curved surface or a broken line. The pipe is joined with a pseudo-curved surface, has a sound velocity different from that of the first member, and has a notch in the end face so that the end face opposite to the joint surface with the first member is in close contact with the outer periphery of the pipe to be measured. The curvature R of the curved surface or pseudo-curved surface is R〓L/tan(tan-1(N×sinφ)/(1-
N×cosφ)) However, φ=tan-1 (L/D) N=V1 /V2 V1, V2: Sound speed of two types of members D: Desired focal length L: At the ultrasonic radiation effective radius of the probe A defined acoustic lens is provided.

According to the present invention, in a method for detecting liquid in a pipe using an ultrasonic probe, the acoustic lens according to claim 1 or 2 is placed between the ultrasonic probe and the outer periphery of the pipe. A liquid in a pipe using an acoustic lens, characterized in that the acoustic lens is provided in the pipe and focuses the ultrasonic waves emitted from the ultrasonic deep probe to increase the propagation efficiency of the ultrasonic waves to the space or liquid inside the pipe. A detection method is provided.

[0008]

[Operation] When the acoustic lens of the present invention is used, the sound waves emitted from the probe are focused toward the center of the tube, so the energy that propagates around the tube wall in the circumferential direction and becomes noise is relatively reduced. , the energy propagating through the space or liquid within the pipe can be relatively increased. Therefore, by improving the S/N ratio, it has become possible to detect pipes with small diameters and large walls, which was previously considered impossible.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing how an acoustic lens 10 of the present invention is attached between an ultrasonic probe 12 and a pipe 14 to be measured. The ultrasonic probe 12 transmits and receives ultrasonic waves of about 2 MHz, for example, and may be a conventional one.

[0010] The probe 12 has two components constituting the acoustic lens 10.
The first member 1 on the upper side in the figure among the two members 10A and 10B
It is attached to one end face of 0A. The other end surface of the first member is joined to one end surface of the second member 10B at a curved surface 10C. In this embodiment, the curved surface is such that it forms part of the outer circumference of the cylinder. Second member 10
On the other surface of B, that is, on the end surface on the side to be attached to the pipe 14, a partial cylindrical cutout 10D matching the outer peripheral shape of the pipe 14 is provided.

The curved surface 10C is an important element in determining the focal length of the acoustic lens 10, and is determined as follows. Ideally, the cemented curved surface of the acoustic lens 10 is a parabola. However, a circular curved surface was used because it is easy to machine and there is no big difference in performance. Therefore, although the sound waves passing through the acoustic lens 10 are not focused on a single line, a sufficient effect can still be obtained.

The radius of curvature R of the joint curved surface 10C between the first member 10A and the second member 10B is determined as follows. R〓L/tan(tan-1(N×sinφ)/(1-
N×cosφ)) where φ=tan-1(L/D) N=Sinθ1/Sinθ2=V1/V2V1,V2:
Sound speed of the two types of members D: Desired focal length L: Ultrasonic radiation effective radius of the probe Q1: Incident angle on the lens curved surface Q2: Refraction angle on the lens curved surface Note that Fig. 2 shows each of the above parameters. FIG.

[0013] As the first member 10A and the second member 10B,
We considered what kind of material should be used, and although metal materials have very good sound wave transmittance, there is a large amount of reflection at the interface, and there is little attenuation inside the lens, so the boundary between the acoustic lens and the outer circumference of the pipe The echo wave from S/
Bad N ratio. On the other hand, the transmittance of polymer materials is not as good as that of metal materials, but the echo waves are attenuated because there is less reflection from the interface, the amount of attenuation of sound waves is large, and the amount of transmission to other materials is relatively large. is large and has a good S/N ratio. For these reasons, we decided to use a polymeric material as the material for the acoustic lens, and tried using the following materials on an experimental basis. (1) Teflon, (2) ABS, (3) Acrylic, (4
) Bakelite, (5) Duracon, (6) polyethylene, (7) polypropylene, (8) polycarbonate,
(9) Vinyl chloride, (10) Nylon

[0014] Table 1 shows the results of the sound speed of the polymer material measured based on the sound speed of steel material of 5850 m/s and the relative comparative attenuation amount (Bakelite is assumed to be 0 db). As a measuring device for the speed of sound, etc., an ultrasonic detector USIP-11 type (manufactured by Krautkremer, Germany) was used. From the above results, in terms of the amount of transmission, a probe frequency of 2 MHz is appropriate, and the material with the fastest sound speed is Bakelite, while the material with the slowest sound speed is Teflon. The material with the greatest attenuation is Teflon, and the material with the least is Bakelite.

[0015]

[Table 1]

In selecting the two types of materials for the first member 10A and the second member 10B, the following points were taken into consideration. (1) In order to increase the refractive index, materials with as much difference in sound speed as possible. (2) In order to reduce reflected waves at the lens boundary surface, a material with large attenuation is required. (3) To increase detection sensitivity, use materials with high transmittance and low attenuation. Based on these conditions, the combinations shown in Table 2 were considered, and the attenuation of sound waves (assuming the combination of acrylic resin and Bakelite as 0) and the amount of transmission through the steel material (relative values) were measured. Here, as the adhesive selection conditions, (1)2
(2) No air bubbles are formed on the adhesive surface; (3) Workability is good.

[0017]

[Table 2] From these conditions, it was found that an instant adhesive based on Bakelite that satisfies the adhesive conditions is suitable in terms of workability and strength.

From this result, combinations with low attenuation of sound waves include (1) vinyl chloride Bakelite, (2) acrylic Bakelite, (3) nylon Bakelite,
(4) There are four types of polyethylene and Bakelite, and in terms of the amount of permeation into steel materials: (1) Acrylic Bakelite, (2)
Nylon Bakelite is relatively large. Based on the above, the following material combinations were selected for the acoustic lens. (1) Vinyl chloride Bakelite (2) Acrylic Bakelite (3) Nylon Bakelite Note 1: (4) Polycarbonate Bakelite Note 1
: (5) Teflon/acrylic Note 1: (6) Teflon/Bakelite (Note 1) Measurements have shown that it is possible to prototype an acoustic lens with the least amount of reflected waves generated at each interface, that is, with a good S/N ratio. Based on this idea, we added a combination of polycarbonate, which has the highest amount of attenuation of sound waves, and Teflon, which has the lowest sound velocity, and acrylic and Bakelite, which are the opposite.

Next, the radius of curvature R of the acoustic lens 10 was calculated using the above-mentioned formula giving R. R is the speed of sound V1, V2
and the desired focal length D, so the first member 10
It changes depending on the materials of A and the second member 10B and the diameter of the pipe to be measured. In the measurement of this example, the pipe 14
An iron pipe (diameter 25 mm, wall thickness 3 mm) and a stainless steel pipe (diameter 25 mm, wall thickness 3 mm) were used as the materials, and spindle oil was used as the liquid. Acrylic (V
1 = 2690 m/s), and when Bakelite (V2 = 3660 m/s) is used as the second member 10B, the focal length D is 12.5 mm, which is 1/2 of the outer diameter of the pipe 25 mm (the center of the pipe (It is desirable to adjust the focal length to =5.2m
m can be obtained. Note that there is no particular restriction on the thickness of the first member 10A and the second member 10B, but the thinner the thickness, the smaller the amount of attenuation of sound waves, but the more difficult it is to process and the more likely problems with strength will occur. In the example, each thickness was approximately 1 mm at its thinnest point. Therefore, the thickness of the acoustic lens 10 as a whole is 2 to 3 mm at the thinnest central portion.

[0020] For the above combinations ① to ②, original acoustic lenses and dummy lenses having no lens function were prepared and comparative experiments were conducted. In other words, in the following, "no lens processing" is used to investigate the superiority of acoustic lenses.
A dummy that does not have a lens function and is made of two members made of the same material. Also, the number on the right side is the radius of curvature. (1) is vinyl chloride bakelite (8.3 mm without acoustic lens and lens processing) (2) is acrylic bakelite (5.2 mm without acoustic lens and lens processing) (3) is nylon bakelite (acoustic lens 6.2 mm) ) (4) is polycarbonate Bakelite (8.8 mm without acoustic lens and lens processing) (5) is Teflon acrylic (acoustic lens 14.2 mm) (6) is Teflon Bakelite (23.8 mm without acoustic lens and lens processing) )

[0021] Furthermore, in order to investigate the superiority of acoustic lenses, (1) vinyl chloride Bakelite, (2) acrylic Bakelite, and (3) nylon Bakelite were made with "no lens processing" and their properties were compared. went. The results are shown in Table 3.

[0022]

[Table 3] From these, it can be commonly determined that (1)
In the "liquid present" state, the amplitudes of the obtained signals are approximately equal. (2) In the "no liquid" state, the amount of sound waves leaking in the circumferential direction of the tube wall is small due to the effect of the acoustic lens, and the remaining echo waves are small. (3) The signal level for "no liquid" has a smaller amplitude for "acoustic lens" than for "no lens processing". Therefore, the acoustic lens has a larger detection difference between "no liquid" and "liquid present." It can be said that the superiority of acoustic lenses has been demonstrated in these respects.

Next, Table 4 shows the measurement results regarding the sensitivity of the acoustic lens. Note that in this embodiment, the first
Since the member 10A has a lower sound velocity than the second member 10B on the pipe side, the joint curved surface between the two curves in the opposite direction to the outer peripheral curved surface of the pipe 14, as shown in FIGS. 1 and 2. If the relationship between the sound speeds is reversed, that is, V1>V2, the joint curved surface can be reversed from that shown in FIGS. 1 and 2, and curved in the same direction as the outer circumferential curved surface of the pipe 14. When selecting a material to be used for an acoustic lens, the following conditions must be satisfied. (1) There must be a sufficient difference in the detection signal between "no liquid" and "liquid present." (2) There must be sufficient detection signal for "liquid present". From these points, it can be said that the combinations of (1) acrylic Bakelite, (2) vinyl chloride Bakelite, and (3) nylon Bakelite showed good results.

[0024]

[Table 4]

FIG. 3 shows an example of a detection circuit to which the probe 12 is connected. 4 is a block diagram showing the functions of the circuit shown in FIG. 3. The timer 21 has a period of 300ms
It oscillates at intervals to generate a trigger signal to the pulser 22. The pulser 22 generates a single pulse to be applied to the probe 12 using the back electromotive force of the inductance L. Peak voltage value is approximately 20-100V (depending on load)
It is. The probe 12 emits ultrasonic waves to the acoustic lens 10 and receives reflected waves. In order to reduce power consumption, the power supply control 24 controls the amplification unit 2 during the period after the sound wave is emitted and until the next sound wave is emitted.
1 performs an operation to control power. The amplifying section 25 receives AGC (Au
automatic Gain Control) is applied. The detection 26 detects the received signal and generates an AGC signal because the received wave has an AC component and it is necessary to identify "liquid present". The echo detection 27 identifies the "liquid present" signal. The power supply check 28 performs a battery check, and if the battery is normal, the buzzer 29 is activated by turning on the switch. The buzzer 29 functions to notify the outside when "liquid present" is detected.

[0026] In implementing this circuit, we took into consideration the usage environment of the device and aimed at (1) dry cell battery specifications and (2) lower power consumption. The acoustic lens 10 was attached to iron pipes and stainless steel pipes with a diameter of 25 mm and a wall thickness of 3 mm, and the operation was confirmed in "liquid" and "no liquid" states.As a result, (1) acrylic bakelite, (2) vinyl chloride bakelite, (3) Good operation was achieved with the combination of nylon and Bakelite. Also, as can be inferred from Table 2 and these experimental examples (4
) The polyethylene-Bakelite combination has also shown good performance. Although the above embodiment uses a single probe to transmit and receive signals, it is also possible to use a so-called transmission type in which a transmitting element is placed on one side of the pipe and a receiving element is placed on the other side. places an acoustic lens between each of these elements and the pipe.

[0027]

[Effects of the Invention] As is clear from the above detailed explanation, the acoustic lens of the present invention and the method for detecting liquid in a pipe using the same can be applied to small-diameter, thick-walled metal pipes, which has been difficult in the past. The liquid inside can be detected well with high S/N. Furthermore, when this acoustic lens and detection method are applied to a pipe having a larger diameter than the pipe used in the embodiment, the effect of the acoustic lens due to the focusing of ultrasonic waves becomes even more apparent.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of one embodiment of an acoustic lens of the present invention.

FIG. 2 is a cross-sectional view showing various parameters of the acoustic lens of the present invention.

FIG. 3 is a circuit diagram showing an example of a detection circuit that can be used in the detection method of the present invention.

FIG. 4 is a block diagram showing the functions of the circuit in FIG. 3;

[Explanation of symbols]

10 Acoustic lens 10A First member 10B Second member 12 Probe 14 Pipe R Radius of curvature L Ultrasonic radiation effective radius D of the probe
Focal length

Claims (3)

[Claims] 1. A first member to which an ultrasonic probe is fixed on one surface, the other surface of the first member being joined to a predetermined curved surface or a pseudo curved surface formed by a broken line. , a second member having a sound velocity different from that of the first member, and having a notch in the end face so that the end face opposite to the joint surface with the first member is in close contact with the outer periphery of the pipe to be measured. , and the curvature R of the curved surface or pseudo-curved surface is R〓L
/tan(tan-1(N×sinφ)/(1-N×c
osφ)) However, φ=tan-1(L/D) N=V1 /V2 V1, V2: Sound speed of two types of members D: Desired focal length L: Determined by the effective radius of ultrasonic radiation of the probe acoustic lens. 2. As the first member and the second member, one of four combinations of acrylic resin and Bakelite, vinyl chloride and Bakelite, nylon and Bakelite, and polyethylene and Bakelite is used. Acoustic lens described. 3. A method for detecting liquid in a pipe using an ultrasonic deep probe, wherein the acoustic lens according to claim 1 or 2 is provided between the ultrasonic probe and the outer periphery of the pipe, A method for detecting liquid in a pipe using an acoustic lens, characterized in that ultrasonic waves emitted from a probe are focused to increase propagation efficiency of the ultrasonic waves to the space or liquid inside the pipe.