JP2020098129A - Waveguide for ultrasonic level meter - Google Patents

Abstract

To provide a waveguide for an ultrasonic level meter capable of preventing wrong measurement due to the reflection of ultrasonic waves on water droplets.SOLUTION: A waveguide 21 is configured such that an ultrasonic sensor 31 for transmitting and receiving ultrasonic waves is attached to a base end 22 side, and a tip 23 side is inserted into a liquid tank 11. When the waveguide 21 is viewed from a radial direction, a tip side opening edge 51 of the waveguide 21 is inclined with respect to a surface S1 perpendicular to a central axis L1 of the waveguide 21. At a place where a distance from the base end 22 in the tip side opening part 55 of the waveguide 21 is the longest, a portion 56 having an acute angle when the waveguide 21 is viewed from the radial direction is provided.SELECTED DRAWING: Figure 2

Description

The present invention relates to a waveguide used in an ultrasonic level meter that measures the height of a liquid surface in a liquid tank.

Conventionally, as an ultrasonic level meter, ultrasonic waves are radiated toward the liquid surface from an ultrasonic sensor installed at the upper part of the liquid tank, and then the reflected wave from the liquid surface is received, so that the ultrasonic sensor to the liquid surface It is known to measure the distance. Further, as such an ultrasonic level meter, there is proposed an ultrasonic level meter provided with a waveguide in which an ultrasonic sensor is attached to a proximal end side and a distal end side is inserted into a liquid tank (for example, Patent Document 1). References 1 to 4). With this configuration, since the ultrasonic wave passes through the inside of the waveguide, unnecessary reflection of the ultrasonic wave is prevented and the reflected wave can be efficiently received.

Specifically, in Patent Document 1, a trapezoidal horn (waveguide) that widens toward the lower side (liquid level side) is used as an ultrasonic liquid level meter transducer (ultrasonic sensor). A structure attached to the lower surface of the is disclosed. In Patent Document 2, an ultrasonic wave propagating body (waveguide) attached to an ultrasonic wave oscillator (ultrasonic wave sensor) is arranged in a liquid storage container with its end face facing downward, and the end face is a liquid surface. There is disclosed a technique for calculating the height of the liquid surface by utilizing the fact that the reflected wave from the end face becomes small when the liquid comes into contact with. Patent Document 3 discloses a liquid level detection device in which the tip of a waveguide is housed in a tank and arranged so as to face the liquid surface of a liquid material stored in the tank. Patent Document 4 discloses an ultrasonic level meter having a structure in which an ultrasonic horn is inserted into one end of a tube and the tip of the tube is immersed in a liquid.

Japanese Unexamined Patent Application Publication No. 2002-340656 (paragraph [0015], FIG. 1 and the like) JP-A-7-146168 (paragraph [0008], FIG. 1, etc.) Japanese Unexamined Patent Publication No. 4-343301 (paragraphs [0011], [0013], [0017], [0025], FIGS. 4 to 6, etc.) Japanese Patent No. 2962535 (paragraphs [0005], [0019], FIG. 5, etc.)

However, water droplets may adhere to the surface of the waveguide due to dew condensation or the like. In this case, the attached water droplets flow downward along the surface of the waveguide, but are not sufficiently drained and remain on the tip side opening edge. As a result, the ultrasonic wave emitted from the ultrasonic sensor may be reflected not only on the liquid surface but also on water droplets accumulated on the tip side opening edge, so the ultrasonic sensor received the reflected wave reflected by the water droplets. In that case, there is a risk of incorrect measurement. Patent Document 3 discloses a technique of obliquely opening the tip of the waveguide in order to disperse and flatten the reflected wave reflected by the opening edge on the tip side. However, if water droplets accumulate on the tip-side opening edge, the water droplets hardly drop, and in this case as well, there is a risk of erroneous measurement due to the reflected wave reflected by the water droplets.

The present invention has been made in view of the above problems, and an object thereof is to provide a waveguide for an ultrasonic level meter capable of preventing erroneous measurement due to reflection of ultrasonic waves by water droplets. Especially.

In order to solve the above-mentioned problems, the invention according to claim 1 is a waveguide in which an ultrasonic sensor for transmitting and receiving ultrasonic waves is attached to a proximal end side and a distal end side is inserted into a liquid tank, When the waveguide is viewed from the radial direction, the front end side opening edge of the waveguide is inclined with respect to a plane perpendicular to the central axis of the waveguide, and the front end side opening of the waveguide is formed. In the location where the distance from the base end is the longest, the waveguide for an ultrasonic level meter is provided with a portion having an acute angle when the waveguide is viewed from the radial direction. The summary will be given.

Therefore, according to the first aspect of the invention, the opening edge on the front end side of the waveguide is inclined with respect to the plane perpendicular to the central axis, and the distance from the base end is the longest at the front end side opening of the waveguide. A portion having an acute angle is provided at the point. Therefore, even if water droplets adhere to the waveguide due to dew condensation, etc., the adhered water droplets will flow downward along the surface of the waveguide and the opening edge on the tip side, and will not accumulate in a portion having an acute angle. It falls to the side of the liquid stored inside. As a result, the ultrasonic waves emitted from the ultrasonic sensor are not reflected by the water droplets, but are reliably reflected by the liquid surface of the liquid, so it is possible to prevent erroneous measurement due to the ultrasonic waves being reflected by the water droplets. You can

A second aspect of the present invention is based on the first aspect, and the gist of the invention is that the portion having the acute angle is provided at only one location in the distal end side opening portion.

Therefore, according to the second aspect of the invention, the water droplets flowing along the surface of the waveguide or the opening edge on the front end side are concentrated at one location (a portion having an acute angle). As a result, as compared with the case where there are a plurality of parts having acute angles, the water droplets that accumulate at the parts having acute angles become larger quickly (heavier), so that the water drops can be reliably dropped. Therefore, the reflection of the ultrasonic waves on the water droplets can be more reliably prevented, and the measurement accuracy of the ultrasonic level meter is improved.

A third aspect of the present invention is summarized in the first or second aspect, in which the acute angle is 10° or more and 60° or less.

Therefore, according to the third aspect of the invention, by setting the angle of the acute angle to 60° or less, the portion having the acute angle becomes thin, so that the water droplets accumulated in the portion having the acute angle can be easily dropped. Further, by setting the angle of the acute angle to 10° or more, the width of the portion having the acute angle is secured, so that the strength of the portion having the acute angle is secured.

According to a fourth aspect of the present invention, in any one of the first to third aspects, a cross section of the tip side opening obtained when the waveguide is cut along the central axis goes to the tip. The gist is that it has a shape that becomes thinner in accordance with the above.

Therefore, according to the fourth aspect of the invention, the water droplets flowing downward along the surface of the waveguide can easily flow without stopping at the tip side opening edge. Therefore, the reflection of the ultrasonic waves on the water droplets can be more reliably prevented, and the measurement accuracy of the ultrasonic level meter is improved.

A fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects, the surface of the waveguide is covered with a layer made of a material having water repellency.

Therefore, according to the fifth aspect of the invention, the layer made of the material having water repellency allows the water droplets attached to the waveguide to easily flow downward without being left there as they are attached. Therefore, the reflection of the ultrasonic waves on the water droplets can be more reliably prevented, and the measurement accuracy of the ultrasonic level meter is improved. As the material having water repellency, for example, a resin material having water repellency, specifically, a fluororesin such as polytetrafluoroethylene (PTFE) can be used.

As described above in detail, according to the inventions described in claims 1 to 5, even when water droplets adhere to the waveguide due to dew condensation or the like, the height of the liquid surface can be accurately measured. A waveguide for an ultrasonic level meter can be provided.

The schematic block diagram which shows the ultrasonic level meter and liquid tank of this embodiment. The side view which shows a waveguide. The side view which shows a waveguide when it sees from a different direction from FIG. The top view which shows the base end side part of a waveguide. The figure which shows the cross section of the front end side opening obtained when a waveguide is cut along a central axis. (A) is a graph showing the waveguide and ultrasonic waveform of Comparative Example 1, (b) is a graph showing the waveguide and ultrasonic waveform of Comparative Example 2, and (c) is a graph showing the waveform of Comparative Example 3. The graph which shows a wave tube and an ultrasonic waveform, (d) is a graph which shows the waveguide and an ultrasonic waveform of an Example. The side view which shows the waveguide in other embodiment. The principal part side view which shows the waveguide in other embodiment. In other embodiment, the figure which shows the cross section of the front end side opening obtained when a waveguide is cut along a central axis. In other embodiment, the figure which shows the cross section of the front end side opening obtained when a waveguide is cut along a central axis.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 1, the ultrasonic level meter 20 of this embodiment is used by being attached to a concrete liquid tank 11 that stores a liquid A1 (water in this embodiment). The ultrasonic level meter 20 of the present embodiment is a device that detects the height of the liquid surface A2 of the liquid A1 by irradiating the liquid A1 in the liquid tank 11 with ultrasonic waves W1. The liquid tank 11 is formed in a substantially rectangular parallelepiped shape, and has a ceiling portion 12, a bottom portion 13, and a pair of side walls 14 facing each other. A protrusion 15 is provided on the outer surface (upper surface in FIG. 1) of the central portion of the ceiling portion 12. Further, a mounting hole portion 16 penetrating the convex portion 15 and the ceiling portion 12 is provided in the central portion of the ceiling portion 12.

As shown in FIGS. 2 and 3, the waveguide 21 for the ultrasonic level meter 20 is a substantially cylindrical single tube having a constant inner diameter and outer diameter, and has an inner peripheral surface 21a and an outer peripheral surface 21b( Surface). The waveguide 21 is open at the base end 22 side (upper end side in FIGS. 1 to 3) and the distal end 23 side (lower end side in FIGS. 1 to 3). Further, as shown in FIGS. 1 to 4, a flange 24 is formed on the base end 22 side of the waveguide 21. Then, eight screw holes 25 are provided on the outer peripheral portion of the flange 24. The screw holes 25 are arranged at equal angles (45°) with respect to the central axis L1 of the waveguide 21. Then, with the waveguide 21 inserted in the mounting hole portion 16, the screw 26 is inserted into each screw hole 25, and the tip end of the inserted screw 26 is screwed to the convex portion 15. As a result, the waveguide 21 is fixed to the liquid tank 11 via the flange 24.

An ultrasonic sensor 31 that transmits and receives the ultrasonic wave W1 is attached to the base end 22 side of the waveguide 21. Specifically, the ultrasonic sensor 31 has a cylindrical shape and is inserted in the waveguide 21. Then, in the ultrasonic sensor 31, the outer peripheral surface 32 is in close contact with the inner peripheral surface 21 a of the waveguide 21 in the waveguide 21, and the front surface 33 is flush with the base end 22 of the waveguide 21. It is located in. Further, as shown in FIG. 4, a display unit 34 is arranged at a substantially central portion of the front surface 33 of the ultrasonic sensor 31. The display 34 displays the waveform of the ultrasonic wave W1 (the reflected wave W2 shown in FIG. 1) reflected by the liquid surface A2.

Then, as shown in FIG. 1, an ultrasonic oscillator 41 and an ultrasonic receiver 42 are electrically connected to the ultrasonic sensor 31. The ultrasonic oscillator 41 outputs an oscillation signal to the ultrasonic sensor 31 to drive the ultrasonic sensor 31. As a result, the ultrasonic sensor 31 irradiates (transmits) the ultrasonic wave W1 toward the liquid A1 in the liquid tank 11. In addition, an electric signal indicating the ultrasonic wave W1 (reflected wave W2) received by the ultrasonic sensor 31 is input to the ultrasonic wave receiver 42.

As shown in FIGS. 1 to 3, the tip end 23 side of the waveguide 21 is inserted into the liquid tank 11 and projects downward from the ceiling portion 12. The front end side opening edge 51 of the waveguide 21 extends in a spiral shape from the base end 52 toward the front end 53. More specifically, the tip-side opening edge 51 is inclined with respect to the plane S1 perpendicular to the central axis L1 of the waveguide 21 when the waveguide 21 is viewed in the radial direction. The inclination angle θ1 of the front end side opening edge 51 with respect to the surface S1 has a constant size from the base end 52 to the front end 53, and is specifically 10° or more and 60° or less (45° in this embodiment). Has become. Further, the base end 52 and the tip end 53 are connected to each other via an edge portion 54 that linearly extends along the central axis L1 of the waveguide 21. The tip 53 of the tip-side opening edge 51 is located at the same position as the tip 23 of the waveguide 21. Further, as shown in FIG. 5, the cross section of the distal end side opening 55 obtained when the waveguide 21 is cut along the central axis L1 has a shape in which the width is the same from the proximal end 22 to the distal end 23. Have In other words, the front end side opening 55 has the same thickness from the base end 22 to the front end 23.

Then, as shown in FIGS. 2 and 3, in the distal end side opening portion 55 of the waveguide 21, the position where the distance from the base end 22 of the waveguide 21 becomes the longest, that is, the distal end side opening edge 51. A portion 56 having an acute angle when the waveguide 21 is viewed in the radial direction is provided at the position where the tip 53 is located. The portion 56 having an acute angle is a portion including the connecting portion between the front end side opening edge 51 and the edge portion 54, and the angle formed by the front end side opening edge 51 and the edge portion 54 is an acute angle. That is, the portion 56 having an acute angle is provided only at one place in the front end side opening 55. The acute angle θ2 is 10° or more and 60° or less (45° in this embodiment).

Next, the electrical configuration of the ultrasonic level meter 20 will be described.

As shown in FIG. 1, the ultrasonic level meter 20 includes a control device 61 that totally controls the entire device. The control device 61 is composed of a well-known computer including a CPU, ROM, RAM and the like. Data indicating the distance from the ultrasonic sensor 31 to the bottom surface of the liquid tank 11 is stored in advance in the ROM of the control device 61. The CPU of the control device 61 is electrically connected to the ultrasonic oscillator 41 and the ultrasonic receiver 42, and controls them by various drive signals. A display 34 is electrically connected to the CPU.

Next, a method of detecting the height of the liquid surface A2 using the ultrasonic level meter 20 will be described.

First, after the liquid A1 is stored in the liquid tank 11, the power source (not shown) of the ultrasonic level meter 20 is turned on. At this time, the CPU of the control device 61 controls the ultrasonic oscillator 41 to output an oscillation signal to the ultrasonic sensor 31 to drive the ultrasonic sensor 31. As a result, the ultrasonic wave W1 is emitted (transmitted) from the ultrasonic sensor 31 toward the liquid A1. Then, when the ultrasonic wave W1 reaches the liquid A1, the ultrasonic wave W1 is reflected by the liquid surface A2 to become a reflected wave W2, propagates upward, and is received by the ultrasonic sensor 31. After that, the ultrasonic wave W1 (reflected wave W2) received by the ultrasonic sensor 31 is converted into an electric signal and input to the CPU via the ultrasonic receiver 42.

Further, the CPU measures the time from when the ultrasonic sensor 31 transmits the ultrasonic wave W1 to when the reflected wave W2 is received. Then, the CPU multiplies the measured time by the sound velocity, and then further multiplies the multiplication result by 1/2. As a result, the distance from the ultrasonic sensor 31 to the liquid surface A2 is calculated. Further, the CPU calculates the difference between the calculated distance from the ultrasonic sensor 31 to the liquid surface A2 and the distance stored in the ROM from the ultrasonic sensor 31 to the bottom surface of the liquid tank 11. As a result, the height of the liquid surface A2 of the liquid A1 in the liquid tank 11 is detected. After that, when the worker turns off the power, the controller 61 stops the ultrasonic oscillator 41 and the ultrasonic receiver 42, and the transmission of the ultrasonic wave W1 and the reception of the reflected wave W2 are completed.

Next, a waveguide evaluation method and the results thereof will be described.

1. Experimental Method First, a measurement sample was prepared as follows. A waveguide (spiral single pipe) having a spiral opening on the tip side, that is, the same waveguide 71 as the waveguide 21 of the present embodiment (see FIG. 6D) is prepared, and this is used as an example. And On the other hand, a waveguide 72 (see FIG. 6A) in which the tip-side opening edge is perpendicular to the central axis of the tube was prepared, and this was set as Comparative Example 1. Moreover, a waveguide 73 (oblique single tube; see FIG. 6B) in which the tip side opening edge is inclined by a predetermined angle (here, 45°) with respect to a plane perpendicular to the central axis is prepared, It was set as Comparative Example 2. Further, a waveguide 75 having a tip-side opening edge inclined at a predetermined angle with respect to a plane perpendicular to the central axis and having water droplets 74 attached to the tip-side opening edge (oblique single tube; see FIG. 6C). Was prepared as Comparative Example 3.

Next, an ultrasonic test was performed on each measurement sample (Example, Comparative Examples 1 to 3). Specifically, first, after inserting the ultrasonic sensor into the proximal end side of the waveguides of Examples and Comparative Examples 1 to 3, the distal end side of the waveguide was inserted into the liquid tank 11 shown in FIG. .. Next, ultrasonic waves were emitted from the ultrasonic sensor toward the liquid surface of the liquid stored in the liquid tank 11. Further, the waveform of the ultrasonic wave received by the ultrasonic sensor was displayed on the display 34. The above results are shown in FIG.

2. Experimental Results and Discussion The graph of FIG. 6 shows the waveform of ultrasonic waves in each of the example and comparative examples 1 to 3. In any of the measurement samples, the ultrasonic waves are reflected by the opening edge on the distal end side depending on the size, but in Comparative Example 1 in which the opening edge on the distal end side is perpendicular to the central axis of the tube, the ultrasonic wave is It was confirmed that the reflection was fairly large at the opening edge on the tip side. In this case, the ultrasonic sensor can easily receive not only the ultrasonic wave (reflected wave) reflected by the liquid surface but also the ultrasonic wave reflected by the opening edge on the front end side. As a result, it was found that the time from the ultrasonic sensor transmitting the ultrasonic wave to the reception of the reflected wave cannot be accurately measured, and the liquid level height may not be accurately calculated.

In Comparative Example 2 which is a slanted single tube, since the ultrasonic waves reflected by the tip-side opening edge are gradually output, the peaks of the ultrasonic waves reflected by the tip-side opening edge become small, and the vicinity of the tip-side opening edge It was confirmed that the waveform of the ultrasonic wave in Example 2 was flattened to some extent as compared with Comparative Example 1. However, in Comparative Example 3 in which water droplets adhere to the tip-side opening edge even though it is an oblique single tube, the ultrasonic waves are likely to be reflected by the water droplets, and the ultrasonic waves are largely reflected twice near the tip-side opening edge. Was confirmed. In this case, the ultrasonic sensor can easily receive not only the ultrasonic wave (reflected wave) reflected by the liquid surface but also the ultrasonic wave reflected by the opening edge on the front end side. As a result, it was found that the time from the ultrasonic sensor transmitting the ultrasonic wave to the reception of the reflected wave cannot be accurately measured, and the liquid level height may not be accurately calculated.

On the other hand, in the example of the spiral single tube, the length L2 along the central axis of the formation region of the tip-side opening edge is longer than the length L1 in Comparative Examples 2 and 3, so that the tip-side opening edge is reflected. It was confirmed that the unnecessary ultrasonic peaks were further reduced, and the waveform of the ultrasonic waves near the tip-side opening edge was flattened more than in Comparative Examples 2 and 3. It was also confirmed that even if water droplets adhered to the opening edge on the tip side, the water droplets immediately dropped from the tip. In this case, it has been found that the ultrasonic sensor can accurately measure the time from the transmission of the ultrasonic wave to the reception of the reflected wave, so that the height of the liquid surface can be accurately calculated.

Therefore, according to this embodiment, the following effects can be obtained.

(1) In the ultrasonic level meter 20 of the present embodiment, the front end side opening edge 51 of the waveguide 21 is inclined with respect to the plane S1 perpendicular to the central axis L1, and the front end side opening portion 55 of the waveguide 21 is provided. A portion 56 having an acute angle is provided at a position where the distance from the base end 22 is the longest. Therefore, even if water droplets adhere to the waveguide 21 due to dew condensation or the like, the adhered water droplets flow downward along the outer peripheral surface 21b of the waveguide 21 and the front end side opening edge 51, and reach the portion 56 having an acute angle. It does not collect and falls to the liquid A1 side. As a result, the ultrasonic wave W1 emitted from the ultrasonic sensor 31 is not reflected by the water droplets but is reliably reflected by the liquid surface A2 of the liquid A1. It is possible to prevent erroneous measurement of the surface A2.

(2) In the waveguide 21 of the present embodiment, the tip-side opening edge 51 extends spirally, and the inclination angle θ1 of the tip-side opening edge 51 with respect to the plane S1 perpendicular to the central axis L1 is constant ( 45°). Therefore, when the waveguide 21 is formed, the circular tube is rotated by using, for example, a lathe and the like, and only by moving the cutting tool against the circular tube at a constant speed in the rotation axis direction, a spiral shape is obtained. The front side opening edge 51 can be formed. Therefore, the waveguide 21 is easily formed.

(3) The ultrasonic level meter 20 of this embodiment has a configuration in which the ultrasonic sensor 31 is inserted inside the waveguide 21 and the ultrasonic wave W1 propagates inside the waveguide 21 toward the liquid surface A2. .. As a result, the ultrasonic wave W1 is less diffused, so that the ultrasonic sensor 31 can efficiently receive the reflected wave W2. Therefore, even if a small sensor is used as the ultrasonic sensor 31, it is possible to reliably perform measurement. Further, in the present embodiment, since the ultrasonic wave W1 is transmitted and received by the single ultrasonic sensor 31, the ultrasonic sensor that transmits the ultrasonic wave W1 and the ultrasonic sensor that receives the ultrasonic wave W1 are separately provided. As compared with the case where the ultrasonic sensor is provided, the mounting portion of the ultrasonic sensor can be made smaller.

In addition, you may change the said embodiment as follows.

-In the waveguide 21 of the above-described embodiment, the tip-side opening edge 51 is formed in a spiral shape to form the portion 56 having an acute angle in the tip-side opening 55 of the waveguide 21. However, as shown in the waveguide 81 of FIG. 7, the tip side opening edge 82 is inclined with respect to the plane S2 perpendicular to the central axis L2, and the tip side opening edge 82 has the longest distance from the base end 83. The portion 85 having an acute angle may be formed by attaching the needle 84 to the position. The portion 85 having an acute angle may be formed by another member such as a rod-shaped member or a protrusion. The needle 84 may be integrally formed with the waveguide 21, or may be a separate body from the waveguide 21.

In the waveguide 21 of the above-described embodiment, the portion 56 having an acute angle is provided in only one place in the front end side opening 55. However, the portion having the acute angle may be provided in a plurality of places in the front end side opening portion 55. For example, as shown in the waveguide 111 of FIG. 8, the concave portions 112 and the convex portions 113 are alternately formed along the circumferential direction of the waveguide 111 so that the portion 114 (the convex portion 113) having an acute angle is formed. Alternatively, they may be provided at a plurality of locations on the tip side opening 115.

In the above-described embodiment, the cross section of the distal end side opening 55 obtained when the waveguide 21 is cut along the central axis L1 has a shape in which the proximal end 22 to the distal end 23 have the same width. .. However, as shown in FIG. 9, the cross section of the tip-side opening 92 obtained when the waveguide 91 is cut along the central axis L1 may have a shape that becomes narrower toward the tip 93. Good. In other words, the front end side opening 55 may have a shape in which the thickness decreases toward the front end 93. With this configuration, the water droplets flowing down along the outer peripheral surface 94 (surface) of the waveguide 91 can easily flow without stopping at the tip-side opening edge 95. Therefore, the reflection of the ultrasonic wave W1 by the water droplet can be more reliably prevented, and the measurement accuracy of the ultrasonic level meter 20 is improved.

In the above embodiment, the outer peripheral surface 21b of the waveguide 21 may be covered with the layer 101 (see FIG. 10) made of a material having water repellency (for example, polytetrafluoroethylene (PTFE) or the like). In this way, the layer 101 allows the water droplets attached to the waveguide 21 to easily drop. Therefore, the reflection of the ultrasonic wave W1 by the water droplet can be more reliably prevented, and the measurement accuracy of the ultrasonic level meter 20 is improved. The layer 101 may cover the inner peripheral surface 21a and the front end side opening edge 51 in addition to the outer peripheral surface 21b.

The waveguide 21 of the above embodiment has a cylindrical shape, but may have another cylindrical shape such as a rectangular tube shape, an elliptic tube shape, and a triangular tube shape.

Next, in addition to the technical ideas described in the claims, the technical ideas grasped by the above-described embodiment will be listed below.

(1) The waveguide for an ultrasonic level meter according to any one of claims 1 to 5, wherein the waveguide is a cylindrical single tube having a constant outer diameter.

(2) The waveguide for an ultrasonic level meter according to any one of claims 1 to 5, wherein the portion having the acute angle is provided at a plurality of locations in the opening on the tip side.

11... Liquid tank 20... Ultrasonic level meter 21, 81, 91, 111... Waveguide 21b, 94... Outer peripheral surface 22 as surface of waveguide 22, 83... Base end 23 of waveguide... Waveguide Tip 31... Ultrasonic sensor 51, 82, 95... Tip side opening edge 55, 92, 115... Tip side opening 56, 85, 114... Section 93 having an acute angle... Tip 101 of tip side opening... Water repellent Material layers L1, L2... Central axes S1, S2... Surface W1 perpendicular to the central axis... Ultrasonic wave .theta.2... Acute angle

Claims (5)

A waveguide in which an ultrasonic sensor for transmitting and receiving ultrasonic waves is attached to the base end side and the tip side is inserted into the liquid tank,
When the waveguide is viewed from the radial direction, the tip side opening edge of the waveguide is inclined with respect to a plane perpendicular to the central axis of the waveguide,
A portion having an acute angle when the waveguide is viewed from the radial direction is provided at a position where the distance from the base end is the longest in the distal end side opening of the waveguide. Waveguide for sound level meter. The waveguide for an ultrasonic level meter according to claim 1, wherein the portion having the acute angle is provided only at one place in the opening on the tip side. The waveguide for an ultrasonic level meter according to claim 1 or 2, wherein the acute angle is 10° or more and 60° or less. 4. The cross section of the distal end side opening obtained when the waveguide is cut along the central axis has a shape that becomes narrower toward the distal end. A waveguide for an ultrasonic level meter according to Item 1. The waveguide for an ultrasonic level meter according to any one of claims 1 to 4, wherein a surface of the waveguide is covered with a layer made of a material having water repellency.

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