JPH04343031A - Waveguide for measuring ultrasonic wave and detecting apparatus of liquid surface of liquid material - Google Patents

Abstract

PURPOSE:To detect the liquid level in a narrow space or under high temperature by directing an opening of a curved waveguide which opens slantwise to the liquid surface, and projecting ultrasonic waves. CONSTITUTION:A waveguide 3 penetrates a side face 8a of a high temperature liquid material tank 8, then curves downward at 3b at right angles. A front opening part 3a of the waveguide is directed with predetermined angles to the liquid surface 9 of a molten liquid material 9 in the tank 8. Moreover, an air feed pipe opened at 7a in the wall of the waveguide 3 feeds a gas to which a weak pressure is added from an outside pressure source, so that the waveguide 3 is cooled. Accordingly, overheating of a transducer 2 is prevented. As the transducer 2 acts, the ultrasonic waves S reach the liquid surface 9a through the waveguide 3 and the reflecting waves S' enter the waveguide 3 and reach a receiving element. After the reflecting waves are amplified by an amplifier 5, an indicating device 6 indicates the distance from a projecting end 3a' of the waveguide 3 to the liquid surface 9a.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is effective for purposes such as ultrasonic measurement or detection of the liquid level in a tank or container containing a liquid substance, especially a high-temperature liquid substance, or the liquid level in a narrow space. The present invention relates to a waveguide that can be used for a waveguide and a liquid level detection device for high-temperature liquid material using the waveguide.

0002

[Conventional technology]

■ Background Ultrasonic measurement is widely used to detect the height of liquid levels, etc., but in order to prevent errors due to vibrations in the transmitting and receiving elements, a minimum detectable distance of at least 30 cm is required. height is 3 from the transducer.
It cannot be used to measure distances in narrow spaces less than 0 cm. Furthermore, the transducer's transmitting and receiving elements are relatively susceptible to heat, and therefore cannot be used for measurements in high-temperature environments where the measurement environment temperature is several hundred degrees or more. However, in cases where the measured environmental temperature is such a high temperature,
Industrially, for example, molten salt electrolysis in the production of sodium, alumina, fluorine, etc., molten metal dyeing methods, molten salt baths in steel sintering, and melt spinning methods use fiber materials in a molten state (polyamide, polyester, polyolefin, etc.). (synthetic resins), hot melt adhesive melting tanks, aluminum alloy melting tanks for die casting, tank kilns for melting glass cullet, melting tanks for low melting point metals such as tin in the manufacture of float plate glass, etc. , there are many. In any of these cases, liquid level control is important for process management.

[0003] Problems with conventional technology Therefore, in the industrial field where ultrasonic measurement is difficult, two electrodes have been inserted into the melt and the liquid level has been adjusted by using changes in the electrical resistance and capacitance between the electrodes. (Therefore, two sets of electrodes are used to detect a certain height range.) However, the electrodes corrode depending on the type of material to be melted. If a noble metal such as platinum is used as an electrode material, it cannot withstand long-term use, and the cost becomes extremely high. In addition, the method of using electrical resistance is
It cannot be used for non-conductive objects, and the capacitance measurement method is affected by the material of the tank, so its applications are limited, and the accuracy of the measurement data is low.

[0004] Therefore, as a non-contact type liquid level detection device, a detector in which an induction coil is housed inside a silicon nitride guide tube lined with a special metal is used, for example, to detect the level of molten aluminum. Although it has been developed, it has the disadvantage that it is not only expensive, but also that the guide tube that comes into contact with the molten metal etc. is severely corroded, resulting in very high maintenance costs.

[0005]

[Problems to be Solved by the Invention] In view of the above circumstances, the present invention expands the scope of application of non-contact measurement technology by developing a new waveguide for ultrasonic measurement, and utilizes ultrasonic waves. The purpose of this invention is to solve the above-mentioned drawbacks in liquid level detection technology in narrow spaces and in high-temperature environments.

[0006]

[Means to solve the problem]

■ Concept As mentioned above, the interior of a melting tank for melting raw materials with high melting points is generally sealed using an inert gas such as nitrogen. Furthermore, even when sealing is not performed, it is normal to make the chamber as closed as possible in order to increase thermal efficiency. For this reason, the space temperature inside the tank becomes extremely high.
It is not possible to install ultrasonic transducers, which are commonly used for distance measurement in spaces at room temperature or in seawater. Furthermore, ultrasonic measurement in a narrow space is affected by emitted echoes because the distance from the transducer to the target liquid surface is too short, making measurement impossible. As described above, measurement using ultrasonic waves has been considered technically difficult due to two factors: environmental temperature and measurement distance.

However, as a result of research, the present inventor found that even if the tube is curved, the ultrasonic waves emitted from one end of the tube mainly travel inside the tube and reach the target object, and some of the reflected sound We discovered that the distance from the oscillation position to the target object can be measured by returning to the oscillation position and analyzing the waveform of the reflected sound. Going further, the inventor found that when the exit side opening surface of the tube is inclined with respect to the object to be measured, the sound waves that are first reflected from the object are no longer affected by the echoes from the tip of the tube. We discovered a remarkable fact.

That is, FIGS. 1 to 5 show a summary of the experimental facts that led to the above knowledge. When a 48 kHz ultrasonic wave is emitted from the transducer 2 to the target (block wall) T without a waveguide in Figure 1, the reflected wave is 179.5 cm, which is an actual measurement from the tip of the transducer to the wall surface, compared to the liquid crystal display. It appears as 182.5 cm, indicating that there is almost no error. Incidentally, since this error is caused by the temperature, atmospheric pressure, etc. at the time of measurement, it can be corrected.

Next, when the transducer of FIG. 2 is housed in a short pipe 3 and ultrasonic waves are emitted in the same way, unexpectedly, a strong reflected wave (noise) from the tip 3a of the pipe appears, and the liquid crystal display device (LCD) displayed a distance of 70.26 cm (actual value was 68.5 cm).

Next, as shown in FIG. 3, the total length of the pipe 3 is 4
00 cm, a value of 400.36 cm was displayed for the actual length of 609 cm, and in this case as well, the reflected wave from the tip of the tube 3 interfered with the measurement.

However, as shown in FIG. 4, when the tip 3a on the outlet side of the pipe in FIG. matched.

Therefore, as shown in Figure 5, when we tested a pipe with the tip cut off by 90 degrees, we found that although noise was generated due to the bending of the pipe, the first reflected wave almost accurately corresponded to the actual distance from the transducer to the wall. (actual distance 520 cm, display distance 51 cm)
5 cm) was found. Therefore, if the distance from the transducer to the tip of the pipe is known, the distance from the tip to the surface to be measured can be almost accurately measured. Incidentally, since objects such as molten salt and molten metal have a high density and are almost flat, the intensity of the reflected waves is even greater.

■ Overview Based on the above findings, the present invention provides a waveguide for ultrasonic measurement characterized by being a curved tube with an oblique opening at the tip, and a curved waveguide with an oblique opening at the tip. A liquid level detection device for a liquid material, characterized in that the opening of the tube faces the liquid level of a tank containing the liquid, and an ultrasonic transducer is closely attached to the opening at the other end of the tube. The gist is: Hereinafter, various elements constituting the invention will be explained in terms of sections.

[0014] Ultrasonic transducer The ultrasonic transducer here includes existing or to be developed materials that have the function of mutually converting electrical energy and mechanical energy in ultrasonic technology, such as nickel vibrators and ferrite vibrators. magnetostrictive oscillators, such as
Piezoelectric vibrators such as lithium niobate and zinc oxide, and electrostrictive vibrators such as zirconate/lead titanate ceramics are used. For oscillation, for example, a direct current bias magnetic field is applied to a core winding made of these materials to cause pulse oscillation, and the same element receives the pulse from the target and converts it into an electrical signal, which is then amplified and detected. It can be observed with a cathode ray tube oscilloscope, displayed digitally through an A/D converter, or an alarm can be issued when a predetermined threshold value is exceeded. Techniques for oscillating ultrasonic pulses and amplifying, displaying, and analyzing received pulses are well known, so detailed explanations will be omitted.

[0015] Waveguide It is recommended that the waveguide be a seamless steel pipe, copper pipe, brass pipe, titanium pipe, etc. made by a normal drawing method. Since scratches on the inner surface of the tube will disturb the pulse waveform and make observation difficult, the use of seamed steel tubes should be avoided. If possible, it is desirable to use a tube whose inner surface has been finished smooth by electrolytic polishing or the like.

[0016] One end of the above-mentioned waveguide penetrates the side wall, ceiling, or top plate of a tank or container containing the target molten material, and its opening face obliquely faces the target liquid. Therefore, the pipe facing the liquid must be curved and pass through the wall, ceiling, or top plate of the tank. The angle to be bent is usually 90°, but it is not limited to a right angle, and depending on the mounting position, it may be possible to bend at a larger or smaller angle, bend in two or more directions in the same or opposite directions, or bend in three-dimensional space. It can assume various curved states, such as bending.

[0017]Although the angle of the opening surface of the distal end of the tube is usually around 45° with respect to the surface to be measured, it does not have to be particularly precisely around 45°. Incidentally, since the unevenness of the curved portion is the main cause of disturbing the waveform, it is preferable to use an integral curved tube as much as possible, but a jointed tube can also be used as long as it is substantially smooth.

The transducer is attached to the other end of the tube outside the tank, preferably via a seal or buffer means such as an O-ring. To increase the efficiency of sound wave transmission, the outer wall of the transducer is preferably in close contact with the inner wall of the tube.

[0019]

[Operation] Ultrasonic pulses from the transducer travel through the waveguide, reach the liquid level in the tank, are reflected, travel through the waveguide again, and return to the transducer. The distance from the delay to the object is observed. From the experimental facts shown in Figure 5, among the reflected waves that propagate inside the waveguide and reach the receiving element, the earliest reflected wave corresponds to the distance from the tip of the tube to the object (target). Therefore, by measuring the time until the first reflected wave returns and subtracting the distance from the transducer position to the tip of the tube, it is possible to accurately measure the distance from the tip to the target. can. Note that noise is observed for about 10 milliseconds after the first reflected wave returns, but by electrically configuring it to pick up only the first reflected wave, the negative effects of these subsequent noises can be suppressed. can be avoided.

In addition, with the device of the present invention, only the distance from the tip of the transducer to the target liquid surface matters, and is not affected by the length of the waveguide, so it can be used in narrow spaces such as hot melt adhesive containers. Not only is it possible to measure the liquid level at a high temperature, but the length of the waveguide can be made long enough to protect the transducer from deterioration due to high temperatures, making stable liquid level detection possible over a long period of time. be. In addition, by cooling the outer peripheral surface of the tube with a refrigerant, or by drilling a hole in the tube wall within a distance of about 30 cm from the circumference or tip of the tube insertion part of the transducer, and sending cold gas into the tube through the hole, Overheating of the transducer can be further reduced. When the latter cooling method is adopted, an inert gas is selected as the gas to be supplied as necessary.

[0021] Applications As is clear from the above description, the waveguide of the present invention and its application to ultrasonic measurement technology are mainly used for detecting liquid levels in narrow spaces and in high-temperature environments. However, it goes without saying that it can also be used for more general liquid level detection and surface detection of powder and granular materials that exhibit behavior similar to liquids. For example, it can naturally be applied to surface detection in environments where ultrasonic transducers may be adversely affected by dust, such as in tanks or hoppers containing powder or granular materials.

[0022]

[Examples] Hereinafter, embodiments of the invention will be explained with reference to Examples. However, the examples are merely for explanation and do not mean any restriction or restriction on the idea of the invention.

FIG. 6 is a diagram schematically showing an example of the apparatus of the present invention and its application method.

The device 1 consists of a transducer 2 and a waveguide 3. The transducer 2 is tightly fitted into the outer end opening of the waveguide 3. Note that a pulse generator 4, an amplifier 5, and an indicating device 6 are connected to the transducer 2, respectively.

The waveguide 3 extends horizontally and penetrates the side wall 8a of the high-temperature liquid storage tank 8, and then curves downward at a right angle 3.
b, and its tip opening surface 3a faces the liquid surface 9a of the molten liquid material 9 in the storage tank 8 at an angle of about 45°.

The air supply pipe 7 has an opening 7a in the waveguide wall slightly in front of the transducer 2, and weakly pressurized gas from an external pressure source is sent into the waveguide to cool the pipe, thereby cooling the transducer. Prevent overheating.

When the transducer 2 is activated, the ultrasonic wave S travels through the waveguide 3 and reaches the liquid level 9a, and then the reflected wave S' passes through the waveguide again and reaches the receiving element 5. After being amplified by the amplifier 5, the indicating device 6 is made to indicate the distance from the tip end 3a' of the waveguide 3 to the liquid surface.

[0028]

As explained above, the present invention not only develops a new waveguide for ultrasonic measurement, but also utilizes the waveguide to measure high-temperature liquid levels in narrow spaces or in high-temperature environments. By providing a means to detect height in a non-contact manner, it will contribute to improving and rationalizing process management in related industries.

[Brief explanation of drawings]

[Figure 1] ~

FIG. 5 is a diagram explaining the principle of the device of the present invention.

FIG. 6 is a diagram schematically showing an example of the device of the present invention and its application method.

[Explanation of symbols]

1: Overall invention device 2:1 transducer 3: Waveguide 3a: Tip of 3 3a' 3 tip 3b: Curved part of 3 4: Pulse generator 5: Amplifier 6: Instruction device 7: Air pipe 7a:7 opening 8: High temperature liquid storage tank 8a: Side wall of 8 9: High temperature liquid 9a:9 liquid level

Claims (5)

[Claims] 1. A waveguide for ultrasonic measurement, characterized in that the tip is a curved tube with an oblique opening. 2. The waveguide of claim 1, wherein the waveguide is curved at right angles from the bath. 3. The waveguide according to claim 1 or 2, wherein the inside of the waveguide is smooth. 4. A curved waveguide having an obliquely opened tip, with the opening thereof facing the liquid level of a tank containing a liquid, and an ultrasonic transducer being closely attached to the opening at the other end of the tube. A liquid level detection device for a liquid material, characterized in that the liquid level detection device is installed in a horizontal position. 5. The apparatus of claim 4, wherein the waveguide has an inlet for introducing gas around or slightly in front of the transducer.