JP2002340654A - Method and device for detecting liquid level by sound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sure and stable detection of liquid level without being affected by the existence of a gas phase or a solid phase, by solving such a problem of conventional ultrasonic level meter that an ultrasonic wave is shielded not to obtain a reflected wave required for the detection of the liquid level when a gas phase or solid phase exists in the liquid phase in a vessel, in an ultrasonic level meter for detecting the liquid level by bringing an ultrasonic sensor into contact with the outer wall of the vessel to receive the reflectted wave from the outer wall of the vessel located on the opposite side. SOLUTION: The liquid level is determined by detecting the reflected wave from the gas phase or the solid phase in the liquid phase in the vessel. Alternatively, a reflected wave from a boundary part (liquid level corner) between the liquid surface and an inner wall of the vessel is received mainly through an inside of the vessel wall without passing through the liquid phase substantially to detect the liquid level stably.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method and apparatus for detecting a liquid level in a container by detecting the liquid level in the container by acoustic means from outside the container, and more particularly, to an improvement in the liquid level of ethylene in a pressure tank. The present invention relates to a liquid level detection method and apparatus suitable for detecting a liquid level.

[0002]

2. Description of the Related Art Conventionally, there have been known many methods for measuring the liquid level inside a container from the outer wall surface by acoustic means. First, in (1) JP-A-61-3012 and JP-A-8-136320, a reflected wave of an inner wall surface on a side opposite to a wall surface on which an ultrasonic wave is incident is received through a liquid phase in a container and the presence or absence of a liquid phase is determined. In addition, the liquid level is determined with certainty by detecting only the reflected wave from the inner wall surface on the opposite side. Also, (2) JP-A-5-13379
No. 2, the ultrasonic wave is emitted from the outer wall surface of the container obliquely upward in the liquid in the container, and the ultrasonic wave reflected and returned from the corner where the liquid surface and the inner wall of the container come into contact is detected. It is disclosed that the liquid level is detected from the propagation time. Further, (3) JP-A-11-218436 and JP-A-2218436
Japanese Patent Application Laid-Open No. 000-12410 discloses a technique in which a reflected wave from an inner wall surface on a side where an ultrasonic sensor is installed is received, and a liquid level is determined from a difference in attenuation characteristics of multiple reflected waves in the wall depending on the presence or absence of a liquid phase in a container. It is disclosed.

[0003]

In the above-mentioned prior arts (1) and (2), it is considered that the ultrasonic wave propagates in the liquid phase in the container and is reflected by the inner wall surface or the corner portion on the opposite side and returns. Because it is used, if there is a gas phase or solid phase in the liquid phase, ultrasonic waves are scattered and attenuated by the gas phase or solid phase, and reflected waves from the inner wall surface and corners on the opposite side cannot be obtained. However, reliable and stable liquid level determination cannot be performed.

The prior art (3) utilizes the fact that the (multiple) reflected waves from the inner wall surface on the side where the ultrasonic sensor is installed are greatly attenuated by the presence of the liquid phase. However, when the material of the container is a plastic material and the difference from the acoustic impedance of the liquid is small, the reflected wave is attenuated to, for example, about 30% due to the liquid phase in the container. Has a drawback that it is attenuated only to 94% even by the presence of the liquid phase, and the determination is not always reliable.

It is an object of the present invention to provide a method and an apparatus for detecting a liquid level by sound which can perform a reliable and stable judgment even when a gas phase or a solid phase exists in a liquid phase in a container.

[0006]

According to a first feature of the present invention, a sound wave is transmitted from a sound wave transmitter / receiver disposed on a container wall toward the inside of a container, and a sound wave is transmitted from an inner wall of the container wall where the transmitter / receiver is disposed. The liquid level is determined based on the presence or absence of the sound wave within the time between the reception of the reflected wave from the container and the reception of the reflected wave from the opposing inner wall of the container.

Another feature of the present invention is that
A number of sound wave transceivers are vertically arranged along the container wall, sound waves are transmitted from these sound wave transceivers toward the inside of the container, and the reflected wave from the container inner wall on the side where the transceiver is arranged and received. It is to determine the presence or absence of the sound wave within the time between the reception of the reflected wave from the opposed inner wall of the container, and the liquid level from the determination result of the presence or absence of the sound wave of the plurality of transceivers.

Another feature of the present invention is that
The sound wave transceiver is moved up and down along the container wall, the sound wave is transmitted from the sound wave transceiver toward the inside of the container, the reflected wave is received from the inner wall of the container wall in which the transceiver is arranged, and the container facing the container. By determining the presence or absence of a sound wave within the time between the reception of the reflected wave from the inner wall, by determining the liquid level from the determination result of the presence or absence of the sound wave before and after the vertical movement of the transducer. is there.

Further, another feature of the present invention is that
The reflected wave at the corner where the liquid surface in the container and the inner wall surface of the container are in contact,
That is, the liquid level is determined by receiving from the container wall side in contact with the corner.

Still another feature of the present invention is that a liquid level is determined by detecting a generated sound and / or a bursting sound of a gas phase in a liquid phase in a container.

Thus, even in the case of a gas phase or a liquid phase including a solid phase, the liquid level is reliably determined acoustically from outside the container.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram illustrating the principle of a liquid level detection method according to an embodiment of the present invention. In the figure, a liquid (liquid phase) 2 such as ethylene exists in a container 1 such as a pressure tank,
The liquid level is the liquid level 21. A plurality of ultrasonic transceivers (hereinafter, simply referred to as sensors) 3 are installed on the outer wall of the container as shown by sensors 31 and 32 in the figure, or one sensor can move up and down along the outer wall of the container. Be placed.
When ultrasonic waves are transmitted in a substantially horizontal direction from the sensor 3 toward the inside of the container, the sensor 3 receives the scattered and reflected waves N due to the gas phase 4 and the solid phase 5 in the liquid phase 2. Normally, ethylene is boiling and there are many gaseous phases 4.

FIG. 2 is an explanatory diagram of a reception waveform by the liquid level detection method in the first embodiment of the present invention. The reception waveform when the ultrasonic sensor 3 is located below the liquid level 21 in the container 1, that is, at the position of the sensor 31, is shown in FIG.
After the transmission pulse T, the gas phase 4 and the solid phase 5 in the liquid phase 2 appear after the first inner wall reflected wave B1.
Scattered and reflected waves N (N1 to N4) are received. The ultrasonic sensor 3 is moved upward, and the upper surface 2 of the liquid phase 2 in the container 1 is moved.
When the ultrasonic sensor 32 is moved to a position higher than 1, the received waveform becomes as shown in FIG. 2B without a liquid phase, and only the inner wall reflected wave B1 and its multiple reflected waves B2, B3. Is done. Therefore, whether a plurality of ultrasonic sensors 3 are provided,
Alternatively, while moving one sensor, the scattered reflected waves N (N1, N2, N3) from the gas phase 4 or the solid phase 5 received between the inner wall reflected wave B1 and the multiple reflected waves B2, B3.
…)) To monitor the presence or absence of
The liquid level in the container 1 can be detected even when the liquid contains the solid phase 5 or the solid phase 5. When the liquid phase 2 does not include the gas phase 4 or the solid phase 5, it is needless to say that the liquid level can be detected by detecting the reflected wave A on the inner wall surface on the opposite side.

FIG. 3 shows a first embodiment of the present invention when the container wall is thin.
FIG. 7 is an explanatory diagram of a reception waveform when a liquid phase exists according to the liquid level detection method in the embodiment of FIG. As shown in FIGS. 3A and 3B, the inner wall reflected wave B1 and its multiple reflected waves B2, B
From the reception time 3 onward, the reflected wave A on the inner wall surface on the opposite side
Gas phase 4 in the liquid phase 2 received before the time when
Monitoring the scattered and reflected waves N (N1, N2...) Due to the liquid phase 2 and the gas phase 4 or the solid phase 5 at the height of the sensor. Can be determined.

FIG. 4 is a block diagram showing the overall configuration of the liquid level detecting device according to the first embodiment of the present invention. As the ultrasonic sensor 3, a large number (N) of sensors 31, 32,... 3N are vertically arranged along the wall surface of the container 1. The switching circuit 6 electrically switches these ultrasonic sensors 3 according to a switching signal from the signal processing and liquid level determination unit 9,
The reflected waves N from the gas phase 4 and the solid phase 5 in the liquid phase 2 in the tank 1 are sequentially received. The reception status of the reflected wave is observed via the ultrasonic transmission / reception unit 7 and the reception signal observation unit 8, and the signal processing and the liquid level determination unit 9 determines the liquid level.

FIG. 5 is a processing flow chart of the liquid level detecting method according to the first embodiment of the present invention shown in FIG. First, step 5
After the sensitivity adjustment at 01, initial conditions for turning on the sensor 31 are set. In step 502, it is determined whether there is a reflected wave N wave from the vapor phase 4 or the solid phase 5 or an opposed inner wall reflected wave A wave. If not, the next sensor is turned on in step 503 and the determination in step 502 is performed again. Do. This is N wave or A
Repeat until a wave is detected, and proceed to step 504. In step 504, the number of the received sensor, that is, the position in the vertical direction is confirmed. The liquid level can be detected by knowing which sensor has received from the preset mounting positions of the plurality of sensors. Thus, the liquid level is determined in step 505, and the result is displayed.

According to this embodiment, by sequentially switching the sensors, the liquid level can be known from the sensor position where the reflected wave N from the gas phase 4 or the solid phase 5 or the reflected wave A on the opposed inner wall surface disappears or appears. Even if the liquid 2 has many gas phases 4 and solid phases 5 and it is difficult to obtain the reflected wave A on the opposed inner wall surface, the liquid level can be reliably determined.

FIG. 6 is a block diagram showing the overall arrangement of a liquid level detecting device according to a second embodiment of the present invention. The same reference numerals as those in FIG. 4 have substantially the same functions, and duplicate description will be omitted.
In this embodiment, the number of the sensors 3 is one, and the driving and position measuring unit 10 drives the sensor 3 in the vertical direction and measures the current position. Reference numerals 31 and 32 represent two positions of one moved sensor.

FIG. 7 is a flowchart of the liquid level determination in the second embodiment of the present invention shown in FIG. First, in step 701, the ultrasonic sensor 3 is brought into acoustic contact with the outer wall surface of the container, receives the reflected wave B on the inner wall surface of the container, and performs initial setting of the apparatus such as sensitivity. Next, in step 702, the presence or absence of the scattered reflected wave N or the opposed inner wall surface reflected wave A due to the gas phase 4 or the solid phase 5 in the liquid phase 2 in the container 1 is determined from the received waveform. When the reflected wave N or A is confirmed, the process proceeds to step 703, where the ultrasonic sensor 3 is moved upward, and the process proceeds to step 704.
The movement of the sensor 3 is repeated until the disappearance of the reflected waves N and A is confirmed. If the disappearance of the reflected waves N and A is confirmed, the position of the ultrasonic sensor at that time is measured by the drive and position measurement unit 10 in step 705. If there is no reflected wave N or A from the beginning in step 702, the flow advances to step 706 to move the sensor 3 downward. Similarly, the sensor 3 is moved until the appearance of the reflected wave N or A is confirmed in step 707, and the sensor position is measured in step 705. At step 708, the liquid level is determined based on the result.

The movement and position reading of the ultrasonic sensor 3 may be manual or automatic.

In the first and second embodiments of the present invention described with reference to FIGS.
In the case of measuring the liquid level of the liquid phase 2 having a large number of liquids, the liquid level determination is sufficiently possible even if only the scattered reflected wave N is received and the opposed inner wall reflected wave A is not received in a timely manner. is there.
In this case, the data is collected with the position of the true liquid level grasped in advance from the position of the ultrasonic sensor and the received signal information, and a model of the reception pattern information and the judgment result is created based on the result, and the actual measurement is performed. In this case, if the liquid level is determined by comparing with such model data, the liquid level can be determined with higher accuracy.

FIG. 8 is a block diagram showing the overall arrangement of a liquid level detecting device according to a third embodiment of the present invention. The oblique ultrasonic sensor 3 is applied to the outer wall surface of the container, and the ultrasonic wave is applied to the liquid surface 21 in the container 1.
Is transmitted from the lower side (liquid phase side) toward the liquid surface 21. The ultrasonic wave is reflected at a boundary (liquid level corner) 12 where the liquid surface 21 contacts the inner wall 11 of the container, that is, at the liquid surface formed by the contact angle of the surface tension, and the reflected wave R is received by the ultrasonic sensor 3 (31 or 32). it can.

FIG. 9 is an explanatory diagram of the reception waveform in the embodiment of FIG. The position of the liquid surface 21 is determined by moving the ultrasonic sensor 3 in the vertical direction and at the maximum reception intensity position of the reflected wave R, the time T from when the ultrasonic wave is transmitted to when the reflected wave R is received
2, the incident angle θ of the ultrasonic wave into the container wall,
It can be calculated from the thickness L of the container wall and the ultrasonic sound velocity in the container wall material. For example, as shown in FIG. 8, when an ultrasonic wave enters the container wall at θ degrees, the distance ΔY from the ultrasonic wave incident point position to the liquid surface 21 can be calculated by Expression (1).

ΔY = (tan ⁻¹ θ) × L (1) Therefore, if the sensor position is P31, the liquid level P is
It is obtained by equation (2).

Liquid level P = P31 + ΔY (2) In this case, the distance from the inner wall surface 11 of the container to the liquid level corner 12 is neglected, but it is necessary to calculate or calibrate by adding this distance as necessary. Can also. Further, a time Th from the time T1 when the ultrasonic wave is transmitted to the time when the reflected wave R is received.
Can be calculated from the distance in the ultrasonic sensor 3 and its sound speed, the distance in the container wall and its sound speed, and the distance from the container inner wall surface to the liquid level corner 12 and its sound speed.

FIG. 10 is a processing flowchart in the embodiment of FIGS. After the initial setting in step 101,
In step 102, the sensor 3 is moved upward from below the liquid level 21, and the process is repeated until the reception of the corner reflected wave R is confirmed in step 103. When the reflected wave R is detected, the acoustic sensor 3 is moved up and down in step 104, and the position where the amplitude of the reflected wave R shows a peak or disappears is specified in step 105. When the ultrasonic wave reaches the inner wall 11 past the liquid level corner 12, the corner reflected wave R cannot be received. Therefore, the position where the corner reflected wave R becomes a peak or disappears is determined as the liquid level P. Step 10
At 7, the liquid level P is determined from the sensor position P31 and the distance ΔY as described above.

FIG. 11 is a block diagram showing the overall arrangement of a liquid level detecting device according to a fourth embodiment of the present invention. 8 have almost the same functions as those in FIG. In this embodiment, the reflection of a wave (called a creeping wave) that propagates as a transverse wave in the container wall, is mode-converted into a kind of longitudinal wave on the inner wall surface, and propagates along the wall surface is used. In this configuration, the type of the acoustic sensor is different, and a vertically propagating ultrasonic wave has been used until now. Here, the ultrasonic wave is obliquely incident at a specific angle. The incident angle θ of the longitudinal wave into the steel is 70 to 90
When incident in degrees, a transverse wave of 30 to 33 degrees is generated. The transverse wave that reaches the inner wall 11 of the tank (container) 1 becomes a creeping wave that propagates along the inner wall 11 surface. The creeping wave propagates while leaking into the liquid, and
The wave reflected and scattered by the curved portion due to the surface tension of the above and returned on the same path is received by the same sensor 31. Alternatively, the scattered reflected wave may be received by another sensor 32. Further, the reflected waves from the corners 12 may always be efficiently received under optimum conditions using an ultrasonic array sensor or the like. further,
When the liquid level swings up and down or when the inner wall surface 11 and the liquid surface 21
When the contact angle becomes an obtuse angle, an ultrasonic wave can be transmitted and received from above the liquid surface 21 of the liquid phase 2 in the container 1 (gas phase side) to detect the liquid level.

FIG. 12 is a flowchart of the liquid level detecting method in the embodiment of FIG. This flowchart is for the case of receiving by the sensor 31. Step 121
After the initial setting, the sensor 3 is moved upward from below the liquid level 21 in step 122, and the process is repeated until the reception of the corner reflected wave R can be confirmed in step 123. When the reflected wave R is detected, the acoustic sensor 3 is moved up and down in step 124, and the position where the reflected wave R disappears is specified in step 125. The received corner reflected wave is received in a timely manner as the sensor approaches the liquid level corner portion, and when the ultrasonic wave reaches the inner wall surface passes the corner portion, the corner reflected wave cannot be received. Therefore, it is determined that the liquid level has a position where the corner reflected wave disappears. In step 126, the sensor position at which the corner reflected wave R disappears is measured, and in step 127, the liquid level P is determined from the sensor position P31 and the distance ΔY as described above.
Is determined.

FIG. 13 is a block diagram showing the overall configuration of a fifth embodiment of the liquid level detecting device according to the present invention. The acoustic sensor 30 of this configuration is a sound wave receiver within a range of several tens of hertz to several hundreds of kilohertz, and only receives a plosive sound or a generated sound of the gas phase 4 generated inside the container 1 and does not generate a sound wave by itself. . Also in this embodiment, duplicate description of similar substances is avoided. Although the configuration is similar to that of the previous embodiments, the only difference is that in addition to the sensor 30 for receiving only (301, 302,... 30N), a simple sound wave receiving unit 70 may be used in place of the ultrasonic wave transmitting / receiving unit 7. Data 13 storing reference patterns of received signals at each of the 30 positions is prepared.

FIG. 14 is a processing flowchart of a liquid level detecting method according to a fifth embodiment of the present invention. Step 141
The initialization is performed in step 142, and the received signal is captured in step 142. In step 143, it is checked whether the received signal matches any of the reference patterns 13, and if not, the next sensor is switched in step 145. If they match, it is determined as a temporary water level in step 146, and the end of all the sensors is confirmed in step 147. Then, in step 148, the final water level is determined, and the result is displayed. In this way, each time the sensors 301 to 30N are switched and a received signal is received, it is checked whether or not it matches any of the above-described reference patterns 13, and if they match, it is determined as a tentative water level. The water level is determined by comprehensively judging the matching status of the received signals of the sensors. In determining the water level, it is desirable to confirm that the received signal patterns of two or more sensors installed near the water level substantially match the reference pattern. At this time, for the received signal,
Processing methods such as position determination of a plosive sound generation position, correlation processing, and frequency analysis may be applied.

In the above-described embodiment, when the container is in a high or low temperature state, the liquid level can be detected by selectively using high and low temperature acoustic sensors.

According to the above embodiment, the reflected wave from the gas phase or solid phase generated in the liquid phase in the container and the reflected wave from the boundary (liquid level corner) between the liquid surface and the inner wall surface in the container are formed. By detecting and detecting the liquid level, even if a gas phase or solid phase exists in the liquid phase in the container and it is difficult to obtain reflected waves from the inner wall surface of the opposite container, the liquid level can be detected from the outer surface of the container. It can be detected with a stable, reliable and simple configuration.

[0034]

According to the present invention, even if a gas phase or a solid phase exists in the liquid phase in the container, the liquid level in the container can be detected stably and reliably from the outer surface of the container.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a liquid level detection method according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a reception waveform according to a liquid level detection method in one embodiment of the present invention.

FIG. 3 is an explanatory diagram of a reception waveform by a liquid level detection method according to one embodiment of the present invention when a container wall is thin.

FIG. 4 is an overall configuration block diagram of a liquid level detection device according to a first embodiment of the present invention.

FIG. 5 is a processing flowchart of a liquid level detection method according to the first embodiment of the present invention.

FIG. 6 is an overall configuration block diagram of a liquid level detection device according to a second embodiment of the present invention.

FIG. 7 is a processing flowchart of a liquid level detection method according to a second embodiment of the present invention.

FIG. 8 is an overall configuration block diagram of a liquid level detection device according to a third embodiment of the present invention.

FIG. 9 is an explanatory diagram of a reception waveform in the liquid level detection method according to the third embodiment of the present invention.

FIG. 10 is a processing flowchart of a liquid level detection method according to a third embodiment of the present invention.

FIG. 11 is an overall configuration block diagram of a liquid level detection device according to a fourth embodiment of the present invention.

FIG. 12 is a processing flowchart of a liquid level detection method according to a fourth embodiment of the present invention.

FIG. 13 is an overall configuration block diagram of a liquid level detection device according to a fifth embodiment of the present invention.

FIG. 14 is a processing flowchart of a liquid level detection method according to a fifth embodiment of the present invention.

[Explanation of symbols]

1 ... container, 2 ... liquid phase, 21 ... liquid level, 3, 31, 32, 3
N: Ultrasonic transceiver (ultrasonic sensor), 30, 301,
302, 30N: sound wave receiver (sonic wave sensor for reception only), 4: gas phase, 5: solid phase, 6: switching circuit, 7: ultrasonic transmission / reception section, 70: sound wave reception section, 8: reception signal observation section,
Reference numeral 9: signal processing and liquid level determination unit, 10: drive and position measurement unit, 11: container inner wall, 12: boundary part (liquid level corner), 1
3 ... stored data of reference pattern of received signal, T: transmitted wave,
A: a reflected wave from the inner wall of the container facing, B: a reflected wave from the inner wall of the container wall where the transmitter / receiver is arranged, N: a reflected wave from the gas phase or solid phase, R: from a boundary (liquid level corner) Reflected waves.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Koike 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Power and Electricity Research Laboratory, Hitachi, Ltd. (72) Inventor Tetsuya Matsui Omika-cho, Hitachi City, Ibaraki Prefecture 7-2-1, Hitachi, Ltd. Electric Power and Electrical Development Laboratory (72) Inventor Fukai ▲ Shin ▼ Tsukasa 24-24 Nishishinbashi, Minato-ku, Tokyo F-term in Nissan Industrial Co., Ltd. ) 2F014 AA07 AA08 FB01 GA05

Claims (9)

[Claims] In a liquid level detection method for detecting a liquid level in a container from outside of a container by an acoustic sensor, a step of transmitting a sound wave from a sound wave transceiver toward the inside of the container, and after the transmission, a liquid in the container A method for detecting a liquid level by sound, comprising a step of receiving a reflected wave from a gas phase in a phase or a solid phase. 2. A liquid level detecting method for detecting a liquid level in a container from outside of a container by an acoustic sensor, wherein a sound wave is transmitted from a sound wave transceiver toward the inside of the container; Determining whether or not a sound wave has been received within a time period between the reception of the reflected wave from the inner wall of the container wall on which the vessel is disposed and the reception of the reflected wave from the opposite inner wall of the container. Liquid level detection method. 3. A liquid level detecting method for detecting a liquid level in a container from outside of a container by using an acoustic sensor, wherein a plurality of sound wave transceivers vertically arranged along an outer wall of the container are used to detect a liquid level in the container. Transmitting a sound wave toward, and the presence or absence of sound wave reception within the time between the reception of the reflected wave from the inner wall of the container wall where the transceiver is arranged and the reception of the reflected wave from the opposite container inner wall. A liquid level detection method using sound, comprising: a step of determining for each of the transceivers; and a step of determining a liquid level from a determination result of the presence or absence of the reception for each of the transceivers. 4. A liquid level detecting method for detecting a liquid level in a container from the outside of a container by an acoustic sensor, wherein a sound wave transceiver is moved up and down along an outer wall of the container.
Transmitting a sound wave from the sound wave transceiver toward the inside of the container, and receiving the reflected wave from the inner wall of the container wall on which the transceiver is arranged and receiving the reflected wave from the opposing container inner wall; Determining whether or not a sound wave has been received within a time period for each movement position of the transceiver; and determining a liquid level from a determination result of the presence or absence of the reception before and after the movement. Liquid level detection method. 5. A liquid level detecting method for detecting a liquid level in a container from outside of a container by using an acoustic sensor, wherein a sound wave is transmitted from a sound wave transmitter / receiver disposed on an outer wall of the container into the container wall at an oblique angle. Receiving the sound wave reflected at the boundary between the liquid surface in the container and the inner wall of the container by the transceiver or another receiver, and detecting the sound wave from the reception timing of the reflected wave. Determining a liquid level using a sound. 6. A liquid level detecting method for detecting a liquid level in a container by an acoustic sensor, wherein the liquid phase in the container is received by receiving a sound wave by a sound wave receiver within several tens of hertz to several hundred kilohertz disposed on the outer wall of the container. Receiving the generated sound of the gaseous phase or the plosive sound of the gaseous phase, and detecting the presence or absence of the received signal or the result of the signal analysis processing such as frequency analysis, position estimation, and correlation processing of the received signal. A method for detecting a liquid level by sound, comprising the step of determining a level. 7. A liquid level detecting device for detecting a liquid level in a container from outside of a container by using an acoustic sensor, the ultrasonic sensors being arranged vertically along the outer wall of the container and emitting ultrasonic waves toward the inside of the container. Then, a number of ultrasonic transceivers for receiving ultrasonic waves from the inside of the container, the reception of reflected waves from the inner wall of the container wall where these transceivers are arranged, and the reception of reflected waves from the opposing inner wall of the container. A reception signal observation unit for observing the presence or absence of sound waves within the time period for each of the transceivers, and a liquid level determination unit for determining a liquid level from an observation result of the reception signal observation unit for each of the transceivers A liquid level detecting device using sound, comprising: 8. A liquid level detecting device for detecting a liquid level in a container from outside of the container by using an acoustic sensor, the ultrasonic sensor being disposed on an outer wall of the container, transmitting ultrasonic waves to the container wall at an oblique angle, and in substantially the same direction. An ultrasonic transmitter / receiver that receives ultrasonic waves from, a reception signal observation unit that observes reception of the ultrasonic waves within a predetermined time after transmitting the ultrasonic waves, and a liquid level from an observation result of the reception signal observation unit. A liquid level detection device using sound, comprising: a liquid level determination unit for determining. 9. A liquid level detecting device for detecting a liquid level in a container from outside of a container by using an acoustic sensor, wherein the liquid level detecting device is vertically arranged along an outer wall of the container, and has several tens of hertz to several tens of hertz generated from inside the container. A large number of sound wave receivers for receiving sound waves of 100 kilohertz, a reception signal observation unit for observing the reception status of these many sound wave receivers for each of the receivers, and a liquid level based on the observation result of the reception signal observation unit. And a liquid level determining unit for determining the liquid level.