JP2008070388A - Liquid level detection method by means of sound and its device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level detection method by means of sound and its device for performing sure and stable determination even if a gaseous phase or a solid phase exists in an intra-container liquid phase. <P>SOLUTION: This liquid level detection device detecting a liquid level in a container from outside the container 1 by an acoustic sensor 30, is equipped with a multitude of sound wave receivers 301 to 30n vertically aligned along an outer wall of the container for receiving sound waves of several tens of hertz to several hundreds of kilohertz generated in the container, a received signal observation part 8 observing the reception conditions of the multitude of sound wave receivers on a receiver-by-receiver basis, and a liquid level determination part 9 determining the liquid level from an observation result of the observation part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an improvement in an acoustic liquid level detection method and apparatus for detecting a liquid level in a container with an acoustic sensor from the outside of the container, and in particular, a liquid level detection suitable for detecting the ethylene level in a pressure tank. It relates to a method and apparatus.

  Conventionally, many methods for measuring an internal liquid level from an outer wall surface of a container by acoustic means are known. First, (1) In Patent Document 1 and Patent Document 2, an inner wall reflected wave on the opposite side of a wall surface on which ultrasonic waves are incident is received through the liquid phase in the container to detect the presence or absence of the liquid phase, By trying to receive only the reflected wave from the wall surface, the liquid level is reliably determined. Also, (2) Patent Document 3 discloses that ultrasonic waves are emitted from the outer wall surface of the container obliquely upward in the liquid in the container and reflected back from the corner portion where the liquid surface and the inner wall of the container are in contact. It is disclosed that the liquid level is detected from the propagation time. Furthermore, (3) Patent Document 4 and Patent Document 5 receive the reflected wave from the inner wall surface on the side where the ultrasonic sensor is installed, and the attenuation characteristics of the multiple reflected waves in the wall due to the presence or absence of the liquid phase in the container. It is disclosed that the liquid level is determined from the difference.

Japanese Patent Laid-Open No. 61-3012 JP-A-8-136320 Japanese Patent Laid-Open No. 5-133792 Japanese Patent Laid-Open No. 11-218436 JP 2000-121410 A

  In the prior arts (1) and (2), since the ultrasonic wave propagates in the liquid phase in the container and is reflected and returned by the inner wall surface or the corner portion on the opposite side, the liquid phase If there is a gas phase or solid phase inside, the ultrasonic wave is scattered and attenuated by the gas phase or solid phase, and the reflected wave from the inner wall surface and corner of the opposite side cannot be obtained, so reliable and stable liquid level judgment is possible Can not.

  Further, in the prior art (3), the fact that (multiple) reflected waves from the inner wall surface on the side where the ultrasonic sensor is installed is greatly attenuated due to the presence of the liquid phase. However, when the material of the container is plastic and the difference from the acoustic impedance of the liquid is small, the reflected wave is noticeably attenuated by about 30% due to the liquid phase in the container, but the container is a steel tank. However, there is a drawback in that the attenuation is only 94% due to the presence of the liquid phase and the determination is not necessarily reliable.

  An object of the present invention is to provide an acoustic liquid level detection method and apparatus that can perform a reliable and stable determination even when a liquid phase in a container has a gas phase or a solid phase.

  In a preferred embodiment of the present invention, in a liquid level detection method for detecting a liquid level in a container by an acoustic sensor, by receiving a sound wave by a sound wave receiver in the tens to hundreds of kilohertz arranged on the outer wall of the container, Based on the step of receiving the gas phase generation sound or gas phase burst sound in the liquid phase in the container, and the presence or absence of this received signal or the signal analysis processing results such as frequency analysis, position evaluation, correlation processing, etc. of this received signal The method includes the step of determining the liquid level in the container.

  In another preferred embodiment of the present invention, in the liquid level detection device for detecting the liquid level in the container from the outside of the container by the acoustic sensor, the liquid level detection apparatus is arranged in the vertical direction along the outer wall of the container and is generated from the inside of the container. A plurality of sound wave receivers for receiving sound waves of several tens of hertz to several hundred kilohertz, a reception signal observation unit for observing the reception status of these many sound wave receivers for each receiver, and the reception signal observation unit And a liquid level determination unit for determining the liquid level from the observation results of the above.

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

  Hereinafter, embodiments of the present invention will be described 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, and the liquid level is a liquid level 21. A plurality of ultrasonic transmitters / receivers (hereinafter simply referred to as sensors) 3 are installed on the outer wall of the container as shown by the sensors 31 and 32 in the figure, or one sensor can move vertically along the outer wall of the container. Be placed. If ultrasonic waves are transmitted from the sensor 3 into the container in a substantially horizontal direction, the sensor 3 receives the scattered reflected wave N from the gas phase 4 and the solid phase 5 in the liquid phase 2. Usually ethylene is boiling and there are many gas phases 4.

  FIG. 2 is an explanatory diagram of received waveforms by the liquid level detection method in the first embodiment of the present invention. The received waveform when the ultrasonic sensor 3 is positioned below the liquid level 21 in the container 1, that is, at the position of the sensor 31, is as shown in FIG. The scattered reflected waves N (N1 to N4) from the gas phase 4 and the solid phase 5 in the liquid phase 2 are received after the first inner wall surface reflected wave B1. When the ultrasonic sensor 3 is moved upward and moved to the position of the ultrasonic sensor 32 above the upper surface 21 of the liquid phase 2 in the container 1, the received waveform is as shown in FIG. Thus, only the inner wall surface reflected wave B1 and its multiple reflected waves B2, B3... Are received. Therefore, scattering from the gas phase 4 and the solid phase 5 received between the inner wall reflected wave B1 and the multiple reflected waves B2, B3... While providing a plurality of ultrasonic sensors 3 or moving one sensor. By monitoring the presence or absence of the reflected wave N (N1, N2, N3...), The liquid level in the container 1 can be detected even when the liquid phase 2 includes the gas phase 4 or the solid phase 5. Needless to say, when the liquid phase 2 does not include the gas phase 4 or the solid phase 5, the liquid level can be detected by detecting the reflected wave A on the opposite inner wall surface.

  FIG. 3 is an explanatory diagram of received waveforms when a liquid phase is present by the liquid level detection method in the first embodiment of the present invention when the container wall is thin. As shown in FIGS. 6A and 6B, from the time after receiving the inner wall surface reflected wave B1 and its multiple reflected waves B2, B3... To the time when the opposed inner wall surface reflected wave A is received. If the scattered reflected wave N (N1, N2,...) By the gas phase 4 or the solid phase 5 in the liquid phase 2 received in between is monitored, the liquid phase 2, the gas phase 4 or the solid phase 5 at the sensor height position. Since the presence or absence can be detected, the liquid level in the container 1 can be similarly determined.

  FIG. 4 is an overall configuration block diagram of the liquid level detection 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 arranged in the vertical direction along the wall surface of the container 1. The switching circuit 6 electrically switches these ultrasonic sensors 3 group by the signal processing and switching signal from the liquid level determination unit 9, and sequentially from the gas phase 4 and the solid phase 5 in the liquid phase 2 in the tank 1. A reflected wave N is received. The reception state of the reflected wave is observed through the ultrasonic transmission / reception unit 7 and the reception signal observation unit 8, and the liquid level is determined by the signal processing and liquid level determination unit 9.

  FIG. 5 is a process flow diagram of the liquid level detection method according to the first embodiment of the present invention shown in FIG. First, after adjusting the sensitivity in step 501, initial conditions are set to turn on the sensor 31. In step 502, the presence or absence of the reflected wave N wave from the gas phase 4 or the solid phase 5 or the opposed inner wall surface reflected wave A wave is determined. If not, the next sensor is turned on in step 503 and the determination in step 502 is performed again. Do. This is repeated until an N wave or an A wave is detected, and the process proceeds to step 504. In step 504, the number of the received sensor, that is, the vertical position is confirmed. The liquid level can be detected if it is known which sensor has received from a plurality of preset sensor mounting positions. Accordingly, the liquid level is determined in step 505, and the result is displayed.

  According to the present 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 opposite inner wall surface disappears or appears. Even in the case of the liquid 2 in which the phase 4 and the solid phase 5 are large and the opposed inner wall surface reflected wave A is difficult to obtain, the liquid level can be reliably determined.

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

  FIG. 7 is a flow chart for determining the liquid level in the second embodiment of the present invention shown in FIG. First, in step 701, the ultrasonic sensor 3 is acoustically brought into contact with the outer wall surface of the container, and the inner wall surface reflected wave B or the like is received to perform 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. If the reflected wave N or A is confirmed, the process proceeds to step 703, the ultrasonic sensor 3 is moved upward, and the movement of the sensor 3 is repeated until the disappearance of the reflected wave N or A is confirmed in step 704. 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 driving and position measuring unit 10 in step 705. If there is no reflected wave N or A from the beginning in step 702, the process proceeds to step 706, and conversely the sensor 3 is moved 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. Based on this result, the liquid level is determined in step 708.

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

  In the first and second embodiments of the present invention described above with reference to FIGS. 4 to 7, in particular, in the case of the liquid level measurement of the liquid phase 2 having many bubbles 4 such as ethylene, only the scattered reflected wave N is used. Even if it is configured so that the reflected wave A on the opposite inner wall surface is not received in a timely manner, the liquid level can be determined sufficiently. In this case, data is collected in advance with the true liquid level position grasped from the position of the ultrasonic sensor and the received signal information, and a model of the received pattern information and judgment result is created based on the result, and 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 of the overall configuration of the liquid level detection device according to the third embodiment of the present invention. The oblique angle ultrasonic sensor 3 is applied to the outer wall surface of the container, and ultrasonic waves are transmitted from the lower side (liquid phase side) of the liquid surface 21 in the container 1 toward the liquid surface 21. The ultrasonic wave is reflected by the boundary surface (liquid surface corner) 12 where the liquid surface 21 is in contact with the inner wall 11 of the container, that is, 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 received waveforms in the embodiment of FIG. The position of the liquid surface 21 is determined by moving the ultrasonic sensor 3 in the vertical direction to a time Th from the ultrasonic transmission time T1 to the time T2 at which the reflected wave R is received at the position of the maximum reception intensity of the reflected wave R, and the container. It can be calculated from the ultrasonic incident angle θ into the wall, the thickness L of the container wall, the ultrasonic velocity of sound in the container wall material, and the like. For example, as shown in FIG. 8, when an ultrasonic wave is incident on the container wall at θ degrees, the distance ΔY from the position of the ultrasonic wave incident point to the liquid surface 21 can be calculated by Expression (1).

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

Liquid level P = P31 + ΔY (2)
In this case, the distance from the inner wall surface 11 of the container to the liquid surface corner 12 is ignored, but can be calculated or calibrated by taking this distance into account as necessary. The time Th from the time T1 at which the ultrasonic wave is transmitted until the reflected wave R is received is the distance in the ultrasonic sensor 3 and its sound speed, the distance in the container wall and its sound speed, and the liquid surface corner 12 from the inner wall surface of the container. Can be calculated by the distance to and the speed of sound.

  FIG. 10 is a processing flowchart in the embodiment of FIGS. After the initial setting in step 101, the sensor 3 is moved from the lower side to the upper side in step 102, and the process is repeated until the reception of the corner reflected wave R can be confirmed in step 103. When the reflected wave R is detected, the acoustic sensor 3 is moved up and down in step 104, and a position where the amplitude of the reflected wave R shows a peak or disappears is specified in step 105. When the arrival point of the ultrasonic wave to the inner wall 11 passes the liquid surface corner 12, the corner reflected wave R cannot be received. Therefore, the position where the corner reflected wave R reaches the peak or disappears is determined as the liquid level P. In step 107, 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 configuration of the liquid level detection device according to the fourth embodiment of the present invention. The same reference numerals as those in FIG. 8 have almost the same functions, and redundant description is avoided. In the present embodiment, the reflection of a wave (referred to as a creeping wave) that propagates in the container wall with a transverse wave, 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 acoustic sensor is different and ultrasonic waves propagating vertically have been used so far, but here, the ultrasonic waves are incident obliquely at a specific angle. If the incident angle θ of the longitudinal wave into the steel is 70 to 90 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 surface of the inner wall 11. The creeping wave propagates while leaking into the liquid, and is reflected and scattered by a curved portion due to the surface tension of the corner 12 of the liquid surface 21, and a wave returning in the same path is received by the same sensor 31. Alternatively, the scattered reflected wave may be received by another sensor 32. In addition, the reflected wave from the corner 12 may be always received efficiently and optimally using an ultrasonic array sensor or the like. Furthermore, when the liquid level fluctuates up and down or when the contact angle between the inner wall surface 11 and the liquid surface 21 becomes an obtuse angle, ultrasonic waves above the liquid surface 21 of the liquid phase 2 in the container 1 (gas phase The liquid level can also be detected by transmitting and receiving from the side).

  FIG. 12 is a process flowchart of the liquid level detection method in the embodiment of FIG. This flowchart is a case where the sensor 31 receives data. After the initial setting in step 121, the sensor 3 is moved from the lower side to the upper side 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 faster in time as the sensor approaches the liquid level corner portion, and when the arrival point of the ultrasonic wave on the inner wall surface passes the corner portion, the corner reflected wave cannot be received. Accordingly, the liquid level is determined with a position where the corner reflected wave disappears. In step 126, the sensor position where 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.

  FIG. 13 is a block diagram showing the overall configuration of a fifth embodiment of the liquid level detection device according to the present invention. The acoustic sensor 30 of this configuration is a sound wave receiver in the range of several tens of hertz to several hundreds of kilohertz, and only receives a burst sound or generated sound of the gas phase 4 generated inside the container 1, and does not generate sound waves by itself. . Also in this embodiment, a duplicate description of similar substances is avoided. Although the configuration is similar to the previous embodiments, the only difference is a sensor 30 (301, 302,... 30N) only for reception, or a simple acoustic wave receiver 70 instead of the ultrasonic transmitter / receiver 7. Data 13 in which reference patterns of received signals at 30 positions are accumulated is prepared.

  FIG. 14 is a process flowchart of a liquid level detection method according to the fifth embodiment of the present invention. In step 141, initialization is performed, and in step 142, a received signal is captured. In step 143, it is checked whether or not the received signal matches any of the reference patterns 13, and if not, the next sensor is switched to in step 145. If they match, it is determined as a temporary water level in step 146, and the end of all sensors is confirmed in step 147. In step 148, the final water level is determined and the result is displayed. In this way, each time the received signals are received by switching the sensors 301 to 30N, it is checked whether or not the reference pattern 13 matches, and if it matches, it is determined as a temporary water level, and finally all 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, a processing method such as position determination of the plosive sound generation position, correlation processing, frequency analysis, or the like may be applied to the received signal.

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

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

The principle explanatory drawing of the liquid level detection method in one Example of this invention. The received waveform explanatory drawing by the liquid level detection method in one Example of this invention. The received waveform explanatory drawing by the liquid level detection method of one Example of this invention when a container wall is thin. 1 is an overall configuration block diagram of a liquid level detection device according to a first embodiment of the present invention. The processing flowchart of the liquid level detection method by 1st Example of this invention. The block diagram of the whole structure of the liquid level detection apparatus by 2nd Example of this invention. The processing flowchart of the liquid level detection method by 2nd Example of this invention. The block diagram of the whole structure of the liquid level detection apparatus by 3rd Example of this invention. The received waveform explanatory drawing in the liquid level detection method of the 3rd Example of this invention. The processing flowchart of the liquid level detection method by the 3rd Example of this invention. The block diagram of the whole structure of the liquid level detection apparatus by 4th Example of this invention. The processing flowchart of the liquid level detection method by 4th Example of this invention. The block diagram of the whole structure of the liquid level detection apparatus by 5th Example of this invention. The processing flowchart of the liquid level detection method by 5th Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Liquid phase, 21 ... Liquid level, 3, 31, 32, 3N ... Ultrasonic transmitter / receiver (ultrasonic sensor), 30, 301, 302, 30N ... Sound wave receiver (acoustic sensor for reception only) DESCRIPTION OF SYMBOLS 4 ... Gas phase, 5 ... Solid phase, 6 ... Switching circuit, 7 ... Ultrasonic transmission / reception part, 70 ... Sound wave reception part, 8 ... Received signal observation part, 9 ... Signal processing and liquid level determination part, 10 ... Drive and Position measurement unit, 11 ... inner wall of container, 12 ... boundary (liquid level corner), 13 ... reference pattern accumulated data of received signal, T ... transmitted wave, A ... reflected wave from inner wall of opposite container, B ... transmitter / receiver A reflected wave from the inner wall of the arranged container wall, N: a reflected wave from a gas phase or a solid phase, R: a reflected wave from a boundary (liquid surface corner).

Claims (2)

  In the liquid level detection method for detecting the liquid level in the container by the acoustic sensor, the gas phase in the liquid phase in the container is received by receiving the sound wave by the sound wave receiver in the tens to hundreds of kilohertz arranged on the outer wall of the container. A step of receiving a generated sound or a gas phase burst sound, and a step of determining the liquid level in the container based on the presence or absence of the received signal or a signal analysis processing result such as frequency analysis, position evaluation, correlation processing, etc. of the received signal. A method for detecting a liquid level by sound.   In the liquid level detection device that detects the liquid level in the container from the outside by the acoustic sensor, the acoustic wave of several tens to several hundreds of kilohertz generated in the container is arranged in the vertical direction along the outer wall of the container. A number of sound wave receivers to be received, 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 for determining a liquid level from the observation results of the reception signal observation unit An acoustic liquid level detection device comprising: a determination unit.

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