JP2013140070A - Liquid level measurement method and liquid level measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a liquid level, when measuring the liquid level of a vessel from the propagation time of an ultrasonic wave propagated through a liquid inside liquid level measurement piping in communication with the vessel.SOLUTION: An ultrasonic wave U is emitted to a liquid 12a inside liquid level measurement piping 12, the ultrasonic wave U reflected on the liquid 12a inside the liquid level measurement piping 12 is received, and on the basis of the relationship between frequency and sonic speed of the ultrasonic wave U propagating the liquid 12a inside the liquid level measurement piping 12, the received signal is converted to a propagation distance signal and the propagation distance signal is converted to the liquid level of a vessel 10.

Description

  The present invention relates to a liquid level measuring method and a liquid level measuring apparatus for measuring a liquid level in a container, and in particular, a liquid level measuring method and a liquid level for detecting a liquid level in a container from the outside of the container by an ultrasonic probe. It relates to a measuring device.

  In tanks and pressure vessels, it is important to accurately measure the liquid level from the viewpoint of ensuring controllability and maintaining safety. Many methods are conventionally known as a method for measuring the liquid level inside from the outer wall surface of the container. For example, there are a method that uses vertical movement of a float that floats on the liquid surface, a method that detects the pressure of the liquid, a method that detects capacitance, and a method that uses ultrasonic waves. Among these, the following techniques are disclosed for methods using ultrasonic waves.

  In Patent Literature 1 and Patent Literature 2, a reflected wave reflected by an opposing inner wall surface of a wall surface on which ultrasonic waves are incident is received through the liquid in the container to detect the presence or absence of the liquid, and from the opposing inner wall surface, There has been disclosed a method for suitably measuring the liquid level by means of receiving only the reflected wave.

  Patent Document 3 and Patent Document 4 utilize the principle that the reflection / transmittance of ultrasonic waves changes depending on whether the inner surface of the container wall is in contact with a liquid or in contact with a gas. It has been disclosed to receive a reflected wave from the inner wall surface of a position and determine the liquid level from the difference in attenuation characteristics of multiple reflected waves in the wall depending on the presence or absence of liquid in the container.

Patent Documents 5 to 8 relate to a method of reflecting an ultrasonic wave on a surface formed by a liquid surface and measuring the liquid level from the propagation time.
Among these, in Patent Document 5 and Patent Document 6, ultrasonic waves are transmitted from the outer wall surface of the container obliquely upward in the container, and are reflected and returned from the corner portion where the liquid surface and the inner wall of the container are in contact with each other. A method for detecting the liquid level and measuring the liquid level is disclosed.
Patent Document 7 and Patent Document 8 disclose a method of transmitting an ultrasonic wave upward from the bottom surface side of the container and measuring the liquid level from the propagation time of the ultrasonic wave propagated in the liquid. Shows how to calibrate the problem of changes in the liquid level measurement value due to changes in the sound velocity (propagation speed) of the ultrasonic wave due to temperature, etc., using a thermometer and the propagation time of the ultrasonic wave propagating through a constant distance path. Yes.

  Further, in Patent Document 9 and Patent Document 10, a pipe communicating with the liquid in the container is separately provided, and the liquid level in the pipe is measured from the propagation time of the ultrasonic wave propagating through the liquid in the pipe. From the principle of showing the same height as the container, a method for obtaining the liquid level of the container is shown.

Japanese Patent Laid-Open No. 61-3012 JP-A-8-136320 Japanese Patent Laid-Open No. 11-218436 JP 2000-121410 A Japanese Patent Laid-Open No. 5-133792 JP 2008-70387 A JP-A-8-219854 JP 2006-322825 A JP 2004-286745 A JP 2009-271056 A

  In Patent Documents 1 to 8, an ultrasonic sensor (ultrasonic probe) is directly installed on the outer surface of the container. In such a configuration, when the container is in an environment such as high temperature or radiation, there are problems such as durability of the ultrasonic sensor and maintainability in which an operator works close to the container.

  On the other hand, in Patent Document 9 and Patent Document 10, an ultrasonic sensor (ultrasonic probe) is installed in a pipe provided separately from the container, and the liquid is calculated from the propagation time of the ultrasonic wave propagating in the liquid in the pipe. Measure the position. For this reason, what is necessary is just to install an ultrasonic sensor in the piping side away from the container, and problems, such as durability and maintainability of an ultrasonic sensor, can be solved.

However, a new problem also arises in the methods of Patent Document 9 and Patent Document 10.
That is, depending on the vibration mode of the ultrasonic wave propagating the liquid in the pipe, dispersion (difference in propagation speed depending on frequency) occurs in the propagation speed. This is not a problem when the aperture is large like a container. On the other hand, when the aperture is small like a pipe, the ultrasonic wave propagating through the cylindrical liquid waveguide (liquid in the pipe) becomes a characteristic ultrasonic wave (guide wave). When velocity dispersion occurs, a wave that originally has a high time resolution and includes multiple frequency components, such as a pulse wave, has a different propagation speed for each frequency component, so the waveform is distorted each time it propagates, and finally the original waveform The shape will not stop.
This is a factor that decreases the measurement accuracy of the propagation time and the measurement accuracy of the liquid level.

  Therefore, the present invention provides a liquid level measurement method and a liquid level measurement apparatus for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid level measurement pipe communicating with the container. It is an object of the present invention to provide a liquid level measuring method and a liquid level measuring device for detecting the position.

  In order to solve such a problem, the present invention is a liquid level measuring method for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid level measuring pipe communicating with the container. A transmission step for transmitting ultrasonic waves to the liquid in the liquid level measurement pipe, a reception step for receiving ultrasonic waves reflected by the liquid in the liquid level measurement pipe, and a liquid in the liquid level measurement pipe A conversion step for converting the reception signal received in the reception step into a propagation distance signal based on the relationship between the frequency and sound velocity in the ultrasonic wave propagating through the ultrasonic wave; and the propagation distance signal converted in the conversion step A liquid level measuring method comprising:

  Further, the present invention is a liquid level measuring device for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid level measuring pipe communicating with the container, the lower part of the liquid level measuring pipe An ultrasonic probe disposed in the ultrasonic probe, an ultrasonic transmitter / receiver that applies a transmission signal to the ultrasonic probe and amplifies a received signal, and an ultrasonic wave that propagates liquid in the liquid level measurement pipe A signal processing unit that converts the received signal into a propagation distance signal based on a relationship between a frequency and a sound speed, and a liquid level conversion unit that converts the propagation distance signal into a liquid level of the container. It is a liquid level measuring device.

  According to the present invention, in a liquid level measuring method and a liquid level measuring apparatus for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid for measuring the liquid level communicating with the container, It is possible to provide a liquid level measuring method and a liquid level measuring device for detecting the level.

It is a lineblock diagram of the container which is a liquid level measuring device and a measuring object concerning a 1st embodiment. It is a figure explaining the example of the structure of the ultrasonic probe of the liquid level measuring device which concerns on 1st Embodiment, (a) is a cross-sectional schematic diagram seen in the horizontal direction, (b) is for liquid level measurement It is the schematic diagram seen from the bottom face outer side of piping. It is a block diagram which shows the detailed structure of an ultrasonic transmitter / receiver. It is a flowchart which shows operation | movement of the liquid level measuring apparatus which concerns on 1st Embodiment. It is a conceptual diagram explaining the liquid level measuring method of the liquid level measuring apparatus which concerns on 1st Embodiment. It is a graph explaining the relationship between the frequency of the ultrasonic wave which propagates the piping for liquid level measurement of the liquid level measuring apparatus which concerns on 1st Embodiment, and sound velocity. It is a figure explaining the example of the structure of the ultrasonic probe of the liquid level measuring device which concerns on 2nd Embodiment, (a) is a cross-sectional schematic diagram seen in the horizontal direction, (b) is for liquid level measurement It is the schematic diagram seen from the bottom face outer side of piping.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

<< First Embodiment >>
Drawing 1 is a lineblock diagram of liquid level measuring device 1 concerning a 1st embodiment, and container 10 which is a measuring object. The liquid level measurement device 1 according to the first embodiment is a device that measures the liquid level of the liquid 10a stored in the container 10 (height from the bottom surface 10c of the container 10 to the liquid level 10b).

<Configuration of container 10>
First, the configuration of the container 10 that is a measurement target will be described with reference to FIG.
The container 10 stores a liquid 10a. The container 10 is also provided with a liquid level measurement pipe 12 so as to communicate with the container 10 via the first communication pipe 11a and the second communication pipe 11b. The first communication pipe 11a communicates with the container 10 at a position higher than the liquid level 10b. Further, the second communication pipe 11b communicates with the container 10 at a position lower than the liquid level 10b. Thereby, the liquid surface 10b of the liquid 10a in the container 10 and the liquid surface 12b of the liquid 10a in the liquid level measurement pipe 12 have the same height.

  That is, the liquid level measuring device 1 to be described later measures the liquid level of the liquid level measuring pipe 12 (the height from the bottom surface 12c of the liquid level measuring pipe 12 to the liquid level 12b), whereby the bottom surface 10c of the container 10 is measured. The liquid level of the container 10 (the height from the bottom surface 10c of the container 10 to the liquid level 10b) can be measured using the positional relationship between the liquid level measurement pipe 12 and the bottom surface 12c of the liquid level measurement pipe 12.

  In addition, as shown in FIG. 1, the container 10 and the liquid level measurement pipe 12 are disposed so as to be separated by the isolation wall 13, and the first communication pipe 11 a and the second communication pipe 11 b penetrate the isolation wall 13. Is configured to do.

  For example, when the liquid level measuring device 1 described later is a device that measures the liquid level of a reactor pressure vessel of a boiling water reactor, the vessel 10 corresponds to the reactor pressure vessel, and the isolation wall 13 is an atom. Corresponds to the wall of the containment vessel. The isolation wall 13 that separates the vessel 10 and the liquid level measurement pipe 12 is not an essential configuration. For example, the vessel 10 (reactor pressure vessel) and the liquid level measurement pipe 12 are connected to the reactor containment vessel. The configuration may be stored inside.

In addition, the liquid level measuring device 1 to be described later is not limited to a device that measures the liquid level of the reactor pressure vessel (vessel 10) of the boiling water reactor. For example, the container 10 may be a tank, and the liquid level measuring device 1 described later may be a device that measures the liquid level in the tank (container 10). Further, the isolation wall 13 is not an essential configuration, and the isolation wall 13 may not be provided.
Further, since the liquid level measuring device 1 to be described later measures the liquid level of the container 10 by measuring the liquid level of the liquid level measuring pipe 12, the container 10 is placed on the bottom surface 10c as described later on like a swimming pool type. The structure which cannot attach the sound probe 2 directly may be sufficient.

<Liquid level measuring device 1>
Next, the configuration of the liquid level measuring apparatus 1 according to the first embodiment will be described with reference to FIGS. 1 to 3.
As shown in FIG. 1, the liquid level measuring device 1 includes an ultrasonic probe 2, an ultrasonic transmitter / receiver 3, an analog / digital converter (hereinafter referred to as “A / D converter”) 4, and a computer 5. And an input device 6 and a display device 7.

  The liquid level measuring device 1 propagates the ultrasonic wave U (guide wave) from the bottom surface 12c of the liquid level measuring pipe 12 to the liquid 12a in the liquid level measuring pipe 12, and reflects the ultrasonic wave U (reflected) at the liquid level 12b. The level of the liquid level measurement pipe 12 (height from the bottom surface 12c to the liquid level 12b of the liquid level measurement pipe 12) can be measured. Then, the liquid level measuring device 1 uses the measured liquid level of the liquid level measurement pipe 12 and the positional relationship between the bottom surface 10c of the container 10 and the bottom surface 12c of the liquid level measurement pipe 12. The liquid level (height from the bottom surface 10c of the container 10 to the liquid surface 10b) can be measured.

  The ultrasonic probe 2 transmits an ultrasonic wave U when a transmission waveform (transmission signal) is applied from the ultrasonic transmitter / receiver 3, receives a reflected wave, and converts the received waveform (reception signal) into an ultrasonic wave. The data is output to the transceiver 3.

  The ultrasonic probe 2 will be further described with reference to FIG. FIG. 2 is a diagram for explaining an example of the structure of the ultrasonic probe 2 of the liquid level measuring device 1 according to the first embodiment, (a) is a schematic cross-sectional view seen in the horizontal direction, and (b) ) Is a schematic view of the liquid level measurement pipe 12 as viewed from outside the bottom surface.

  As shown in FIG. 2A, the ultrasonic probe 2 is disposed outside the bottom surface 12c of the liquid level measurement pipe 12, and as shown in FIG. 2B, a plurality of concentric and equidistant intervals are provided. The ultrasonic transducer (hereinafter simply referred to as a transducer). In the following description, the ultrasonic probe 2 will be described as including four transducers 2a, 2b, 2c, and 2d.

  Each transducer 2a, 2b, 2c, 2d is constituted by a piezoelectric element, for example, and has a function of transmitting / receiving the ultrasonic wave U. Each transducer 2a, 2b, 2c, 2d passes through the bottom surface 12c of the liquid level measurement pipe 12, and generates an ultrasonic wave U in the liquid 12a.

  The outer diameter of the outermost transducer 2a among the transducers 2a, 2b, 2c, and 2d that are concentrically arranged at equal intervals constituting the ultrasonic probe 2 is shown in FIG. Thus, it arrange | positions so that it may correspond generally with the internal diameter (namely, outer diameter of the liquid column of the liquid 12a) of the piping 12 for liquid level measurement.

  In this manner, the transducers 2a, 2b, 2c, 2d of the ultrasonic probe 2 are arranged concentrically and at equal intervals, and in addition, the outer diameter of the outermost transducer 2a is the liquid level measurement pipe 12. The liquid level measuring device 1 has a characteristic ultrasonic U (guide wave) mode that propagates in the liquid 12a of the liquid level measurement pipe 12 by roughly matching the inner diameter (the outer diameter of the liquid column of the liquid 12a). The received waveform (received signal) can be extracted. The mode extraction method will be described later.

  Returning to FIG. 1, the ultrasonic transmitter / receiver 3 transmits an ultrasonic wave U from the ultrasonic probe 2 based on an ultrasonic transmission command (transmission control signal) of a computer 5 (a central control device 5a described later). A transmission waveform (transmission signal) is applied to each transducer 2a, 2b, 2c, 2d. In addition, the reception waveform (reception signal) of the reflected wave received by each transducer 2a, 2b, 2c, 2d is amplified and output to the A / D converter 4.

The ultrasonic transceiver 3 will be further described with reference to FIG. FIG. 3 is a configuration diagram showing a detailed configuration of the ultrasonic transceiver 3.
As shown in FIG. 3, the ultrasonic transceiver 3 includes a controller 31, a signal generator 32, a power amplifier 33, an element switch 34, an element switch 35, and a reception amplifier 36. Yes.

The signal generator 32, the power amplifier 33, and the element switching unit 34 send transmission waveforms (transmission signals) to the corresponding transducers 2a, 2b, 2c, and 2d of the ultrasonic probe 2 in order to generate the ultrasonic wave U. It is a mechanism for applying.
The element switch 35 and the reception amplifier 36 are mechanisms for amplifying the reception waveforms (reception signals) received from the transducers 2a, 2b, 2c, and 2d and outputting them to the A / D converter 4.

The controller 31 is connected to the central controller 5 a (see FIG. 1) of the computer 5, a signal generator 32, an element switch 34, and an element switch 35.
The controller 31 outputs an excitation command (excitation control signal) for instructing the signal generator 32 to generate a signal based on the ultrasonic transmission command (transmission control signal) of the central control device 5a. The ultrasonic transmitter / receiver 3 is controlled by outputting a switching command (switching control signal) for commanding switching to the switching device 35.

The signal generator 32 is connected to the element switch 34 via the power amplifier 33. The element switch 34 is connected to each transducer 2a, 2b, 2c, 2d of the ultrasonic probe 2.
The signal generator 32 generates an excitation signal based on an excitation command (excitation control signal) from the controller 31, and the power amplifier 33 supplies a transmission waveform (transmission signal) obtained by amplifying the excitation signal to the element switch 34. Output.
The element switch 34 switches the connection between the power amplifier 33 and each of the vibrators 2a, 2b, 2c, and 2d based on a switching command (switching control signal) from the controller 31.
Thus, a transmission waveform (transmission signal) can be applied to any transducer 2a, 2b, 2c, 2d.

The element switch 35 is connected to each transducer 2 a, 2 b, 2 c, 2 d of the ultrasonic probe 2, and is connected to the A / D converter 4 via the reception amplifier 36.
The element switch 35 switches the connection between the reception amplifier 36 and each transducer 2a, 2b, 2c, 2d based on a switching command (switching control signal) from the controller 31.
The reception amplifier 36 amplifies the reception waveform (reception signal) and outputs it to the A / D converter 4.

  The vibrators 2a, 2b, 2c, 2d and the element changers 34, 35 are connected via coaxial cables. The reception amplifier 36 and the A / D converter 4 are connected via a coaxial cable.

Returning to FIG. 1, the A / D converter 4 has a function of converting a reception waveform (reception signal) that is an analog signal into a digital signal (digital waveform).
The A / D converter 4 is connected to the signal processing device 5b of the computer 5, converts each received waveform (received signal) input from the receiving amplifier 36 of the ultrasonic transceiver 3 into a digital signal, and outputs a signal. The data is output to the processing device 5b.
As the A / D converter 4, for example, a commercially available external A / D converter or a board-type A / D converter built in a computer can be used.

The computer 5 includes a central control device 5a that controls the entire liquid level measuring device 1, and a signal processing device 5b that processes a digital signal of a received waveform (received signal) output from the A / D converter 4. ing.
The central control device 5 a outputs an ultrasonic transmission command (transmission control signal) for instructing transmission of the ultrasonic wave U to the controller 31 of the ultrasonic transceiver 3.
The signal processing device 5b processes the digital signal (received waveform) from the A / D converter 4 to generate display information such as image information. Further, the signal processing device 5 b can process the digital signal (received waveform) from the A / D converter 4 and convert it into the liquid level of the container 10.

  The central control device 5 a is connected to an input device 6 such as a keyboard and a mouse, and a measurement operator (operator) can receive an instruction by operating the input device 6.

  The central control device 5a is connected to the display device 7, and can display display information such as image information generated by the signal processing device 5b on the display device 7. Further, the central control device 5a, if necessary, receives a digital signal input from the A / D converter 4 to the signal processing device 5b (that is, a reception waveform (reception received from the reception amplifier 36 of the ultrasonic transceiver 3). Signal)) can be displayed on the display device 7. The central controller 5a can display the liquid level of the container 10 converted by the signal processor 5b on the display device 7.

<Liquid level measuring method by the liquid level measuring device 1>
Next, a liquid level measurement method using the liquid level measurement apparatus 1 according to the first embodiment will be described with reference to FIGS. 1 to 3 and FIGS. 4 to 6. FIG. 4 is a flowchart showing the operation of the liquid level measuring apparatus 1 according to the first embodiment.

  First, before starting the liquid level measurement shown in FIG. 4, as a preparation, the measurement operator (operator) attaches the ultrasonic probe 2 (vibrators 2a, 2b, 2c, 2d) to the liquid level measurement pipe 12. It is arranged outside the bottom surface 12c. Further, the measurement operator (operator) operates the input device 6 of the liquid level measuring device 1 to density the liquid 12a (liquid 10a), the elastic coefficient of the liquid 12a (liquid 10a), and the liquid level measurement pipe. 12, and the positional relationship in the height direction between the bottom surface 10 c of the container 10 and the bottom surface 12 c of the liquid level measurement pipe 12 are input.

In step S <b> 101, the computer 5 derives a dispersion curve indicating the relationship between the frequency and sound velocity in the ultrasonic wave U that propagates through the liquid 12 a in the liquid level measurement pipe 12.
The dispersion curve is calculated based on the density of the liquid 12a previously input by the measurement operator (operator), the elastic coefficient of the liquid 12a, and the inner diameter of the liquid level measurement pipe 12 (that is, the outer diameter of the liquid column of the liquid 12a). It is derived for each mode of the ultrasonic wave U by simulating the liquid column of the liquid 12a. The method for deriving the dispersion curve is, for example, (Hideo Nishino, Noritaka Nakabachi, “A pipe flaw detection with a guided wave propagating the liquid in the pipe”) This is described in Japan Nondestructive Inspection Association, 2003, p. 13-14), and the description is omitted.
A dispersion curve is calculated and stored in the computer 5 in advance, and is based on the density of the liquid 12a, the elastic coefficient of the liquid 12a, and the inner diameter of the liquid level measurement pipe 12 input by a measurement operator (operator). The dispersion curve to be used may be read out.

FIG. 6 shows an example of the derived dispersion curve (relationship between frequency and sound velocity in the ultrasonic wave U propagating through the liquid 12a in the liquid level measurement pipe 12).
In FIG. 6, Vg0 indicates a basic mode (0th order mode) in which the sound speed is constant depending on the frequency, Vg1 indicates a primary mode, Vg2 indicates a secondary mode, Vg3 indicates a tertiary mode, and Vg4 indicates a quaternary mode. In addition, since the ultrasonic probe 2 of the liquid level measuring device 1 according to the first embodiment is composed of the four transducers 2a, 2b, 2c, and 2d, from the 0th-order mode Vg0 to the secondary mode Vg2. The third-order mode Vg3 and subsequent modes need not be derived.

In step S <b> 102, the central controller 5 a outputs an ultrasonic transmission command (transmission control signal) to the controller 31 of the ultrasonic transmitter / receiver 3, and transmits ultrasonic waves from the ultrasonic probe 2 to the liquid level measurement pipe 12. Send U.
Here, the controller 31 outputs a switching command (switching control signal) for switching the power amplifier 33 and all the vibrators 2a, 2b, 2c, and 2d to the element switch 34. Further, the controller 31 outputs an excitation command (excitation control signal) to the signal generator 32. The excitation signal generated by the signal generator 32 is amplified by the power amplifier 33 and transmitted to the transducers 2a, 2b, 2c, and 2d as a transmission waveform (transmission signal). That is, the four transducers 2a, 2b, 2c, and 2d of the ultrasonic probe 2 transmit ultrasonic waves as one transducer as a whole.

In step S103, the ultrasonic wave U (reflected wave) reflected by the liquid surface 12b is received using the ultrasonic probe 2 (vibrators 2a, 2b, 2c, 2d).
Here, the controller 31 outputs a switching command (switching control signal) for individually switching the connection between each transducer 2a, 2b, 2c, 2d and the receiving amplifier 36 to the element switching device 35.
That is, the reception waveforms (reception signals) received by the transducers 2a, 2b, 2c, and 2d of the ultrasonic probe 2 are separately amplified by the reception amplifier 36 and converted into digital signals by the A / D converter 4. The signal is converted and input to the signal processing device 5 b of the computer 5.

In the following description, a signal received by the transducer 2a, amplified by the receiving amplifier 36, and converted into a digital signal by the A / D converter 4 is referred to as a received signal S _a (t). The signal received by the transducer 2b, amplified by the reception amplifier 36, and converted into a digital signal by the A / D converter 4 is referred to as a reception signal S _b (t). A signal received by the vibrator 2c, amplified by the reception amplifier 36, and converted into a digital signal by the A / D converter 4 is defined as a reception signal S _c (t). A signal received by the vibrator 2d, amplified by the receiving amplifier 36, and converted into a digital signal by the A / D converter 4 is defined as a received signal S _d (t). In addition, t is the time after transmitting the ultrasonic wave U, and (t) represents that the received signal is a function of time.

  In step S104, the signal processing device 5b uses the frequency and sound velocity dispersion curve derived in step S101 (see, for example, FIG. 6), and in step S103, the ultrasonic probe 2 (vibrators 2a, 2b, 2c, 2d) converts the received signal received into a propagation distance signal.

First, the signal processing device 5b calculates a reception signal for each mode of the ultrasonic wave U. Assuming that the received signal in the 0th-order mode is f ₀ (t), the received signal in the first-order mode is f ₁ (t), and the received signal in the second-order mode is f ₂ (t), the following equations (1) to ( It is calculated in 3).
f ₀ (t) = S _a (t) + S _b (t) + S _c (t) + S _d (t) (1)
f ₁ (t) = S _a (t) + S _b (t) −S _c (t) −S _d (t) (2)
f ₂ (t) = S _a (t) −S _b (t) + S _c (t) −S _d (t) (3)

Next, the signal processing device 5b refers to the dispersion curve (for example, see FIG. 6) of the frequency and sound velocity derived in step S101 for each mode, and receives the received signals f ₀ (t) and f ₁ (t for each mode. ), F ₂ (t) are converted into propagation distance signals g ₀ (x), g ₁ (x), g ₂ (x).
That is, in the 0th-order mode, the received signal f ₀ (t) is converted into the propagation distance signal g ₀ (x) with reference to Vg0 shown in FIG. Similarly, in the primary mode, the received signal f ₁ (t) is converted into the propagation distance signal g ₁ (x) with reference to Vg1 shown in FIG. In the secondary mode, the received signal f ₂ (t) is converted into a propagation distance signal g ₂ (x) with reference to Vg2 shown in FIG. Note that x is the propagation distance of the ultrasonic wave U, and (x) represents that the propagation distance signal is a function of the propagation distance.

The principle of converting the received signal f (t) into the propagation distance signal g (x) will be described with reference to FIG. FIG. 5 is a conceptual diagram illustrating a liquid level measuring method of the liquid level measuring apparatus 1 according to the first embodiment.
The received signal f (t) is decomposed for each frequency, and is converted into a propagation distance signal g (x) at t = 0 by fitting a dispersion curve (for example, see FIG. 6) of the frequency and sound speed.

In step S105, the signal processing device 5b converts the propagation distance signal g (x) into the liquid level of the container 10 (the height from the bottom surface 10c of the container 10 to the liquid surface 10b).
In the propagation distance signal g (x) obtained in step S104, the position where the amplitude appears is the propagation distance of the ultrasonic wave U. In other words, the liquid level (from the bottom surface 12c to the liquid surface 12b) of the liquid level measurement pipe 12. The distance). That is, the liquid level (distance from the bottom surface 12c to the liquid surface 12b) of the liquid level measurement pipe 12 can be obtained from the propagation distance signal g (x). Then, the liquid level of the liquid level measurement pipe 12 obtained from the propagation distance signal g (x), the bottom surface 10c of the container 10 and the bottom surface 12c of the liquid level measurement pipe 12 input in advance by a measurement operator (operator). Based on the positional relationship in the height direction, the liquid level of the container 10 (the height from the bottom surface 10c of the container 10 to the liquid surface 10b) can be converted.

  In the first embodiment, three propagation distance signals are obtained because evaluation is performed in three modes from the 0th order to the second order. For this reason, for example, an average value or a median value of the liquid level obtained from the propagation distance signal for each mode may be used as the liquid level of the liquid level measurement pipe 12. Moreover, the structure which displays the liquid level obtained for every three modes on the display apparatus 7 may be sufficient.

<Summary>
Since the liquid level measurement pipe 12 has a smaller diameter than that of the container 10, depending on the vibration mode of the ultrasonic wave U propagating through the liquid column of the liquid 12 a, as shown in FIG. The sound speed (propagation speed) varies depending on the frequency), and the relationship between the frequency of the ultrasonic wave U and the sound speed differs for each vibration mode. For this reason, as the transmission waveform (transmission signal) of the ultrasonic wave U in step S102, for example, an ultrasonic wave having a high time resolution such as a pulse wave, and an ultrasonic wave including a plurality of frequency components has different sound speeds for each frequency component. The waveform is distorted every time.

  In the conventional method (the method of the comparative example of FIG. 5), for example, as in Patent Document 9, propagation from the sound speed (group speed) and the arrival time of the reflected wave is not considered without considering velocity dispersion due to the vibration mode and frequency of the ultrasonic wave. The distance (liquid level) was measured. For this reason, the distortion of the waveform due to propagation directly leads to a decrease in the measurement accuracy of the propagation distance (liquid level).

On the other hand, according to the method of the present embodiment (the liquid level measurement method using the liquid level measurement device 1 according to the first embodiment), the received signal f (t) is decomposed (extracted) for each vibration mode. Thus, it can be converted into a propagation distance signal g (x).
Thereby, the liquid level measuring device 1 can correct the distortion of the reflected wave due to velocity dispersion and measure the liquid level with high accuracy. As a result, it can contribute to improvement of controllability and safety of the entire system (not shown) having the container 10.

<< Liquid level measuring device according to the second embodiment >>
Next, the configuration of the liquid level measurement device according to the second embodiment will be described with reference to FIG. FIG. 7 is a diagram for explaining an example of the structure of the ultrasonic probe 2A of the liquid level measurement device according to the second embodiment, (a) is a schematic cross-sectional view seen in the horizontal direction, and (b). These are the schematic diagrams seen from the bottom side outer side of piping for liquid level measurement.
The difference between the liquid level measuring apparatus 1 according to the first embodiment and the liquid level measuring apparatus according to the second embodiment is that the ultrasonic probe 2 of the liquid level measuring apparatus 1 according to the first embodiment vibrates four. Whereas the ultrasonic probe 2A of the liquid level measuring device according to the second embodiment is composed of the elements 2a, 2b, 2c and 2d (see FIG. 2), as shown in FIG. It differs in that it is composed of children. Other configurations are the same as those of the liquid level measuring apparatus 1 according to the first embodiment, and a description thereof will be omitted.

  Note that the ultrasonic probe 2A of the liquid level measurement device according to the second embodiment will be described as being configured by one transducer (see FIG. 7), but in the case of having a plurality of transducers (for example, 2), it may be configured to be connected so as to form a single vibrator in terms of electrical circuit by a fixed wiring or switch.

As shown in FIG. 7A, the outer diameter of the ultrasonic probe 2A is arranged so as to generally coincide with the inner diameter of the liquid level measurement pipe 12 (that is, the outer diameter of the liquid column of the liquid 12a). Yes.
By arranging the ultrasonic probe 2A in this way, the ultrasonic probe 2A selectively transmits / receives the basic mode (0th-order mode) indicated by the dispersion curve in FIG. Yes.
That is, the liquid level measurement device according to the second embodiment receives only the ultrasonic signal of a single transducer and receives only the fundamental mode (0th order mode). ) To the propagation distance signal g (x) (see step S104 in FIG. 4 and FIG. 5) can be simplified.

  According to the liquid level measurement apparatus according to the second embodiment, since the ultrasonic probe 2A is configured by one transducer, the configuration and wiring of the apparatus are changed from the ultrasonic probe 2A to the ultrasonic transmitter / receiver 3. Wiring to can be simplified. In addition, since reception is limited to the basic mode (0th-order mode), it is possible to use an inexpensive computer 5 having a lower processing capacity than the liquid level measuring device 1 according to the first embodiment. .

<Modification>
The liquid level measurement device according to the present embodiment is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the spirit of the invention.
Although the ultrasonic probe 2 of the liquid level measuring device 1 according to the first embodiment has been described as including the four transducers 2a, 2b, 2c, and 2d, the present invention is not limited to this. For example, the ultrasonic probe 2 includes two transducers that are arranged concentrically and at equal intervals, and the outer diameter of the outermost transducer substantially matches the inner diameter of the liquid level measurement pipe 12. Also good. In this case, the received signals in the 0th order mode and the primary mode can be extracted, and the water level of the container 10 can be measured.
Further, the number of transducers of the ultrasonic probe 2 may be more than four. In order to extract the mode, the ultrasonic probes 2 are arranged concentrically and at equal intervals, and 2 ⁿ pieces (the outer diameter of the outermost transducer approximately matches the inner diameter of the liquid level measurement pipe 12 ( However, it is desirable to provide a vibrator of n being 0 or a positive integer).

1 Liquid Level Measuring Device 2, 2A Ultrasonic Probe 2a, 2b, 2c, 2d Transducer (Ultrasonic Transducer)
3 Ultrasonic Transceiver 31 Controller 32 Signal Generator 33 Power Amplifier 34 Element Switcher 35 Element Switcher 36 Reception Amplifier 4 A / D Converter 5 Computer 5a Central Controller 5b Signal Processor (Signal Processor, Liquid Level Conversion) means)
6 Input device 7 Display device 10 Container 10a Liquid 10b Liquid surface 10c Bottom surface 11a First communication pipe 11b Second communication pipe 12 Liquid level measurement pipe 12a Liquid 12b Liquid surface 12c Bottom surface 13 Isolation wall U Ultrasound

Claims (4)

A liquid level measurement method for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid for liquid level measurement communicating with the container,
A transmission step of transmitting ultrasonic waves to the liquid in the liquid level measurement pipe;
A reception step of receiving ultrasonic waves reflected by the liquid in the liquid level measurement pipe;
A conversion step for converting the reception signal received in the reception step into a propagation distance signal based on the relationship between the frequency and the sound velocity in the ultrasonic wave propagating the liquid in the liquid level measurement pipe,
A liquid level measurement method comprising: a conversion step of converting the propagation distance signal converted in the conversion step into a liquid level of the container. A liquid level measuring device for measuring the liquid level of the container from the propagation time of the ultrasonic wave propagating the liquid in the liquid for liquid level measurement communicating with the container,
An ultrasonic probe arranged at the bottom of the pipe for measuring the liquid level;
An ultrasonic transmitter / receiver that applies a transmission signal to the ultrasonic probe and amplifies the reception signal;
Signal processing means for converting the received signal into a propagation distance signal based on the relationship between the frequency and sound velocity in the ultrasonic wave propagating the liquid in the liquid level measurement pipe;
A liquid level measuring device comprising: a liquid level conversion means for converting the propagation distance signal into the liquid level of the container. The ultrasonic probe is
Having at least two ultrasonic transducers arranged concentrically,
The liquid level measuring device according to claim 2, wherein an outer diameter of the outermost ultrasonic transducer of the ultrasonic transducers substantially coincides with an inner diameter of the liquid level measurement pipe. The ultrasonic probe is
A single ultrasonic transducer,
The liquid level measuring device according to claim 2, wherein an outer diameter of the ultrasonic transducer substantially coincides with an inner diameter of the liquid level measuring pipe.

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