JP3701947B2 - Method for measuring the amount of liquid remaining in the container - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the remaining amount of liquid stored in a sealed container from the outside, and more particularly to a simple, inexpensive and highly accurate measurement method.
[0002]
[Prior art]
Laughing gas used as an anesthetic during surgery is held in a sealed container as a low-temperature, high-pressure liquid. As this container, a double container having a structure in which a vacuum layer for heat insulation is formed in the middle is used like a thermos. In order to prevent the container from being emptied during the surgical operation, it is necessary to confirm the remaining amount of liquid (hereinafter referred to as “residual liquid amount”) before the operation. Since this type of sealed container is made of an opaque material such as metal, the amount of the remaining liquid cannot be confirmed visually.
[0003]
2. Description of the Related Art Conventionally, an ultrasonic level meter is known as an apparatus for measuring the amount of remaining liquid in an airtight container that is made of an opaque material and whose liquid level cannot be visually observed from the outside. In this ultrasonic level meter, an ultrasonic transducer is attached to the bottom surface outside the container. The ultrasonic wave radiated into the liquid from the ultrasonic transducer through the wall of the ultrasonic wave is reflected in the liquid surface after propagating in the liquid, and returns to the bottom surface to be received as a reflected wave. The time required for propagation of the ultrasonic wave in the reciprocating direction is measured, and the height of the liquid level is measured (Patent Document).
[0004]
[Patent Literature]
Japanese Patent Laying-Open No. 2001-272266 (FIG. 1)
[0005]
[Problems to be solved by the invention]
However, since the container for storing the laughing gas described above uses a double-structured container that forms a vacuum layer for heat insulation, the above-described ultrasonic level meter cannot be used. Even if ultrasonic waves are generated by an ultrasonic transducer attached to the outside of the bottom surface of the outer container, it cannot propagate in the vacuum layer formed between the inner container and the ultrasonic waves propagate in the liquid. It is because it cannot be made to.
[0006]
For this reason, conventionally, a method has been employed in which the weight of the residual liquid is measured by measuring the weight of the container containing the residual liquid and subtracting the known weight of the empty container from this value. However, this method has a problem that it takes time and effort to put the container on the balance every time the amount of the remaining liquid is measured. Accordingly, an object of the present invention is to provide a simple method for measuring the amount of residual liquid.
[0007]
[Means for Solving the Problems]
The method for measuring the amount of residual liquid in a container according to the present invention that solves the problems of the prior art described above is to generate vibration in a container that stores liquid in a sealed state and to create a frequency spectrum of the generated vibration. In this frequency spectrum, search for a region where only one vibration component whose frequency changes according to the amount of residual liquid appears, and no vibration component determined by the vibration characteristics of this container, and measure this region. Simple method by selecting the target area and measuring the residual liquid volume from the frequency of the vibration component appearing in the selected measurement target area by generating vibration in the container whose residual liquid volume is to be measured Thus, the remaining liquid amount can be measured.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
According to one preferred embodiment of the invention, generating vibration in the container is performed by striking the container wall of the container or a structure mechanically coupled to the container.
[0009]
According to another preferred embodiment of the present invention, the measurement target region is set so that the frequency of the vibration component that changes in accordance with the residual liquid amount in the container changes substantially linearly in accordance with the residual liquid amount. Is selected.
[0010]
According to still another preferred embodiment of the present invention, the measurement target region is selected so that the frequency of the vibration component that changes in accordance with the amount of remaining liquid in the container is present in the audible frequency band.
[0011]
According to still another preferred embodiment of the present invention, the generation of the frequency spectrum of the generated vibration is performed by a fast Fourier transform (FFT).
[0012]
According to still another preferred embodiment of the present invention, the container is a double container that forms a vacuum layer in the middle, and the structure to be hit is a residual liquid extraction tube that is inserted into the double container. It is.
[0013]
【Example】
FIG. 1 is a conceptual diagram of a system for carrying out a method for measuring the amount of residual liquid in a container according to an embodiment of the present invention. 1 is a sealed cylinder (container) for measuring the amount of residual liquid inside, 2 is a hammer for striking this cylinder, 3 is a microphone for receiving vibrations generated in the cylinder due to hammering, 4 is a microphone An amplifier 6 amplifies the received signal, and a fast Fourier transformer (FFT) 6 generates and displays a frequency spectrum of the amplified received signal.
[0014]
First, for the sake of simplicity, it is assumed that the cylinder 1 is not a double but a single normal cylinder. An appropriate amount of water is put into the cylinder 1 and sealed, and then the outer wall of the cylinder is struck with the hammer 2 only once. The hammer 2 is made of a material having an appropriate hardness such as wood, rubber, or metal. The hammer 1 generates vibrations in the cylinder 1. This vibration is received by the broadband microphone 3 arranged near the wall of the cylinder 2 and amplified by the broadband amplifier 4, and then a frequency spectrum is created by the FFT 5.
[0015]
FIG. 2 is an example of a frequency spectrum of vibrations generated in a sealed cylinder by striking. The cylinder has a length of 760 mm and a diameter of 136 mm, and this cylinder is empty. A vibration component whose frequency changes according to the amount of the remaining liquid appears in the central part near 1000 Hz, and four vibration components whose frequency does not change appear above and below the vibration component. These four vibration components maintain a constant value specific to the cylinder, which is determined according to the size / shape (length, diameter, etc.) and structure of the cylinder. Hereinafter, the vibration component that maintains a constant value unique to the cylinder is referred to as “natural vibration component of the container”.
[0016]
The hammering and frequency spectrum creation described above are repeated while changing the height (water level) of the water surface in the cylinder 1. The experimental data shown in FIG. 2 is a plot of the relationship between the water level and the frequency for the vibration component whose frequency changes according to the water level. When the water level accumulated in the cylinder 1 drops from 800 mm to zero mm (empty), the frequency increases almost linearly from 750 Hz to 1040 Hz.
[0017]
Then, referring again to the frequency spectrum of FIG. 2, there is only one frequency component whose frequency changes according to the water level in the frequency range from 750 Hz to 1040 Hz, which varies according to the water level in the cylinder. In addition, there is no natural frequency component of the container in this frequency range. Such a frequency range is selected as the measurement target region.
[0018]
Conventionally, it has been known that when water is poured into a glass cylinder whose upper end is opened and the wall surface is gradually raised, the frequency of the sound generated by the cylinder gradually increases. It is explained that this is because a standing wave of a sound wave having a water surface as a vibration node and an open end surface as an antinode is formed. In the experimental data of FIG. 3 described above, the relationship between the water level and the frequency in the above-described known phenomenon is reversed. In the case of FIG. 1, this is presumed to be because the sound that appears in the vicinity of 1000 Hz is not a fundamental wave but a beat (harm) that is generated when harmonics interfere with each other. In the present invention, it is presumed that the upper end of the container is not an open end but is sealed.
[0019]
For a cylinder having an arbitrary shape, size, and structure, the measurement target region of the frequency of the vibration component is determined by the same method as described above. After that, the wall of the cylinder 1 having an unknown residual liquid amount is hit with the hammer 2, the vibration generated at that time is received by the microphone 3, amplified by the amplifier 4, and a frequency spectrum is created by the FFT 5. Then, the liquid surface, that is, the remaining liquid amount is measured by measuring the frequency of the vibration component appearing in the measurement target region set in advance.
[0020]
FIG. 4 is a conceptual diagram of a system for carrying out a method for measuring the amount of residual liquid in a container according to another embodiment of the present invention. In this embodiment, the cylinder 1 for measuring the amount of residual liquid has a double-structured wall with a vacuum layer formed in the middle. A residual liquid extraction tube 1 a is inserted into the cylinder 1. In this embodiment, the cylinder 1 is not directly hit with the hammer 2, but the residual liquid extraction pipe 1a is hit.
[0021]
The subsequent processing is exactly the same as the processing already described with reference to FIG. That is, the vibration generated in the cylinder 1 by the hammer 2 is received by the broadband microphone 3, amplified by the broadband amplifier 4, and then the frequency spectrum is created by the FFT 5. Then, the measurement target region is set, and the residual liquid amount is measured based on the frequency that changes in accordance with the residual liquid amount of the vibration component that appears here.
[0022]
The case where FFT is used as means for creating a frequency spectrum has been described above. However, other suitable spectrum analyzers can be used.
[0023]
Moreover, the structure which operates a hammer manually is illustrated. However, the hammer can be automatically operated using an electromagnetic valve or the like. Further, instead of hitting with a hammer, it is also possible to hit the instrument wall with an ultrasonic vibrator or the like attached to an appropriate location such as a container or a residual liquid extraction tube.
[0024]
In addition, after setting the measurement target area, instead of using a spectrum analyzer such as FFT, the amplifier in the previous stage is given a non-linear characteristic that promotes the generation of beats, and the vibration component of the measurement target area is provided in the subsequent stage of the amplifier. There is a possibility that a simple configuration can be achieved in which a band-pass filter that passes only the filter is installed and the frequency of the vibration component is roughly determined by hearing.
[0025]
【The invention's effect】
As described above in detail, the method for measuring the amount of residual liquid in a container according to the present invention generates vibrations in a container whose residual liquid amount is to be measured, and generates vibration components that appear in a predetermined measurement target region. Since it is the structure which measures the residual liquid amount from a frequency, the effect that a residual liquid amount can be measured by simple operation is show | played.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a system for carrying out a method for measuring the amount of residual liquid in a container according to an embodiment of the present invention.
FIG. 2 is experimental data showing an example of a frequency spectrum of vibration generated by the impact of a cylinder in the system of FIG.
FIG. 3 is experimental data showing the relationship between the frequency of the frequency component of vibration generated by the impact of a cylinder in the system of FIG. 1 and the water level.
FIG. 4 is a conceptual diagram of a system for carrying out a method for measuring the amount of residual liquid in a container according to another embodiment of the present invention.
[Explanation of symbols]
1 cylinder (container)
1a Extraction tube for residual liquid
2 Hammer
3 Microphone
4 Amplifier
5 FFT

Claims (6)

Generating vibration in a container that stores liquid in a sealed state;
Creating a frequency spectrum of this generated vibration;
In this frequency spectrum, only one vibration component whose frequency changes according to the remaining amount of liquid in the container (hereinafter referred to as “residual liquid amount”) appears, and the vibration is determined by the vibration characteristics of the container. Search for a region where no component appears, select this region as the measurement target region,
Generating vibration in the container to be measured for residual liquid volume, and measuring the residual liquid volume from the frequency of the vibration component appearing in the selected measurement target region. Method for measuring the amount of residual liquid. In claim 1,
The vibration generation in the container is performed by striking a wall of the container or a structure mechanically coupled to the container. . In each of claims 1 and 2,
The measurement target region is selected such that the frequency of a vibration component that changes in accordance with the amount of remaining liquid in the container changes substantially linearly in accordance with the amount of remaining liquid. Method for measuring liquid volume. In each of claims 1 to 3,
The method for measuring a residual liquid amount in a container, wherein the measurement target region is selected such that a frequency of a vibration component that changes in accordance with the residual liquid amount in the container exists in an audible frequency band. In each of claims 1 to 4,
The frequency spectrum of the generated vibration is generated by fast Fourier transform (FFT). In each of claims 1 to 5,
The container is a double container that forms a vacuum layer in the middle, and the structure to be hit is a residual liquid extraction tube that is inserted into the double container. Measuring method.

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