JPH08304144A - Liquid level gage - Google Patents

Abstract

PURPOSE: To prevent the heat inflow from the outside surely at the time of liquid level measurement. CONSTITUTION: A storing container 1 contains a freezing mixture L, whose liquid surface is in the boiling and evaporating state. A pressure sensor 2 is provided at the top wall of the storing container 1 so as to face a gaseous space S in the storing container 1 and detects the boiling/evaporating sound generated from the freezing mixture L. These parts are provided. A CPU in a main body 3 of a liquid level gage performs the frequency analysis of the sound pressure signal outputted from the pressure sensor 2, sets the frequency, at which the sound pressure indicates the maximum value, as the resonant frequency, computes the position of the liquid level of the freezing mixture L based on the frequency and indicates the position on an indicator 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level gauge suitable for measuring the liquid level position of a cryogen such as liquid helium or liquid nitrogen stored in a container.

[0002]

2. Description of the Related Art Superconducting materials have been widely used in various weak electric circuits such as communication for the purpose of reducing resistance noise in addition to the conventional use in strong electric circuits for reducing power consumption. ing. In order to develop and maintain such a superconducting state of the superconducting material, it is necessary to cool the superconducting material below a predetermined absolute temperature.

By the way, an electric circuit using a superconducting material (hereinafter referred to as a superconducting circuit) is cooled to about the vaporization temperature of liquid nitrogen by using a gas helium cooler utilizing a Stirling cycle. The superconducting circuit is usually placed in a vacuum atmosphere, but heat is introduced from the ambient atmosphere at room temperature through a support portion that supports the circuit board and a signal extraction line. Therefore, accurate measurement of this inflowing heat amount is extremely important when designing the capacity of the cooling machine.

Boil-off
Calorimetry method is known, in which a cooling agent such as liquid nitrogen is injected into the heat exchange pipe of the cooler in place of the heat exchanger, and the heat exchange pipe is cooled to a predetermined temperature by the heat of vaporization, In this state, the amount of heat flowing into the heat exchange pipe is known from the amount of vaporized gas of the cryogen. In this case, if too much cryogen is injected into the heat exchange pipe, the liquid level rises and the low-temperature region increases, causing a large difference from the temperature distribution when actually using the cooler, resulting in an accurate inflow. I cannot know the amount of heat. Therefore, it is necessary to properly measure the liquid level of the cryogen at the time of injection.

Conventionally, as a liquid level gauge for measuring the liquid level position of a cryogen, one which electromagnetically or mechanically detects the vertical movement of a float floated on the liquid level, a double cylinder electrode is immersed in a cryogen, Detects capacitance change between electrodes due to rise and fall of liquid level, superconducting wire is stretched in the vertical direction, and the superconducting part where resistance is zero when immersed in cryogen increases and decreases with rise and fall of liquid level There are known ones that detect a change in resistance value of a superconducting wire.

[0006]

However, when a float having a mechanism portion communicating with the outside or an electrode or the like to which an external signal line is connected is immersed in a cryogen, heat flows from the outside atmosphere through the mechanism portion or the like. Therefore, there is a problem that the control of the liquid level causes an error in the measurement of the inflowing heat quantity. Further, the conventional liquid level gauge has a problem that it is necessary to discharge the cryogen to the outside of the storage container at the time of maintenance and inspection, which is troublesome.

The present invention solves such a problem, and can reliably prevent the inflow of heat from the outside at the time of measuring the liquid level to accurately measure the liquid level of a cryogen and the like, and also requires the trouble of maintenance and inspection. The purpose is to provide a liquid level gauge that does not.

[0008]

In order to achieve the above object, the present invention provides a liquid according to claim 1 in which a liquid is contained in a storage container (1) and has a liquid level in a boiling evaporation state. A liquid level meter for measuring the position, the sound detecting means (2) provided facing the gas space above the liquid level in the storage container, for detecting the boiling evaporation sound emitted from the liquid; Liquid level calculation means (3, 103, 104) for extracting the resonance frequency of the boiled vaporization sound thus generated and calculating the liquid level position of the liquid based on the extracted resonance frequency is provided.

In the invention described in claim 2, the liquid is a cryogen such as liquid helium or liquid nitrogen. In the invention according to claim 3, the sound detecting means (2) is
The sound pressure of the boiling evaporation sound is detected. Claim 4
In the invention described in (1), the liquid level calculation means (3) is
The sound pressure signal output from the sound detecting means is subjected to frequency analysis, and the frequency at which the sound pressure has a maximum is set as the resonance frequency.

In the invention according to claim 5, the storage container (1) is a heat exchange pipe of a cooling device whose inflowing heat quantity is measured by a boil-off calorimetry method. The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0011]

According to the invention described in claim 1, the boiling evaporation sound of the liquid resonates in the gas space above the liquid surface, and the resonance frequency thereof changes according to the volume of the gas space. That is, when the liquid level rises and the volume of the gas space decreases, the resonance frequency increases, while when the liquid level descends and the volume of the gas space increases, the resonance frequency decreases. Therefore,
The liquid level position can be accurately known by extracting the resonance frequency from the boiling evaporation sound detected by the sound detecting means.

In the liquid level gauge of the present invention, since the sound detecting means is provided on the container wall of the storage container facing the gas space outside the liquid, maintenance work can be easily performed without discharging the cryogen. You can Further, according to the invention of claim 2, the liquid level gauge does not have a liquid level detection unit which is immersed in a cryogen as in the conventional case, so that heat flows from the outside through the liquid level detection unit. Then, the problem of promoting excessive boiling evaporation of the cryogen does not occur.

According to the fifth aspect of the invention, since there is no heat inflow from the liquid level gauge, it is possible to measure the inflow heat quantity into the heat exchange pipe by the boil-off calorimeter method with high accuracy.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a case where the amount of heat flowing into the superconducting circuit board in the cooled state is measured by the boil-off calorimetry method, and the cooling device 4 is upside down from the actual use. The cylindrical housing 41 of the cooling device 4 is hermetically sealed and has a vacuum inside, and a support cylinder 42 is hung concentrically with the inside of the housing 41, and the center of the support cylinder 42 is vertically penetrated. Then, the heat exchange pipe 1 is located. In this heat exchange pipe 1, a gas helium heat exchanger is provided in actual use.

A substrate 5 for a superconducting circuit is provided in contact with the closed lower end surface of the heat exchange pipe 1. A ring-shaped terminal plate 6 is provided at the lower end opening edge of the support cylinder 42, and the left and right positions of the terminal plate 6 penetrate the side wall of the housing 41 and bend downward along the outer periphery of the support cylinder 42. The coaxial cables 62 and 63 are held. The tips of the coaxial cables 62 and 63 are turned upside down and connected to the superconducting circuit board 5.

Liquid nitrogen L is provided in the lower end of the heat exchange pipe 1.
Is injected to a predetermined height to cool the superconducting circuit board 5 to almost the same temperature (vaporization temperature of liquid nitrogen) as in actual use, and in the vertical direction of the heat exchange pipe 1 as in actual use. Causing a temperature gradient of. This allows
Heat flows from the outside atmosphere at room temperature into the substrate 5 mainly through the heat exchange pipe 1 and the coaxial cables 62 and 63,
The liquid nitrogen having a predetermined heat of vaporization is boiled and evaporated according to the amount of inflow heat.

The nitrogen gas thus vaporized and flowing out from the upper end opening of the heat exchange pipe 1 is measured in gas amount by the gas meter 72 provided in the gas outflow pipe 71, and the gas amount to the superconducting circuit board 5 is measured from this gas amount. The heat input is known. The nitrogen gas is adjusted to a predetermined temperature and pressure just before the gas meter 72 by a known method. Now, in FIG. 1, the pressure sensor 2 constituting the liquid level gauge of the present invention is installed on the cover body 43 that closes the upper end opening of the heat exchange pipe 1 so as to face the gas space S of the heat exchange pipe 1. The signal cable 21 extends from this. The pressure sensor 2 detects a sound emitted by liquid nitrogen boiling and evaporating in the lower end portion of the heat exchange pipe 1, and outputs a signal proportional to the sound pressure.

FIG. 2 shows the equipment structure of the liquid level gauge. In the figure, the heat exchange pipe 1 is schematically depicted as a closed cylindrical storage container. A signal cable 21 extending from the pressure sensor 2 provided on the top wall of the storage container 1 extends to reach the main body 3 of the liquid level gauge. Each of the electric circuits described later is housed in the liquid level gauge main body 3 and its front panel 3
A display 31 is provided in a.

Inside the liquid level gauge main body 3, electric circuits 32 to 35 as shown in FIG. 3 are housed. That is, the sound pressure signal output from the pressure sensor 2 is filtered and amplified by the amplifier circuit 32, and then the A / D converter 33.
Is input to the CPU 34, converted into digital data, and input to the CPU 34. The CPU 34 calculates the liquid level by the procedure described later, and the liquid level data is displayed on the display 31 via the output interface circuit 35.

FIG. 4 shows a signal processing procedure in the CPU 34. In step 101, a predetermined number of sound pressure data are sampled at regular time intervals, and in subsequent step 102, these sound pressure data are subjected to fast Fourier transform. Step 10
In 3, the frequency at which the sound pressure has a maximum, that is, the resonance frequency is extracted from the conversion result. The reason why the sound pressure shows the maximum is that the boiling evaporation sound emitted from the liquid nitrogen resonates in the gas space S above the liquid nitrogen, and the resonance frequency is the volume of the gas space S, that is, the inside of the storage container 1. There is a one-to-one correspondence with the liquid level of the liquid nitrogen L.

Therefore, in step 104, the liquid level of the liquid nitrogen and the map data of the sound pressure resonance frequency at this time, which are obtained in advance by using the conventional liquid level gauge, are referred to, and the extracted resonance frequency is corresponded. The liquid level of liquid nitrogen is calculated by interpolation calculation. In the following step 105, the calculated liquid level of liquid nitrogen is output to the display unit 31. FIG. 5 shows the experimental results on the liquid level of the liquid nitrogen L and the resonance frequency of the fifth harmonic corresponding to this liquid level. In this case, the storage container 1 has an inner diameter of 12.7φ and a depth of 185 mm. As is known from the figure, the resonance frequency and the liquid level of liquid nitrogen change with a unique relationship, and the liquid level is known from the resonance frequency.
The liquid levels and resonance frequencies at points A, B, and C in the figure are as follows.

[0022] In the above examples, the amount of heat flowing into the superconducting circuit board provided at the tip of the heat exchange pipe was described as an example of using the liquid level gauge when measuring by the boil-off calorimetry method, but the liquid level gauge of the present invention Since the liquid level detector has the property that it is not immersed in the liquid, it can be widely used for measuring the liquid level of a cryogen that needs to prevent excessive boiling evaporation due to heat input from the outside.

Further, the liquid level gauge of the present invention can of course be used for measuring the liquid level of a normal liquid whose liquid level is in a boiling state. In this case, the liquid surface does not always have to be in a boiling state, and may boil intermittently. A commercially available microphone may be used instead of the pressure sensor in the above embodiment.

Each step in the flow chart of the above embodiment may be realized by a hardware logic structure as a function executing means.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a cooling device for a superconducting circuit in which an inflowing heat quantity is measured by a boil-off calorimetry method.

FIG. 2 is a perspective view showing a device configuration of a liquid level gauge.

FIG. 3 is a block diagram of an electric circuit of the liquid level gauge.

FIG. 4 is a processing flowchart in a CPU.

FIG. 5 is a graph showing the relationship between liquid level and resonance frequency.

[Explanation of symbols]

1 ... Heat exchange pipe, 2 ... Pressure sensor, 3 ... Liquid level gauge main body,
34 ... CPU

Claims (5)

[Claims] 1. A level gauge for measuring the liquid level of a liquid contained in a storage container and having a liquid level in a boiling evaporation state, the liquid level gauge facing a gas space above the liquid level in the storage container. A sound detecting means provided for detecting a boiling evaporation sound emitted from the liquid, and a liquid level calculating means for extracting the resonance frequency of the detected boiling evaporation sound and calculating the liquid surface position of the liquid based on the resonance frequency. And a liquid level gauge. 2. The liquid level gauge according to claim 1, wherein the liquid is a cryogen such as liquid helium or liquid nitrogen. 3. The liquid level gauge according to claim 1, wherein the sound detecting means detects a sound pressure of the boiling evaporation sound. 4. The liquid level calculating means frequency-analyzes the sound pressure signal output from the sound detecting means, and sets the frequency at which the sound pressure has a maximum as the resonance frequency. The liquid level gauge according to claim 3. 5. The liquid according to claim 2, wherein the storage container is a heat exchange pipe of a cooling device whose inflowing heat quantity is measured by a boil-off calorimetry method. Face gauge.