JP3124881U - Liquid level sensor - Google Patents

Abstract

A continuous liquid level sensor that can be applied to a tank filled with liquefied gas in either a closed system or an open system, has no restrictions on the type of liquefied gas, has a simple structure, is inexpensive, and has excellent durability.
In a liquid level sensor for measuring a liquid level of a liquefied gas in a tank, a metal pipe having one end inserted into the liquefied gas and the other end arranged outside the tank, and the metal pipe The differential thermocouple for detecting the temperature difference between the two locations, the temperature measuring device 8 to which the differential thermocouple is connected, and the temperature difference data of the liquefied gas from the temperature difference data output by the two temperature measuring devices 8. A data processing unit 9 for obtaining the depth is provided.
[Selection] Figure 1

Description

  The present invention relates to a liquid level sensor that can detect the depth of a liquid level of liquefied gas such as liquefied nitrogen, liquefied oxygen, and liquefied natural gas inside a container such as a tank with high accuracy.

  Conventionally, various types of liquid level sensors for liquefied gas have been proposed. In a liquid level sensor using a temperature sensor, a temperature sensor such as a thermocouple or a platinum resistance thermometer is disposed at a predetermined depth of a tank filled with liquefied gas. When the temperature measured by the temperature sensor is the temperature of the liquefied gas, the liquid level of the liquefied gas is above the predetermined depth, and when the temperature is higher than the temperature of the liquefied gas, the liquid level of the liquefied gas is the predetermined depth. It is below.

  In a liquid level sensor using a refractive index sensor, a refractive index sensor composed of an optical fiber and a prism is disposed at a predetermined depth of a tank filled with liquefied gas, and the refractive index sensor is disposed outside the tank. Passed light is detected. The refractive index sensor is adjusted so as to allow light to pass through when not immersed in the liquefied gas, and to prevent light from passing through due to the difference in refractive index when immersed in the liquefied gas. Therefore, when the light passing through the refractive index sensor is not detected, the liquid level of the liquefied gas is above the predetermined depth, and when the light passing through the refractive index sensor is detected, the liquid level of the liquefied gas is Below a predetermined depth.

  When the tank filled with the liquefied gas is a closed system, a liquid level sensor using a pressure sensor can be configured. A pressure above the liquid level in the tank is measured, and an arbitrary continuous liquid level can be known from the measurement result, that is, a continuous liquid level sensor is configured.

A continuous liquid level sensor that measures the liquid level of the liquefied gas is configured by measuring a voltage value when a current smaller than the critical current is passed through the superconducting wire inserted in the liquefied gas. When the liquefied gas is liquefied nitrogen, liquefied oxygen or liquefied natural gas, an oxide superconductor is used as the superconducting wire. The oxide superconductor may be a Ti-based oxide superconductor, a Hg-based oxide superconductor, a Bi-based oxide superconductor with an Ag alloy sheath, or a Bi-based oxide superconductor on a metal having low thermal conductivity. It is composed of a conductor. (For example, see Patent Document 1)
JP 2002-202175 A

In order to construct a continuous liquid level sensor with a liquid level sensor using a conventional temperature sensor or refractive index sensor, it is necessary to continuously arrange a large number of temperature sensors and refractive index sensors, which is difficult to implement.
Moreover, when measuring the pressure in a tank, although a continuous liquid level sensor can be comprised, there exists a restriction | limiting that the tank must be a closed system.
In a continuous liquid level sensor that measures the liquid level of a liquefied gas by passing a current through a superconducting wire inserted in the liquefied gas and measuring the voltage, the type of the liquefied gas is limited.
It is an object of the present invention to configure a continuous liquid level sensor that does not have a restriction that the tank must be a closed system and does not have a restriction on the type of liquefied gas.

  In the liquid level sensor that measures the liquid level of the liquefied gas in the tank, one end is inserted into the liquefied gas, and the other end is disposed outside the tank, and the heat conductor is disposed at two locations. And a means for obtaining the liquid surface depth of the liquefied gas from the temperature difference between the two locations.

  The continuous liquid level sensor of the present invention can be applied regardless of whether the tank filled with liquefied gas is a closed system or an open system, and there is no restriction on the type of liquefied gas. Further, it is composed of a heat conductor and a temperature sensor, has a simple structure and is inexpensive, and only the heat conductor is exposed to an extremely low temperature and has excellent durability.

  The heat conductor is composed of a metal tube having a hollow center, and the material is copper or silver having good heat conductivity. The outer periphery of the metal tube is covered with a heat insulating material to suppress heat dissipation and frost formation at the portion exposed from the liquefied gas of the metal tube.

  A heat radiating fin is formed at one end outside the tank of the heat conductor, and the heat radiating fin is blown with air at room temperature by a fan and kept at room temperature.

  Embodiments of the present invention will be described below. FIG. 1 is a diagram schematically showing the configuration of the present invention. In FIG. 1, 1 is a tank, which functions as a container for filling liquefied nitrogen. Reference numeral 2 denotes a metal tube having a hollow central axis and made of copper, silver, or the like, and functions as a heat conductor. A heat radiating fin is formed at one end of the metal tube 2 and disposed outside the tank 1. The radiating fin is blown with air at room temperature by the fan 4 and is kept at room temperature. The other end of the metal tube 2 is immersed in liquefied nitrogen, and the immersed part is maintained at -196 ° C. Reference numeral 3 denotes a heat insulating material having a function of suppressing heat radiation and frost formation in a portion exposed from the liquefied nitrogen of the metal tube 2.

  One end of the chromel wire 5 and one end of the constantan wire 6 are welded, and the other end of the constantan wire 6 and one end of the chromel wire 7 are welded to form a differential thermocouple. The welding point between the chromel wire 5 and the constantan wire 6 is embedded via an insulating material at the point X in the metal tube 2, and the welding point between the constantan wire 6 and the chromel wire 7 is insulated at the point Y in the metal tube 2. It is buried through. The differential thermocouple is connected to a temperature measuring device 8, and the temperature difference between the X point and the Y point in the metal tube 2 is measured and displayed. The temperature difference changes depending on the depth of the liquid level of liquefied nitrogen. The temperature difference data obtained by the temperature measuring device 8 is input to the data processing unit 9. The data processing unit 9 obtains the liquid surface depth of the liquefied nitrogen from the relationship between the temperature difference stored in advance and the liquid surface depth of the liquefied nitrogen, and displays this.

In FIG. 1, the depth of the liquid surface of liquefied nitrogen is shown in two levels, level A and level B, for ease of explanation.
FIG. 2 is a graph showing the operating principle of the present invention. In FIG. 2, curve A shows the temperature distribution in the axial direction of the metal tube 2 when the liquid level of liquefied nitrogen is at level A (d = dA), and curve B shows the depth of the liquid level of liquefied nitrogen. Shows the temperature distribution in the axial direction of the metal tube 2 when is at the level B (d = dB).

The temperature difference between the point X and the point Y in the metal tube 2 is obtained from the intersection of the curve A and the dotted line when the liquid level of the liquefied nitrogen is at level A (d = dA), and becomes ΔTA. Similarly, when the liquid surface depth is at level B (d = dB), the temperature difference is obtained from the intersection of the curve B and the dotted line and becomes ΔTB. Thus, the temperature difference is determined in accordance with the liquid level depth of liquefied nitrogen.
FIG. 3 is a graph showing the relationship between the liquid level of liquefied nitrogen and the temperature difference. In FIG. 3, a d−ΔT curve shows the relationship between the liquid level of liquefied nitrogen and the temperature difference measured by the temperature measuring device 8, and is stored in the data processing unit 9.

  Since the present invention has the above-described configuration, the liquid level sensor shown in the embodiment of FIG. 1 functions as a continuous liquid level sensor, and the tank 1 filled with liquefied nitrogen can be applied to either a closed system or an open system. The temperature sensor is simple and inexpensive, and only the heat conductor is exposed to extremely low temperatures and has excellent durability.

In the embodiment of FIG. 1, the liquefied gas filled in the tank 1 is liquefied nitrogen, but the liquefied gas other than liquefied nitrogen is also stored in the data processing unit 9 for the liquefied gas. Thus, the present invention is applicable, and the apparatus is not limited to the illustrated example.
In the embodiment, the differential thermocouple includes a chromel wire 5, a constantan wire 6, and a chromel wire 7, but an alumel wire may be used instead of the constantan wire 6. Alternatively, the present invention can also be applied to a differential thermocouple composed of a metal wire completely different from these metal wires.
In the embodiment, the temperature difference between the X point and the Y point is detected by a differential thermocouple. However, another temperature sensor, for example, a platinum resistance thermometer is embedded in the X point and the Y point, and the respective temperatures are detected. And the temperature difference between the X point and the Y point may be obtained from the difference. Thus, the apparatus can have various configurations, and the present invention includes these modifications.

  The present invention relates to a liquid level sensor that can detect the depth of a liquid level of liquefied gas such as liquefied nitrogen, liquefied oxygen, and liquefied natural gas inside a container such as a tank with high accuracy.

It is a figure which shows the structure of this invention roughly. It is a graph which shows the operation principle of this invention. It is a graph which shows the relationship between the depth of the liquid level of liquefied nitrogen, and a temperature difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tank 2 Metal pipe 3 Thermal insulation material 4 Fan 5 Chromel wire 6 Constantan wire 7 Chromel wire 8 Temperature measuring instrument 9 Data processing part

Claims (1)

  In the liquid level sensor that measures the liquid level of the liquefied gas in the tank, one end is inserted into the liquefied gas, and the other end is disposed outside the tank, and the heat conductor is disposed at two locations. A liquid level sensor comprising: a temperature sensor that is configured to obtain the depth of the liquid level of the liquefied gas from the temperature difference between the two locations.

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