Calibration formula calculation method

Abstract

[Problem] To calculate a calibration formula for calibrating a superconductor-using liquid hydrogen level gauge easily and at low cost, without using expensive liquid hydrogen. [Solution] Provided is a calibration formula calculation method for calculating a calibration formula for calibrating a superconductor-using liquid hydrogen level gauge that detects the liquid hydrogen level height in a container by voltage measurement, the calibration formula calculation method being characterized in that, while a liquid at a temperature higher than the critical temperature (Tc) of a superconductor used in the liquid hydrogen level gauge is injected into the container in which the liquid hydrogen level gauge is vertically installed, the calibration formula is calculated from the relationship between the voltage values of the liquid hydrogen level gauge at at least three points having different liquid level heights and the liquid level heights.

Description

Calibration formula calculation method

[0001] The present invention relates to a method for calculating a calibration formula for calibrating a liquid hydrogen level gauge using a superconductor.

[0002] In February 2023, Japan's "Basic Policy for Realizing GX (Green Transformation)" was approved by the Cabinet, and with the promotion of hydrogen introduction being advocated, there is a need for accurate measurement of liquid hydrogen levels in the transportation, storage, and consumption of liquid hydrogen. In this context, efforts are underway to develop liquid hydrogen level gauges using superconductors such as MgB2.

[0003] For a liquid hydrogen level gauge to be used in practice, calibration is required between the voltage measurement of the gauge and the actual liquid hydrogen level. However, using liquid hydrogen for calibration is costly, and constructing a liquid hydrogen facility in-house is impractical due to strict applicable laws such as the High Pressure Gas Safety Act, the Industrial Safety and Health Act (Explosion-Proof Structure Standards for Electrical Machinery and Equipment), and the Fire Service Act. On the other hand, there are very few test facilities capable of testing liquid hydrogen, making it difficult to easily obtain an environment for testing and calibrating liquid hydrogen level gauges.

[0004] Patent Document 1 describes a configuration for a liquid level gauge for liquefied gases such as liquid nitrogen, in which a superconductor and a non-superconductor are arranged in parallel.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 04-99923

[0006] However, Patent Document 1 does not describe how to calibrate the voltage measurement value in the liquid level gauge with the actual liquid level of the liquefied gas. If the liquefied gas is liquid hydrogen, as mentioned above, not only is it costly, but there is also the problem that it is difficult to perform the calibration in-house due to legal restrictions.

[0007] The present invention aims to solve the above problems and to easily calculate a calibration formula for calibrating a liquid hydrogen level gauge using a superconductor at low cost.

[0008] To solve the above problems, the present invention provides a calibration formula calculation method for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, characterized in that the calibration formula is calculated from the relationship between the voltage of the liquid hydrogen level gauge and the respective liquid level heights at at least three points where the liquid level heights are different, while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into the container in which the liquid hydrogen level gauge is installed vertically.

[0009] This configuration allows for the easy and low-cost calculation of a calibration formula for a liquid hydrogen level gauge using a superconductor, without the need for expensive liquid hydrogen. Furthermore, the calibration test can be performed using a conventional liquid hydrogen level gauge instead of visual inspection.

[0010] Furthermore, in order to solve the above problems, the present invention provides a calibration formula calculation method for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, characterized in that, while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into a container in which the liquid hydrogen level gauge is installed vertically, the third voltage of the liquid hydrogen level gauge when the liquid level is 0% and the first voltage of the liquid hydrogen level gauge when the liquid level is 100% are measured, and the second voltage of the liquid hydrogen level gauge at at least one liquid level height between 0% and 100% is measured, and the calibration formula is calculated from the relationship between the values ​​of the first voltage, the second voltage, and the third voltage and their respective liquid level heights.

[0011] This configuration allows for the easy and low-cost calculation of a calibration formula for a liquid hydrogen level gauge using a superconductor, without the need for expensive liquid hydrogen. Furthermore, the calibration test can be performed using a conventional liquid hydrogen level gauge instead of visual inspection.

[0012] A calibration formula calculation method may be provided, wherein the liquid hydrogen level gauge includes a superconducting wire and a non-superconducting wire of the same length, the first voltage is the voltage at 100% liquid level of the non-superconducting wire, and the second voltage is the voltage obtained by subtracting the voltage at 100% liquid level of the superconducting wire and any liquid level between 100% and 0% from the voltage at 100% liquid level of the non-superconducting wire.

[0013] This configuration prevents measurement errors caused by temperature changes in the gas phase.

[0014] The calibration formula calculation method may be configured such that the liquid injected into the container is liquid nitrogen.

[0015] This configuration allows for the calculation of a calibration formula for easily and inexpensively calibrating a liquid hydrogen level gauge using a superconductor, utilizing readily available, easy-to-handle, and low-cost liquid nitrogen.

[0016] The calibration formula calculation method may be configured such that the second voltage is the voltage of the liquid hydrogen level gauge when the liquid level is 50%.

[0017] This configuration allows the liquid level at which the second voltage is measured to be midway between the 100% and 0% liquid levels, thus enabling the calculation of a more accurate calibration formula.

[0018] The calibration formula calculation method of the present invention allows for the low-cost and easy calculation of a calibration formula for calibrating a liquid hydrogen level gauge using a superconductor. Furthermore, while it is difficult to measure liquid hydrogen with conventional other-type level gauges, using easily handled liquid nitrogen makes it possible to conduct comparative tests with liquid level heights measured by other-type level gauges.

[0019] This figure illustrates the installation of the liquid hydrogen level gauge in Embodiment 1 of the present invention. This figure illustrates the state when 50% of the liquid has been injected into the container in Embodiment 1 of the present invention. This figure illustrates the state when 100% of the liquid has been injected into the container in Embodiment 1 of the present invention. This figure illustrates the installation of the liquid hydrogen level gauge in Embodiment 2 of the present invention.

[0020] Embodiment 1 of the present invention will be described with reference to Figures 1-3. Figure 1 is a diagram illustrating the installation state of the liquid hydrogen level gauge in Embodiment 1 of the present invention. Figure 2 is a diagram illustrating the state when 50% of the liquid has been injected into the container in Embodiment 1 of the present invention. Figure 3 is a diagram illustrating the state when 100% of the liquid has been injected into the container in Embodiment 1 of the present invention.

[0021] (Liquid Hydrogen Level Gauge) First, the liquid hydrogen level gauge 10 in Example 1 will be described. The liquid hydrogen level gauge 10 has a superconducting wire 11 and a non-superconducting wire 12 that are provided in parallel and of the same length. By passing a current through each end and measuring the voltage, the liquid level height is detected from the measured voltage, taking advantage of the fact that the area below the liquid surface becomes superconducting and has zero resistance. Both the superconducting wire 11 and the non-superconducting wire 12 are long core wires with a length of about 1 m and a diameter of about 0.3 mm, and are covered with a metal coating. The superconductor contained in the superconductor 11 is made by mixing 1 part magnesium (Mg) (325 mesh, manufactured by alfa Aesar, particle size about 44 μm) with boron (B) with an average particle size of 14 μm in a molar ratio of 2 (mixing process), drawing the mixture in a wire drawing process, and then firing it in a calcination process to make it a MgB2 superconductor. In the wire drawing process, a powdered mixture of Mg and B obtained from the mixing process was placed in a single tube and drawn to create a long wire. The critical temperature (Tc) of the superconductor manufactured in this way is approximately 32K to 34K.

[0022] In Example 1, a long core wire with a length of approximately 1 m and a diameter of approximately 0.3 mm was formed, but this is not necessarily limited to this and can be changed as appropriate. For example, the length could be approximately 5 m or 0.5 m, and it should be prepared according to the depth of liquid hydrogen in the container. Also, in Example 1, the diameter was approximately 0.3 mm, but this is not necessarily limited to this and can be changed as appropriate. For example, it could be 0.5 mm or 0.2 mm, and the diameter may be selected in consideration of the critical temperature (Tc).

[0023] The coating metal can be any metal with high conductivity. In Example 1, a CuNi alloy was used, but other metals such as stainless steel may also be used.

[0024] The non-superconducting wire 12 is composed of a non-superconducting metal of the same length and thickness as the superconducting wire described above, and is covered with a CuNi alloy coating. In Example 1, any ordinary conductor can be used as the non-superconducting metal.

[0025] When 50% of liquid hydrogen is injected into container 20 as shown in Figure 2, the portion of the superconducting wire 11 submerged in liquid hydrogen becomes superconducting, and the voltage V between A and C increases. ＡＣ When measured, the voltage V between A and B is not superconducting. ＡＢ This can be measured and the liquid level can be determined. However, because the resistance changes with temperature changes in the non-superconducting gas phase, the voltage V can change even if the liquid level does not change. ＡＢ The voltage Vac of the non-superconducting wire 12 changes. ＡＣ Subtracting this, we get the voltage V of the superconducting wire 11 where the gas phase portion has the same temperature distribution. ＡＢ The voltage at the same liquid level in the non-superconducting wire 12 cancels out, leaving only the voltage Vbc in the non-superconducting wire 12. Since the temperature in the liquid is constant, the liquid level can be detected by calculating the voltage Vbc.

[0026] (Calibration of a liquid hydrogen level gauge using liquid hydrogen) In order to accurately measure the liquid level using the liquid hydrogen level gauge 10, it is necessary to obtain a calibration formula that calibrates the difference between the voltage Vbc of the non-superconducting wire 12 (output voltage of the liquid hydrogen level gauge 10) and the actual liquid level. For this reason, the liquid hydrogen level gauge 10 is usually installed in a container that can be visually observed from the outside, liquid hydrogen (Tc = 20-30K) is injected into the container, and as the liquid level drops due to evaporation, the liquid level is visually checked using the scale, and a calibration formula is calculated to calibrate the visually observed liquid level and the output voltage of the liquid hydrogen level gauge 10.

[0027] Calibrating this liquid hydrogen level gauge 10 using liquid hydrogen presents the following problems: • The cost of liquid hydrogen is extremely high. • There are very few testing facilities nationwide that can perform tests using liquid hydrogen. • Constructing a liquid hydrogen facility in-house is difficult in terms of time and cost due to the strict application of laws and regulations such as the High Pressure Gas Safety Act, the Industrial Safety and Health Act (Explosion-Proof Structure Standards for Electrical Machinery and Equipment), and the Fire Service Act.

[0028] Therefore, the applicant has found a method for calculating a calibration formula for calibrating the liquid hydrogen level gauge 10 using a liquid other than liquid hydrogen with low cost and few applicable laws. Next, a method for calculating a calibration formula for calibrating the liquid hydrogen level gauge in Example 1 of the present invention will be described.

[0029] (Method for calculating calibration formula without using liquid hydrogen) First, as shown in FIG. 1, the liquid hydrogen level gauge 10 is vertically installed in the container 20. At this time, the liquid hydrogen level gauge 10 should be such that the liquid level height can be measured even when 100% liquid is injected into the container 20.

[0030] Next, with the liquid not being injected (liquid level at 0%), a voltage is applied to both ends of the superconducting wire 11, and the voltage V ＡＣ between point A and point C is measured. At this time, the voltage when the superconducting wire 11 is not superconducting is measured. Then, when the voltage Va of the non-superconducting wire is subtracted from the voltage V ＡＣ of the superconducting wire 11, the result is zero, and the voltage measurement value at the liquid level height of 0% is zero.

[0031] Next, a liquid 30 at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 10 is injected into the container up to a height of 50% (point B in FIG. 2). The critical temperature (Tc) of the superconductor in Example 1 is about 32K to about 34K. In Example 1, the liquid injected into the container 20 is liquid nitrogen (boiling point at 1 atm = 77K).

[0032] At this time, since the liquid is liquid nitrogen (boiling point at 1 atm = 77K), the superconducting wire 11 in the liquid phase part is not superconducting. When the voltage V ＡＣ is measured, the voltage V ＢＣ between point B and point C of the superconducting wire 11 does not become zero, and the voltage in the non-superconducting state is measured. However, if V ＢＣ is intentionally set to zero, the same V ＡＣ in the superconducting state can be measured. That is, by subtracting the voltage V ＡＢ between point A and point B of the superconducting wire 11 from the voltage Vac between point a and point c of the non-superconducting wire 12, the voltage Vbc of the non-superconducting wire 12 can be obtained, and the result is the same as that when the liquid phase part (below the liquid level) of the superconducting wire 11 is in the superconducting state.

[0033] Next, a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 10 is injected into the container up to a height of 100% (point A in FIG. 3). Then, the voltage Vac between point a and point c of the non-superconducting wire 12 is measured.

[0034] Finally, a calibration formula, which is an approximate formula, is calculated by the least squares method or the like from the relationships between the three points of the voltage zero (third voltage) at a liquid level height of 0%, the voltage Vbc (second voltage) of the non-superconducting wire 12 at a liquid level height of 50%, and the voltage Vac (first voltage) of the non-superconducting wire 12 at a liquid level height of 100% and their respective liquid level heights. The liquid level height may be measured with another level gauge.

[0035] In Example 1, the point B shown in FIG. 2 is taken as the height of 50% of the liquid level height, but it is not necessarily limited to this and can be appropriately changed. For example, it may be the height of 30% of the liquid level height, or it may be the height of 70% of the liquid level height, and it can be any point at a height between the height of 0% of the liquid level height and the height of 100% of the liquid level height. Also, point B does not have to be at one location, and a calibration formula can be calculated by setting a plurality of points B between the height of 0% of the liquid level height and the height of 100% of the liquid level height.

[0036] Furthermore, in Example 1, the calibration formula is calculated from the voltage at the height of 0% of the liquid level height, the voltage at the height of 100% of the liquid level height, and the voltage at the height of 50% of the liquid level height, but it is not necessarily limited to this and can be appropriately changed. For example, a calibration formula consisting of an approximate formula may be calculated from the relationships between the values of the voltages at any three points with different liquid level heights between the liquid level height of 0% and the liquid level height of 100% and their respective liquid level heights.

[0037] Also, in Example 1, the liquid 30 injected into the container 20 is liquid nitrogen, but it is not necessarily limited to this and can be appropriately changed. For example, it may be a liquefied gas such as liquefied carbon dioxide gas, or it may be water if the water temperature is stable, as long as it is a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 10.

[0038] Thus, in Example 1, a calibration formula calculation method is provided for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement. The calibration formula calculation method is characterized by the following steps: injecting a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into a container in which the liquid hydrogen level gauge is installed vertically, and calculating the calibration formula from the relationship between the voltage value of the liquid hydrogen level gauge and the respective liquid level height at at least three points, each with a different liquid level height. This method allows for the calculation of a calibration formula for a liquid hydrogen level gauge using a superconductor at low cost and without using expensive liquid hydrogen. Furthermore, while it is difficult to measure liquid hydrogen with other types of liquid level gauges, using easily handled liquid nitrogen makes it possible to perform comparative tests with liquid level heights measured by other types of liquid level gauges.

[0039] Furthermore, a calibration formula calculation method for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, wherein the liquid hydrogen level gauge is installed vertically in a container, and while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into the container, the third voltage of the liquid hydrogen level gauge when the liquid level height is 0% and the first voltage of the liquid hydrogen level gauge when the liquid level height is 100% are measured, and the second voltage of the liquid hydrogen level gauge at at least one liquid level height between 0% and 100% is measured, and the calibration formula is calculated from the relationship between the values ​​of the first voltage, the second voltage, and the third voltage and their respective liquid level heights, the calibration formula for calibrating a liquid hydrogen level gauge using a superconductor can be easily calculated at low cost without using expensive liquid hydrogen. Furthermore, while it is difficult to measure liquid hydrogen with conventional liquid level gauges, using readily available liquid nitrogen allows for comparative testing with liquid level measurements taken with other types of liquid level gauges.

[0040] The liquid hydrogen level gauge 110 in Embodiment 2 of the present invention differs from Embodiment 1 in that it is composed solely of superconducting wires and does not have non-superconducting wires. Embodiment 2 will be described with reference to Figure 4. Figure 4 is a diagram illustrating the installation state of the liquid hydrogen level gauge in Embodiment 2 of the present invention.

[0041] The liquid hydrogen level gauge 110 in Example 2 does not include a non-superconducting wire but has a superconducting wire 111. The superconducting wire 111 has the same configuration as in Example 1 and detects the liquid hydrogen level by measuring the voltage. Because the liquid hydrogen level gauge 110 does not have a non-superconducting wire, there is a risk of errors due to temperature changes in the gas phase portion. Therefore, it is mainly used in environments where the temperature of the gas phase portion can be kept constant.

[0042] The method for calculating the calibration formula will now be explained. First, as shown in Figure 4, the liquid hydrogen level gauge 110 is installed vertically in the container 20. At this time, the liquid hydrogen level gauge 110 should be long enough to measure the liquid level even when the container 20 is filled with 100% liquid.

[0043] Next, the voltage V across both ends of the superconducting wire 111 when no liquid has been injected (liquid level 0%). ＡＣ We do not measure it and consider it to be zero.

[0044] Next, a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 110 is poured into the container to a height of 50% (point B). In Example 2, the critical temperature (Tc) of the superconductor is approximately 32K to 34K. The liquid poured into the container 20 is liquid nitrogen (77K), but it is not necessarily limited to this and can be changed as appropriate. For example, a liquefied gas such as liquefied carbon dioxide may be used, or water may be used if the water temperature is stable, as long as the liquid is at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 110.

[0045] In this case, since the liquid is liquid nitrogen, the superconducting wire 111 in the liquid phase is not superconducting, and the voltage V between point A and point C ＡＣ When measured, the voltage V of the superconducting wire 111 between point B and point C is ＢＣ The voltage is not zero, and the voltage in the non-superconducting state is measured, V ＢＣIf we intentionally set V to zero, then V is the same as in the superconducting state. ＡＣ This can be measured. In other words, the voltage V of the superconducting wire 111 at liquid surface point B. ＡＢ Measure.

[0046] Next, a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge 110 is poured into the container to 100% of its height (point A). Then, the voltage V between points A and C of the superconducting wire 111 is measured. ＡＣ Measure the voltage. When measuring the voltage, it is advisable to connect an appropriate current source.

[0047] Finally, the voltage is zero when the liquid level is 0%, and the voltage V between points A and B of the superconducting wire 111 when the liquid level is 50% (point B). ＡＢ The voltage V between point A and point C of the superconducting wire 111 when the liquid level is 100% (point A) ＡＣ The calibration formula for calibration is calculated by approximating it using the least squares method or similar, based on the relationship between the voltage values ​​at the three points and their respective liquid levels.

[0048] In Example 2, point B shown in Figure 4 was set to a height of 50% of the liquid level, but this is not necessarily limited to this and can be changed as appropriate. For example, it could be 30% of the liquid level, 70% of the liquid level, or any height between 0% and 100% of the liquid level. Furthermore, there is no need to be just one point B; multiple points B can be set between 0% and 100% of the liquid level to calculate the calibration formula.

[0049] Furthermore, in Example 2, the calibration formula was calculated from the voltage at a liquid level of 0%, a liquid level of 100%, and a liquid level of 50%, but this is not necessarily limited to this and can be modified as appropriate. For example, the calibration formula may be calculated from the relationship between the voltage values ​​at three arbitrary points with different liquid levels between 0% and 100% liquid levels and their respective liquid levels.

[0050] Thus, in Example 2, a calibration formula calculation method is provided for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement. The calibration formula calculation method is characterized by the following steps: injecting a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into a container in which the liquid hydrogen level gauge is installed vertically, and calculating the calibration formula from the relationship between the voltage value of the liquid hydrogen level gauge at at least three points with different liquid level heights and their respective liquid level heights. This method allows for the calculation of a calibration formula for a liquid hydrogen level gauge using a superconductor at low cost and without the use of expensive liquid hydrogen. Furthermore, while it is difficult to measure liquid hydrogen with other types of liquid level gauges, using easily handled liquid nitrogen makes it possible to perform comparative tests with liquid level heights measured by other types of liquid level gauges.

[0051] Furthermore, a calibration formula calculation method for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, wherein the liquid hydrogen level gauge is installed vertically in a container, and while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into the container, the third voltage of the liquid hydrogen level gauge when the liquid level is 0% and the first voltage of the liquid hydrogen level gauge when the liquid level is 100% are measured, and the second voltage of the liquid hydrogen level gauge at at least one point between 0% and 100% liquid level is measured, and the calibration formula is calculated from the relationship between the values ​​of the first voltage, the second voltage, and the third voltage and their respective liquid level heights, the calibration formula for calibrating a liquid hydrogen level gauge using a superconductor can be easily calculated at low cost without using expensive liquid hydrogen. Furthermore, while it is difficult to measure liquid hydrogen with conventional liquid level gauges, using readily available liquid nitrogen allows for comparative testing with liquid level measurements taken with other types of liquid level gauges.

[0052] The calibration formula calculation method in this invention can be widely applied to the field of liquid hydrogen level gauges.

[0053] 10: Liquid hydrogen level gauge 11: Superconducting wire 12: Non-superconducting wire 20: Container 30: Liquid 110: Liquid hydrogen level gauge 111: Superconducting wire

Claims

1. A method for calculating a calibration formula for calibrating a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, characterized in that the calibration formula is calculated from the relationship between the voltage value of the liquid hydrogen level gauge and the respective liquid level height at at least three points, each with a different liquid level height, while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into the container in which the liquid hydrogen level gauge is installed vertically.

2. A calibration formula calculation method for calculating a calibration formula for a liquid hydrogen level gauge using a superconductor that detects the liquid hydrogen level height in a container by voltage measurement, characterized in that, while pouring a liquid at a temperature higher than the critical temperature (Tc) of the superconductor used in the liquid hydrogen level gauge into a container in which the liquid hydrogen level gauge is installed vertically, the third voltage of the liquid hydrogen level gauge when the liquid level height is 0% and the first voltage of the liquid hydrogen level gauge when the liquid level height is 100% are measured, and the second voltage of the liquid hydrogen level gauge at at least one liquid level height between 0% and 100% are measured, and a calibration formula is calculated from the relationship between the values ​​of the first voltage, the second voltage, and the third voltage and their respective liquid level heights.

3. The calibration formula calculation method according to claim 2, characterized in that the liquid hydrogen level gauge includes a superconducting wire and a non-superconducting wire of the same length, the first voltage is the voltage at 100% liquid level of the non-superconducting wire, and the second voltage is the voltage obtained by subtracting the voltage at any liquid level between 100% liquid level and 0% liquid level of the superconducting wire from the voltage at 100% liquid level of the non-superconducting wire.

4. The calibration formula calculation method according to any one of 1-3, characterized in that the liquid injected into the container is liquid nitrogen.

5. The calibration formula calculation method according to claim 2 or 3, characterized in that the second voltage is the voltage of the liquid hydrogen level gauge when the liquid level is 50%.

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