Experimental study of liquid level gauge for liquid hydrogen using Helmholtz resonance technique

• A liquid hydrogen level gauge using the Helmholtz resonance technique is successfully developed.
• A loudspeaker impedance measurement is used to detect the Helmholtz resonance.
• A large temperature gradient is confirmed in the vapor phase by using two Pt-1000 resistance thermometers.
• An empirical equation is proposed for a situation where a large temperature gradient is formed in the vapor phase, and it is confirmed that the equation is appropriate.

The Helmholtz resonance technique was applied to a liquid level gauge for liquid hydrogen to confirm the applicability of the technique in the cryogenic industrial field. A specially designed liquid level gauge that has a Helmholtz resonator with a small loudspeaker was installed in a glass cryostat. A swept frequency signal was supplied to the loudspeaker, and the acoustic response was detected by measuring the electrical impedance of the loudspeaker’s voice coil. The penetration depth obtained from the Helmholtz resonance frequency was compared with the true value, which was read from a scale. In principle, the Helmholtz resonance technique is available for use with liquid hydrogen, however there are certain problems as regards practical applications. The applicability of the Helmholtz resonance technique to liquid hydrogen is discussed in this study.