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A convenient liquid helium level detector
LETTERTOTHEEDITOR A convenient liquid helium level detector Dear Sir Many techniques have been developed to locate the level in a liquid helium storage vessel. The cheapest and one of the simplest is still the one that uses a light rubber diaphragm to detect the change in frequency and amplitude of thermal oscillations in a narrow tube as its open end passes from the gaseous to liquid regions of the storage vessel. 1 For suitable rubber the early books recommend expensive surgeon's gloves, old helium users recommend condoms (unsensitized are adequate) and economists recommend dental rubber sheet. These all have the problem that the rubber perishes fairly rapidly when left on the dip stick under tension. Replacing the rubber with very thin brass sheet (0.05 mm) eliminates the perishing problem but such metal sheets are very fragile. These problems can be avoided by using a dip stick composed of the usual long, narrow diameter (about 2.5 mm) tube attached directly to a miniature pressure gauge of the Bourdon type. A 0-4 bar Schrader miniature
pressure gauge, with the needle set at midscale to avoid the stop pin at the start of the scale, works well. With the open end above the liquid the needle oscillates rapidly between the 1½ and 2½ bar marks so that the needle almost appears invisible whilst with the open end in the liquid the needle oscillates with a much reduced amplitude. Such a gauge costs less than $7 so this is still a cheap method. J.A. Campbell Physics Department University of Canterbury Christchurch, New Zealand Reference 1
White,G.K. Experimental Techniques in Low Temperature Physics Clarendon Press, (1979)
our
Futura Vocation INDUSTRIAL and PROFESSIONAL TRAINING via MSc and PhD Study for MSc and PhD at the University of Surrey prepares scientists and engineers for vocationally oriented careers. Opportunities exist for full and part-time study in a wide range of engineering and scientific subjects.
UNIVERSITY OF SURREY CRYOGENICS. FEBRUARY 1981
Most Surrey BSc degrees include periods of industrial and professional training and this provides opportunities for similar collaboration with industrial and professional employers at higher degree level. For further details of courses of study for MSc and P h D
write to: Deputy Academic Registrar, University of Surrey, Guildford, Surrey GU2 5XH, England
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pressure gauge, with the needle set at midscale to avoid the stop pin at the start of the scale, works well. With the open end above the liquid the needle oscillates rapidly between the 1½ and 2½ bar marks so that the needle almost appears invisible whilst with the open end in the liquid the needle oscillates with a much reduced amplitude. Such a gauge costs less than $7 so this is still a cheap method. J.A. Campbell Physics Department University of Canterbury Christchurch, New Zealand Reference 1
White,G.K. Experimental Techniques in Low Temperature Physics Clarendon Press, (1979)
our
Futura Vocation INDUSTRIAL and PROFESSIONAL TRAINING via MSc and PhD Study for MSc and PhD at the University of Surrey prepares scientists and engineers for vocationally oriented careers. Opportunities exist for full and part-time study in a wide range of engineering and scientific subjects.
UNIVERSITY OF SURREY CRYOGENICS. FEBRUARY 1981
Most Surrey BSc degrees include periods of industrial and professional training and this provides opportunities for similar collaboration with industrial and professional employers at higher degree level. For further details of courses of study for MSc and P h D
write to: Deputy Academic Registrar, University of Surrey, Guildford, Surrey GU2 5XH, England
121