Temperature profile of an experimental helium dewar

✍ Scribed by J.V. Prodan; J.R. Long

• Publisher: Elsevier Science
• Year: 1976
• Tongue: English
• Weight: 203 KB
• Volume: 16
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(76)90044-8

✦ Synopsis

meter-relay circuits for driving a solenoid operated valve which is situated in the liquid transfer tube.

Commercial copper wire at present available is pure enough to obtain an almost linear change in resistance at temperatures down to 60 K with sufficient reproducibility. The resistance at 77 K was 1/5-1/8 of that at 300 K for 0.1-0.2 mm dia copper wires with Formvar insulation. For these reasons, copper wires are suitable for monitoring of liquid nitrogen (or oxygen, air etc) level. Fig. shows the resistance of a copper coil versus the distance between the coil and liquid nitrogen level as a typical example. It can be seen in the figure, as the liquid level is lowered, the temperature or the resistance of the coil increases quite rapidly. Using a single coil, both the upper and lower limits of liquid level can be easily determined to within 1 cm by rough monitoring of the resistance. The change in room temperature did not affect the resistance versus distance relation when the coil is placed 5 cm below the top of the dewar. A choke coil of about 50/all inductance works satisfactorily as a liquid level monitor.