Testing of Cryogenic Components and Relevant Cabling Requirements
Some users consider the -297°F (-183°C) boiling point of liquid oxygen to be "cryogenic" (warmer than hydrogen). However, truly cryogenic means the ability to work down to at least -423°F (-253°C), the boiling point of liquid hydrogen. Both liquid hydrogen and liquid oxygen are utilized as propellants for air launch vehicles (rockets).
Due to safety reasons, practical testing in a lab environment requires utilization of less hazardous liquids, such as liquid nitrogen with a boiling point of -321°F (-196°C) or liquid helium with a boiling point of -452°F (-269°C). Liquid nitrogen allows one to mimic liquid oxygen while liquid helium allows one to mimic liquid hydrogen.
Cabling must also survive the above temperatures, especially soft-line cable assemblies which are not hermetically sealed and are vented to the atmosphere. As air is cooled to cryogenic temperatures, water vapor condenses and decreases the resistance of the cable insulators. To prevent moisture from creeping into the inside, some customers cover the connector ends with some type of RTV potting. The potting material acts as a barrier to prevent moisture from being sucked into the cable from the atmosphere as the cable is cooled rapidly during exposure to liquid helium. Any material under cryogenic temperature conditions will become brittle. Care should be taken to secure the cable and not allow it to flex until it is returned to room temperature.
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