Level control apparatus and method for cryogenic liquids

In a level control apparatus for a cryogenic liquid, a source of cryogenic liquid, an insulated flask having a chamber for holding a cryogenic liquid, inlet means mounted on the flask for introducing a cryogenic liquid into the chamber, outlet means mounted on the flask for permitting cryogenic liquid to be removed from the flask, first and second probe assemblies mounted in the flask and having their lower extremities at different elevations within the chamber which are adapted to be covered by the cryogenic liquid within the chamber, each of said probe means including thermocouple means for generating a voltage in response to temperature and heating means for generating heat and supplying the same to the thermocouple means whereby the thermocouple means produces a signal of one type when the heating means is in contact with the cryogenic liquid and a signal of a different type when at least a portion of the heating means is out of contact with the cryogenic liquid, and means responsive to the signals from said thermocouple means of the first and second probe assemblies for automatically controlling the flow of cryogenic liquid from said source into said inlet means, said means responsive to the signals from said thermocouple means in said first and second probe assemblies including a meter relay having upper and lower set points corresponding to two temperatures, one hot and one cold, with the hot temperature being reached when the heating means for both of said first and second probe assemblies are no longer covered by the cryogenic liquid and with the cold temperature being reached when the heating means for both of said first and second probe assemblies are substantially covered by said cryogenic liquid, solenoid operated valve means connected between the source and the inlet for controlling the flow of cryogenic liquid from said source to said inlet and relay means responsive to the meter relay for controlling operation of said solenoid operated valve means whereby filling of chamber with cryogenic liquid from said source is started when the upper set point is reached and continues until the lower set point is reached.