Method and apparatus for monitoring the level of liquid nitrogen in a cryogenic storage tank

A combination cap and monitoring system for monitoring a level of liquid nitrogen in an insulated, cryogenic storage tank of the type having an access port therein, said combination cap and monitoring system comprising:

• (a) a stopper adapted in size for the occlusion of the access port within the cryogenic storage tank;
• (b) a sensor probe extending downward into said cryogenic storage tank from said stopper;
• (c) an electrically actuatable sensor carried by said sensor probe and adapted for submersion in said liquid nitrogen;
• (d) wherein said electrically actuatable sensor provides a first monitoring response when fully submerged within said liquid nitrogen, and a second monitoring response when not fully submerged within said liquid nitrogen;
• (e) an electrical monitoring circuit for monitoring said first monitoring response of said sensor, and for monitoring said second monitoring response of said sensor;
• and
• (f) an audio output device coupled to said monitoring circuit, for providing an audio output alarm when said sensor is not fully submerge in said liquid nitrogen.

A method of monitoring a level of liquid nitrogen in an insulated, cryogenic storage tank of the type having an access port therein, said method comprising the steps of:

• (a) inserting a stopper into said access port such that a sensor probe extends downward into said cryogenic storage tank from said stopper, said stopper being adapted in size for the occlusion of the access port within the cryogenic storage tank;
• (c) submersing an electrically actuatable sensor below said level of liquid nitrogen, said electrically actuatable sensor being carried by said sensor probe and adapted for submersion below said level of liquid nitrogen such that said electrically actuatable sensor provides a first monitoring response when fully submerged below said level of liquid nitrogen, and a second monitoring response when not fully submerged below said level of liquid nitrogen;
• (e) monitoring said first monitoring response of said sensor and monitoring said second monitoring response of said sensor with an electrical monitoring circuit;
• and
• (f) responding to an audio output alarm when said sensor is not fully submerged below said level of liquid nitrogen, said audio output alarm being provided by an audio output device coupled to said monitoring circuit.