A method for liquid cryogen level measurement in cryopreservation containers

A simple liquid sensing and measurement system for determining the level of cryogen in a tissue cryopreservation container is described. Liquid-gas boundary determination is made by detecting a thermal transient of the series-connected light emitting diodes. An electronic control and display unit located on the outer wall of the container indicates the level of cryogenic liquid, and alarms the operator if it reaches a pre-determined critical level.