Patent ID: 7293458

Claim:
Apparatus for detecting a level of a surface of a liquid in a container having an upper opening, the apparatus comprising: an enclosure including a lever moveable between an upward unlocked position and a downward locked position; a support housing mounted to said lever, said support housing being adapted to mate with the upper opening of the container when said lever is in said downward locked position; primary liquid level sensing means mounted in said support housing for non-intrusively measuring the level of the surface of the liquid in the container; and secondary liquid level sensing means mounted in said support housing for intrusively sensing a predetermined level of the surface of the liquid in the container for preventing accidental overflows in the event of a malfunction of the primary liquid level sensing means, wherein the container and the liquid in the container are electrically conductive, and said secondary liquid level sensing means comprises a first electrically conductive retractable probe movably mounted to said support housing and adapted to extend to a predetermined level within the container, and a second electrically conductive probe adapted to contact the container, whereby electrical continuity between said first and second electrically conductive probes indicates that the level of the surface of the liquid in the container has reached the predetermined level within the container.