Liquid level sensor for ink jet printers

A sensor for measuring a level of an electrically conductive liquid comprising:

• a) an enclosed container having an inlet, an outlet, a button and a shield secured to and extending downwardly from a top portion of said container to a position short of the container bottom thereby to define shielded and unshielded compartments, said conductive liquid entering said unshielded compartment through said inlet and being permitted to flow under said shield to the shielded compartment while any foam, froth or mist present in said container is retained in said unshielded compartment;
• b) a plurality of conductive rods of differing lengths extending downwardly into the shielded compartment for contact with the liquid;
• c) circuit means, connected to said rods, for generating output signals representative of the liquid level in the shielded compartment;
• and
• d) means for equalizing pressure between said shielded and unshielded compartments to ensure that foam, froth and mist do not enter said shielded compartment, said means for equalizing comprising vent means, for separately venting each of the said compartments to atmospheric pressure.

A liquid level sensor for measuring a level of conductive ink in an ink jet printing system including an ink reservoir, a nozzle supplied by said reservoir, a supply of make-up ink and a controllable valve by which make-up ink is added to said reservoir comprising:

• a) an enclosed container having an inlet, an outlet, a button and a shield secured to and extending downwardly from a top portion of said container to a position short of the container bottom thereby to define shielded and unshielded compartments, said conductive ink entering said unshielded compartment through said inlet and being permitted to flow under said shield to the shielded compartment while any foam, froth or mist in said container is retained in said unshielded compartment;
• b) a plurality of conductive rods of differing lengths downwardly extending from said top into the shielded compartment;
• c) circuit means, connected to said rods, for generating output signals representative of the conductive ink level inside the container;
• and
• d) means for equalizing pressure between said shielded and unshielded compartments to insure that foam, froth and mist do not enter said shielded compartment, said means for equalizing including a vacuum source communicating with both of said compartments to maintain equal, below atmospheric pressure in said compartments.

A sensor for measuring a level of electrically conductive ink in a container having a top and a bottom, said container receiving ink mixed with air, said sensor comprising:

• a) a shield secured to and extending downwardly from said top of the container to a position short of the container bottom to define an unshielded compartment and a shielded compartment, said ink being permitted to flow under said shield to the shielded compartment while any ink foam, froth or mist is retained in said unshielded compartment;
• b) at least two conductive rods of differing length which extend downwardly from the container top into the shielded compartment;
• c) circuit means, connected to said rods, for generating signals representative of the ink level inside the container;
• and
• d) air outlet means, communicating with said shielded and unshielded compartments, for i) providing air flow through the unshielded compartment to prevent the entry of foam, froth or ink mist into said shielded compartment and ii) maintaining equal pressure in said shielded and unshielded compartments.