LIQUID LEVEL SENSOR FOR INK JET PRINTERS

摘要

The ink level sensor of the invention comprises an ink container (46) having a generally cylindrical shield (56) extending downward from its top to define sheielded and unshielded compartments (52, 54) within the container (46). Ink, but not foam, froth or mist, flows under the shield (56) to the shielded compartment (52). A plurality of conductive rods (66,68,70,72) of differing lengths extend downwardly into the shielded compartment (52) from the container top. The rods are connected to an impedance network (48) which provides signals representative of the ink level inside the container (46). A vacuum source (42) can be connected in each compartment to maintain pressure equilibrium in the compartments (52, 54) and to prevent foam, froth or mist from entering the shielded compartment (52). Alternatively, a return pump is used to force ink into the container (46) such that each compartment can be vented to the atmosphere.