RF admittance measuring method and apparatus for determining the level of a conductive liquid

A probe system for measuring the level of conductive liquids comprising:

• a vessel containing a conductive liquid, said vessel having a support surface extending at least somewhat vertically such that the liquid rises and falls along said surface with variations in the level of said liquid;
• a probe mounted on said surface such that the longitudinal axis of said probe extends at least somewhat vertically, said probe comprising:
• a conductive probe electrode extending longitudinally along said probe;
• conductive guard electrode means including a rear portion juxtaposed between said support surface and said probe electrode and lateral portions extending laterally outwardly beyond the lateral extremities of said probe electrode a substantially greater distance than the minimum spacing between said lateral portions and said probe electrode;
• exterior solid insulation means surrounding the exterior of said probe for insulating said guard electrode means and said probe electrode from said conductive liquid and said surface such that said lateral portions are substantially as closely coupled to said liquid as said probe electrode, said exterior insulation means having an exposed surface in contact with said conductive liquid and a concealed surface in contact with said support surface the thickness of said insulation from said exposed surface to said concealed surface being substantially less than the lateral extension of said lateral portions;
• and
• means for maintaining the potential of said guard electrode at substantially the same potential as said probe electrode.

A method of measuring the level of liquids in a vessel regardless of accumulated coating comprising:

• longitudinally submersing a portion of a probe comprising an insulated probe electrode and laterally outwardly positioned insulated guard electrodes in the conductive liquid adjacent a support member such that any coating accumulating on said probe extends across said guard electrodes before contacting said effectively grounded support member;
• driving said guard electrodes at substantially the same potential as said probe electrode;
• and
• capacitively coupling the potential of the guard electrode to the conductive coating through said insulation covering said guard electrodes so as to maintain the potential drop of the coating between the lateral extremities and the center of the probe electrode within 25% of the potential drop between the probe electrode and the coating at the center of the probe electrode.

A probe for use in liquid level measuring systems comprising:

• a conductive probe electrode extending longitudinally along the probe;
• conductive guard electrode means including lateral portions extending laterally outwardly beyond the lateral extremities of said probe and a rear portion;
• interior insulation means located between said probe electrode and said rear portion of said guard electrode means;
• and
• exterior insulation means contacting said probe electrode and said lateral portions of said guard electrode and forming an exposed frontal surface of the probe adapted to directly contact the liquids, said lateral portions being substantially as closely coupled as said probe electrode to said frontal surface;
• said lateral portions extending laterally outwardly from the lateral extremities of said probe electrode a substantially greater distance than the minimum thickness of said exterior insulation means in contact with said probe electrode between said lateral extremities.

A probe system for measuring the level of a conductive liquid in a vessel, said probe system comprising:

• a thin, flexible probe adapted to be removably mounted on a surface of said vessel so as to extend through the surface level of said liquid while conforming with any curvature in the surface of said vessel, said probe including
• a conductive probe electrode extending longitudinally along the probe adjacent the front thereof and away from said surface,
• conductive rear guard electrode means extending longitudinally along the probe,
• interior solid insulation means located between and insulating said probe electrode and said rear guard electrode means, and
• exterior solid insulation means contacting said conductive probe electrode;
• means for maintaining the potential of said rear guard electrode means at substantially the same potential as said probe electrode;
• and
• a track on a wall of said vessel for removably receiving said probe.

A probe system for measuring the level of a liquid in a vessel comprising:

• a probe including:
• a conductive probe electrode extending longitudinally along the probe adjacent the front thereof;
• a conductive rear guard electrode means extending longitudinally along the probe adjacent the rear thereof;
• interior solid insulation means located between and integrally attaching said probe electrode to said rear guard electrode means;
• and
• exterior solid insulation means containing said conductive probe electrode, and
• a track located on the wall of said vessel and adapted to removably receive said integrally formed probe.