Acoustic impedance system for liquid boundary level detection
AssigneeBeckman Instruments, Inc.
InventorsDale R. Pfost, R. Fred Pfost, Eric W. Lachenmeier
Life of this patent
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Abstract
A liquid boundary level detector employing an open-ended conduit which directs pressure waves toward a liquid boundary layer. The conduit is moved from a starting position toward the liquid boundary and, upon contact with the boundary, there is a change in acoustic impedance within the conduit. This change is monitored and a signal is generated indicative of such contact. Once the initial liquid boundary position is determined, that may become the reference position for subsequent liquid boundary measurements or motions.
Claims21
Apparatus for measuring contact between a conduit and a liquid boundary comprising,
- an open-ended conduit adapted for insertion into a liquid boundary of a liquid body, said open-ended conduit being movable towards and away from said liquid body,
- pressure wave generating means directing pressure waves into said conduit for establishing a first acoustic impedance,
- insertion means for moving the open end of said open-ended conduit into said liquid boundary, thereby closing said open end and establishing a second acoustic impedance, said insertion means generating a conduit position signal,
- detector means for detecting a change in acoustic impedance during insertion of the liquid handling means into the liquid boundary from said acoustic impedance to said second acoustic impedance and for producing an electrical output signal in response thereto, and
- signal correlating means receiving said electrical output signal and said conduit position signal for indicating liquid boundary position.
Apparatus for measuring contact between a vertically supported pipette and a liquid in a container,
- a pipette having an open tip at an end thereof,
- means for imparting vertical motion to said pipette in a direction approaching a container with liquid therein and for generating a position signal,
- a first hollow tube communicating with the interior of the pipette,
- pressure wave transmitter means directing pressure waves down the first tube into said pipette establishing a first acoustic impedance in said open tip,
- means for detecting a second acoustic impedance and producing an electrical output signal indicative of closure of said tip, and
- signal correlating means receiving said electrical output signal and said conduit position signal for indicating liquid boundary position.
A method for monitoring height of a liquid boundary in a liquid container comprising,
- directing pressure waves down a movable open-ended conduit toward a liquid boundary, the liquid boundary having an unknown position relative to a reference,
- moving the conduit toward the liquid boundary by known amounts,
- monitoring acoustic impedance in the conduit,
- recording the conduit position at the location of change in the acoustic impedance of the conduit, said change occurring during the transition from an open conduit to a conduit closed by a liquid boundary, and
- correlating the conduit position at said location of change in acoustic impedance to the reference position to establish the liquid boundary height.
Dependencies are inferred from the claim text.