Apparatus using a feedback network to measure fluid pressures

An apparatus for determining the level of a liquid column in a sealed, pressurized cell having a blanket region overlying said liquid column, comprising:

• first pressure sensor means positioned above the surface level of said liquid column in pressure-sensing relationship with said blanket region for generating a first sensor signal representative of the pressure difference between the pressure in said blanket region and a reference pressure;
• second pressure sensor means positioned below the surface level of said liquid column in pressure-sensing relationship with said liquid column at or near the bottom of said column for generating a second sensor signal representative of the pressure difference between pressure caused by said column as burdened by the pressure in said blanket region and said reference pressure;
• and
• feedback means responsive to said first sensor signal for continuously adjusting said reference pressure to substantially match the pressure of said blanket region.

A method of determining the level of a liquid column contained within a pressurized cell and having a blanket region overlying said liquid column, comprising the steps of:

• generating a blanket pressure signal representative of the pressure difference between the pressure in said blanket region and a reference pressure at a first height H1, where H1 is above the level of such liquid column;
• generating a cell pressure signal representative of the pressure difference between pressure caused by said column as burdened by the pressure in said blanket region and said reference pressure at a second height H2, where H2 is lower than H1, and H2 is below the level of said liquid column;
• generating a pneumatic signal representative of said blanket pressure signal;
• and
• dynamically adjusting said reference pressure in accordance with said pneumatic signal whereby the difference between said blanket pressure signal and said cell pressure signal is representative of said level measured with respect to H2.