Triple Plate Balanced Resistance Water‐Level Gauge

A water‐level gauge developed for the automatic monitoring and control of a small‐scale tidal estuary model is described. The gauge is a self‐contained unit that incorporates a probe driven by a motor to follow the water surface. A linear transducer converts probe movement to an output voltage proportional to water level. A novel feature of the gauge is the triple electrode probe, which consists of three parallel vertical plates, the outer two being of unequal width and length. The electrical resistances between the outer electrodes and the central common electrode become equal at a unique depth of immersion. The probe is driven up and down by a servosystem that seeks to balance the electrical resistances, the driving speed varying in proportion to the electrical imbalance. The probe approaches the balanced position smoothly, and accurately follows a fluctuating water level. The principles of the gauge are described, and details of the mechanical and electrical design are presented.