Development of a point-electrode conductivity salinometer with high spatial resolution for use in very saline solutions

A conductivity probe and circuit were developed to measure salinities in sodium chloride salt-gradient solar ponds. A point-electrode salinometer design was chosen to give spatial resolution approximately 0.039 in. (1 mm). Such high spatial resolution was necessary to study the behavior of thermohaline columns in the vicinity of convective/conductive zone interfaces. The point-electrode conductivity instrument was designed for use in up to 25% (by weight) salinities with immersion times on the order of magnitude of 0.1 year or longer. Drift in the instrument, caused principally by changes in the surface condition of the platinum probe tip and reflected by changes in the probe cell constant, required periodic in situ calibration against the measured specific gravity of withdrawn fluid samples.