A new conductivity-temperature-depth device for high resolution oceanographic measurements

A new high resolution CTD system has been developed for deep-sea use. A newly patented 4-electrode conductivity cell with no external field, very low thermal mass and temperature measurements internal to the cell has been coupled with a pressure-protected, stable thermistor, Druck pressure transducer and self-calibrating electronics. Finite element modeling of the electric field was used to optimize cell geometry and electrode placement. Two internal temperature probes provide a rapid response temperature measurement ideally suited for optimal dynamic response to minimize salinity spiking. The sensor circuitry was designed to be inherently stable, but self-referencing is used to continuously correct the analog electronics for thermal drifts. Over the 0-30degC oceanographic range, thermal drifts in the electronics have been determined to be less than 4 parts per million in the corrected data. This stability will serve to eliminate the common problem of down-up hysteresis in property profiles. The CTD data flow is managed by a Persistor CF1 microcontroller, and is recorded at 25 Hz