A Microprocessor-Controlled Digitizer for Conductivity-Temperature-Depth Probes

A microprocessor-controlled instrument for digitizing multichannel, frequency modulated (FM) signals from a Plessey [1] Model 9400 conductivity-temperature-depth (CTD) probe has been developed. This instrument features high resolution (24 bits), good accuracy (±31 ppm) and rapid digitizing rate (10 measurements per second). Particular care has been taken regarding the interfacing of the instrument to computers for real-time acquisition of the CTD data so that most problems of interfacing have been eliminated. Cost of the instrument is probably an order of magnitude less than available commercial equipment and construction is within the capabilities of most universities and similar organizations.