Development of an expendable current profiler based on modulation and demodulation

Abstract. We designed a low-cost expandable current profiler (XCP) including software and hardware. An XCP is an observation instrument that rapidly measures currents based on the principle that currents cut the geomagnetic field to induce electric fields. The cost of an XCP must be reduced because it is a single-use device. The digitization of the previously developed XCP is carried out underwater, which requires the probe to contain not only analogue circuits for acquiring signals but also digital circuits and digital chips, which are relatively expensive. In this study, an XCP was developed that adopts signal modulation and demodulation to transmit analogue signals on an enamelled wire, and the signal digitization occurs above the surface of the water. The cost of the instrument was effectively reduced by half while maintaining its ability to measure parameters such as sea current and temperature in real time. After comparison with data processed from laboratory tests, the acquisition circuit showed an accuracy within 0.1 % and the XCP analogue circuit developed for the overall system was stable and reliable. The system exhibited an acquisition accuracy higher than 50 nV for 16 Hz, and the quality of the acquired signal satisfied the requirements for an XCP instrument.