Development of a Low-Cost Inductive Conductivity Sensor

Expensive instrumentation has made studying the ocean cost-prohibitive for oceanographers. As a part of the SMART Ala Wai Project, which aims to reduce this barrier, my project initiated the development of a low-cost, long-term deployment conductivity sensor. Current inexpensive sensors conduct electricity in the water utilizing electrodes; however, direct exposure to the water results in undesired polarity and biofouling. This design's solution involves a pair of epoxied toroids instead of electrodes to induce an electric current in the water, which is proportional to its conductivity. When the sensor was tested in saline solutions ranging from fresh to seawater, as expected, a linear relationship between the output signal and salinity was obtained. To determine the sensor's functionality, it was tested against the performance of research-grade conductive electrode and inductive sensors in varying saline conditions. In the hypo (3 - 20 ppt) and mesosaline (20 - 50 ppt) levels, the sensor performed well-enough in lab conditions to replace the research-grade ones. The sensor was not as effective in the subsaline (0.5 - 3 ppt) realm. Further development of this sensor will yield more accurate results when the electronics are compactly packaged and deployable.