Sea Technology

FEB 2014

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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38 st / February 2014 Sensorlab pH Sensors SensorLab was established in 2011, and QUIMA group prototypes gave birth to the frst commercial submarine sen- sor, the SP100-SM. The experience acquired with this sensor led to the new SP101-SM, packing several improvements over the previous generation of sensors. These improve- ments included a 40 percent reduction in the sensor pow- er consumption, thanks to a redesigned higher effciency electronic controller, and a new low-power LED light source. The corrosion resistance has also been improved with the addition of an epoxy coating, plus polyurethane fnishing on top of the 6060 hard anodized aluminum housing. The sensors use spectrophotometric-based methods to measure the pH, removing the dye effect in each determi- nation. The dye used is m-cressol purple. The design of the pH sensors allows for the same accu- racy achievable in the lab, but autonomously deployed in the ocean, enabling long-term measurements without hu- man intervention. As environmental conditions change, the sensor is designed to adjust all the measurement pa- rameters automatically to provide maximum accuracy. An important point to note is that the system also returns the internally calculated error for each measurement. This con- tinuously tracks the system measurement accuracy and can be used as an indicator to plan preventive maintenance cycles. Sensorlab pH sensors are full data logging devices, were tested, but most of them interfered with the pH read- ings. The chosen solution was using ETFE tubing with the sample intake placed at least 1 foot away from the sensor body, which helped to avoid the fouling interference. This proved to be very effective for long-term deployments. All the prototypes developed are still being used today by the QUIMA group and have been used in various scientifc pub- lications. (Left) Immersed part of the VULCANO buoy with the Sen- sorLab pH sensor. (Bottom) VULCANO buoy record of pH in total scale at in-situ condi- tions of temperature and salin- ity (blue dots) and sea surface temperature (SST in ÂșC, red dots) from deployment day November 7 to December 8, 2013. (Right) Saronikos buoy with pH sensor before deploy- ment in September 2013. Feb2014.indd 38 2/11/14 1:11 PM

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