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In-Situ® Inc. AnnouncesR DO®Direct Connect Sensor for Sub-2 Inch Multiparameter Water Quality Instrument

Posted: Thursday 19th March 2009

In-Situ’s next generation Rugged Dissolved Oxygen (RDO®) sensor integrates seamlessly into the sub-2 inch TROLL® 9500 water quality instrument, which allows the breakthrough technology to be used in 2-inch monitoring wells and other restricted space deployments.

The TROLL 9500 is used for long-term groundwater or surface water monitoring, ambient water quality checks, and low-flow groundwater sampling. The RDO optical dissolved oxygen sensor uses the latest technology for dissolved oxygen (DO) measurement. The RDO sensor features a rugged, wiper-free design that excels in demanding environments. The sensor’s abrasion-resistant foil withstands fouling, high sediment loads, and rapid flow rates. The sensor cap is pre-loaded with calibration coefficients, which speeds set up and eliminates programming errors.

By configuring the multiparameter TROLL 9500 with the RDO direct connect sensor, environmental monitoring specialists can simultaneously monitor DO, conductivity, temperature, and one additional parameter, such as pH, pH/ORP, or an ionic species. The RDO sensor responds rapidly to changes in DO and is an ideal tool for characterizing remediation sites, assessing remediation system performance, performing routine low-flow groundwater sampling, conducting vertical water quality profiles, and monitoring dynamically changing conditions.

“Water quality professionals will again benefit from In-Situ Inc.'s aggressive investment into new product development," said Bob Blythe, CEO and President of In-Situ Inc. "By improving upon the breakthrough optical DO sensor technology that In-Situ Inc. first brought to market in early 2004, our next generation RDO sensors provide higher quality data and more robust performance at a significantly lower cost than currently available optical DO sensors. With the new direct connect RDO sensor, field personnel can now measure and log the top four water quality parameters with a convenient sub-2 inch instrument.”

Compared to Clark-cell type sensors, the new RDO sensor can lower the total cost of acquiring consistent, high-quality data. The In-Situ RDO sensor significantly reduces site visits for instrument checks and recalibration. The RDO sensor is factory-calibrated and requires a quick two-point calibration upon deployment. The calibration can last for several months if sensor fouling is minimal and if the foil is not mechanically damaged or removed. If fouling is high, the sensor can typically be cleaned and redeployed without recalibration. Field-replaceable caps streamline maintenance, reduce costs, and eliminate programming errors.

The In-Situ RDO sensor measures DO using the principle of “dynamic luminescence quenching” according to ASTM Method D888-05. Sensor optics include a lens, blue LED and filter, red LED and filter, and a photodetector or photodiode. When the blue LED emits light, it causes the lumiphore molecules embedded in the gas-permeable sensing foil to emit red photons. The In-Situ RDO sensor measures the “phase” (or delay) of the returned signal compared to the excitation signal, and is thus based on the “lifetime” rather than the “intensity” of the luminescence. The presence of oxygen in the foil quenches the luminescence and causes a phase shift in returned signal, detected by the photodiode. The phase difference between the blue excitation light and the return red light is measured, and the result is used to quantify DO.

While measuring the intensity of luminescence is easier to implement in optical DO sensors, it gives less robust data than measuring the lifetime of luminescence, which is a physical constant. In addition, instruments measuring intensity require more frequent calibration. Measuring lifetime luminescence requires more sophisticated signal processing and delivers higher accuracy over a wide operating range. Optical DO sensor readings are not affected by sample color or turbidity, and the method delivers highly accurate results in hypoxic conditions.

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