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In-Situ® Inc. Announces the Technologically Advanced RDO®PRO Optical Dissolved Oxygen Sensor for Process Applications

Posted: Wednesday 18th March 2009

In-Situ has launched the In-Situ Rugged Dissolved Oxygen (RDO®) PRO sensor for demanding process applications. Building on In-Situ Inc.’s core expertise in optical dissolved oxygen (DO) technology, the RDO PRO sensor features an abrasion-resistant foil that withstands fouling, high sediment loads, and rapid flow rates. The sensor cap is pre-loaded with calibration coefficients to speed set up and eliminate programming errors.

The RDO PRO sensor offers open-architecture communication protocols, including Modbus over RS485, SDI-12 (version 1.3), or 4-20 mA signal outputs. The RDO PRO eliminates the need for costly external transmitters or controllers and operates on a 8 to 36 VDC input or 4-20 mA three-wire current loop. Corrosion-resistant construction and durable sensing foil design provide consistent, reproducible results (<0.05 mg/L reproducibility) in demanding environments. The RDO PRO offers reliable, low-maintenance performance to water quality specialists in municipal or industrial water and wastewater treatment plants, aquaculture settings, dam discharge applications, and food/beverage process control environments.

“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, the RDO PRO sensor provides higher quality data and more robust performance at a significantly lower cost than currently available optical DO sensors. Superior optical DO technology combined with the lower total cost of the new RDO PRO sensor will essentially render the membrane-based Clark cell electrode obsolete.”

Compared to Clark-cell type sensors, the new RDO PRO sensor can lower the total cost of acquiring consistent, high-quality data. The In-Situ RDO sensor significantly reduces instrument checks and recalibration. The RDO PRO 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.

The In-Situ RDO sensor and sensing foil are manufactured entirely by In-Situ Inc. in its Fort Collins and Boulder, CO facilities. OEM and direct purchase opportunities are now available for the In-Situ RDO PRO sensor.

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