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Oregon Water Science Center

Field Comparison of Optical and Clark Cell Dissolved Oxygen Sensors in the Tualatin River, Oregon, 2005

By Matthew W. Johnston and John S. Williams

Open-File Report 2006-1047

ONLINE ONLY (download the report)
Photo: Tualatin River

Diversion dam on the Tualatin River, Oregon. Dissolved oxygen sensors used in the comparison described in the report were deployed just to the right of this photograph. (Photograph by Stewart Rounds)


Comparison of two Clark cell type dissolved oxygen sensors with three optical sensors in the Tualatin River, Oregon, indicated that the optical sensors were less prone to fouling drift and calibration drift. In two cleanings and calibrations over the 3-week study, the Clark cells had fouling drifts ranging from 0.17 to 0.37 mg/L and calibration drifts ranging from –0.22 to 0.03 mg/L. The optical sensors had fouling drifts ranging from 0 to 0.02 mg/L and calibration drifts ranging from –0.09 to 0.02 mg/L after 2–3 weeks of deployment. Measurements by the Clark cell and optical sensors compared well to each other and to point measurements of oxygen concentration using the Winkler method, indicating that the optical sensors were as accurate as the Clark cell sensors under the study conditions.

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For information about the Tualatin River Water Quality Study, please visit the study Web site.

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