The Rosemount Analytical RDO optical dissolved oxygen sensor and analyser by Emerson Process Management is designed for use in wastewater aeration basins and ponds. The sensor is more resistant to fouling than polarographic sensors, an important advantage in wastewater where coating is a common problem. Less sensitivity to fouling means reduced operating costs as there is less need for cleaning. The sensor is available with either an integral or quick-disconnect cable. A 1-¼” FPT fitting at the rear of the sensor allows a threaded pipe to be screwed into the sensor so it can be submerged in the basin. One advantage of the sensor’s design is that it does not need a flowing sample, so it works well in a low flow basin or pond. Maintenance is fast and easy and consists primarily of replacing the sensing cap once a year. The analyser accepts one or two sensors. It has a two-line display, which can be customised to show mg/L (ppm) oxygen, percent saturation, oxygen partial pressure, or temperature for either sensor. The display can also be configured to show the current barometric pressure. The analyser has two loop-powered 4-20 mA analogue outputs assignable to either sensor and to any measurement (concentration, temperature, or partial pressure). Modbus/RS485 communication is also available as a standard feature. Calibration is simple and can be done either against a referee instrument or in water-saturated air. Air calibration is completely automatic.