Why measure dissolved oxygen online?
In biological processes like fermentation and cell culture dissolved oxygen is critical to support proper cell growth. In industrial processes, oxygen is often limited in applications where corrosion is of concern. Online oxygen measurement enables real-time control of dissolved oxygen at a predefined set point or enables the detection of a leak in the process that is resulting in oxygen infiltration.
Much has been written about different strategies for proper DO control. However, little information has been publicly available regarding optimization of the actual measurement accuracy and reducing common sources of process-related error.
Get Hamilton's whitepaper on potential sources of optical dissolved oxygen measurement error and ways to mitigate the impact.
Optical Oxygen Sensors
The VisiFamily of sensors have a blue LED in the sensor shaft and an oxygen sensitive dye (luminophore) fixed to a glass window in the replaceable sensor cap. The blue light excites the luminophore and then a photodetector in the sensor shaft senses the red light that is returned from the luminophore. A microprocessor in the sensor correlates the emitted blue light and the measured red light to partial pressure of oxygen. This measurement can then be output as a simulated nA signal, 4 - 20 mA, or digital protocol.
Polarographic "Clark Cell" Sensors
Classical Clark cell sensors have a platinum cathode and a silver anode that are separated from the sample by a gas permeable membrane. As oxygen diffuses across the membrane it is reduced resulting in a small nA current. The more oxygen the stronger the current. This current is then detected by a separate transmitter which amplifies the signal for process control.
App Note - Arc DO, pH, Cond in production scale fermentation processGEA, a global equipment and process technology provider, integrates Arc sensor technology in fermentation plants at their GEA Diessel subsidiary in Hildesheim, Germany.
Brochure - VisiFerm mA Dissolved Oxygen Sensors
Catalog - Process AnalyticsDownload the Process Analytics sensor catalog to learn about the complete offering of Hamilton process sensors and accessories.
Brochure - Optical Dissolved OxygenDownload the dissolved oxygen brochure to explore the many benefits of making the switch to optical oxygen measurement.
Guide - Dissolved Oxygen MeasurementThis Hamilton guide provides the basic knowledge of dissolved oxygen measurement in a brief and understandable form.
Does salinity impact my DO measurement?Yes, salinity of a solution generally has an inverse relationship to the dissolved oxygen content within the solution. Arc sensors can have the salinity value of the liquid added in to correct the measurement by using ArcAir.
Does temperature impact my oxygen measurement?Yes, in a closed system, gas phase temperature is directly proportional to pressure and therefore measured oxygen content. In solution, temperature is inversely proportional to dissolved oxygen content.
Does carbon dioxide sparging impact my DO measurement?CO2 sparging will not impact the DO measurement using an optical DO sensor. CO2 can impact traditional polarographic DO sensors over time thus more frequent electrolyte replacement may be needed.
Dissolved Oxygen Knowledge Base ArticlesA summary page with links for all dissolved oxygen related articles
Best Practices: Zero Point Oxygen CalibrationThere are several methods to achieving a good zero point calibration of optical and polarographic DO sensors. This paper looks at each procedure in depth.
How to Measure Sensor A-lengthSensor A-length determines the insertion depth of the sensor. This article shows how this measurement is made for various styles of sensors.
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