Why use an online dissolved oxygen sensor?
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 Dissolved 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"
Dissolved Oxygen Probes
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.
Get a better understanding of dissolved oxygen (DO) measurement in Hamilton's comprehensive O2 Measurement Guide. This 72-page booklet is intended for anyone with an interest in DO sensor technology or anyone who needs to implement DO sensors in controlled environments such as laboratories and industrial plants. The guide covers the following essential topics:
- The basics of oxygen and its chemical and physical properties.
- The physics of dissolved oxygen.
- Types of DO sensors and how they work.
- Applications, calibration, and maintenance of DO sensors.
App Note - Recycling carbon dioxide in high qualityA new way targeting small and midsize breweries
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.
App Note - Real-time Monitoring of DCO2 in Addition to DOIn this application note, the utilization of a DCO2-probe in addition to a DO-probe at Ostwestfalen-Lippe University of Applied Sciences and Arts, is briefly described using cell cultivation with varying stirring speeds to demonstrate the value added of inline dissolved gas measurement.
Catalog - Process AnalyticsDownload the Process Analytics sensor catalog to learn about the complete offering of Hamilton process sensors and accessories.
Brochure - BioPharmaInnovative solutions for process analytics in biotechnological and pharmaceutical industries.
Brochure - Arc Intelligent SensorsArc Intelligent sensors offer a new way to connect to your process control system.
Does temperature impact my oxygen measurement?
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 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.
When should I calibrate my DO sensor?The frequency of calibration will depend upon the duration of process runs and the accuracy required for process control. In bioreactor applications calibration can be performed before sterilization; however many customers choose to calibrate after sterilization as well.
Dissolved Oxygen Knowledge Base 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.
What variables impact an oDO calibration?Optical dissolved oxygen (oDO) sensors still require calibration, though less frequently than the polarographic versions. New sensors (or new caps on existing sensors) require a two point calibration in air and an air free environment, ideally high purity nitrogen.
Cross-Referencing VisiFerm Part NumbersPlease use the following table for referencing the Visiferm RS485 ECS part numbers against the Visiferm ECS and Arc part numbers. There is also a separate column present for an equivalent sensor with the new H3 or H4 cap design.
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