What Is a Dissolved Oxygen Analyzer?
A dissolved oxygen analyzer measures the amount of oxygen dissolved in water. They range from portable instruments to stationary instruments installed at measurement sites and can transmit data to centralized control devices, such as a DCS for real-time display. These analyzers are essential for water quality control, fisheries, environmental surveys, and more, providing accurate measurements of dissolved oxygen in water.
Uses of Dissolved Oxygen Analyzers
Dissolved Oxygen Analyzers are used in wastewater treatment facilities to monitor water contamination and in aerobic wastewater treatment processes. They are crucial in ensuring sufficient oxygen for effective treatment. In the food industry, these analyzers measure fermentation levels in fermented foods.
Principle of Dissolved Oxygen Analyzer
Dissolved oxygen analyzers use the diaphragm electrode method or the fluorescent method for measurement
1. Diaphragm Dissolved Oxygen Analyzer
Diaphragm types use an electrolyte solution and a membrane sensor. Regular maintenance, including electrolyte replacement, is necessary
2. Fluorescent Dissolved Oxygen Analyzer
Fluorescent types are suitable for sewage and wastewater treatment plants. They do not require a membrane or electrolyte and can be measured in environments without flow. Many are waterproof and can measure additional parameters like pH.
Types of Dissolved Oxygen Analyzers
Dissolved Oxygen Analyzers are available as stationary, portable, and tabletop models.
1. Stationary Type
Stationary models monitor water quality in rivers and industrial effluents, featuring automatic cleaning mechanisms to maintain detector sensitivity.
2. Portable Type
Portable models are lightweight, compact, and easy to use, ideal for aquariums, aquaculture, and outdoor water quality surveys. They often have dustproof and waterproof features.
3. Tabletop Type
Tabletop models are used in research institutes and laboratories for high-precision measurements. They are compact and portable like the portable models.
Other Information on Dissolved Oxygen Analyzers
Dissolved Oxygen Analyzer Calibration
Dissolved oxygen analyzers should be calibrated periodically.
Zero calibration using a zero standard solution (approximately 25 g of anhydrous sodium sulfite as specified in JIS K 8061 dissolved in water and adjusted to 500 mL by adding water) to accurately measure low concentrations of dissolved oxygen or to adjust the zero point of the dissolved oxygen analyzer to a theoretical value if the low concentration value is considered abnormal.
Another method is to use the fact that the partial pressure of saturated dissolved oxygen in water is almost equal to the partial pressure of oxygen in air. There are two methods: a simple span calibration using the partial pressure of oxygen in the atmosphere, and a saturated water calibration using water saturated with dissolved oxygen (about 500 mL of water aired for 10 to 20 minutes).
However, since saturated water calibration is also affected by atmospheric pressure, a manual calibration method is also available, in which the measured water is measured with a reference instrument and adjusted to that value. Since there is no standard solution traced to a national standard for the calibration of dissolved oxygen analyzers, a calibration certificate cannot be issued.