Characteristics and Troubleshooting of Dissolved Oxygen Meter
A dissolved oxygen meter measures the amount of oxygen dissolved in an aqueous solution. Oxygen is dissolved in water by the surrounding air, air movement and photosynthesis. Through respiration and decomposition, dissolved oxygen will be consumed in water, mainly relying on air and photosynthesis to replenish. The oxygen content in water depends mainly on the temperature. Warm water has a lower oxygen concentration than cold water. But too high dissolved oxygen content will be harmful to animals and plants.
The dissolved oxygen electrode can be used to measure the dissolved oxygen content in the aqueous solution of the tested sample in the field or in the laboratory. Since dissolved oxygen is one of the main indicators of water quality, dissolved oxygen electrodes can be widely used in the measurement of dissolved oxygen content in various occasions, especially in aquaculture water, photosynthesis and respiration and on-site measurement. In evaluating the ability of stream and lake water to support organisms, the Biochemical Oxygen Demand (BOD) test is performed to measure oxygen-depleting organic-containing sample solutions as they decay and to determine the relationship between dissolved oxygen concentration and sample solution temperature. relationship between.
Dissolved oxygen concentration is usually expressed in mg/L (dissolved oxygen per liter of water) or ppm (parts per million). Some meters compare the calculated oxygen content with the observed concentration to give a percent saturation (O2% sat.)
There are two ways to determine dissolved oxygen, polarographic and galvanic. Polarographic electrodes need the instrument to input a voltage to polarize the electrodes. Since the applied voltage may take 15 minutes to stabilize, polarographic electrodes are usually preheated before use to ensure proper polarization of the electrodes. The two poles of a galvanic cell consist of two different metals that can be polarized spontaneously to generate a voltage. Since the voltage of the galvanic electrode is generated spontaneously rather than provided by the outside, the "preheating" required for polarographic electrode polarization is not required when the galvanic electrode is used.
environmental impact
Proper dissolved oxygen is essential to good water quality and all life forms require oxygen. The natural stream purification process requires proper oxygen levels to supply aerobic life forms. If the oxygen content in the water is lower than 5.0mg/L, it will be difficult for aquatic organisms to survive, and the lower the concentration, the more difficult it will be. If the oxygen content is lower than 1-2mg/L and lasts for several hours, it will lead to the death of a large number of aquatic organisms.
Applications
Dissolved oxygen electrodes can be used to measure and monitor processes where oxygen levels can affect reaction rates, process efficiency or the environment: such as aquaculture, biological reactions, environmental testing (lakes, streams, oceans), water/wastewater treatment, wine production.
Temperature compensation
For standard dissolved oxygen measurements, temperature affects the solubility and diffusion rate of oxygen, so temperature compensation must be performed.
salinity correction
The presence of dissolved salts limits the amount of oxygen that can be dissolved in water. The relationship between oxygen concentration and partial pressure varies with the salinity of each sample solution, so most meter manufacturers provide manual adjustment of salinity to correct for changes caused by different ion concentrations.
