Dissolved oxygen refers to the amount of oxygen present in water and is a common indicator of water quality as levels too high or too low can harm aquatic life. Dissolved oxygen meters, also called dissolved oxygen analyzers, are the most common and effective means of measuring oxygen levels in water. A standard model consists of a probe and a monitor for reading off and recording oxygen levels. To make measurements more precise, many models make automatic adjustments to account for fluctuations in factors such as pressure and temperature that might otherwise affect oxygen readings. In some cases, the probes serve dual purposes or can be switched out to monitor other variables such as pH or CO
2 levels.
The two main types of oxygen meters are optical (also called luminescent meters) and electrochemical meters. Electrochemical meters take faster readings but need to be stirred in a solution to calibrate before use. Optical meters last longer and do not need to be calibrated before each use, but they their readings take longer and they require more power.