The DO30 sensor for dissolved oxygen is designed for use in water treatment plants such as sewage treatment works, effluent activated sludge process, and potable water treatment. It is also effective in river monitoring, intake protection, fish farming, and other fields where water quality is important. This galvanic cell has a fast response time and good long-term stability, and features replaceable diaphragm and cable for easy maintenance. A temperature sensor is incorporated for compensation. The DO30 sensor can be used in either the PB30 floating ball fitting or in the FD30 immersion fitting.