Dissolved oxygen meter stays accurate over decades

February 2003 Analytical Instrumentation & Environmental Monitoring

It is the dream of any technician working on a high-accuracy plant, such as wastewater, to have instruments that are still accurate after 10 years of operation - even if it means having to manufacture these instruments from gold and silver. Danfoss says that it has turned this dream into reality with the development of its Ole_LINK1EVITA* OXY dissolved oxygen sensor.

Using gold as cathode and a silver wire as anode, the EVITA meets the toughest environmental standards, offers high accuracy and introduces flexible pricing through a modular design. It also lays claim to the industry's only truly disposable Clark oxygen sensor - replaceable in just five minutes.

"Whether you are equipping a single-basin installation or an entire computer-controlled plant, this product range allows you to meet your exact price/performance requirements through a diverse choice of components and configurations," says Mick Baugh, Danfoss business unit manager, motion control and flow.

With a turndown of 1:1000 and automatic compensation for temperature, pressure, relative humidity and salt concentration, EVITA more than complies with the high-accuracy standards of EN 25814. In addition, the five-minute-replacement disposable oxygen sensor means it can still be equally accurate after a decade of operation.

The device requires no special cables, nor are there any complicated diagrams to be followed. "You simply press a button and the system calibrates itself," says Baugh. "There is no need to calibrate the zero point either, as the low-cost disposable sensor gets replaced before zero-point calibration becomes necessary."

EVITA also keeps an eye on itself through a comprehensive self-monitoring program, and instantly lets the operator know if there is a problem with the sensor, transmitter, cable or electronics. Unique features include real membrane leakage detection, which allows faults in the sensor membrane to be detected within 35 seconds, using direct resistance measurement. Similarly, real sensor lifetime monitoring ensures continuous accuracy. EVITA also incorporates an oxygen profile controller for lifetime economy.

"One of the biggest advantages of EVITA, is that it needs vastly less maintenance than traditional oxygen meters," says Baugh. "Maintenance checks are needed only 2 to 6 times a year." An 'auto clean' floating ball uses the water's motion to clean the sensor membrane, negating the use of chemicals, fresh water or power.

Danfoss has sold more than 70 000 sensors over 20 years of operation in oxygen measurement and has focused on developing products that are more accurate, simpler to use and less costly. Testimony to the success of this approach can be seen in the company's growing market share throughout Europe, North America, Africa and Asia.

For more information contact Mick Baugh, Danfoss, 011 803 8390, [email protected], www.danfoss.co.za

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