March 2004Analytical Instrumentation & Environmental Monitoring
The Hach Dissolved Oxygen (LDO) probe, available from PREI Instrumentation, works quite differently from the galvanic and polarographic methods that have been used for more than 50 years. There are no membranes, no anodes or cathodes, and no electrolyte solutions. Maintenance consists by merely wiping the sensor with a wet rag!
The LDO probe has an inexpensive replaceable sensor cap that is guaranteed for one year. The sensor cap is coated with a luminescent material. Blue light from an LED is transmitted to the sensor surface. The blue light excites the luminescent material. As the material relaxes it emits red light. The time from when the blue light was sent and the red light is emitted is measured. The more oxygen that is present the shorter the time it takes for the red light to be emitted. This time is measured and correlated to the oxygen concentration. Between the flashes of the blue light a red LED is flashed on the sensor and used as an internal reference. Calibration is not necessary.
The Hach LDO probe is able to produce more stable and accurate measurements for a longer time because the sensor is not affected by pH swings, hydrogen sulphide, wastewater chemicals or heavy metals. No warm-up time is necessary. Once the analyser is on, it responds quickly, giving readings in less than 60 seconds. It provides accurate readings, even with organic build-up on the sensor. The analyser can have dual inputs and outputs.
The advantages of the Hach LDO are reduced maintenance, infrequent calibration, simple operation and replacement, all combined with accuracy, stability and speed. The technology used to achieve this represents a breakthrough in the measurement of dissolved oxygen.
For more information contact Steve Herbst, PREI Instrumentation, 011 448 2172, [email protected]
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