The Hach Dissolved Oxygen (LDO) probe, available from PREI Instrumentation, works quite differently from the galvanic and polarographic methods, which have been used for more than 50 years. There are no membranes, no anodes or cathodes, and no electrolyte solutions. Maintenance consists of merely wiping the sensor with a wet rag.
The LDO probe has an inexpensive replaceable sensor cap that is guaranteed for a 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. Because the sensor is not affected by pH swings, hydrogen sulphide, wastewater chemicals or heavy metals, the Hach LDO probe executes stable and accurate measurements for an extended time.
Warm-up time is not necessary - measuring may begin immediately. Once the analyser is on, it responds quickly, giving readings in less than 60 seconds. Accurate readings are still possible 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, combined with accuracy, stability and speed. The technology used to achieve this is believed to be a breakthrough in dissolved oxygen measurement.
For more information contact Steve Herbst, PREI Instrumentation, 011 448 2172, [email protected]
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