LDO sensor

The Hach/Hydrolab LDO sensor is approved by the EPA. It uses a sensor cap that is coated with a luminescent material. Blue light from an LED strikes the luminescent chemical on the sensor, which instantly becomes excited. As the excited chemical relaxes, it releases red light. The higher the oxygen concentration, the less red light given off by the sensor cap. The red light is detected by a photo diode. The time it takes for the chemical to return to a relaxed state is measured.

The oxygen concentration is inversely proportional to the time it takes for the luminescent material on the sensor cap to return to a relaxed state. Between flashes from the blue LED, a red LED of known intensity is flashed. The red LED acts as an internal standard for reference comparison to the red light given off by the luminescent sensor cap. This comparison allows the sensor readings to remain stable for long periods of time.

Unlike polarographic dissolved oxygen sensor technologies, the Hach LDO sensor does not consume oxygen. It does not require frequent calibration or cleaning, resulting in longer sensor life and more stable and accurate readings. In addition, because the sensor is not consuming oxygen, a circulator is no longer required to maintain flow around the LDO sensor.

There are no electrodes or electrolyte to consume. There is no membrane to puncture or tear. Frequent calibration is not required as the instrument continually references itself to a red LED of known intensity.

The sensor is available on series 5, which consists of the Hydrolab DS5X (DataSonde 5X) DS5 (DataSonde 5) and MS5 (MiniSonde 5).