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Luminescent Dissolved Oxygen

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LDO (Luminescent Dissolved Oxygen) is a technology for measuring oxygen in liquids and gases. This technology is widely used in a variety of industries including environmental, water treatment, aquaculture, brewing, energy and other areas where it is important to monitor oxygen levels in liquids.

Dissolved oxygen measurement technology using luminescent sensors has its roots in the early 20th century, but it has continued to evolve and improve over the decades.

Stages in the development of LDO technology:

Early work (early 20th century):

In the early 20th century, scientists noticed that some substances could glow (luminesce) when light fell on them. Researchers began experimenting with different materials, including solutions, to study this effect.

Development of photochemistry (1920-1960):

This period saw the rapid development of photochemistry, which studies chemical processes caused by light. Researchers began to apply this principle to the study of oxygen and its interaction with light.

Transition to liquid sensors (1970-1980):

In 1970-1980, scientists began to actively develop liquid sensors capable of measuring oxygen concentration in liquids using the principles of photochemistry and luminescence.

Use of luminescent sensors (1990-2000):

Between 1990 and 2000, the first commercially available luminescent sensors for measuring oxygen concentration in liquids appeared. These sensors became widely used in various applications related to water monitoring.

Current Technologies (2000-present):

With advances in electronics and materials, oxygen sensing technologies have continued to evolve. Modern LDO sensors have high accuracy, durability and special functions to optimise oxygen monitoring in various conditions.

Today, LDO technology is widely used in medical, industrial, environmental and scientific applications to accurately measure oxygen concentrations in aqueous media.

LDO working principle

1. Phosphorescent sensor: An LDO sensor contains a light emitting element (usually an LED) and a phosphorescent detector (photodiode). The LED sends a light signal to a phosphorescent material. This material emits light when exposed to light radiation.

2. Effect of oxygen: when light hits the phosphorescent material, the oxygen in the solution begins to affect the phosphorescence. The higher the oxygen concentration, the greater the inhibition of phosphorescence.

3. measuring luminescence intensity: The sensor measures the intensity of the luminescence from the phosphorescent material. This intensity is related to the oxygen concentration in the liquid.

4. Calibration: In order to convert the measured luminescence intensity value to oxygen concentration, LDO sensors must be calibrated. This is usually done using standard gas mixtures with a known oxygen concentration.

5. Conversion to common units of measurement: Luminaphor fluorescence quenches in the presence of oxygen. To calculate the oxygen concentration, a measurement of the decay time of the fluorescence intensity is used. As the oxygen concentration increases, the decay time decreases. By modulating the excitation, the decay time is converted into a phase shift of the modulated fluorescence signal, which is independent of the fluorescence intensity and therefore of potential aging.

Translated with DeepL.com (free version)

Advantages of LDO technology:

High accuracy,
Long service life (up to 10 years as stated by manufacturers),
Minimal maintenance and no need for regular replacement of the optical element (once every 6-12 months).
Real-time oxygen measurement
Wide measurement range (standard applications use 2 main ranges from 0 to 2 ppm and from 20 ppb to 40ppm).

However, it should be noted that LDO sensors can be sensitive to contaminants in water and corrosive solutions such as acids and alkalis, so it is important to perform regular calibration and maintenance to ensure accurate measurements.