Optical Concentration Sensor: Measuring Liquid Solutions

Researchers developed an optical sensor for monitoring concentration in liquid solutions, specifically in the Universal Waste Management System (UWMS), an International Space Station toilet. The optical concentration sensor is light-based and can be used in various sectors. Typical concentration sensors, such as the one employed in the UWMS at first, rely on changes in electrical conductivity to determine the concentration of a solution. These conductivity measurements are susceptible to voltage drift over time, resulting in incorrect measurements as the sensor matures.

The sensor measures solution concentration using light scattering rather than voltage drift. Light from a green LED is fed into the sensor housing and hits a first detector (a photodiode) to create a reference of the amount of light before scattering. Simultaneously, the light from the LED scatters through the pretreat solution and is measured by a second photodiode.

Based on Beers Law, the difference in the amount of light measured by the two detectors is used to calculate the concentration of the pretreat solution. The optical concentration sensor has been shown to measure pretreat concentrations effectively in still and flowing liquid circumstances, and it is resistant to contamination concerns, as required by the UWMS. The optical pretreat concentration sensor has reached technology readiness level (TRL) 4 (component and breadboard validation in a laboratory environment) and is patentable.

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