Optical Pretreat Concentration Sensing Without Electrode Decay
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Solution Overview
Problem
Current conductivity sensors for monitoring pretreat solution concentration in space toilets decay over time due to electrode interaction, leading to unreliable measurements, which is critical for effective urine treatment and water recovery in space missions.
Innovation Solution
An optical sensor system using photodiodes and a microprocessor to measure light characteristics before and after traversing a fluid mixture, calculating pretreat fluid percentage based on Beer's Law and scattering principles without direct contact with the solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conductivity sensors with electrodes are used to monitor pretreat solution concentration, then the measurement capability is provided, but the sensor output voltage decays over time due to electrode interaction with the solution
Solution Approach 1:
The patent replaces the electrical conductivity measurement system with an optical measurement system. Instead of using electrodes that physically contact the solution and degrade, the invention uses light sources and photodetectors to measure pretreat concentration optically, eliminating the mechanical/electrical contact that causes sensor decay.
Solution Approach 2:
The patent introduces an optical intermediary system (light path through the solution) to measure concentration without direct contact. The light acts as an intermediary carrier that interacts with the solution's optical properties (absorbance, scattering) to provide measurement data without the electrodes needing to physically contact and chemically interact with the pretreat solution.
2Measurement precision
If electrodes are placed in direct contact with diluted pretreat solution, then conductivity measurement is enabled, but current flow decay occurs due to electrode-solution interaction
Solution Approach 1:
The patent substitutes the electrical conductivity measurement approach with an optical measurement approach. The optical system uses light transmission and detection rather than electrical current flow through electrodes, thereby eliminating the chemical interaction between electrodes and pretreat solution that limits sensor lifespan.
Solution Approach 2:
The patent uses light as an intermediary to transfer measurement information from the solution without physical contact. The optical path allows the system to probe the solution's properties (concentration, clarity) through light absorption and scattering characteristics, extending operational duration by avoiding degrading electrode-solution contact.
3Ease of manufacture
If a universal standardized toilet design is used across multiple vehicles, then overall costs are reduced, but the habitable volume must be minimized
Solution Approach 1:
The patent describes a universal toilet design that can be adapted for multiple spacecraft vehicles. The optical sensor system is part of a standardized urine pretreatment and monitoring subsystem that can be integrated across different vehicle types, reducing development and manufacturing costs through economies of scale and standardized components.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Provides accurate pretreat fluid concentration measurement within ±1% accuracy, ensuring reliable urine treatment and efficient water recovery by avoiding sensor decay issues.
Implementation Method 1
calculate the percentage of pretreat in water from 2.7% to 10.7% (by volume) to +1% accuracy
Implementation Method 2
measure the characteristics of light after it has traversed through the vessel and the fluid mixture
Data Source
AI summary
The subject invention is an optical sensor system for calculating the percentage of wastewater pretreat fluid within a fluid mixture. The system provides light from a light source to a transparent vessel containing a fluid mixture. The light source and a portion of the vessel are enclosed within a housing to prevent ambient light from polluting the system's measurements. Two photodiodes are placed within the housing to measure the characteristics of the light. One photodiode is placed in a location prior to the light reaching the vessel to measure the characteristics of light emanating from the light source and a second photodiode is placed in a location to measure the characteristics of the light after it has traversed through the vessel and fluid mixture. Using data collected by the photodiodes, a microprocessor can determine the characteristics of the fluid mixture, and more specifically, the percentage of a pretreat fluid within the fluid mixture.