Pump Inlet Valve Timing Modulation for Accurate Solvent Mixing
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Solution Overview
Problem
Conventional liquid chromatography systems face errors in solvent proportioning due to the underdamped intake flow behavior of pump systems, leading to inaccuracies in the composition of solvent mixtures during gradient chromatography.
Innovation Solution
Modulating the actuation times of switching valves in the gradient proportioning valve based on the frequency characteristics of the intake response to maintain average component volumes and reduce composition errors, using a method that involves determining switching time offsets to achieve desired solvent proportions in the output flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional metering techniques are used with fixed switching times, then the system structure is simple, but flow errors occur due to underdamped intake response causing inaccurate solvent proportioning
Solution Approach 1:
The patent applies dynamics by transitioning from fixed switching times to dynamically adjusted switching times. The valve actuation times are modulated based on the detected intake flow response characteristics, allowing the system to adapt to varying flow conditions and eliminate systematic errors in solvent proportioning while maintaining overall system simplicity
Solution Approach 2:
The patent implements parameter changes by modifying the switching time parameter of the proportioning valves. By adjusting the switching time offset according to the intake flow's frequency characteristics, the system compensates for underdamped responses and achieves accurate solvent mixing without requiring complex additional hardware
2Manufacturing precision
If valve switching occurs at non-zero error crossings, then the proportioning valve can maintain desired average component volumes, but flow oscillations cause composition errors in the output mixture
Solution Approach 1:
The patent employs feedback by using the detected intake flow response to inform subsequent valve actuation decisions. The system measures the actual flow behavior, determines the frequency characteristics, and uses this information to adjust switching times, creating a closed-loop control that maintains both accuracy and compositional stability
Solution Approach 2:
The patent applies periodic action through modulation of the valve switching times at frequencies matched to the intake flow oscillations. By applying periodic adjustments to the switching times, the system counteracts the oscillatory behavior and maintains stable solvent proportions in the output mixture
3Manufacturing precision
If additional valve switching events are introduced to correct proportioning errors, then component volume accuracy may improve, but new intake flow disturbances are generated causing further composition errors
Solution Approach 1:
The patent applies partial action by making small, targeted adjustments to the valve switching times rather than introducing multiple large corrective actions. The switching time offset is carefully calculated to provide just enough correction to overcome the underdamped response without generating excessive new disturbances in the intake flow
Data Source
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AI summary
Described is a method of reducing liquid composition errors in a low-pressure mixing pump system. Packets representing the switching intervals of each component of the desired fluid mixture are provided to an intake of the mixing pump system. For each packet, a switching time associated with at least one of the components in the packet is modulated. Modulated switching times are based on time offsets that are specifically selected according to the undesirable frequency characteristic of an intake response of the mixing pump system. The average of the volumes contributed by the packets thus modulated is equal to a component volume that achieves a desired proportion of the component in the output flow of the mixing pump system. Modulated switching times enable the reduction or elimination of composition error in the output flow of the mixing pump system.