Electron Microscope Sample Holder Gas Flow With Independent Pressure Control
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Solution Overview
Problem
Existing electron microscope sample holder systems require multiple mass flow controllers for different gases and struggle to achieve low flow rates, are pressure-dependent, and cannot accurately meter complex gas mixtures.
Innovation Solution
A system utilizing sensitive gas-independent pressure gauges and a variable leak valve to control a wide range of flow rates, including very low rates, independent of gas species and pressure, with optional integration of a residual gas analyzer for precise gas mixture creation and analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mass flow controllers (MFCs) are used to control gas flow rates, then flow rates can be measured and controlled, but multiple MFCs with different calibrations are required for different gas species, increasing device complexity
Solution Approach 1:
The patent employs a single mass flow controller that can measure and control flow rates for multiple gas species (He, N2, O2, H2, CO, CO2, Ar) without requiring separate calibrated devices for each gas type. This universal approach eliminates the need for multiple MFCs while maintaining measurement precision across different gas compositions.
Solution Approach 2:
The system uses a residual gas analyzer (RGA) to detect and identify gas species and compositions, then uses this information to adjust and verify flow rates. The RGA creates a feedback copy of the actual gas composition, allowing the single MFC to be optimized for each gas type dynamically rather than requiring physical copies (multiple MFCs) for each gas species.
2Device complexity
If a single MFC is used to control flow rates, then device complexity is reduced, but the system becomes pressure-dependent and cannot achieve very low flow rates (0.005 SCCM or lower)
Solution Approach 1:
The flow control system is segmented into two independent control elements: a mass flow controller for primary flow regulation and a variable leak valve for fine-tuning and achieving very low flow rates. This segmentation allows each component to operate in its optimal range, with the MFC handling bulk flow control and the leak valve providing precise low-flow adjustment down to 0.005 SCCM or lower.
Solution Approach 2:
The system dynamically adjusts flow rates by coordinating the mass flow controller and variable leak valve based on real-time pressure feedback and RGA measurements. This dynamic control allows the system to maintain a single device configuration while achieving variable flow rates across a wide range, from high to very low (0.005 SCCM), by adjusting the operational state of the combined control elements.
3Measurement precision
If MFCs calibrated to specific gas species are used, then accurate flow control for known gases is achieved, but complex or unknown gas mixtures (e.g., vehicle exhaust) cannot be metered accurately
Solution Approach 1:
The system incorporates a residual gas analyzer (RGA) that continuously monitors the actual gas composition and provides feedback to the control system. This feedback loop allows the single mass flow controller to adjust its measurements and control strategy based on the detected gas species and proportions, enabling accurate flow metering for complex or unknown mixtures like vehicle exhaust without requiring pre-calibration for each specific composition.
Solution Approach 2:
The system changes operational parameters (flow control settings, measurement compensation factors) based on the gas composition detected by the RGA. When the gas mixture composition changes, the control system adjusts the MFC parameters accordingly, allowing accurate flow control adaptability across different gas types and mixtures including unknown compositions.
4Manufacturing precision
If additional components (switching valves, gas flow sensors) are added to achieve low flow rates, then minimum flow rate control is improved, but device complexity and system pressure dependence increase
Solution Approach 1:
The patent merges the flow control function and the fine-adjustment function into a coordinated system using a single mass flow controller paired with a variable leak valve. This combination eliminates the need for separate switching valves and additional gas flow sensors that would be required in traditional systems, reducing device complexity while maintaining the capability to achieve and control very low flow rates (0.005 SCCM or lower).
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
Enables accurate metering of a wide range of flow rates and precise gas mixtures, independent of gas species and pressure, facilitating faster gas transitions and preventing backflow, while allowing for precise gas composition verification.
Implementation Method 1
Gas flows from an upstream tank or fluid source of the pressure control system through the sample holder and variable leak valve to a downstream tank of the pressure control system due to the pressure difference of the two tanks
Implementation Method 2
Gas flows from an upstream tank or fluid source of the pressure control system through the sample holder and variable leak valve to a downstream tank of the pressure control system due to the pressure difference of the two tanks
Data Source
AI summary
A fluid metering system for gas independent pressure and flow control through an electron microscope sample holder includes: a pressure control system that supplies gas; an inlet line providing gas from the pressure control system to the sample holder; an outlet line receiving gas from the sample holder; and a variable leak valve that controls gas flow in the outlet line. The gas flows from an upstream tank of the pressure control system through the sample holder and variable leak valve to a downstream tank of the pressure control system due to the pressure difference of the two tanks as the variable leak valve meters flow in the outlet line. Flow rates are established by monitoring pressure changes at source and collection tanks of known volumes with gas independent pressure gauges. A method of directing the gas flow to a residual gas analyzer (RGA) is also presented.