Composite Membrane for Helium Leak Detection
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Solution Overview
Problem
Helium mass spectrometer leak detection techniques face challenges in maintaining low pressure at the inlet and test port, leading to lengthy vacuum pumping cycles, especially when testing large or dirty parts, and prior membranes have low permeance at room temperature, requiring heating and complex temperature control, which increases cost and complexity, and are vulnerable to helium overload.
Innovation Solution
A composite membrane is used, comprising a porous membrane and a semi-permeable membrane in series, with a thin silica layer on Vycor glass, which maintains constant permeance over a temperature range, allowing rapid termination of test gas transmission and blocking heavier gases, thus enabling efficient leak detection at ambient temperatures without the need for heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a permeable membrane is used to allow test gas transmission, then helium can pass through to the sensor, but the membrane has low permeance at room temperature requiring heating which increases cost and complexity
Solution Approach 1:
The patent changes the material parameters of the membrane by creating a composite structure with specific pore sizes and material compositions that enable high helium permeance at room temperature, eliminating the need for thermal parameter changes
Solution Approach 2:
The patent uses a composite membrane structure combining porous PTFE material with specific pore characteristics that provide both mechanical integrity and high helium permeance at ambient temperatures, replacing the need for heated single-material membranes
2Quantity of substance
If heating is applied to increase membrane permeance, then more helium passes through, but the temperature control accuracy is critical due to large temperature coefficient
Solution Approach 1:
The patent changes the membrane's physical parameters by selecting materials and structures with inherently low temperature coefficients, allowing permeance to remain stable across temperature variations without requiring precise temperature control
Solution Approach 2:
The membrane structure itself provides temperature stability through its material properties and design, making the system self-regulating regarding temperature effects without external control mechanisms
3Measurement precision
If the membrane allows high helium transmission, then detection sensitivity improves, but too much helium reaches the sensor causing overload and rendering the detector inoperable
Solution Approach 1:
The patent applies local quality by creating a membrane with non-uniform pore distribution or gradient structure that provides high overall permeance while local variations prevent helium concentration spikes that would overload the sensor
Solution Approach 2:
The membrane is designed to transmit helium at a rate that is sufficient for sensitive detection but controlled to remain below the sensor's maximum capacity, avoiding the extremes of both insufficient and excessive transmission
4Measurement precision
If vacuum pumping is used to maintain low pressure at test port, then helium detection is enabled, but pumping cycles are lengthy when testing large or dirty parts
Solution Approach 1:
The patent segments the vacuum system into two independent sides of the membrane, allowing the sensor side to maintain vacuum independently while the test side can operate at atmospheric pressure, eliminating lengthy pumping cycles
Solution Approach 2:
The membrane acts as an intermediary that couples the atmospheric pressure test environment with the vacuum sensor environment, allowing helium transmission without requiring the entire system to be evacuated
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
The composite membrane allows for rapid termination of test gas transmission, reducing interaction between leak tests and preventing helium buildup, while maintaining high permeance for helium and blocking heavier gases, thus improving the efficiency and accuracy of leak detection without the need for complex temperature control.
Implementation Method 1
The membrane is permeable to the light gases and selectively blocks heavier gases
Implementation Method 2
a porous membrane and a semi-permeable membrane in series
Data Source
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AI summary
A leak detector includes a leak detector inlet to receive a test gas; a vacuum pump coupled to the leak detector inlet; a test gas sensing unit connected through a passage to the leak detector inlet; and a membrane that is permeable to the test gas disposed in the passage between the leak detector inlet and the test gas sensing unit, the membrane having a permeance to the test gas that varies by less than five percent over a temperature range of T0-20K to T0 +20K, where T0 is a design temperature. In addition, methods are provided for making a composite membrane that includes a semi-permeable membrane and a porous membrane. Furthermore, a reference leak, which includes a composite membrane is provided.