Capacitance Sensor Diaphragm Groove Stress Relief
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Solution Overview
Problem
Capacitance manometers face challenges in measuring low pressure differential due to diaphragm buckling during welding, which introduces non-parallelism and distortion, making it difficult to maintain the required flatness and gap spacing between the diaphragm and electrodes, especially for low-pressure sensors.
Innovation Solution
A capacitance sensor assembly with a diaphragm having a fixed portion secured to the housing assembly and an active portion that flexes relative to the electrode arrangement, featuring at least one groove to relieve mechanical stress on the diaphragm, allowing for secure attachment without distorting the diaphragm's flatness, enabling the use of lower-cost welding techniques like GTAW or Plasma welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the diaphragm is secured closely to the housing assembly to maintain flatness for low pressure measurements, then measurement precision is improved, but the diaphragm buckles during welding causing non-parallelism
Solution Approach 1:
The diaphragm is segmented into three distinct regions: a fixed portion that is welded to the housing assembly, a groove portion that absorbs welding stresses, and an active portion that remains stress-free for measurement. This segmentation allows the fixed portion to be securely attached while protecting the active portion from welding-induced buckling, maintaining both measurement precision and manufacturing precision.
Solution Approach 2:
The groove portion acts as an intermediary element between the fixed portion and the active portion of the diaphragm. It absorbs and relieves the mechanical stresses generated during welding, preventing these stresses from propagating to the active portion. This intermediary structure enables the use of lower-cost welding techniques while maintaining the required flatness and parallelism for accurate low pressure measurements.
2Ease of manufacture
If lower-cost welding techniques like GTAW or Plasma welding are used, then manufacturing cost is reduced, but greater stress is placed on the diaphragm causing buckling
Solution Approach 1:
By segmenting the diaphragm into fixed, groove, and active portions, the design allows lower-cost welding techniques to be applied to the fixed portion without compromising the overall structural integrity. The groove portion serves as a stress relief zone that protects the active portion from welding stresses, enabling cost-effective manufacturing while maintaining diaphragm strength and flatness.
Solution Approach 2:
The invention converts the harmful effect of welding stress into a beneficial feature by intentionally designing the groove portion to absorb these stresses. What would normally be a detrimental effect (welding stress causing buckling) is transformed into a protective mechanism that shields the active portion, enabling the use of economical welding techniques without sacrificing measurement accuracy.
3Measurement precision
If the diaphragm thickness is reduced to accommodate lower pressures, then measurement sensitivity is improved, but the diaphragm becomes difficult to secure without distorting
Solution Approach 1:
The diaphragm is divided into a fixed portion for attachment, a groove portion for stress relief, and an active portion for measurement. This segmentation allows thin diaphragms to be manufactured with high precision while maintaining ease of assembly. The fixed portion provides a robust attachment zone that compensates for the reduced thickness, enabling secure mounting without distortion while preserving the high sensitivity of the thin active portion.
Solution Approach 2:
Different regions of the diaphragm are given different local qualities: the fixed portion has increased thickness and structural reinforcement for secure attachment, the groove portion has a specific geometry for stress absorption, and the active portion maintains minimal thickness for high sensitivity. This local differentiation allows the diaphragm to be both easy to manufacture and highly sensitive to pressure changes.
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 groove design maintains the diaphragm's flatness and gap spacing, ensuring accurate capacitance measurements and pressure readings across the desired pressure range, even with lower-cost welding methods, enhancing the sensor's reliability and cost-effectiveness for low-pressure measurements.
Implementation Method 1
at least one groove is formed in the fixed portion of the diaphragm between the locations at which the diaphragm is fixed relative to the housing assembly and the active portion so as to relieve any stress on the active portion of the diaphragm
Implementation Method 2
the differential pressure can be measured as a function of the difference in capacitance between the diaphragm and the center electrode and the capacitance between the diaphragm and the ring electrode
Implementation Method 3
the diaphragm flexes relative to the two electrodes. By electrically connecting the diaphragm so that it also functions as an electrode, the differential pressure can be measured
Data Source
AI summary
A sensor assembly includes a housing assembly, an electrode arrangement and a diaphragm having a fixed portion secured to the housing assembly and an active portion movable relative to the electrode arrangement in response to a differential pressure applied to opposite sides of the diaphragm. The fixed portion of the diaphragm is secured at one or more locations relative to at least a portion of the housing assembly; and at least one groove is formed in the fixed portion of the diaphragm between the locations at which the diaphragm is fixed relative to the housing assembly and the active portion so as to relieve any stress on the active portion of the diaphragm. A method of making the sensor assembly is also disclosed.