Pressure Sensor Stainless Steel Diaphragm Kovar Elastic Body
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Solution Overview
Problem
Pressure sensors using silicon diaphragms face issues with corrosion resistance and temperature-induced dimensional differences when paired with stainless steel diaphragms, leading to measurement errors and potential breakage, while reducing the elastic coefficient for increased sensitivity can result in excessive stress and limited design flexibility.
Innovation Solution
A pressure sensor design featuring a stainless steel diaphragm with an elastic body covering its surface, where the elastic body is made from materials like kovar or invar alloys with a linear expansion coefficient matching the strain sensor, allowing for temperature stability and increased sensitivity without excessive stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon-made strain sensor is adhered to a stainless-steel-made diaphragm, then corrosion resistance is improved, but a large dimensional difference is caused by temperature variation leading to exfoliation and breakage
Solution Approach 1:
An elastic body made of kovar or invar alloy is introduced as an intermediary component between the stainless steel diaphragm and the silicon strain sensor. This intermediate layer has a linear expansion coefficient matching the silicon sensor, thereby mediating the thermal expansion mismatch and preventing exfoliation and breakage while maintaining corrosion resistance.
Solution Approach 2:
The pressure sensor employs a composite structure consisting of multiple materials: stainless steel diaphragm for corrosion resistance, kovar/invar elastic body for thermal compatibility, and silicon strain sensor for measurement. This composite approach allows each material to perform its optimal function while mitigating the weaknesses of individual materials.
2Measurement precision
If the elastic coefficient of the diaphragm is reduced to increase sensitivity, then sensitivity is improved, but the principal stress exceeds the elastic limit causing continuous operation to be impossible
Solution Approach 1:
The system is segmented into two functional parts: the stainless steel diaphragm for receiving pressure and the elastic body for transmitting deformation to the strain sensor. This segmentation allows the diaphragm to maintain high strength while the elastic body provides the necessary elasticity for sensitive detection without exceeding stress limits.
Solution Approach 2:
The linear expansion coefficient of the elastic body is specifically selected to match that of the silicon strain sensor, creating a thermal parameter match that eliminates dimensional differences during temperature variations. This parameter optimization allows the system to maintain both sensitivity and structural integrity.
3Reliability
If a stainless steel diaphragm is used to improve corrosion resistance, then corrosion resistance is improved, but the difference in linear expansion coefficient with silicon causes measurement errors due to temperature variation
Solution Approach 1:
The elastic body made of kovar or invar alloy serves as a thermal expansion intermediary, matching the silicon strain sensor's linear expansion coefficient. This eliminates dimensional mismatches during temperature changes, ensuring that the strain sensor accurately measures only the pressure-induced deformation of the diaphragm without thermal interference.
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
This configuration prevents diaphragm and strain sensor exfoliation, reduces temperature influence, and enhances design freedom by decoupling sensitivity from diaphragm material characteristics, enabling continuous operation and improved sensitivity at low pressures.
Implementation Method 1
detecting deformation of the elastic body which works together with deformation of the diaphragm as a strain
Implementation Method 2
the elastic body is formed of a material having a linear expansion coefficient close to the linear expansion coefficient of a material constituting the strain sensor
Data Source
AI summary
The present invention makes it possible to, even when a stainless steel is adopted in a diaphragm: prevent the diaphragm and a strain sensor from exfoliating from each other; be hardly susceptible to the influence of temperature in an operating environment; not allow the sensitivity of a pressure sensor to be dominated only by the mechanical characteristic of a material constituting the diaphragm; and increase the degree of freedom in design of members constituting the pressure sensor. A pressure sensor according to the present invention is, in order to solve the above problems, characterized in that: the pressure sensor has a diaphragm deforming by the pressure of a fluid, an elastic body covering the whole surface of the diaphragm and joining to the diaphragm on one side, and a strain sensor being arranged by joining on the other side of the elastic body and on an end side apart from a position corresponding to the center of the diaphragm and detecting the deformation of the elastic body working together with the deformation of the diaphragm as a strain; and the elastic body is formed of a material having a linear expansion coefficient close to the linear expansion coefficient of a material constituting the strain sensor.