Dual-Diaphragm Capacitive Sensor for Harsh Pressure Measurement
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Solution Overview
Problem
Current micromechanical differential-pressure sensors face challenges in accurately measuring small pressure differentials at high absolute pressures and in harsh, particle-laden environments due to limited measuring accuracy of absolute-pressure sensors.
Innovation Solution
A micromechanical sensor element with a dual-diaphragm structure, where two parallel diaphragms are rigidly connected via crosspieces, allowing direct force transmission and capacitive signal acquisition, enabling sensitive measurement of pressure differentials without requiring design for absolute pressures, and featuring a sealed volume with a fixed counter-electrode for protection and enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If two independent absolute pressure sensors are used to determine differential pressure, then the measurement can be performed with simple device structure, but the measurement precision is insufficient particularly at high absolute pressures and small differential pressures
Solution Approach 1:
The sensor is segmented into two separate diaphragms (first and second diaphragms) that are pressurized independently from opposite sides. Each diaphragm responds to absolute pressure independently, and their differential deflection is measured to determine the pressure difference. This segmentation allows each diaphragm to be optimized for absolute pressure sensing while the differential measurement achieves high precision.
Solution Approach 2:
A fixed counter-electrode is introduced as an intermediary element positioned between the two diaphragms. This counter-electrode serves as a common reference for capacitive measurements of both diaphragms, enabling precise differential pressure measurement through capacitive coupling without direct mechanical contact between the diaphragms and the measurement system.
2Reliability
If the diaphragm structure is designed for high absolute pressures, then the sensor can withstand harsh measuring environments, but the sensitivity for measuring small pressure differentials is reduced
Solution Approach 1:
The single diaphragm is segmented into two separate diaphragms that can be independently pressurized. This allows each diaphragm to be designed with appropriate thickness and mechanical properties for withstanding absolute pressure, while the differential deflection measurement maintains high sensitivity for small pressure differences.
Solution Approach 2:
The measurement parameter is changed from absolute pressure measurement to differential pressure measurement. By measuring the difference in deflection between two diaphragms rather than the absolute deflection of a single diaphragm, the sensor achieves high sensitivity for small pressure differentials while each diaphragm can be designed to withstand high absolute pressures.
3Device complexity
If electrodes are exposed to the measuring environment, then the sensor structure is simple, but the electrodes are susceptible to corrosion and contamination reducing service life
Solution Approach 1:
The electrodes are nested within the sealed volume formed by the two diaphragms and the sensor housing. The first diaphragm, second diaphragm, and housing create a protected internal chamber where the electrodes are positioned, isolating them from the external harsh measuring environment while maintaining sensor functionality.
Solution Approach 2:
The diaphragms serve as intermediary barriers between the harsh external environment and the protected internal electrodes. These diaphragms allow pressure transmission while preventing direct contact between the measuring media and the electrodes, thus protecting the electrodes from corrosion and contamination.
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 design allows for reliable recording of small pressure differentials with improved accuracy and extended service life, even in harsh environments, by minimizing offset errors and protecting electrodes from corrosion and contamination.
Implementation Method 1
This connection allows each application of force to one of the two diaphragms to be directly transmitted to the respective other diaphragm
Implementation Method 2
Sensor element for capacitive differential-pressure sensing having a deflectable diaphragm structure which is provided with at least one deflectable electrode, and having a fixed support structure for at least one fixed counter-electrode
Data Source
AI summary
A sensor design, respectively a micromechanical sensor structure for capacitive relative-pressure measurement, that will allow very small pressure differentials to be reliably recorded at high absolute pressures even in harsh, particle-laden measuring environments. For that purpose, the micromechanical sensor element includes a deflectable diaphragm structure which is provided with at least one deflectable electrode, and a fixed support structure for at least one fixed counter-electrode which is located opposite the deflectable electrode. The diaphragm structure includes two mutually parallel configured diaphragms that are joined rigidly to one another via at least one connecting crosspiece, so that each application of force to one of the two diaphragms is directly transmitted to the respective other diaphragm. The first diaphragm is able to be pressurized by a first measuring pressure emanating from the front side of the sensor element, and the second diaphragm is able to be pressurized by a second measuring pressure emanating from the rear side of the sensor element. The fixed counter-electrode is located in the sealed volume between the two diaphragms of the diaphragm structure.