Capacitive Pressure Sensor High Dielectric Fill Fluid
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Solution Overview
Problem
Existing capacitive pressure sensors are limited in size due to constraints on electrode spacing and dielectric constant of fill fluids, making it difficult to produce smaller sensors with sufficient capacitance for industrial process control systems.
Innovation Solution
The use of a fill fluid with a dielectric constant higher than 3.5, such as a blend of silicon-based oil and liquid additives like isopropyl alcohol, acetone, or ethylene glycol, allows for a reduction in sensor size while increasing capacitance, enabling smaller capacitive pressure sensors with diameters less than 1.25 inches and capacitances of approximately 5 to 10 pico-farads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the dielectric constant of the fill fluid is increased, then the capacitance of the sensor is improved, but the compatibility with the hydraulic system is limited
Solution Approach 1:
The patent uses a composite fill fluid comprising a base hydraulic fluid (such as silicone oil) blended with a high dielectric constant liquid additive (such as isopropyl alcohol, acetone, ethylene glycol, or glycerin). This composite approach combines the hydraulic properties of the base fluid with the high dielectric constant of the additive, achieving both system compatibility and enhanced capacitance. The blend ratio can be optimized to balance hydraulic performance and dielectric properties.
Solution Approach 2:
The patent changes the dielectric parameter of the fill fluid by adding liquid additives with high dielectric constants to the base hydraulic fluid. This parameter modification allows the fill fluid to simultaneously satisfy hydraulic system requirements and provide enhanced capacitance for the capacitive pressure sensor, resolving the contradiction between measurement precision and adaptability.
2Volume of moving object
If the sensor size is reduced, then the number of applications is increased, but the capacitance signal strength becomes insufficient
Solution Approach 1:
By changing the dielectric parameter of the fill fluid through the addition of high dielectric constant liquid additives, the patent achieves higher capacitance values in smaller sensor configurations. The enhanced dielectric constant compensates for the reduced electrode area and spacing, maintaining sufficient signal strength despite the smaller sensor size.
Solution Approach 2:
The composite fill fluid with high dielectric constant allows the capacitive pressure sensor to achieve adequate capacitance signal strength in a compact form factor. The blend of base hydraulic fluid and high dielectric constant additive enables the sensor to maintain performance requirements while reducing overall size for broader application compatibility.
3Manufacturing precision
If the electrode spacing is reduced, then the sensor precision is improved, but the capacitor functionality is compromised
Solution Approach 1:
The patent changes the dielectric parameter of the medium between the electrodes by using a fill fluid with high dielectric constant. This allows the capacitor to maintain adequate capacitance and functionality even with reduced electrode spacing, thereby enabling higher sensor precision without compromising capacitor reliability.
4Volume of moving object
If the electrode plate area is reduced, then the sensor size is decreased, but the signal strength becomes insufficient
Solution Approach 1:
By changing the dielectric constant parameter of the fill fluid through the addition of high dielectric constant liquid additives, the patent compensates for the reduced electrode plate area. The enhanced dielectric property maintains sufficient capacitance and signal strength despite the smaller electrode area, enabling compact sensor design without sacrificing measurement precision.
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 approach enables the production of smaller capacitive pressure sensors with enhanced capacitance, allowing for increased precision and flexibility in industrial process control systems, while also reducing manufacturing costs and enabling the use of higher line pressures and faster response times.
Implementation Method 1
The fill fluid is a blend of silicon-based oil and a liquid additive, such that it has a dielectric constant higher than about 3.5
Implementation Method 2
The hydraulic system comprises a sealed passageway in which the sensing diaphragm is positioned at a first end, and a flexible isolation diaphragm is positioned at a second end to engage the process fluid. The sealed passageway is filled with a precise amount of hydraulic fluid that adjusts the position of the sensing diaphragm as the process fluid influences the isolation diaphragm.
Data Source
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AI summary
A capacitive pressure sensor 30 for an industrial process transmitter 12 comprises a housing (62A & 62B), a sensing diaphragm 58, an electrode (60A or 60B) and a fill fluid. The housing (62A & 62B) includes an interior cavity 78 and a channel extending from an exterior of the housing (62A & 62B) to the cavity 78. The sensing diaphragm 58 is disposed within the interior cavity 78 opposite the electrode (60A or 60B). The fill fluid occupies the interior cavity 78 such that a pressure from the channel is conveyed to the sensing diaphragm 58 to adjust a capacitance between the electrode (60A or 60B) and the sensing diaphragm 58. The fill fluid has a dielectric constant higher than about 3.5. In various embodiments, the pressure sensor 30 has a diameter less than approximately 3.175 centimeters (~1.25 inches), the electrode (60A or 60B) has a diameter less than approximately 1 cm (~0.4 inches), the pressure sensor 30 has a capacitance of approximately 5 to approximately 10 pico-farads, and the fill fluid is comprised of hydraulic fluid having a liquid additive.