Vibration Sensor Rod Positioning for Thermal Stress Reduction
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Solution Overview
Problem
Existing field devices with electromechanical converter units face efficiency limitations and mechanical stress at high temperatures, particularly due to the differences in thermal expansion coefficients between metal and ceramic materials, leading to potential sensor failure.
Innovation Solution
A device with an oscillatable unit, including a membrane and non-positively attached rods, where the drive/receiver unit is spatially separated from the process, using rods to efficiently transmit vibrations and maintain high efficiency across a wide temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If piezoelectric drive/receiver units are used to efficiently transmit vibrations, then power transmission efficiency is improved, but mechanical stress and thermal expansion differences cause sensor failure at high temperatures
Solution Approach 1:
The device segments the oscillatable unit into separate components: a membrane for process contact and rods for vibration transmission. This segmentation allows the membrane to handle thermal expansion independently while the rods efficiently transmit vibrations, resolving the contradiction between power transmission efficiency and high-temperature reliability
Solution Approach 2:
The rods act as intermediaries between the drive/receiver unit and the membrane. They non-positively connect to the membrane at specific locations, allowing efficient vibration transmission while accommodating thermal expansion differences without causing mechanical stress or sensor failure
2Reliability
If the drive/receiver unit is spatially separated from the process, then high-temperature reliability is improved, but vibration transmission efficiency may be reduced
Solution Approach 1:
The rods are positioned at specific locations on the membrane where the second derivative of deflection is substantially zero. This local positioning optimizes vibration transmission efficiency at critical points while allowing the drive/receiver unit to remain spatially separated from the process for high-temperature reliability
Solution Approach 2:
The solution moves the drive/receiver unit to a different spatial dimension (outside the process environment) while maintaining effective vibration transmission through strategically positioned rods that extend from the membrane into the housing, achieving both separation and efficiency
3Strength
If rods are non-positively attached to the membrane, then mechanical stress is reduced, but connection stability may be compromised
Solution Approach 1:
The attachment parameters are optimized by positioning rods at specific locations where the second derivative of membrane deflection is substantially zero. This parameter change allows non-positive attachment that reduces mechanical stress while maintaining connection stability through optimal geometric positioning
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 solution provides a highly efficient and reliable field device capable of operating in an extended temperature range, minimizing energy requirements and maintaining efficient power transmission while avoiding mechanical stress, thus enhancing the device's operational lifespan.
Implementation Method 1
the drive/receiver unit is, in particular, in the form of an electromechanical converter unit which, in turn, can be, for example, a piezoelectric, electromagnetic or magnetostrictive drive/receiver unit
Implementation Method 2
the drive/receiver unit is designed to set the rods into mechanical vibrations by the rods being pushed apart or together with the correct frequency by means of the drive/receiver unit
Data Source
Figure 1
Figure 2a~2b
Figure 3a~3b
AI summary
The invention relates to a device (1) for determining and/or monitoring at least one process variable of a medium (4) in a container (5), the device comprising: at least one unit (3) that is capable of vibration and has at least one membrane (9) that can be made to mechanically vibrate; at least three bars (10a-10d) fastened to the membrane (9) perpendicularly to a base surface of the membrane (9); a housing (8), wherein the membrane (9) forms at least a partial region of a wall of the housing (8) and wherein the bars (10a-10d) are directed into the housing interior; at least one drive unit/receiving unit (6) arranged in the end region of the bars (10a-10d) facing away from the membrane (9), the drive unit/receiving unit (6) being designed to cause the unit (3) capable of vibration to mechanically vibrate by means of an electrical excitation signal and by means of the bars (10a-10d) and to receive the mechanical vibrations of the unit (3) capable of vibration and to convert said vibrations into an electrical receipt signal; and an electronic unit (7) designed to generate an excitation signal from the receipt signal and to determine the at least one process variable at least from the receipt signal. According to the invention, at least one of the bars (10a-10d) is fastened to the membrane (9) substantially at a location along the base surface (A) of the membrane (9) at which the second derivative of the deflection of the membrane (9) from a resting position as a function of the location along the base surface (A) is substantially zero.