Capacitive Pressure Measuring Cell Monitoring for Membrane Damage
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Solution Overview
Problem
Capacitive pressure sensors face challenges in accurately distinguishing between temperature-induced and mechanical damage-induced deformations of the membrane, leading to erroneous pressure readings, particularly during thermal shocks.
Innovation Solution
A method involving a lookup table to store characteristic curves of capacitance versus pressure and temperature, comparing actual measurements with expected values, and switching to a safety mode upon significant deviations, allowing for early detection of mechanical damage by analyzing temperature element signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature compensation is applied based on reference capacitance values, then temperature-induced measurement errors are reduced, but mechanical damage detection capability deteriorates due to false compensation of damaged membranes
Solution Approach 1:
The patent segments the membrane deformation analysis into two independent components: temperature-induced deformation (compensated through reference capacitance comparison) and mechanical damage deformation (detected through residual deviation analysis). By separating these effects, the system can compensate for temperature while independently detecting mechanical damage, resolving the contradiction between measurement precision and damage detection reliability.
Solution Approach 2:
The patent introduces an intermediary evaluation unit that acts as a mediator between the capacitance measurement and the final pressure reading. This evaluation unit compares measured capacitance values with temperature-compensated reference values, isolates the residual deviation caused by mechanical damage, and generates separate indicators for temperature compensation and damage detection. This intermediary layer enables both temperature compensation and reliable damage detection to coexist.
2Productivity
If the pressure sensor operates during thermal shock, then continuous pressure monitoring is maintained, but measurement accuracy deteriorates due to temperature-induced membrane deformation
Solution Approach 1:
The patent applies preliminary temperature compensation by comparing the measured capacitance value with the temperature-dependent reference capacitance value before final pressure calculation. This preliminary action removes the temperature-induced deformation component from the measurement, allowing continuous monitoring during thermal shock to maintain accuracy despite temperature fluctuations.
Solution Approach 2:
The patent implements a feedback mechanism where the evaluation unit continuously compares the measured capacitance with the temperature-compensated reference capacitance, detects deviations caused by thermal shock or mechanical damage, and adjusts the pressure reading accordingly. This feedback loop enables continuous monitoring while maintaining measurement precision even during thermal shock conditions.
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
Enables early detection of mechanical damage to the pressure sensor membrane, reducing erroneous readings by initiating targeted countermeasures and minimizing error influence through temperature compensation.
Implementation Method 1
At the underside of the membrane and at the opposite upper side of the base body electrodes are provided, respectively, which together form a measuring capacitor. The effect of pressure causes the membrane to deform, which results in a change in the capacitance of the measuring capacitor.
Implementation Method 2
the temperature prevailing during the pressure measurement, in particular that of the medium to be measured, can have a considerable influence on the accuracy of the measurement results obtained. For this reason, parallel to the pressure measurement in addition the temperature is detected by means of a temperature element arranged on the back side of the base body
Data Source
AI summary
The invention relates to a method for monitoring the function of a capacitive pressure measuring cell (10) comprising a measuring capacitor (CM) and a reference capacitor (CR) as well as a temperature element, wherein a pressure measurement value p is obtained by forming the quotient Q from the capacitance values of the reference capacitor (CR) and the measuring capacitor (CM). The method is characterized by the following method steps:in a matching procedure the characteristic curve of the quotient Q and the capacitance values of the measuring capacitor (CM) are each stored in a lookup table versus the pressure and at different temperature scenarios;then the corresponding absolute value of the quotient Q and of the capacitance value of the measuring capacitor (CM) from the lookup table are continuously assigned respectively to the determined pressure measurement value p at the temperature detected at this moment by the temperature element;the behavior of the course in which the two absolute values of the quotient Q and the capacitance value of the measuring capacitor (CM) is compared with each other;in the case of a significant deviation from an expected behavior, the evaluation unit is temporarily switched into a safety mode and meanwhile the gradient of the temperature element is detected and evaluated;in the case of a significant increase of the gradient of the temperature element, a temperature compensation is initiated; orin the case of an unchanged gradient of the temperature element, an error signal is generated.