Capacitive Displacement Sensing With Analog Background Compensation
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Solution Overview
Problem
Capacitive sensing technologies face challenges in measuring small changes in capacitance against a large background capacitance, particularly in displacement sensing applications, where accurate detection of subtle changes is crucial for reliable operation.
Innovation Solution
The proposed solution involves a capacitance sensing apparatus with a compensation circuitry that adjusts analogue capacitance measurement signals by subtracting an offset value derived from previous measurements, allowing for improved detection of small changes in capacitance and reducing the dynamic range requirements of the processing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive sensing techniques are used to measure displacement, then reliability is improved (less mechanical wear), but measurement precision deteriorates (difficulty measuring small capacitance changes against large background capacitance)
Solution Approach 1:
The patent divides the capacitance measurement into two separate measurements: a first capacitance measurement taken before the object is positioned, and a second capacitance measurement taken after positioning. By segmenting the measurement process in time and subtracting the first measurement from the second, the system isolates the small capacitance change caused by object positioning from the large background capacitance, thereby improving measurement precision while maintaining the reliability benefits of capacitive sensing.
2Device complexity
If standard capacitive measurement circuitry is used, then device complexity is reduced, but measurement precision deteriorates (inability to resolve small capacitance changes)
Solution Approach 1:
The patent performs a preliminary capacitance measurement before the object is positioned on the substrate. This preliminary measurement captures the background capacitance state, which is then subtracted from the final measurement to isolate the small capacitance change caused by object positioning. This preliminary action enables standard circuitry to achieve high measurement precision by removing the dominant background capacitance component.
Solution Approach 2:
The system uses the first capacitance measurement as feedback to compensate for background capacitance in the second measurement. By subtracting the first measurement value from the second measurement value, the system dynamically compensates for the large background capacitance, allowing standard circuitry to detect small capacitance changes with high 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 enhances the sensitivity and resolution of capacitance measurements, enabling more effective detection of displacements by ensuring that the change in capacitance is represented by a larger proportion of the dynamic range, thereby improving the detection resolution and reducing the complexity and cost of the required circuitry.
Implementation Method 1
capacitance measurement circuitry configured to make measurements of a capacitance associated with the first and second electrodes
Data Source
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AI summary
A displacement sensor comprising: a first electrode and a second electrode displaceably mounted relative to the first electrode; capacitance measurement circuitry configured to make measurements of a capacitance associated with the first and second electrodes and to generate analogue capacitance measurement signals in response thereto; compensation circuitry configured to generate a compensated analogue capacitance measurement signal by reducing a magnitude of a current analogue capacitance measurement signal by an amount indicated by a compensation signal derived from at least one previous analogue capacitance measurement signal; and processing circuitry configured to digitise the compensated analogue capacitance measurement signal and to determine if there is a displacement of the second electrode relative to the first electrode based on the compensated analogue capacitance measurement signal.