Capacitive Displacement Sensing With Background Capacitance 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, which affects detection resolution and dynamic range requirements.
Innovation Solution
The implementation of a compensation circuitry that adjusts analogue capacitance measurement signals by subtracting an offset derived from previous measurements, allowing for reduced signal magnitudes and improved detection of small changes, thereby enhancing detection resolution and reducing dynamic range requirements.
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 (small capacitance changes against large background capacitance)
Solution Approach 1:
The patent extracts and removes the large background capacitance component from the measurement signal through compensation circuitry. By measuring the background capacitance separately and subtracting it from the total capacitance measurement, the system isolates the small capacitance changes caused by displacement, thereby improving measurement precision while maintaining the reliability benefits of capacitive sensing.
2Device complexity
If standard capacitance measurement is used, then device complexity is reduced, but measurement precision deteriorates (inability to resolve small changes against large background)
Solution Approach 1:
The patent segments the capacitance measurement process into distinct components: background capacitance measurement and displacement-induced capacitance change measurement. By dividing the measurement signal into separable components that can be processed independently, the system achieves high measurement precision without requiring overly complex instrumentation, as each segment can be handled by relatively simple circuitry.
Solution Approach 2:
The patent introduces compensation circuitry as an intermediary element between the capacitance sensor and the measurement system. This intermediary component processes the raw capacitance signal by removing the background capacitance contribution, enabling the downstream measurement system to focus on detecting only the relevant small capacitance changes without being overwhelmed by the large background signal.
3Adaptability or versatility
If full dynamic range is used to accommodate large background capacitance, then measurement range is maintained, but detection resolution deteriorates (small changes lost in large signal range)
Solution Approach 1:
By extracting and removing the large background capacitance component from the measurement signal, the system effectively compresses the dynamic range to focus on the small capacitance changes of interest. This allows the measurement system to use a smaller, more precise analog-to-digital converter range while still accommodating the full measurement range through separate background calibration, thereby improving detection resolution without sacrificing measurement range.
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 improves the detection resolution and reduces the dynamic range needed for processing, enabling more efficient and sensitive measurement of small capacitance changes in capacitive sensors, particularly in displacement sensing scenarios.
Implementation Method 1
capacitance measurement circuitry configured to make measurements of a capacitance associated with the first and second electrodes and to generate an analogue capacitance measurement signal in response thereto
Data Source
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.