Capacitive Proximity Sensing Circuit for Moisture-Resistant Detection
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Solution Overview
Problem
Capacitive proximity sensors face challenges in accurately detecting changes in fringing capacitance due to environmental factors like moisture, temperature, and aging, especially when multiple sensor elements are involved, requiring a solution that minimizes power consumption and electromagnetic radiation while accounting for common-mode variations.
Innovation Solution
A switched capacitance circuit that uses non-overlapping timing signals to sample fringing capacitance, with frequency control to maintain accuracy in the presence of moisture and electromagnetic radiation for single sensor elements, and differencing, absolute-valuing, and summing capacitance values for multiple sensor elements to cancel out common-mode effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching frequency of the detection circuit is increased to maintain measurement accuracy in the presence of sensor moisture, then measurement accuracy is improved, but power consumption and electromagnetic radiation increase
Solution Approach 1:
The patent applies periodic action by using non-overlapping timing signals to switch the capacitance circuit at optimized intervals. The switching occurs periodically at specific phases where measurement accuracy is maintained while minimizing the duration of high-frequency operation, thereby reducing overall power consumption and electromagnetic radiation exposure.
Solution Approach 2:
The patent changes the timing parameters of the switching signals to optimize the balance between measurement accuracy and power consumption. By adjusting the phase and duration of the non-overlapping timing signals, the system maintains sufficient sampling accuracy while minimizing the time spent in high-power states, thus reducing overall energy consumption and electromagnetic emission.
2Adaptability or versatility
If multiple sensor elements are used to improve detection coverage, then detection capability is improved, but common-mode effects due to sensor moisture, temperature and aging are amplified
Solution Approach 1:
The patent extracts and removes the common-mode effects from the measurement signal by using differential measurement techniques. The capacitance values from multiple sensor elements are processed to isolate and eliminate the common-mode components caused by environmental factors, leaving only the differential signals that represent actual proximity detections.
Solution Approach 2:
The patent introduces an intermediary processing stage where capacitance values from multiple sensor elements are differenced, absolute-valued, and summed. This intermediary mathematical operation serves as a mediator that cancels out common-mode effects while preserving the useful detection signals from each sensor element.
3Measurement precision
If separate detection circuits are used for each sensor element to improve measurement accuracy, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple sensor elements into a single shared detection circuit. By combining the capacitance measurements from multiple sensor elements and processing them through common circuitry with non-overlapping timing signals, the system achieves measurement accuracy comparable to separate circuits while significantly reducing device complexity and component count.
Solution Approach 2:
The patent creates a universal detection circuit that can handle multiple sensor elements simultaneously. The single detection circuit is designed to be multi-functional, capable of measuring capacitance from different sensor elements by switching between them using non-overlapping timing signals, thereby eliminating the need for dedicated circuits for each element.
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 ensures reliable detection of changes in fringing capacitance, minimizing power consumption and electromagnetic radiation, while effectively canceling out common-mode variations due to environmental and aging factors, thereby improving the accuracy and robustness of capacitive proximity sensors.
Implementation Method 1
capacitive proximity sensors have two conductive plates and a detection circuit that detects changes in the capacitance between the plates since objects in proximity to the sensor change the intensity of fringing electric fields between the plates
Implementation Method 2
a switched capacitance circuit that samples the fringing capacitance of the sensor element using a pair of non-overlapping timing signals
Data Source
AI summary
A switched capacitance detection circuit is responsive to changes in the fringing capacitance of a capacitive proximity sensor having at least one capacitive sensor element. In cases where the sensor has a single sensor element, the switching frequency of the detection circuit is controlled to maintain measurement accuracy in the presence of sensor moisture while minimizing power consumption and electromagnetic radiation. In cases where the sensor has multiple sensor elements, the capacitance values for each sensor element are differenced, absolute-valued and summed to form an output in which common-mode effects due to sensor moisture, temperature and sensor aging are canceled out.