Proximity Detection Circuit Timing for Moisture-Robust Sensing
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Solution Overview
Problem
Existing capacitive detection methods in vehicles are compromised by environmental conditions, particularly moisture in the form of water films with electrical ground contact, leading to unreliable detection and evaluation.
Innovation Solution
The method adapts capacitive detection to simultaneously measure both reactance and resistance by adjusting the phase and duty cycle of the clock signal, utilizing quadrature amplitude modulation (QAM) to demodulate sensor signals, incorporating both components for robust evaluation under adverse conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional capacitive detection methods are used to detect sensor signals, then the detection process is simple, but the detection reliability deteriorates under environmental conditions such as moisture and water films with electrical ground contact
Solution Approach 1:
The sensor signal is segmented into two distinct components: reactance component and resistance component. This segmentation is achieved through specific rectification timing using a clock signal with duty cycle between 0.25 and 0.6, where different time intervals capture different impedance components. The first interval captures primarily reactance while the second interval captures primarily resistance, allowing independent evaluation of each component to improve reliability under various environmental conditions.
Solution Approach 2:
The detection method dynamically adjusts the rectification timing and clock signal parameters based on the sensor signal characteristics. The duty cycle of the clock signal is set between 0.25 and 0.6 to optimally separate the reactance and resistance components. This dynamic timing adjustment allows the system to adaptively distinguish between capacitive effects (reactance) and resistive effects (including those from water films), thereby maintaining detection reliability under changing environmental conditions.
2Measurement precision
If only reactance is detected in capacitive sensors, then the detection method remains simple, but the measurement precision deteriorates when resistance components are present due to environmental factors
Solution Approach 1:
The sensor signal is segmented into two distinct components: reactance component and resistance component. This segmentation is achieved through specific rectification timing using a clock signal with duty cycle between 0.25 and 0.6, where different time intervals capture different impedance components. The first interval captures primarily reactance while the second interval captures primarily resistance, allowing independent evaluation of each component to improve reliability under various environmental conditions.
Solution Approach 2:
The detection method employs periodic rectification cycles synchronized with the sensor signal frequency. A clock signal with period matching the sensor signal frequency is used to periodically switch between capturing reactance components and resistance components. This periodic action ensures that both components are systematically measured in alternating phases, improving measurement precision by accounting for both capacitive and resistive effects that occur cyclically in the sensor signal.
3Loss of information
If the sensor signal is rectified without specific timing, then the processing is straightforward, but the ability to distinguish between reactance and resistance components is lost
Solution Approach 1:
The rectification process is prepared in advance with a predetermined clock signal configuration. The clock signal's duty cycle is pre-set between 0.25 and 0.6, and the rectification timing is pre-synchronized with the sensor signal frequency before measurement begins. This preliminary configuration ensures that when rectification occurs, the first time interval is predetermined to capture reactance while the second interval is predetermined to capture resistance, preventing information loss about impedance components.
Solution Approach 2:
The detection system incorporates feedback mechanisms where the rectified signals from both time intervals are fed back to the evaluation unit. The first rectified signal (containing reactance information) and the second rectified signal (containing resistance information) are both processed and compared. This feedback loop allows the system to continuously monitor and distinguish between reactance and resistance components, ensuring that no impedance information is lost during rectification by verifying both components are properly captured.
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 enables reliable detection and evaluation of approaches to vehicle sensors even under problematic environmental conditions, such as water films with ground contact, by effectively distinguishing and integrating resistive and capacitive signal components.
Implementation Method 1
a sensor element having a sensor electrode can provide a variable capacitance that is sensitive to changes in the sensor element's environment. Detecting the variable capacitance makes it possible to detect changes in the sensor element's environment.
Implementation Method 2
a rectifier arrangement rectifies the sensor voltage between an electrical storage arrangement and the sensor element
Implementation Method 3
The invention uses a clock signal to time the rectification of the voltage signal detected by the sensor means and the storage of the charge contained in the rectified signal so that the additive amplitudes of both the reactance and the resistance contained in the signal are measured. The method used according to the invention is similar to the concept of quadrature amplitude modulation (QAM) and the associated demodulation.
Data Source
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AI summary
A method for detecting an operating action, wherein a sensor (20, 20') is controlled by a periodic control signal via a coupled control/evaluation circuit (100). A sensor signal (510) tapped from the sensor (20, 20') is output to a controllable rectifier arrangement (220) in order to transmit a rectified sensor signal to a storage arrangement (250) for predetermined phase sections of the sensor signal, depending on a clock signal output by the control/evaluation circuit (100). The control/evaluation circuit (100) is coupled to the storage arrangement to generate an evaluation signal that depends on the accumulated charge.The clock signal (520) for controlling the rectifier (220) is synchronized with the sensor signal (510) and has a duty cycle according to which a clock signal is active for at least 25% and at most 75% of the period of the sensor signal, wherein the rectifier (220) is controlled during the active clock signal and wherein the phase of the clock signal (520) is specified such that at least one zero crossing of the sensor signal (510) is included in the rectification.