Capacitive Presence Sensing with Switched Impedance Calibration
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Solution Overview
Problem
Prior capacitive detection devices for motor vehicles lack precision in measuring complex impedance or admittance, especially due to climatic variations and electronic component variability, which affects the accuracy of detecting presence near or in contact with vehicle components.
Innovation Solution
A capacitive detection device with a switching mechanism that connects a voltage source to an electrode in measurement mode and to a calibration resistor in calibration mode, using two calibration resistors with different resistive values to correct measurements and compensate for drift, and applying offset and phase corrections to ensure accurate complex impedance or admittance calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If prior capacitive detection devices are used for measuring complex impedance or admittance, then the detection function is provided, but the measurement precision is insufficient due to climatic variations and electronic component variability
Solution Approach 1:
The patent applies preliminary calibration action by measuring the complex impedance of calibration resistors with known values before actual detection. This calibration process establishes reference data that compensates for climatic variations and component variability, thereby improving measurement precision without sacrificing reliability
Solution Approach 2:
The patent implements feedback through iterative calibration and correction processes. The measured complex impedance values are compared against calibration references, and correction factors are applied to compensate for drift and variability, ensuring both high precision and reliability under varying conditions
2Measurement precision
If calibration resistors are introduced to correct measurements, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies universality by designing the calibration circuit to serve multiple functions: it calibrates the detection system, provides reference impedance values, and enables compensation for various error sources. This multi-functionality reduces the need for separate calibration devices, thereby improving accuracy without proportionally increasing complexity
Solution Approach 2:
The calibration resistors act as intermediaries between the voltage source and the detection circuit. They provide known impedance references that mediate the calibration process, enabling accurate measurement correction without requiring direct modification of the core detection architecture, thus balancing accuracy improvement with manageable complexity
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 enables precise detection of presence by compensating for measurement drift and variability, ensuring accurate complex impedance measurements and continuous calibration, thereby improving the detection of hands or occupants on vehicle components.
Implementation Method 1
a voltage source arranged to deliver an alternating voltage
Implementation Method 2
The capacitive sensor comprises two electrodes separated by a dielectric material
Implementation Method 3
measuring a complex value corresponding to an impedance or an admittance
Data Source
Figure 1~3
Figure 2
Figure 4~5
AI summary
The invention relates to a capacitive detection device (100) comprising at least one electrode (20) of a capacitive sensor of said component, an alternating voltage source (23), a device (24) for measuring a complex value of impedance or admittance between the detection electrode (20) and an electrical circuit reference point and a calibration resistance (Rc1, Rc2), and a switching device (26, SW1-SW6) arranged so as to connect the voltage source (23) to the electrode (20), in the measurement mode, and to connect the voltage source (23) to the calibration resistance (Rc1, Rc2)and disconnect the voltage source from the electrode (20), in the calibration mode. The measuring device (24) is arranged so as to measure a first complex value of the calibration resistance (Rc1, Rc2) during operation in the calibration mode, to measure a second complex value between the electrode (20) and the electrical circuit reference point during operation in the measurement mode, and to correct the second measured complex value according to the first measured complex value.