Capacitive Proximity Switch Shielding Against Interfering Capacitance
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Solution Overview
Problem
Capacitive proximity switches are susceptible to interfering capacitances from adjacent conductors, leading to malfunctioning due to their sensitivity to electromagnetic and capacitive signals in the surroundings.
Innovation Solution
The capacitive proximity switch incorporates an electrically conductive body that acts as a Faraday cage to shield the evaluation circuit and electronic components, with the active component of the evaluation circuit protruding into a cavity surrounded by the conductive body to reduce interference, and the entire setup is designed to minimize the influence of external interfering signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the evaluation circuit is placed close to the sensor area to reduce connection length, then the susceptibility to interfering capacitances from adjacent conductors increases
Solution Approach 1:
The patent introduces an electrically conductive body as an intermediary element between the sensor area and the evaluation circuit. This conductive body serves multiple functions: it provides electrical connection while acting as a shielding structure (Faraday cage) to protect the evaluation circuit from interfering capacitances and electromagnetic signals. The intermediary structure resolves the contradiction by allowing close placement while maintaining reliability through active shielding.
Solution Approach 2:
The patent employs composite construction by combining the electrically conductive body with the evaluation circuit board. The conductive body may be integrated with the PCB or mounted as a separate component, creating a composite structure that provides both electrical connectivity and electromagnetic shielding. This composite approach enables the evaluation circuit to be placed close to the sensor area while maintaining immunity to interfering signals.
2Reliability
If the sensor area is covered by an insulating cover plate to prevent direct contact, then the sensitivity to capacitive signals is reduced
Solution Approach 1:
The insulating cover plate acts as a mediator between the user's finger and the sensor area. While it prevents direct contact, the capacitive coupling through the insulating material allows the sensor to detect changes in capacitance caused by proximity of conductive objects. The evaluation circuit compensates for the reduced sensitivity by detecting subtle capacitance changes through the insulating barrier.
Solution Approach 2:
The patent changes the operational parameters of the capacitive sensor to account for the insulating cover plate. The evaluation circuit is designed to detect smaller capacitance changes that occur when objects approach through the insulating material, rather than direct contact. This parameter adjustment maintains measurement precision while preserving the protective function of the cover plate.
3Ease of operation
If the evaluation circuit components are exposed to the surroundings for easy access, then the susceptibility to electromagnetic interference increases
Solution Approach 1:
The evaluation circuit components are nested within the electrically conductive body, which forms a protective cavity. This nesting arrangement provides electromagnetic shielding while maintaining a compact structure. The conductive body acts as a Faraday cage that encloses the sensitive electronic components, protecting them from external electromagnetic interference while allowing the overall device to remain accessible.
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 configuration significantly reduces malfunctions caused by interfering signals, allowing for reliable operation of the proximity switch even near metal housing parts and improving the overall reliability of the capacitive proximity switch.
Implementation Method 1
The electrically conductive body forms a type of Faraday cage for the electronic component of the evaluation circuit, serving to shield said component against electromagnetic and/or capacitive interfering signals from the surroundings.
Data Source
AI summary
A capacitive proximity switch includes an electrically conductive sensor area, which is covered by an electrically-insulating cover plate, as part of a capacitor having a capacitance which varies as a result of proximity. An associated evaluation circuit is provided, and an electrically-conducting body, via which the sensor area is connected to the evaluation circuit and which is arranged between the electrically-insulating cover plate and a mount disposed at a distance therefrom. A domestic appliance includes such a proximity switch. At least one electronic component of the evaluation circuit is arranged on the mount such that it protrudes into a cavity, which is surrounded by the electrically conductive body.