Capacitive Sensing With Common Mode Choke Resolving AC Interference
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Solution Overview
Problem
Existing capacitive sensing systems using heating elements as antenna electrodes face challenges with high inductance and operating DC currents, leading to expensive components and residual alternating current issues that affect heating power and measurement accuracy.
Innovation Solution
A capacitive sensing system employing a common mode choke with three windings on the same core, where one winding is connected in parallel, measures a portion of the alternating current across the third winding to account for residual currents, ensuring accurate AC-decoupling and minimizing heating power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a common mode choke is used to AC-decouple the heating element from the power supply, then measurement accuracy is improved, but residual alternating current still flows through the choke affecting heating power
Solution Approach 1:
The patent divides the single common mode choke into three separate windings (first, second, and third windings). The first two windings handle the main heating current, while the third winding specifically measures the residual alternating current. This segmentation allows independent optimization of each winding's function, enabling accurate measurement of small residual currents without affecting the main heating function.
Solution Approach 2:
The third winding acts as an intermediary measurement channel that detects the residual alternating current flowing through the common mode choke. By introducing this intermediate measurement path, the system can quantify and compensate for the residual current's effect on heating power, thereby maintaining both accurate capacitance measurement and proper heating function.
2Reliability
If high inductance components are used to block alternating current, then AC-decoupling is improved, but component cost and complexity increase
Solution Approach 1:
The common mode choke with three windings serves multiple functions simultaneously: the first two windings provide the main AC-decoupling function to block alternating current from the power supply, while the third winding provides measurement function for residual current detection. This multi-functionality eliminates the need for separate measurement circuits or additional components, reducing overall system complexity.
Solution Approach 2:
The patent combines the AC-decoupling function and the residual current measurement function into a single common mode choke structure with three windings. By merging these functions into one component, the system avoids the complexity of using separate chokes, transformers, or measurement circuits, thereby reducing component count and system complexity while maintaining effective AC-decoupling.
3Device complexity
If the heating element is used as the antenna electrode, then device complexity is reduced, but residual alternating current interferes with measurement accuracy
Solution Approach 1:
The third winding provides feedback information about the residual alternating current flowing through the common mode choke. This feedback allows the control system to compensate for the interference caused by residual current on capacitance measurements, thereby maintaining high measurement precision while using the simplified structure of the heating element as the antenna electrode.
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 achieves effective AC-decoupling of the heating element from its power supply, allowing precise capacitance measurement and reducing residual alternating current interference, thereby enhancing the accuracy and efficiency of occupant detection systems.
Implementation Method 1
a common mode choke for essentially preventing alternating current from flowing from the heating element to the heating current supply
Implementation Method 2
a heating element producing heat upon electrical current being caused to flow there across
Implementation Method 3
the sensor comprises at least one sensing electrode at which the influence of an object or living being on the electric field is detected
Data Source
AI summary
A capacitive sensing system for being connected to a heating element comprises a capacitive detector connectable to the heating element and a common mode choke for essentially preventing alternating current from flowing from the heating element to the heating current supply. The capacitive detector is configured for driving an alternating current into the heating element and for producing an output indicative of capacitance based upon the alternating current. The choke has a first and a second winding for connecting the heating element with the heating current supply. The choke comprises a third winding connected in parallel of the first and/or second winding. The capacitive detector is configured for measuring a portion of the alternating current flowing across the third winding and for taking into account the measured portion of alternating current when producing the output.