Capacitive Sensing System Using Compensation Capacitor to Balance Inductive Load
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Solution Overview
Problem
Capacitive occupant sensing systems using heating elements as antenna electrodes face challenges due to high inductance and operating DC currents, which result in expensive components and reduced measurement resolution caused by dominant inductive loads.
Innovation Solution
A capacitive sensing system employing a non-ideal common mode choke for AC-decoupling and a compensation capacitor to balance the complex impedance, ensuring the capacitive load contributes significantly to the overall impedance, thereby enhancing measurement resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a common mode choke is used for AC-decoupling the heating element from the heating current supply, then heating efficiency is maintained, but the inductive load dominates the complex impedance causing reduced measurement resolution
Solution Approach 1:
The patent changes the electrical parameters of the system by introducing a compensation capacitor connected in parallel with the common mode choke. This capacitor compensates for the dominant inductive reactance of the choke, transforming the overall impedance characteristics from inductive-dominated to capacitive-dominated, thereby improving measurement resolution while maintaining heating efficiency
Solution Approach 2:
The compensation capacitor acts as an intermediary element that mediates between the common mode choke and the capacitive sensing circuit. It counterbalances the inductive effects of the choke, allowing both heating and sensing functions to coexist with improved measurement precision
2Measurement precision
If an ideal common mode choke with high AC impedance is used, then measurement resolution improves, but component cost and complexity increase significantly
Solution Approach 1:
The patent replaces the expensive ideal common mode choke with a combination of a standard (non-ideal) common mode choke and a compensation capacitor. This substitution uses more readily available, cost-effective components to achieve the same functional outcome, reducing overall system cost and complexity
Solution Approach 2:
Instead of relying on a single expensive component with specific impedance characteristics, the patent uses parameter adjustment through the compensation capacitor to modify the overall impedance behavior, achieving high measurement resolution with standard components
3Reliability
If the inductive load is dominated by the common mode choke, then AC-decoupling is effective, but amplitude variations of alternating current are reduced making measurement difficult
Solution Approach 1:
The compensation capacitor provides an opposing electrical effect to the inductive load of the common mode choke. By connecting the capacitor in parallel, it counterweights the inductive reactance, thereby increasing the amplitude variations of the alternating current and making them detectable while preserving the AC-decoupling function
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 system improves measurement resolution by bringing amplitude variations of the alternating current within the same order of magnitude as the constant current, effectively mitigating the impact of dominant inductive loads and maintaining heating efficiency.
Implementation Method 1
a heating element producing heat upon electrical current being caused to flow across the heating element
Implementation Method 2
a common mode choke for connecting the heating element with a heating current supply, the common mode choke representing an inductive load
Implementation Method 3
the capacitive detector is configured for driving an alternating current into the heating element and for producing an output depending on the capacitive load that the alternating current is subject to
Data Source
AI summary
A capacitive sensing system for a heating element comprises a capacitive detector connectable to the heating element and a common mode choke for connecting the heating element with a heating current supply. The detector drives an alternating current into the heating element and produces an output depending on the capacitive load, which the alternating current is subject to. Depending on the object sensed, the load varies in a range between a minimum and a maximum value. The choke represents an inductive load in parallel of the capacitive load. The capacitive load and the inductive load contribute to a complex impedance dominated by the inductive load. A compensation capacitor arranged parallel to the choke represents an additional capacitive load also contributing to the complex impedance. The compensation capacitor is dimensioned such that the sum of additional capacitive load and maximum value amounts to at least 50% of the inductive load.