Heating element operated as capacitive sensing electrode
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Solution Overview
Problem
Existing combined seat heater and capacitive occupancy sensors face issues with unsatisfactory capacitance measurements due to voltage differences that cannot be fully compensated by buffer amplifiers, leading to inaccurate occupancy detection.
Innovation Solution
A combined seat heater and capacitive occupancy sensor design featuring a heater network with electronically controlled switches and a capacitive sensing circuit that maintains equal AC potential on the heating element, using a transimpedance amplifier and field-effect transistors to derive capacitive load from the current flowing into the heating element, and an oscillator to apply an oscillating voltage, thereby minimizing parasitic capacitances and ensuring accurate capacitance measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a buffer amplifier is used to compensate voltage differences in the heating element, then the voltage compensation is improved, but the measurement accuracy remains unsatisfactory due to residual voltage differences and parasitic capacitances
Solution Approach 1:
The patent applies equipotentiality by connecting the oscillator directly to both terminals of the heating element, ensuring that the entire heating element is at the same AC potential. This eliminates voltage differences across the heating element that would otherwise create parasitic capacitances and measurement errors, directly resolving the contradiction between voltage compensation and measurement accuracy.
Solution Approach 2:
The patent extracts and eliminates parasitic capacitances by removing the buffer amplifier stage that introduced voltage differences. By directly coupling the oscillator to the heating element terminals and using electronically controlled switches to isolate parasitic capacitances during sensing mode, the patent extracts the harmful parasitic elements from the measurement path, improving both capacitance measurement accuracy and occupancy detection reliability.
2Device complexity
If the heating element is used as a capacitive sensing electrode, then the device complexity is reduced, but parasitic capacitances from the heating circuit interfere with accurate capacitance measurements
Solution Approach 1:
The patent applies periodic action by using electronically controlled switches to alternately connect the heating element to the power source for heating mode and to the oscillator for sensing mode. This periodic switching isolates parasitic capacitances from the measurement circuit during sensing, allowing the heating element to serve dual purposes while maintaining measurement accuracy.
Solution Approach 2:
The patent introduces electronically controlled switches as intermediaries between the heating element and the measurement circuit. These switches act as mediators that can be opened during sensing mode to isolate parasitic capacitances from the oscillator, enabling accurate capacitance measurements while maintaining the simplified structure of using the heating element as the sensing electrode.
3Measurement precision
If electronically controlled switches are added to isolate parasitic capacitances, then the capacitance measurement accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent applies multi-functionality by designing the electronically controlled switches to serve dual purposes: isolating parasitic capacitances during sensing mode and enabling heating mode operation. This universal approach allows the same switching components to improve measurement accuracy while maintaining the heating function, reducing the need for separate isolation circuits.
Solution Approach 2:
The patent merges the parasitic capacitance isolation function with the existing heating circuit control switches. By combining the isolation function into the same switching components that control heating, the patent reduces overall device complexity while still achieving accurate capacitance measurements through proper timing and configuration.
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 design ensures accurate capacitance measurements by maintaining equal AC potential and phase, reducing the impact of parasitic capacitances, and allowing the system to effectively differentiate between occupied and empty states, enhancing the reliability of occupancy detection.
Implementation Method 1
a heating element (103) connected between a first node and a second node to dissipate heat when a heating current is caused to flow between the first and second nodes
Implementation Method 2
The current measuring means is configured to keep the AC-potential of the heating element equal, or at least substantially equal, in amplitude and phase, to the oscillating voltage and to derive the capacitive load from a current flowing into the heating element in response to the AC-potential
Data Source
AI summary
A combined seat heater and capacitive occupancy sensor comprises a heater network including a heating element (11) and a capacitive sensing circuit connected to the heating element to sense a capacitive load. A first and a second interface are provided for connecting the heating element to a first and a second terminal of a power source, respectively. Each interface comprises electronically controlled switches (3, 5; 4, 6) arranged in series and defining an intermediate node (20; 21). An oscillator (8) is AC-coupled to the intermediate nodes to apply an oscillating voltage thereto. A current measuring means (9), AC-coupled between the oscillator and the heating element, keeps the AC-potential of the heating element at least substantially equal, in amplitude and phase, to the oscillating voltage on the intermediate nodes and to derive the capacitive load from a thus resulting current flowing into the heating element.