Seat Heater Circuit Modulation for Capacitive Sensor Interference
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Solution Overview
Problem
Existing seat heaters in vehicles interfere with capacitive occupancy sensors due to the formation of a larger capacitance between the heating element and the sensor's antenna electrode, affecting the accuracy and reliability of occupant detection.
Innovation Solution
The use of active electric components, such as transistors, connected in series with the heating element to modulate conductance and maintain a constant voltage drop across the heating element, allowing for the application of an oscillating signal that synchronizes with the capacitive sensing frequency, effectively isolating the heating element from the power supply and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the heating element is connected directly to the power supply, then the heating function operates efficiently, but the capacitive occupancy sensor accuracy deteriorates due to increased capacitance interference
Solution Approach 1:
An intermediary circuit comprising active electric components (transistors or MOSFETs) is introduced between the heating element and the power supply. This intermediary circuit acts as a mediator that isolates the heating element from the power supply during capacitive sensing operations, thereby eliminating the capacitance interference while maintaining heating functionality when needed.
Solution Approach 2:
The heating element is operated periodically rather than continuously. The control network alternates between applying the oscillating signal for capacitive sensing and applying DC voltage for heating. This periodic action allows the system to achieve both accurate occupancy detection and effective heating at different time intervals.
2Productivity
If the heating circuit operates continuously, then heating efficiency is maintained, but interference with capacitive sensing increases
Solution Approach 1:
The heating circuit operates in periodic cycles, alternating between heating mode and sensing mode. During sensing intervals, the heating circuit is disconnected and an oscillating signal is applied instead. This periodic operation reduces electromagnetic interference during critical sensing periods while maintaining overall heating productivity.
Solution Approach 2:
Before capacitive sensing operations are performed, the heating circuit is preemptively disconnected and the intermediary circuit is prepared to apply the oscillating signal. This preliminary action prevents interference from occurring in the first place, ensuring accurate occupancy detection.
3Measurement precision
If isolation circuits with transistors are used, then capacitive sensing accuracy is improved, but device complexity increases
Solution Approach 1:
The active electric components in the intermediary circuit serve multiple functions: they act as switches to disconnect the heating element, as signal sources to generate the oscillating signal for capacitive sensing, and as control elements regulated by the control network. This multi-functionality reduces the need for separate dedicated components for each function.
Solution Approach 2:
The heating control circuit and the capacitive sensing circuit are merged into a single integrated control network that manages both functions. The control network regulates the active electric components to achieve both heating control and capacitive sensing operations, thereby reducing overall system complexity despite the added isolation functionality.
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 solution enhances the accuracy and reliability of capacitive occupancy sensing by minimizing the adverse effects of the heating element on the capacitive measurement, while also enabling the heating element to function as a driven shield for the antenna electrode, reducing interference and improving the operability of vehicle systems.
Implementation Method 1
an electric heating element (e.g. formed of metal wire, conductive fiber, metal foil, metal ribbon, and/or conductive print on an electrically isolating substrate) connected between a first node and a second node to dissipate heat when a heating current is caused to flow across the heating element, between the first and second nodes
Implementation Method 2
A first (active) electric component is connected between the first node and the third node, and provides there a controllable first conductance (or resistance). A second (active) electric component is connected between the second node and the fourth node and provides there a controllable second conductance (or resistance). The control network is configured to modulate the first conductance and the second conductance in such a way that a variation of a voltage drop between the third and first nodes is opposite to a variation of a voltage drop between the second and fourth nodes
Data Source
AI summary
A seat heater (10) with a heating element (12) connected between a first (14) and a second (16) nodes comprises a third (18) and a fourth (20) node operatively connectable to a first and a second terminal, respectively, of a power supply. A first electric component (22) providing a controllable first conductance is connected between the first and the third nodes. A second electric component (24) providing a controllable second conductance is connected between the second and the fourth nodes. A control network (26) is connected to the electric components to control the respective conductances and has a mode of operation in which it applies an oscillating signal to the heating element by modulating the first and second conductances in such a way that a voltage drop variation between the third and first nodes is opposite to a voltage drop variation between the second and fourth nodes.