Capacitive Seat Sensor Compensation for Heater Interference
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Solution Overview
Problem
Capacitive sensors in automotive applications, such as seat occupancy detection and Hands Off Detection, are susceptible to malfunctions due to changes in the connection status of heater members, leading to detection and classification issues.
Innovation Solution
A capacitive detection device with a complex impedance measurement circuit and a control and evaluation unit, featuring a sense electrode and an auxiliary electrode, which allows for selective electrical connection to a reference voltage or a guard signal, enabling combined loading mode and coupling mode measurements that are less affected by heater member connection status changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitive sensor is used for seat occupancy detection in proximity to a heater member, then the sensor can detect occupancy and provide input for ADAS, but the detection reliability deteriorates due to changes in heater member connection status
Solution Approach 1:
A guard electrode is introduced as an intermediary element between the sense electrode and the heater member. The guard electrode is connected to a guard signal that is substantially free of the oscillating measurement signal, thereby shielding the sense electrode from direct capacitive coupling with the heater member. This intermediary structure prevents changes in heater member connection status from directly affecting the measurement signal, thus maintaining detection reliability.
Solution Approach 2:
The capacitive sensor is segmented into distinct functional components: a sense electrode for detection, a guard electrode for shielding, and separate connection paths. The guard electrode creates a separate capacitive path that isolates the measurement path from the heater member, allowing the system to maintain reliable detection even when heater member connection status changes.
2Device complexity
If the sense electrode is placed close to the heater member for compact design, then device complexity is reduced, but measurement precision deteriorates due to capacitive coupling with the heater member
Solution Approach 1:
The guard electrode serves as a protective intermediary that enables the sense electrode to be positioned close to the heater member without direct capacitive interference. By providing a shielded path, the guard electrode allows compact sensor design while maintaining measurement precision, as the guard signal prevents the heater member's electrical state from coupling into the measurement signal.
3Measurement precision
If a guard electrode is added to shield the sense electrode from the heater member, then measurement precision improves by reducing capacitive coupling, but device complexity increases
Solution Approach 1:
The guard electrode is implemented as a relatively simple conductive element that can be integrated into existing sensor designs. While it does increase structural elements, the guard electrode provides significant measurement precision improvement by eliminating capacitive coupling errors, and can be connected to existing guard signal sources in the system.
Solution Approach 2:
The guard electrode structure serves multiple functions: it shields the sense electrode from heater member interference, defines the sensing zone, and can be integrated with existing vehicle seat structures. This multi-functionality justifies the additional structural element by providing comprehensive benefits beyond simple shielding.
4Ease of operation
If the capacitive sensor operates in loading mode with direct connection to heater member, then ease of operation is maintained, but reliability deteriorates due to susceptibility to heater connection changes
Solution Approach 1:
The guard electrode creates an intermediary shielding layer that allows the sensor to maintain its simple loading mode operation while protecting against heater member interference. The guard signal is provided through existing system infrastructure, so the operational simplicity is preserved while reliability is enhanced through the automatic shielding effect.
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 solution provides robust and reliable seat occupancy detection and Hands Off Detection, unaffected by heater member connection status changes, ensuring stable classification and reduced impact from other metal part variations during vehicle operation.
Implementation Method 1
A signal voltage source (20) is configured for providing an alternating measurement voltage with reference to a reference voltage (24), namely an AC ground potential, at an output port (22)
Implementation Method 2
A complex impedance measurement circuit (26) is electrically connected to the output port (22), to the sense electrode (16) and to the auxiliary electrode (18) for measuring complex sense currents generated in the sense electrode (16)
Implementation Method 3
A control and evaluation unit (32) is connected to the complex impedance measurement circuit (26) for receiving data signals, wherein the control and evaluation unit (32) is at least configured to control the complex impedance measurement circuit (26) to carry out a complex impedance measurement
Data Source
AI summary
A capacitive detection device includes a capacitive sensor having a sense electrode and an auxiliary electrode that are arrangeable in the vicinity of an electric heater member for mutual capacitive coupling. The capacitive detection device has a signal voltage source providing an alternating measurement voltage, a complex impedance measurement circuit for measuring complex sense currents and for determining a complex impedance based on the measured complex sense current, and for electrically connecting the auxiliary electrode either with the reference voltage or with the guard signal. The method includes providing the measurement signal to the sense electrode and electrically connect the auxiliary electrode selectively either to the reference voltage or to the guard voltage; determining capacitance values in the two different connection states of the auxiliary electrode; and calculating a compensated capacitance value as a weighted sum of the two determined capacitance values, wherein the weighting factors are predefined constant values.