Capacitive Sensor Diagnostics via Sense-Guard Impedance Switching
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Solution Overview
Problem
Capacitive sensing systems, particularly in automotive applications, face challenges in diagnosing sensor interruptions and ensuring reliable operation with low hardware effort and moderate costs, especially in multichannel systems.
Innovation Solution
A capacitance measurement circuit with an alternating signal voltage source, current measurement circuit, and remotely controllable switching unit is used to diagnose capacitive sensors by measuring the complex sense-to-guard impedance and AC ground connection, allowing for reliable detection of sensor interruptions and minimizing measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive sensor system uses guard electrodes to shape sensitivity regime, then measurement precision is improved, but device complexity increases due to additional electrodes and wiring
Solution Approach 1:
The sense electrode serves dual functions: it acts as the primary sensing element for detecting objects and simultaneously functions as a guard electrode when connected to the guard electrode potential. This multi-functionality eliminates the need for separate guard electrodes, reducing device complexity while maintaining the ability to shape the sensitivity regime through potential control.
2Reliability
If diagnostic functions are added to detect sensor interruptions, then reliability is improved, but device complexity increases due to additional measurement circuits
Solution Approach 1:
The existing current measurement circuit is designed to handle multiple functions: it measures both the sense current during normal operation and the diagnostic current for detecting sensor interruptions. By utilizing the same circuit for both measurement and diagnosis, the patent avoids adding separate diagnostic hardware, thereby improving reliability without increasing device complexity.
Solution Approach 2:
The system performs diagnostic measurements periodically by switching between sense current measurement and diagnostic current measurement modes. The control unit activates the diagnostic function at specific intervals, allowing the same measurement circuit to serve dual purposes without continuous operation, thus maintaining reliability while managing circuit complexity.
3Ease of operation
If remote control switching is implemented for diagnostic functions, then ease of operation is improved, but device complexity increases due to switching unit
Solution Approach 1:
The remotely controllable switching unit serves multiple purposes: it switches the sense electrode between the sense current measurement circuit and the diagnostic current measurement circuit, and also controls the connection of the guard electrode to different potentials. This multi-functionality allows a single switching unit to manage both measurement and diagnostic operations, improving ease of operation while minimizing the increase in device complexity.
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 enables reliable operation and high operational availability of capacitive sensing systems by effectively diagnosing sensor interruptions and maintaining accurate measurements, even in multichannel configurations, with reduced hardware requirements and costs.
Implementation Method 1
providing an alternating measurement voltage with respect to a reference potential at an output port
Implementation Method 2
The capacitive sensor comprises a sense electrode and a guard electrode that are arranged close to each other... determining a complex sense current through the sense electrode with reference to an alternating voltage that is applied to the guard electrode
Implementation Method 3
a current measurement circuit that is configured to determine, with reference to the alternating measurement voltage, a complex sense current through the sense electrode
Data Source
AI summary
A capacitance measurement circuit for determining a complex electric current of at least one capacitive sense-guard sensor. The circuit includes an alternating signal voltage source, wherein each guard electrode is electrically connectable to the signal voltage source, a current measurement circuit having at least one measurement channel to determine a measurement current through a sense electrode, and at least one diagnostics channel to determine, with reference to an AC ground potential, a diagnostic current flowing through a guard electrode and a sense electrode of a capacitive sensor, and a remotely controllable switching unit, which in a measurement switching state is configured to electrically connect the sense electrode of the capacitive sensor to the measurement channel, and in a diagnostic switching state is configured to electrically connect the sense electrode to the diagnostics channel.