Particulate Sensor Wiring Integrity Diagnostic via Parasitic Capacitance
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Solution Overview
Problem
Existing particulate sensor systems face difficulties in distinguishing between a 'clean' state and a faulty state, particularly when an electrical open circuit in the wiring leads is present, as both scenarios exhibit high resistance, leading to potential misdiagnosis of wiring faults.
Innovation Solution
A particulate sensor system with a diagnostic feature that includes a heater electrode isolated from sensing electrodes, a heater driver to generate a stimulus signal, and a detector to verify the integrity of connections through parasitic capacitance, allowing for differentiation between a clean and faulty state by detecting the presence of the stimulus signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a particulate sensor uses resistance measurement to detect soot accumulation, then the sensor can detect particulate concentration, but it cannot distinguish between a clean state and a wiring fault state
Solution Approach 1:
The patent introduces a heater electrode as an intermediary element that is electrically isolated from the sensing electrodes but coupled through parasitic capacitance. The heater electrode serves as a mediator to generate a stimulus signal that can be detected through the capacitance coupling, enabling diagnostic functionality without interfering with the primary sensing function. This intermediary element allows the system to differentiate between clean state and wiring faults by detecting the presence or absence of the stimulus signal.
Solution Approach 2:
The patent utilizes parasitic capacitance as a new measurement parameter to complement the existing resistance measurement. By measuring the coupling through parasitic capacitance between the heater electrode and sensing electrodes, the system gains an additional diagnostic dimension. This parameter change enables the system to distinguish between high resistance states caused by soot accumulation versus those caused by wiring faults, resolving the diagnostic ambiguity.
2Reliability
If the heater electrode is electrically isolated from sensing electrodes, then wiring faults can be detected, but the device complexity increases
Solution Approach 1:
The heater electrode serves multiple functions: it acts as a heating element for soot burn-off, a stimulus signal generator for diagnostic purposes, and a capacitance coupling element for fault detection. By making the heater electrode multi-functional, the patent avoids adding separate dedicated components for each function, thereby limiting the increase in device complexity while achieving reliable wiring fault detection.
Solution Approach 2:
The parasitic capacitance between the heater electrode and sensing electrodes, which is inherently present due to their spatial arrangement, is utilized as a diagnostic tool. The system uses its own structural characteristics (the parasitic capacitance) to enable fault detection, rather than requiring additional external diagnostic components. This self-service approach minimizes added 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 system effectively verifies the integrity of wiring connections, preventing false diagnostics and ensuring accurate differentiation between a clean sensor and one with wiring faults, thereby enhancing reliability in particulate concentration measurements.
Implementation Method 1
The heater electrode is configured such that when energized according to predefined criteria, the substrate is heated to remove any deposited particulates
Implementation Method 2
The sensor has a parasitic capacitance between the heater electrode and the sensing electrodes. The stimulus signal is therefore coupled through the parasitic capacitance from the heater electrode to the sensing electrodes.
Implementation Method 3
The operating principle of the particulate sensor is based on the conductivity of the particulates (e.g., soot) deposited on (or over) the sensing electrodes. The electrical resistance between the sensing electrodes is relatively high when the sensor is clean but such resistance decreases as soot particulates accumulate.
Implementation Method 4
a heater that is selectively activated to burn off the soot particulates to 'reset' the sensor to a known, base 'clean' state
Data Source
AI summary
A particulate (soot) sensor system has a diagnostic feature for verifying the integrity of the wiring leads. The sensor system includes a sensor and processing circuitry. The sensor has a substrate, first and second sensing electrodes on the substrate and a heater electrode. The heater electrode is electrically isolated from the first and second sensing electrodes, although there is a parasitic capacitance between them. The processing circuitry includes a heater driver, a measurement circuit connected to the sensing electrodes by wire leads, and a detector. The heater driver, in addition to energizing the heater, produces a stimulus signal that is applied to the heating electrode, which is then coupled via the parasitic capacitance to the sensing electrodes. The detector is coupled to the wiring leads and is configured to detect the stimulus signal when there is electrical conductivity over the leads to the sensing electrodes.