Capacitive Sensor Stray Current Subtraction via Twisted Wire Harness

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Solution Overview

Problem

Capacitive liquid level sensors in harsh environments, such as aircraft APU gearboxes, face challenges in accurately detecting sensor capacitance due to stray capacitance from wiring harnesses, which induces stray currents and corrupts signal data, and the use of diodes in such environments is unreliable.

Innovation Solution

A wire harness with twisted wires, including an additional wire that carries only stray current, allows for equal coupling and measurement of stray currents, enabling their subtraction from sensor data wires to isolate pure sensor data without the need for diodes in the sensor electronics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the sensor is located several feet away from sensor electronics to accommodate harsh engine environment, then the sensor can be positioned in the required location, but stray capacitance from the wiring harness induces stray currents that corrupt the sensor signal

Engineering Contradiction:

Improveengine environment toleranceVSAvoidsensor capacitance detection accuracy

Core Design Contradiction:

TemperatureVSMeasurement precision

Solution Approach 1:

An additional wire is introduced as an intermediary element that carries only stray current. This wire acts as a mediator to separate the stray current component from the sensor signal, allowing the two to be independently measured and processed. The additional wire does not carry sensor data but provides a dedicated path for stray current measurement.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The signal measurement is segmented into two separate measurements: one for the combined sensor signal and stray current (through the sensor data wire), and another for stray current alone (through the additional wire). This segmentation allows the stray current component to be isolated and subtracted from the total signal, leaving only the pure sensor data.

Inventive Principle:

Principle #1Segmentation

2Difficulty of detecting and measuring

If diodes are installed in the sensor to measure stray current, then stray current measurement is possible, but reliability issues arise due to the harsh environment affecting diodes and solder joints

Engineering Contradiction:

Improvestray current measurement capabilityVSAvoidsensor reliability in harsh environment

Core Design Contradiction:

Difficulty of detecting and measuringVSReliability

Solution Approach 1:

The stray current measurement function is extracted from the sensor assembly itself and relocated to the sensor electronics location. Instead of embedding diodes in the harsh environment where they fail, the measurement capability is taken out and placed in the controlled environment of the sensor electronics, where reliable processing can occur.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The additional wire used for stray current measurement is a simple, passive, and highly reliable element compared to active components like diodes. It has no moving parts, no semiconductor junctions, and is inherently more reliable in harsh environments, effectively replacing the unreliable diode-based solution.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of operation

If a wire harness with multiple wires is used to connect sensor and electronics, then signal transmission is enabled, but stray capacitance in the wiring harness creates harmful stray currents

Engineering Contradiction:

Improvesignal transmission capabilityVSAvoidstray current from wiring harness

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The stray capacitance that was previously a harmful source of noise is converted into a useful measurement opportunity. By adding the additional wire that carries only stray current, the harmful stray current becomes a measurable signal that can be quantified and subtracted, transforming the problem into a solution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach ensures accurate determination of sensor data while reducing the risk of system failure by effectively minimizing stray currents and eliminating the reliability issues associated with diodes in harsh environments.

Implementation Method 1

the sensor data wires, which carry both sensor data and stray current, and the additional wire are twisted together in the wire harness to ensure similar coupling of stray currents in each of the wires

Methodology Applied

Scientific EffectElectromagnetic coupling: Electromagnetic Induction

Data Source

PatentUS8365574B2Systems and methods for minimizing stray current in capacitive sensor data

Publication Date: 2013.02.05 HAMILTON SUNDSTRAND CORP

AI summary

A method for minimizing stray current in capacitive sensor data includes receiving a first input from a first wire of a wire harness, the wire harness comprising a plurality of twisted wires, the first input comprising a first signal comprising first sensor data and stray current; receiving a second input from a second wire of the wire harness, the second input comprising a second signal comprising stray current; and subtracting the second signal from the first signal to determine the first sensor data. A system for minimizing stray current in capacitive sensor data is also provided.