Flexible Printed Circuit Temperature Sensor for Heated Aircraft Windows
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Solution Overview
Problem
Existing sensors for heated windows, especially in aircraft, are prone to premature failure due to extreme temperature changes and stress, leading to unreliable temperature regulation and issues like ice and fog formation.
Innovation Solution
A temperature sensing element comprising a coil of filament with changing resistivity, electrically coupled to flat conductive materials and lead wires, which is designed to withstand extreme conditions and reduce stress on connections, allowing for reliable temperature measurement in heated window assemblies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sensors are used in heated windows, then temperature sensing function is provided, but the sensors are prone to premature failure due to stress and extreme temperature changes
Solution Approach 1:
The patent uses a flexible printed circuit board (FPC) as the substrate for mounting the temperature sensor. The FPC can bend and flex to accommodate thermal expansion and contraction of the window glass, reducing mechanical stress on the sensor and its connections. This flexible substrate allows the sensor assembly to conform to the curved or irregular shapes of aircraft windows while maintaining reliable electrical connections throughout temperature cycles.
Solution Approach 2:
The patent employs a temperature sensor with a resistance temperature detector (RTD) element whose electrical resistance changes predictably with temperature. By monitoring the resistance parameter of the RTD element, the system can accurately determine the window temperature without requiring the sensor itself to withstand extreme temperature differentials, as the FPC provides thermal isolation and stress relief.
2Measurement precision
If sensors are mounted directly to window glass, then temperature measurement is achieved, but solder joints are subject to considerable stress and tend to loosen
Solution Approach 1:
The patent introduces a flexible printed circuit board as an intermediary between the temperature sensor and the window glass. The FPC provides a compliant mounting surface that absorbs mechanical stress, preventing direct transmission of stress to the solder joints. The sensor is mounted on the FPC using conventional techniques, while the FPC itself is attached to the window in a manner that allows for thermal movement, thereby protecting the delicate solder connections from loosening.
Solution Approach 2:
The FPC is designed with inherent flexibility and compliance to cushion against thermal expansion and contraction forces before they can reach the solder joints. The flexible substrate acts as a stress-absorbing element that protects the rigid solder connections from mechanical fatigue, thereby preventing premature failure of the electrical connections during temperature cycling.
3Reliability
If rigid sensor mounting is used, then stable temperature sensing is achieved, but the sensor cannot withstand extreme temperature changes and stress
Solution Approach 1:
The flexible printed circuit board substrate enables the sensor assembly to flex and conform to thermal expansion and contraction of the window glass without compromising the integrity of the sensor or its connections. This flexibility allows the system to withstand extreme temperature changes from -55°C to +125°C while maintaining reliable temperature measurement capability.
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 sensing element effectively measures temperature in heated windows, reducing the risk of failure and ensuring proper regulation, even under extreme conditions, by distributing stress and maintaining accuracy across varying temperatures and pressures.
Implementation Method 1
a coil of filament having a first end and a second end, the coil having a resistivity that changes based on temperature
Data Source
AI summary
A sensing element for sensing a temperature of an electrically heated window includes a coil of filament wire having a first end and a second end, the coil having a resistivity that changes based on temperature, a first substantially flat conductive material electrically coupled to the first end of the coil, a second substantially flat conductive material electrically coupled to the second end of the coil, a first lead wire electrically coupled to the first substantially flat conductive material and extending outwardly, and a second lead wire electrically coupled to the second substantially flat conductive material and extending outwardly.