Pt-Al Temperature Sensor Junction Thermal Stress
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Solution Overview
Problem
Conventional temperature sensors with Pt electrode wires and SUS310S signal wires are prone to breakage due to significant thermal expansion coefficient differences, leading to increased thermal stress during hot and cold cycles, especially when exposed to a wide temperature range from -40°C to 1000°C.
Innovation Solution
The use of Pt electrode wires and Al-containing signal wires with a higher thermal expansion coefficient, where the junction parts are formed by melting and coagulating the wires and coated with Al oxide films to reduce oxidation and thermal stress, enhancing the resistance to breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pt electrode wires and SUS310S signal wires are used, then electrical conductivity and basic mechanical strength are ensured, but thermal stress increases due to large thermal expansion coefficient difference
Solution Approach 1:
The patent changes the material parameter of the signal wire from SUS310S to an Al-containing alloy with higher thermal expansion coefficient, which better matches the Pt electrode wire's thermal expansion characteristics, thereby reducing thermal stress in the junction part during temperature cycles
Solution Approach 2:
The patent creates a composite structure at the junction part by melting and coagulating the Pt electrode wire and Al-containing signal wire together, forming a metallurgical bond that reduces thermal stress concentration and prevents wire breakage
2Stress or pressure
If intermediate layer is added between electrode wire and signal wire, then thermal expansion mismatch is reduced, but oxidation resistance deteriorates
Solution Approach 1:
The patent removes the intermediate layer completely and directly joins the Pt electrode wire with the Al-containing signal wire through melting and coagulation, eliminating the oxidation problem while maintaining thermal stress reduction through material selection
Solution Approach 2:
The patent utilizes the oxidation resistance of the Al-containing signal wire itself to protect the junction part, converting the potential harm of Al oxidation into a benefit where the Al-containing alloy provides both thermal expansion matching and oxidation resistance
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 configuration significantly reduces the likelihood of electrode wire breakage by minimizing thermal stress and oxidation, allowing the temperature sensor to withstand repeated hot and cold cycles without significant degradation.
Implementation Method 1
the intermediate member and its vicinity are laser-welded to form an intermediate layer
Implementation Method 2
each of an overlap portion of the first electrode wire and the first signal wire and an overlap portion of the second electrode wire and the second signal wire includes a junction part formed by melting and thereafter coagulating the first or second electrode wire and the first or second signal wire
Implementation Method 3
the junction part includes a first oxidation film containing Al formed on a surface thereof
Implementation Method 4
the difference between the thermal expansion coefficient of the electrode wire and the thermal expansion coefficient of the signal wire is large. Accordingly, the thermal stress in a junction part between the electrode wire and the signal wire increases with the increase of the temperature difference between the hot state and cold state in use
Data Source
AI summary
The temperature sensor includes a thermo-sensitive element, first and second electrode wires electrically connected to the thermo-sensitive element, first and second signal wires partially overlapped with and connected to the first and second electrode wires, respectively. The first and second electrode wires are made of a first metal material consisting primarily of Pt. The first and second signal wires are made of a second metal material containing Al and having a linear thermal expansion coefficient larger than that of the first metal material. Each of an overlap portion of the first electrode wire and the first signal wire and an overlap portion of the second electrode wire and the second signal wire includes a junction part formed by melting and thereafter coagulating the first or second electrode wire and the first or second signal wire. The junction part includes an oxidation film containing Al formed on a surface thereof.