Strain Gauge Moisture Protection via Insulated Metal Shield
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Solution Overview
Problem
Conventional strain gauges face reliability issues due to moisture intrusion and emission, which cause substrate expansion and contraction, leading to variations in output and reduced reliability, as the substrate between the measurement grid and the cover is exposed, allowing moisture to penetrate.
Innovation Solution
A strain gauge design featuring a substrate with an insulating resistive body and a metallic metal sheet that covers the substrate between connection sites and the sensing portion, along with an insulating layer, to prevent moisture intrusion and ensure electrical insulation, while avoiding short-circuiting by not overlapping the connection site openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the substrate between the measurement grid and the cover is left exposed to allow wiring connection, then the ease of manufacture and wiring connection is improved, but moisture intrusion into the substrate occurs causing substrate expansion and contraction which deteriorates reliability
Solution Approach 1:
An insulating layer is introduced as an intermediary component between the exposed substrate and the metal sheet. This insulating layer has openings at connection sites that allow wiring to pass through while preventing moisture intrusion into the substrate. The insulating layer thus mediates between the need for wiring access and the need for moisture protection, resolving the contradiction by enabling both functions simultaneously.
2Reliability
If a metal sheet is added to cover the exposed substrate to prevent moisture intrusion, then reliability is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The metal sheet is designed to serve multiple functions simultaneously: it provides moisture protection for the exposed substrate, acts as an electrical shield, and serves as a mechanical support structure. By consolidating these multiple functions into a single component, the invention improves reliability without proportionally increasing device complexity, as the metal sheet replaces what would otherwise require multiple separate components.
3Reliability
If the metal sheet covers the entire substrate surface to maximize moisture protection, then reliability is improved, but short-circuiting between the metal sheet and resistive body may occur
Solution Approach 1:
The metal sheet coverage is segmented into distinct regions: areas that cover the exposed substrate for moisture protection and areas that leave the resistive body exposed for electrical functionality. The insulating layer further segments the coverage by providing openings at connection sites. This segmentation allows the metal sheet to provide maximum moisture protection while maintaining electrical isolation between the metal sheet and the resistive body, preventing short-circuits.
Data Source
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AI summary
Provided is a strain gauge 1 including a substrate 2, a resistive body 3, and a metal sheet 5. The resistive body 3 includes a sensing portion 30, a first connection portion 31, and a second connection portion 32. The metal sheet 5 covers at least the substrate 2 that is exposed between two connection sites 33 and 34, to which wirings L1 and L2 to an external circuit are respectively connected, provided respectively in the first connection portion 31 and the second connection portion 32, and the sensing portion 30.