Flexible Strain Gauge Substrate Expansion Control
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Solution Overview
Problem
Strain gauges with flexible substrates experience warping, which can lead to deteriorated gauge characteristics and failure due to cracks in the resistor, when compared to those with ceramic substrates of high mechanical strength.
Innovation Solution
A strain gauge design featuring a flexible substrate with an expansion coefficient between 7 ppm/K and 20 ppm/K, combined with a Cr composite film resistor and a functional layer to manage internal stress and prevent warping, is implemented. The substrate is made of insulating resin films like polyimide, and the resistor is formed using chromium or nickel materials with a stable crystalline phase, along with a cover layer for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a flexible substrate is used to make the strain gauge adaptable and easy to attach, then adaptability is improved, but warping occurs due to internal stress which deteriorates gauge characteristics
Solution Approach 1:
The patent controls the expansion coefficient of the flexible substrate within a specific range (7-20 ppm/K) to balance flexibility and warping reduction. By optimizing this physical parameter, the substrate maintains adaptability while minimizing internal stress-induced warping that would deteriorate gauge characteristics
Solution Approach 2:
The strain gauge employs a composite structure consisting of the flexible substrate, resistor layer, and protective cover layer. This multi-layer composite design allows each layer to contribute specific properties: the substrate provides flexibility and adaptability, while the cover layer compensates for warping and protects the resistor, thereby maintaining gauge characteristics
2Ease of operation
If a flexible substrate with low mechanical strength is used, then ease of attachment is improved, but cracks appear in the resistor due to warping which reduces reliability
Solution Approach 1:
The protective cover layer is applied in advance to cushion and protect the resistor from cracks caused by warping. This preventive measure ensures that even when the flexible substrate deforms during attachment, the resistor remains intact and the strain gauge maintains reliability
Solution Approach 2:
By controlling the expansion coefficient of the substrate within 7-20 ppm/K, the patent minimizes differential thermal expansion and internal stress, thereby reducing warping-induced cracks in the resistor while preserving the ease of attachment provided by the flexible substrate
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 solution effectively reduces warping in the strain gauge, maintaining stable gauge characteristics and ensuring the strain gauge functions correctly by managing internal stress and preventing mechanical and moisture damage.
Implementation Method 1
The strain gauge includes a resistor for detecting strain
Implementation Method 2
a substrate which is flexible and has an expansion coefficient in a range from 7 ppm/K to 20 ppm/K
Data Source
Figure 1~2
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AI summary
A strain gauge includes a flexible substrate, and a resistor formed of material including at least one from among chromium and nickel, on or above the substrate. The substrate has an expansion coefficient in a range of from 7 ppm/K to 20 ppm/K.