I conducted this research while working as an engineering trainee at Straintec (Pvt) Ltd., Sri Lanka, a subsidiary of Flintec Inc.—a global leader in load cell manufacturing. This project gave me valuable experience collaborating with industry professionals, adhering to industrial standards, and effectively aligning research with real-world industrial requirements.
This project aimed to develop a reliable method to measure the Temperature Coefficient of Resistance (TCR) of strain gage materials—an essential parameter influencing product quality in precision sensing devices. Conducted during an engineering traineeship at Straintec (Pvt) Ltd., a subsidiary of Flintec Inc. The method enables early-stage detection of material inconsistencies due to production processes, offering both technical and economic benefits to strain gage manufacturing by ensuring material consistency and process control.
In the manufacturing of strain gages, maintaining material quality is crucial. One essential parameter for ensuring accuracy and reliability in these devices is the Temperature Coefficient of Resistance (TCR). The TCR characterizes how resistance changes with temperature, and deviations in this parameter can impact precision in strain-sensitive applications such as aerospace, automotive engineering, and structural health monitoring [1].
However, traditional methods for measuring TCR are either inconsistent or fail to capture the microstructural variations that occur during production. This study presents a novel approach to accurately determine TCR, enabling better quality control and efficiency in strain gage production.
Flintec Inc.
July 2018 - December 2018
Research & Development
Trainee Engineer
Current strain gage production lacks a standardized, reliable method for evaluating TCR before and after the manufacturing process. Without such a system, microscopic variations in the foil material can go unnoticed, leading to potential errors in performance. Conventional measurement techniques often fail to provide a homogeneous testing environment, leading to inconsistent results. Furthermore, fluctuations in grain structure, work hardening, and thermal expansion significantly affect resistivity, making it imperative to measure TCR at multiple production stages [2]. The absence of a systematic database for TCR values further exacerbates the challenge, making it difficult to track material quality over time.
Traditional resistance measurements use ambient temperature conditions, where fluctuations in the environment introduce noise and inaccuracies. Contact resistance and material aging also affect readings, leading to inconsistent datasets. Recent studies suggest that employing oil baths or vacuum-sealed chambers can mitigate these issues by ensuring a uniform temperature distribution [3]. However, existing industrial setups rarely implement such solutions due to cost and complexity.
To address these challenges, this study developed an advanced TCR measurement system incorporating an oil bath for temperature control, high-precision digital multimeters, and a customized measurement apparatus. This system ensures:
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The core of the measurement system consists of an oil bath that provides a controlled temperature environment, a Resistance Temperature Detector (RTD) for temperature readings, and a foil sample submerged in the oil bath for analysis. The key equipment used includes:
This setup ensures a highly controlled experiment with minimized external influences. Studies have shown that immersion in an oil bath significantly improves temperature stability, reducing measurement uncertainty compared to air-based systems [4].
The resistance of test samples was recorded at multiple temperature points. The data was then analyzed using both first-order and second-order approximations of the resistance-temperature relationship. The collected data was processed in Microsoft Excel to calculate TCR and visualize trends. Multiple sets of readings were averaged to reduce noise and improve accuracy. Data management was also structured to allow traceability, with each sample indexed against batch numbers for long-term monitoring.
The study successfully determined the TCR of strain gage materials, revealing that:
Recent metallurgical studies confirm that grain refinement and impurity levels in nickel-based alloys can contribute to variations in TCR [5]. This reinforces the necessity of in-depth evaluation methods, as demonstrated in this study.
This new TCR measurement system has significant implications for strain gage manufacturing:
Several obstacles arose during the development of this system, including:
Advanced experimental techniques, such as four-probe resistance measurement, could further refine accuracy in future studies [6].
This study presents a robust approach to measuring TCR in strain gage materials, addressing long-standing issues in quality control. By providing an accurate, reproducible, and cost-effective solution, this methodology has the potential to set a new standard in the industry. The ability to track microstructural changes through resistance data could lead to breakthroughs in materials engineering and predictive maintenance strategies.
Moving forward, this methodology can be refined further by:
Images courtesy: macrovector & fatmawatilauda
