Design of a double-gradient scanner apparatus to assess the uncertainty component associated with inhomogeneity in flexible wire thermocouples

Abstract

Current thermocouple calibration standards identify primary sources of uncertainty, but often lack systematic methodologies for their evaluation. As a result, practitioners frequently rely on generic normative references, which can compromise metrological quality and increase measurement uncertainty. This study develops and validates an experimental setup for assessing calibration uncertainty components related to the thermoelectric inhomogeneity of flexible thermocouple wires. The system features adjustable temperature gradients and a precision movement mechanism, comprising inclined metallic clamps mounted on linear rails, driven by stepper motors, and controlled via an Arduino board. A uniform wire displacement is ensured by an aluminum insert within a metrology well-characterized by known axial thermal homogeneity. The inhomogeneity scanner was validated using tests that simulate artificially aged segments ranging from 15 mm to 400 mm in type T flexible wires, with gauges from 24 AWG to 30 AWG. The results confirmed the system’s ability to detect and quantify thermoelectric inhomogeneity, even under varying artificial aging conditions. Furthermore, the experimentally determined uncertainty values were compared with estimates from the EURAMET Calibration Guide No. 8, demonstrating the robustness and reliability of the proposed approach. This solution provides a cost-effective and easily implementable alternative for calibrating new and used thermocouple wires, ensuring compliance with normative requirements while enhancing metrological quality in temperature measurements.