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Measurement Uncertainty Analysis for the Thermal Conductivity Test Method Using a Heat Flow Meter Apparatus



In ASTM Standard Test Method C518-10, the Steady-State Thermal Conductivity Measurement by Means of a Heat Flow Meter (HFM) Apparatus, the analysis of measurement uncertainty (entittled “Equipment Error Analysis†in ASTM C518-10 Annex A2) is essentially the same as the one for ASTM C177-10, Standard Test Method for Steady-state Heat Flux Measurements and Thermal Conductivity by Means of the Guarded-Hot-Plate (GHP) apparatus. However, C518-10 is a secondary method that substantially relies on the equipment’s calibration with calibration transfer specimens (CTS) issued by national standards laboratories or other standard samples. For a large number of HFM apparatuses, the calibrations of individual measurement components such as voltage and temperature are difficult because of the HFM design. Hence, the uncertainty analysis procedure may not be easily performed by a large number of users. This paper proposes an alternative analysis method to the measurement uncertainty associated with C518-10 that depends on calibration using calibration transfer specimens. The uncertainty analysis starts with the identification of the uncertainty components and error classification associated with the calibration standards, the calibration transfer process to the specific apparatus and the measurement of the stability of the HFM. These uncertainty components are then used to calculate the total measurement uncertainty by means of the “root-sum-ofsquares†(RSS) method. To report the total uncertainty for the final measurement result, an expanded uncertainty using a chosen coverage factor that is based upon the level of confidence is required. This paper will demonstrate the proposed uncertainty analysis procedure.

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