Advanced Assessment of Environmental Factors Affecting Calibration Traceability and Measurement Reliability

Abstract

The accuracy, traceability, and reliability of calibration measurements is highly dependent on the environment in today's metrology laboratories. Ambient temperature, relative humidity, atmospheric pressure, vibration and airflow have significant impact on measurement uncertainty and on the long-term stability of calibrated instruments (JCGM 100:2008; Bell 2001). In this study, these environmental factors are evaluated using an advanced experimental and analytical methodology. Experiments were performed in controlled lab facilities with high accuracy balances, volumetric measuring glassware, and digital measurement system in the temperature range of 18 °C to 32 °C, relative humidity from 35% to 75% and under observed atmospheric pressure. The tests were repeated 10 times for each test condition (n=10), and 10 times for each instrument type for a total of 30 measurements per environmental condition (3 instruments × 10 repeats). Using the Guide to the Expression of Uncertainty in Measurement (JCGM 100:2008) relationships between environmental fluctuations and calibration deviations were quantified through statistical analysis and uncertainty modelling. The calibration uncertainty was largest for the volumetric measurement, 42%, and had a good linear dependence (R2 = 0.93) with temperature variation. For electronic instrumentation and mass measurements, the impacts of humidity were more pronounced, with the effect showing a non-linear relationship above 60% RH, which is consistent with Ahmed et al. (2019) and Wang et al. (2017). The overall calibration uncertainty was reduced by 18.7% (paired t-test, p < 0.01) using the novel environmental compensation algorithm based on empirical transfer functions generated in real-time using polynomial correction factors. These results
highlight the need for regular monitoring of the environment alongside compensation to guarantee a traceable calibration, in line with the ISO/IEC 17025:2017 (ISO/IEC 2017).