Uncertainty analysis of encoder-based method for the calibration design of on-board vehicle speed meters

Vehicle speed meters have an important role in various application fields such as monitoring and controlling speed limit for safety purposes, evaluating driver and vehicle performance, managing the traffic in real-time, etc. Compliance with ISO/IEC 17,025 and the ILAC (International Laboratory Accreditation Cooperation) policy on measurement traceability is required in calibration procedures to guarantee the quality of traceability of the results obtained by speed meters. The scientific literature, as well as the activity of some calibration centers, reports a variety of methodologies for calibration. Designing the most suitable calibration procedure for a specific category of instrument is not an easy task due to the high number of parameters affecting the calibration uncertainty. In this context, the paper proposes a design tool for encoder-based methods for the calibration of on-board vehicle speed meters. After the definition of all the measurement uncertainty contributions involving the calibration process, a sensitivity analysis was carried out to assess the applicability and limitations of the selected calibration method for speeds up to 300 km/h. Afterwards, a design tool is proposed to enable the optimal design of the calibration method aiming to find the best trade-off between technical requirements (calibration uncertainty, speed range) and economic aspects.