A Compact Non-Intrusive Measurement System for Critical Dimensions and Calibration Chart Generation of Underground Fuel Tanks

This paper presents a compact, non-intrusive measurement system designed for determining the critical dimensions and generating calibration charts of underground fuel tanks via a 2-inch access port. The system employs a laser electronic distance measurement (EDM) device located outside the Zone 0 hazardous environment, with the beam directed into the tank through a mirror-based tilt mechanism. A key contribution is the ability to generate accurate calibration charts. Mirror tilt actuation is controlled via a linear actuator, where the non-linear relation between displacement and angular rotation can be resolved either through a lookup table or analytically as the mechanical linkage properties are known. The methodology involves coarse scanning for tank geometry estimation followed by targeted high-resolution scans at critical angles to derive diameter, length, dome geometry, and inclination. Real-world results demonstrate volumetric accuracy better than 0.2%, with an expected performance of 0.3% [1] in calibration chart generation, confirming that the system meets industrial standards for underground storage tank metrology, including OIML R 71.