Abstract
Capacity measures are commonly used volume standards for testing measuring systems for liquids other than water. Manual readings from the measuring scale can often be difficult due to the location of the capacity measure or to the nature of the measured liquid. This article focuses on the automation of this procedure by using a single camera machine vision system. A camera positioned perpendicular to the transparent neck captures the image of the liquid meniscus and the measuring scale. The volume reading is determined with the user-defined software in the LabVIEW programming environment, which carries out the image preprocessing, detection of the scale marks and the liquid level, correction of lens distortion and parallax effects and final unit conversions. The realized measuring system for liquid level detection in standard capacity measures is tested and validated by comparing the automated measurement results with those taken by the operators. The results confirm the appropriateness of the presented measuring system for the field of legal metrology.
Highlights
IntroductionLiquid Level Detection in Capacity measures are commonly used volume standards for the testing and inspection of measuring systems for liquids other than water
The aim of this article is to present a simple, configurable and low-cost machine vision system capable of reading the liquid level with respect to the attached measuring scale, which is applicable for the purposes of legal metrology
We describe the lens distortion as one-dimensional, because the lens correction parameters can be calculated using the positions of the scale marks detected along the given vertical line
Summary
Liquid Level Detection in Capacity measures are commonly used volume standards for the testing and inspection of measuring systems for liquids other than water. Despite the fact that the last two types are made of steel, their neck part is made of a glass tube, or has glass plates or separate and fixed gauge glasses [1]. They are all equipped with scale marks corresponding to their nominal capacity and to at least 1%. The operator needs to be certain that the reading uncertainty is small enough in view of the requirement for the combined expanded uncertainty
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