BS ISO 2971:2013 pdf download – Cigarettes and filter rods — Determination of nominal diameter — Method using a non-contact optical measuring apparatus Note 1 to entry:Caution should be exercised in interpreting maximum diameters, absolute ovality, relative ovalityand relative roundness as these can be affected by the quality of the gum line (raised laps) or other productdefects, generating erroneous individual readings. 4Principle The principle of measurement of the mean diameter of a shape having a convex cross section follows thegeneralization of ‘Barbier’s Theorem’, which states that the mean diameter of a section is equal to thearithmetic mean of the apparent (or projected) diameters of the section as it is rotated at equiangularintervals in the field of view.It is required that the section is rotated by an integer multiple of 180°. NOTE The principle is demonstrated in Annex B.1. 5 Apparatus 5.1 Sample conditioning enclosure, to be capable of maintaining the conditions given in ISO 3402. 5.2optical measuring apparatus, to consist of the following. 5.2.1optical measuring instrument This must have an uncertainty of no more than 0,01 mm and be suitable for the determination of thediameter of rod-like test pieces with a nearly circular cross section. A schematic diagram of such aninstrument is presented in Figure 1 and three different implementations are described in Annex D. The scanning rate of the instrument shall be such that no eccentric motion of the test piece parallel tothe longitudinal axis,within the measurement area, shall affect the accuracy of the measurement ofmean diameter. The ratio between the scanning rate of the apparatus and the rotational speed of the test piece shall beconstant and high enough to ensure that the measured diameter, as well as the minimum and maximumvalues, shall be determined with sufficient accuracy, despite the possible ovality of the test piece. The length of the scan path shall be sufficiently greater than the maximum diameter to be measured toavoid errors due to test piece eccentricity.The test piece shall be scanned a minimum of 32 times duringa half-rotation (180°) or 64 times during a full (360°) rotation. NOTE The rationale for the required number of scans is presented in Annex B.2. 5.2.2 Apparatus or fixture for rotating the test piece or scan path This shall rotate the test piece within the measurement area or rotate the direction of view around the test piece while maintaining the longitudinal axis of the test piece perpendicular to the...
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