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.
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.
5.1 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 measurement area during a full 360° rotation.
Take a statistically representative sample of the population of test pieces to be characterized.
Samples shall be free of obvious visible defects which may affect the measurement.
7.1 Preparation of test pieces
Condition the test pieces, prior to measurement, in a conditioning enclosure in accordance with ISO 3402.
Select at random, from the sample taken in accordance with Clause 6, the number of test pieces required for the test.
The time required for the curing of filter rods and the duration of conditioning for both filter rodsand cigarettes are not specified in this International Standard and are to be determined by practicalexperience.They shall be reported in the test report together with the results.
7.2Adjustment and calibration
Working standards are routinely used to adjust calibrate or check the calibration of the measurementsystem. Calibration shall be performed in accordance with the manufacturer’s instructions.
NOTE The essential properties of calibration standards are given in Annex A.
ln accordance with the manufacturer’s instructions, position the test piece within the measurementarea, as close as possible to the centre of the measurement area.
The test piece, or the measuring apparatus, shall be capable of being rotated around the rotation axissuch that any eccentric motion of the test piece, relative to the plane of the measurement, remains inparallel with the plane of the measurement and perpendicular to the longitudinal axis of the test piece.Adjust the instrument and/or feeding and rotational apparatus for the plane of the measurement tomeasure the required section of the test piece.
Operate the apparatus in accordance with the manufacturer’s instructions and accurately record themean, minimum and maximum diameters.
At least 10 test pieces from one sample shall be used to determine the mean value of the diameterfor the sample.
NOTE1 ln practice, laboratories often take a different number of measurements depending on the applicationof the measurement.
NOTE2 Possible sources of error in measurement of diameter are given in Annex C.
8Expression of results
The value of the sample mean diameter shall be the mean value of the individual measurements.See7.3.The results shall be expressed as follows:
a) diameter, the arithmetic average of at least 64 individual scans per full revolution or 32 scans per half revolution, is expressed in millimetres to the nearest 0,01 mm;
b) sample mean diameter, the average of x diameter measurements (x is normally 10 but may vary; see note 1 in 7.3) is expressed in millimetres to the nearest 0,001 mm ;
c)sample maximum diameter, the maximum diameter obtained from a sample of x test pieces,is expressed in millimetres to the nearest 0,01 mm ;