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Table 30 Comparison of measured and target particle opening (#14 sieve), while COM-B measured 90% size of Type 3 samples for 10%, 50%, and 90% passing smaller than 1.84 mm. Sieve Target Particle Summary of D10, D50, and D90 Measurements by No. of Size Percent Diameter-Xcm Percent COM-B. Since an insufficient number of laboratories Labs (mm) Passing (mm) Smaller submitted D10, D50, and D90 data, a firm conclusion 1 0.85 5 0.91 10 regarding the accuracy of COM-B for measuring size 1 1.00 40 1.09 50 distribution of glass bead samples cannot be made. 1 1.18 95 1.43 90 However, analysis of the limited datasets in this study indicated that for all size classes of Type 1 samples and for four out of six size classes of Type 3 and The same trend is observed from the other sieve Type 5 samples, COM-B correctly predicted the D10, classes for the Type 1 samples. D50, and D90 values of the glass beads. Type 3 Samples. The D10, D50, and D90 values of COMPARISON OF PRECISION ESTIMATES the Type 3 samples were received from one COM-B OF VARIOUS MEASUREMENT METHODS instrument. Column 4 of Table 30 shows the D10, D50, and D90 values; the second and third columns Comparing the precision estimates for size and provide the sieve openings and the corresponding tar- roundness measurements by the various traditional get percent passing for the Type 3 samples. The com- mechanical and computerized optical methods will parison of the measured and target values of particle indicate which method provided the most precise size with respect to percent smaller and percent pass- measurements. This comparison was conducted on the size class of each glass bead type that contained ing indicates that the COM-B instrument has cor- the largest mass percentage of the beads--the #50 size rectly measured D10 and D50 but not D90. As shown class for the Type 1 samples, the #18 size class for the in Table 30, 95% of the Type 3 particles, by mass, Type 3 samples, and the #14 size class for the Type 5 should be smaller than the 1.18 mm sieve opening samples. (#18 sieve); however, COM-B measured 90% of par- ticles smaller than 1.43 mm. Size Measurements Type 5 Samples. The D10, D50, and D90 values of Type 1 Samples the Type 5 samples were available from one COM-B instrument. Column 4 of Table 31 shows the values The precision estimates for measuring the mass of D10, D50, and D90; the second and third columns percent retained in the #50 size class for the Type 1 provide the sieve openings and the corresponding tar- samples by various methods of measurement are get percent passing for Type 5 samples. The compar- provided in Table 32. The precision estimates are ison of the measured values of D10, D50, and D90 based on the size distribution of three 50-g Type 1 glass bead replicates measured by participating lab- with the target sieve sizes and their corresponding oratories. The results in Table 32 indicate that for percent passing indicates that COM-B has correctly Type 1 beads the mechanical sieve provided the measured D10 and D50 for the Type 5 samples but smallest and COM-B provided the largest within- not D90. As shown in Table 31, 95% of the Type 5 laboratory (repeatability) and between-laboratory particles should be smaller than a 1.70 mm sieve (reproducibility) precisions. The better precision in size measurement of Type 1 beads using the mechan- Table 31 Comparison of measured and target particle ical sieve may result from agglomeration of the small size of Type 5 samples for 10%, 50%, and 90% passing beads due to electrostatic forces. Mechanical shaking would overcome these forces and separate the beads, Sieve Target Particle while they would likely stay clustered passing through No. of Size Percent Diameter-T Percent computerized optical equipment. Labs (mm) Passing (mm) Smaller 1 1.18 5 1.22 10 Type 3 Samples 1 1.40 40 1.54 50 The precision estimates for measuring the percent 1 1.70 95 1.84 90 retained in the #18 size class of the Type 3 samples by 16

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Table 32 Precision estimates for measuring percent retained for Type 1 samples by various methods Repeatability STD, % Reproducibility STD, % Method of Measurement-- No. of Sample Type Labs 1s d2s 1s d2s Mechanical Sieve--Type 1 14 1.0 2.8 1.7 4.6 COM-A--Type 1 8 1.3 3.8 3.0 8.3 COM-B--Type 1 4 2.1 5.9 3.5 9.7 Table 33 Precision estimates for measuring percent retained for Type 3 samples by various methods Repeatability STD, % Reproducibility STD, % Method of Measurement-- No. of Sample Type Labs 1s d2s 1s d2s Mechanical Sieve--Type 3 13 1.1 3.1 3.4 9.4 COM-A--Type 3 8 0.7 1.9 2.1 5.9 the mechanical sieve and by COM-A are provided in smaller repeatability and reproducibility standard Table 33. The comparison does not include COM-B deviations of Type 5 glass beads than did the mechan- results because only one set of measurements on ical sieve. Type 3 samples was available by COM-B. The pre- cision estimates are based on the size distribution Summary of Precision in Size Measurement of three 100-g Type 3 glass bead replicates mea- Comparison of the precision estimates for mea- sured by participating laboratories. As shown in suring the percent retained in the most prevalent Table 33, the COM-A data provided significantly size classes of Type 1, Type 3, and Type 5 glass smaller repeatability and reproducibility standard beads revealed important information about the deviations of Type 3 glass beads than did the mechan- methods of measurement. For Type 1 samples, the ical sieve. mechanical sieve provided the least within and between variability. However, for the Type 3 and Type 5 Samples Type 5 glass beads, COM-A provided significantly The precision estimates for the percent retained lower variability than the mechanical sieve. The in the #14 size class of the Type 5 samples by the reason for this observed difference may lie in the mechanical sieve and COM-A are provided in tendency of fine glass bead particles to agglomerate Table 34. There are no precision estimates available through electrostatic attraction. Mechanical sieving for COM-B measurements since only one set of data can break down the agglomerated glass beads, but was provided on Type 5 glass beads by COM-B. this will not occur when agglomerations pass through The precision estimates are based on the size distri- computerized optical method units. A definite con- bution of three 200-g Type 5 glass bead replicates clusion about the variability of the COM-B results measured by the participating laboratories. As shown cannot be made at this point since only a small in Table 34, the COM-A data provided significantly number of laboratories reported size measurement of Table 34 Precision estimates for measuring percent retained for Type 5 samples by various methods Repeatability STD, % Reproducibility STD, % Method of Measurement-- No. of Sample Type Labs 1s d2s 1s d2s Mechanical Sieve--Type 5 13 2.2 6.0 4.3 12.0 COM-A--Type 5 7 0.9 2.4 1.2 3.3 17