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Table 23 Percent retained statistics of Type 1 samples using COM-B No. Measured Target Repeatability Reproducibility Sieve of % Retained, % Sizes Labs Average Retained STD, % CV, % STD, % CV, % #30 3 5.1 5.0 0.3 5.5 0.5 10.8 #50 4 46.7 50.0 2.1 4.6 3.5 7.4 #100 3 46.8 45.0 1.2 2.5 2.0 4.2 measurements (D90 of Type 3) did not compare well bias for the COM-B method and to compare its pre- with the target sieve opening and its corresponding cision and bias with those of the traditional methods percent passing. and the COM-A method. The size distribution and roundness of the three sample types were measured by analysis of 2-D images of the glass beads. Multi- Analysis of Results from ple images of single particles were taken from differ- COM-B Measurements ent angles as they tumbled through the measuring unit Four computerized optical systems from the of the equipment. COM-B manufacturer were available for measuring the size and roundness of the glass bead samples. Size Measurements These included three of one type of system and one of With the COM-B devices, the size of the glass another type that uses the same measuring system and beads was determined from the thickness (T) of the software as does the other COM-B equipment but is glass beads as described in Table 4. exclusively built for use with fine particles and pow- ders. Therefore, only properties of the Type 1 samples Type 1 Samples. The percent retained in various were measured using this second instrument. size classes of the Type 1 samples was reported by Although the COM-B device has the capability of four laboratories. The precision estimates for the per- measuring properties of large particles (Type 3 and cent retained were determined after eliminating the Type 5 samples), two of the three COM-B systems outlier data. All remaining data were re-analyzed used in the study were not calibrated for use with according to the E691 method to determine the large particles and therefore were not used for the repeatability and reproducibility statistics shown in Type 3 and Type 5 samples. As a result, the proper- Table 23. As indicated in the table, the measured and ties of the Type 1 samples were reported by four lab- target percent retained values agree relatively well oratories but the properties of the Type 3 and Type 5 with the target retained values. The repeatability and samples were measured by only one laboratory. For reproducibility coefficients of variation correspond- convenience, the data measured using the two differ- ing to these size classes are relatively small. ent kinds of COM-B equipment were combined and are jointly referred to as COM-B data. Type 3 Samples. As previously noted, only one lab- The COM-B measurements were conducted fol- oratory equipped with COM-B equipment had the lowing the instructions provided by the manufacturer. capability of measuring the properties of the large The data were analyzed to evaluate the precision and glass beads. As shown in Table 24, there is reasonable Table 24 Percent retained statistics of Type 3 samples using COM-B No. Measured % Sieve of Retained, Target % Standard Coefficient of Sizes Labs Average Retained Deviation, % Variation, % #16 1 13.1 5.0 1.3 10.0 #18 1 52.5 55.0 0.8 1.5 #20 1 25.6 35.0 2.1 8.2 #25 1 4.1 5.0 0.8 19.5 13
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Table 25 Percent retained statistics of Type 5 samples using COM-B No. Measured % Sieve of Retained, Target % Standard Coefficient of Sizes Labs Average Retained Deviation, % Variation, % #12 1 9.9 5.0 0.3 2.8 #14 1 51.9 55.0 2.6 4.9 #16 1 29.4 35.0 2.4 8.3 #18 1 4.8 5.0 0.4 7.9 agreement between the measured and target percent described in Table 4. COM-B also measures round- retained in the size class with the largest mass per- ness using the NSP parameter defined in Table 4; centage of the beads. The measured retained value of however, the NSP results of roundness measurement 52.5% for the #18 size class is relatively close to the were not complete and, therefore, were not included target retained value of 55%. This size class also pro- in the statistical analysis. vided the smallest coefficient of variation. Type 1 Samples. Based on outlier analysis, no data Type 5 Samples. The percent retained data on vari- were eliminated from the determination of the pre- ous size classes of the Type 5 samples were reported cision estimates for the mass percent round of the by one laboratory. As shown in Table 25, there is a Type 1 specimens. Therefore, all the reported data fair agreement between the measured and target per- were included in determining the repeatability and cent retained. The measured retained value of 51.9% reproducibility statistics shown in Table 26 accord- for the #14 size class agreed fairly well with the tar- ing to the E691 method. Table 26 indicates that the get retained value of 55%. The coefficient of varia- roundness of the most prevalent size class is over- tion indicated by this size class, which has the high- estimated by the T/L parameter. The measured per- est mass percentage of the beads, was also relatively cent round of 77.2% for the #50 beads is larger than small. the target percent round of 70%. The reason for this difference may be the 2-D image analysis artifact pre- Summary of Percent Retained by COM-B. Despite viously discussed or a wrong cutoff value for the T/L the small number of laboratories reporting COM-B results, the measured percent retained in the most parameter. The repeatability and reproducibility coef- prevalent size classes provided reasonable agreement ficients of variation for the most prevalent size class with the target values. The measurements in the most of the Type 1 beads are relatively large. prevalent size classes also indicated small repeata- Type 3 Samples. The percent round data in various bility and reproducibility coefficients of variation for size classes of the Type 3 samples were reported Type 1 samples and small coefficient of variation for by one laboratory. The data are summarized in the Type 3 and Type 5 samples. Table 27, which shows that the roundness of the P samples is significantly overestimated. The percent Roundness Measurements round of 86.8% in the #18 size class, which has the The roundness of the glass beads measured by highest mass percentage of the beads, is compared COM-B was determined based on the T/L parameter with the target percent round of 80%. Despite the Table 26 Percent round of Type 1 samples using T/L parameter of COM-B, target round of 70% No. Measured % Repeatability Reproducibility Sieve of Round, Sizes Labs Average STD, % CV, % STD, % CV, % #30 4 69.0 2.4 3.5 7.2 10.5 #50 4 77.2 4.3 5.6 7.0 9.1 #100 4 78.2 3.8 4.8 5.8 7.4 14
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Table 27 Percent round of Type 3 samples using T/L parameter of COM-B, target round of 80% Measured % Standard Coefficient of Sieve Sizes No. of Labs Round, Average Deviation, % Variation, % #16 1 79.9 3.2 4.0 #18 1 86.8 2.7 3.1 #20 1 84.6 9.0 10.7 #25 1 85.2 2.2 2.6 Table 28 Percent round of Type 5 samples using T/L parameter of COM-B, target round of 90% Measured % Standard Coefficient of Sieve Sizes No. of Labs Round, Average Deviation, % Variation, % #12 1 84.2 3.6 4.3 #14 1 91.0 0.3 0.3 #16 1 91.9 0.6 0.6 #18 1 91.0 2.8 3.1 significant bias, the coefficient of variation corre- ters and their corresponding percent passing for the sponding to the #18 size class is relatively small. three glass bead types. Type 5 Samples. The percent round of the Type 5 Type 1 Samples. The D10, D50, and D90 values of samples is summarized in Table 28, which shows a the Type 1 samples were received from two COM-B very good agreement between the measured and tar- instruments. Column 4 of Table 29 shows the average get roundness of the Type 5 samples. The percent D10, D50, and D90 values from the two COM-B round of 91.0% in the #14 size class, which has the devices; the second and third columns provide the greatest mass percentage of beads, is compared with sieve openings and the corresponding target percent the target of 90% percent round. The coefficient of passing for the samples. The comparison of the mea- variation corresponding to this size class is also the sured and target values of particle size with respect smallest. to percent smaller and percent passing values indi- cates that the COM-B instrument has measured the size distribution of the Type 1 samples reasonably Summary of Percent Round by COM-B. The analy- well. As shown in Table 29, 95% of Type 1 particles sis of mass percent round with the COM-B T/L would pass a 0.6 mm sieve opening (#30 sieve) and parameter indicates that the threshold value for the the COM-B device measured D90 to be 0.52 mm, parameter is not the same for all glass bead types. meaning that 90% of the beads are smaller than While the threshold value of 0.83 seems adequate 0.52 mm. This is reasonable, since fewer particles for Type 5 glass beads, it did not correctly determine would pass through an opening smaller than 0.6 mm. the percent round of Type 1 and Type 3 beads. Table 29 Comparison of measured and target particle D10, D50, and D90 Measurements size of Type 1 samples for 10%, 50%, and 90% passing The accuracy of the COM-B method in measur- Sieve Target Particle ing the size distribution of the beads was evaluated. No. of Size Percent Diameter-T Percent For this purpose, the values of D10, D50, and D90 Labs (mm) Passing (mm) Smaller were computed and compared with the sieve sizes and their percent passing used in making the bead 2 0.15 0 0.20 10 samples. Tables 29, 30, and 31 present the measured 2 0.30 45 0.32 50 2 0.60 95 0.52 90 values of D10, D50, and D90, and the target diame- 15