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OCR for page 13
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
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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
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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-
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