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between measured and target roundness for the #18 sured round was larger than the target round. For
size class, which is the most prevalent size class. It Types 3 and 5 the average measured round was
can also be observed from the table that the percent smaller than the target round value. The reason for
roundness was underestimated for all size classes, this difference may be the different methods used for
e.g., the measured percent round of 73.9% for the #20 separating the glass beads. The spiral separator and
beads is smaller than the target roundness of 80%. roundometer were used in the preparation of the sam-
This might be due to the difference between separa- ples but only the roundometer was used for testing of
tion methods of the roundometer and the spiral sepa- the ILS samples. The measured values indicated that
rator, which were both used in the preparation of the smallest repeatability and reproducibility coeffi-
ILS samples. Similar to the previous observations, cients of variation correspond to the sieve with the
the repeatability and reproducibility coefficients of largest number of beads.
variation of roundness measurements correspond-
ing to the size class with the largest amount of beads Analysis of Results from
(#18 sieve) are smaller than those of other size classes. COM-A Measurements
Type 5 Samples. Nine out of the 14 laboratories that A total of eight laboratories returned measure-
conducted mechanical sieve analysis on the Type 5 ments by COM-A. The measurements included size
samples also returned results on the roundness of the distribution and percent roundness. The roundness
samples. The variability of percent round of the Type measurement was made using two parameters, b/l and
5 samples was determined after eliminating the out- SPHT, as explained in Table 3. The measurements
lier data. All remaining data were re-analyzed accord- using COM-A were conducted following the instruc-
ing to the E691 method to determine the repeatabil- tions provided by the COM-A manufacturer. The data
ity and reproducibility statistics shown in Table 10. were analyzed to evaluate the precision and bias of
A review of the statistics in the table indicates the each measured property and to compare these with the
roundness of the Type 5 beads was underestimated precision and bias of the properties measured using
for all size classes, e.g., the measured percent round the traditional methods and COM-B computerized
of 83.4% for the #14 beads is smaller than the target optical method.
roundness of 90%. This again could be due to the dif-
ference between the methods of separating the beads Size Measurements
using the roundometer and the spiral separator. The The size distributions of the three sample types
repeatability and reproducibility coefficients of vari- were measured using two-dimensional (2-D) analy-
ation of the Type 5 beads are relatively low for all sis of the images of the glass beads passing through
size classes. This might indicate better control over the COM-A measurement unit.
the roundness determination of larger beads than of
smaller beads. Type 1 Samples. The precision estimates for size dis-
tribution of Type 1 specimens were determined after
Summary of Percent Round by the Roundometer. eliminating the outlier data. All remaining data were
The analysis of the roundometer percent round data re-analyzed according to the E691 method to deter-
suggests that for Type 1 samples, the average mea- mine the repeatability and reproducibility statistics
Table 10 Roundness statistics of Type 5 samples using roundometer,
target roundness of 90%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#12 7 86.1 3.1 3.6 5.0 5.8
#14 8 83.4 1.8 2.1 4.5 5.3
#16 7 87.0 2.1 2.4 4.1 4.7
#18 7 87.3 2.9 3.4 4.8 5.4
7
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Table 11 Percent retained statistics of Type 1 samples using COM-A
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#30 6 5 4.5 0.3 5.6 0.3 7.1
#50 8 50 46.4 1.4 3.0 3.0 6.5
#100 8 45 48.6 1.6 3.3 3.3 6.7
shown in Table 11. As indicated in Table 11, the mea- retained value of 57.2% compares relatively well with
sured mass percents retained are in relatively good the target retained value of 55%. The repeatability and
agreement with the target values. For example, the reproducibility coefficients of variation for the #18
average retained of 46.4% for the #50 sieve size is sieve are smaller than those for the other sieves.
compared with the target retained of 50%. Similar to
the mechanical sieve analysis of Type 1 samples, the Type 5 Samples. The precision estimates for size dis-
repeatability and reproducibility coefficients of varia- tribution of the Type 5 specimens were determined
tion of all class sizes are relatively small. after eliminating the outlier data. All remaining data
were re-analyzed according to the E691 method to
Type 3 Samples. The precision estimates for size dis- determine the repeatability and reproducibility sta-
tribution of Type 3 specimens were determined after tistics shown in Table 13. A very good agreement
eliminating the outlier data. All remaining data were between the measured and target percent retained is
re-analyzed according to the E691 method to deter- observed for the #14 size class, which has the largest
mine the repeatability and reproducibility statistics number of beads. The measured retained value of
shown in Table 12. A comparison of the measured and 55.5% compares very well with the target retained
target percent retained in Table 12 indicates a good value of 55%. It is also indicated from the table that
agreement between the measured percent retained the smallest repeatability and reproducibility coeffi-
and the target percent retained in the #18 size class, cients of variation for the percent retained correspond
which has the largest number of beads. The measured to #14 sieve.
Table 12 Percent retained statistics of Type 3 samples using COM-A
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#16 7 5 10.3 0.4 4.0 3.4 32.6
#18 8 55 57.2 0.7 1.2 2.1 3.7
#20 8 35 26.8 0.8 3.0 1.8 6.7
#25 8 5 4.6 0.7 15.4 0.9 19.6
Table 13 Percent retained statistics of Type 5 samples using COM-A
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#12 8 5 6.9 0.7 10.2 1.4 19.6
#14 7 55 55.5 0.9 1.5 1.2 2.1
#16 7 35 30.1 1.7 5.7 2.1 6.9
#18 7 5 6.5 0.3 4.2 0.7 10.3
8
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Table 14 Statistics of percent round of Type 1 samples using SPHT parameter
of COM-A, target 70%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#30 4 80.8 1.9 2.3 5.8 7.2
#50 3 84.5 0.7 0.8 1.5 1.8
#100 4 84.8 2.5 2.9 2.2 2.6
Summary of Percent Retained by COM-A. The analy- cantly larger than the target roundness of 70%. This
sis of COM-A mass percent retained data suggests that suggests that the SPHT threshold value may be unsuit-
the measured percent retained in the size class with the able because it allows non-round beads to be classified
largest number of beads provides closest agreement as round. Despite the inaccuracy of the SPHT param-
with the target value. Looking at the percent retained eter, both the repeatability and reproducibility coef-
in the size classes with the largest number of beads ficients of variation of the SPHT parameter are rela-
in the Type 1, Type 3, and Type 5 samples indicates tively small for all size classes.
that both accuracy and precision of measurements
improved with the coarseness of the glass bead types. Type 3 Samples. The precision estimates for the mass
percent roundness of the Type 3 specimens were
Roundness Measurements determined after eliminating the outlier data. All
Using the SPHT Parameter remaining data were re-analyzed according to the
A total of four laboratories reported the percent E691 method to determine the repeatability and
roundness of the three sample types measured by the reproducibility statistics shown in Table 15. A review
SPHT parameter (see Table 3) using the COM-A of the statistics in Table 15 indicates that the percent
device. A threshold value of 0.9 was used for round- round of the size classes with the most number of
ness determination using the SPHT parameter, mean- beads (#18 and #20) was overestimated by the SPHT
ing that any particle with an SPHT value of 0.9 and parameter. The measured percent round of 86.3% for
above was considered to be round. the #18 beads is compared with the target roundness
of 80%. This might indicate that the SPHT threshold
Type 1 Samples. The precision estimates for the value is too low, which allows non-round beads to
mass percent roundness of the Type 1 specimens be classified as round. The repeatability and repro-
were determined after eliminating the outlier data. ducibility coefficients of variation of the roundness
All remaining data were re-analyzed according to the data obtained based on the SPHT parameter are rela-
E691 method to determine the repeatability and repro- tively small for all size classes.
ducibility statistics shown in Table 14. Table 14 indi-
cates that the roundness of all size classes are over- Type 5 Samples. Based on outlier analysis, no data
estimated by the SPHT parameter, e.g., the measured were eliminated from the determination of the preci-
percent round of 84.5% for the #50 beads is signifi- sion estimates for the mass percent roundness of the
Table 15 Statistics of percent round of Type 3 samples using SPHT parameter
of COM-A, target 80%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#16 4 77.7 2.6 3.4 2.9 3.7
#18 4 86.3 0.9 1.0 1.0 1.2
#20 3 92.1 0.4 0.4 0.8 0.8
#25 4 85.1 3.4 4.0 4.1 4.9
9
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Table 16 Statistics of percent round of Type 5 samples using SPHT parameter
of COM-A, target 90%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#12 4 88.5 1.0 1.1 2.6 2.9
#14 4 92.1 0.6 0.7 1.2 1.4
#16 4 91.2 1.7 1.8 5.7 6.2
#18 4 92.1 0.7 0.7 0.7 0.7
Type 5 specimens. The computed repeatability and cally, a threshold value of 0.9 appears acceptable for
reproducibility statistics of the Type 5 sample round- Type 5 beads, but it did not measure the intended
ness are shown in Table 16. A review of the statistics roundness of Type 1 and Type 3 beads accurately.
in Table 16 indicates that the roundness of all size
classes was measured reasonably correctly by the Roundness Measurements Using b/l Parameter
SPHT parameter. The measured percent round of Eight laboratories reported the percent roundness
92.1% for the #14 beads agrees well with the target of the three sample types measured by the COM-A b/l
roundness of 90%. In addition, a review of the vari- parameter. The threshold value for measuring per-
ability values in Table 16 indicates that both the cent round by the b/l parameter was 0.83, meaning
repeatability and reproducibility coefficients of vari- that any particle with b/l > 0.83 was considered to be
ation of the SPHT parameter are very small for all size round.
classes. This suggests that (1) the threshold value of
0.9 is more appropriate for larger beads than for Type 1 Samples. The variability of percent round
smaller beads and (2) a higher threshold value is of Type 1 specimens was determined after elimi-
needed for more accurate measurements of the round- nating the outlier data. All remaining data were re-
ness of smaller glass beads. analyzed according to the E691 method to determine
the repeatability and reproducibility statistics shown
Summary of Percent Round by COM-A SPHT. The in Table 17. A review of the statistics in Table 17
analysis of mass percent round using the COM-A indicates that the roundness of all size classes of the
SPHT parameter indicates that the measured percent Type 1 samples is overestimated by the b/l param-
round in the most prevalent size classes provided eter. The measured percent round of 78.6% for the
closest agreement with the target value. However, the #50 beads is larger than the target roundness of 70%.
level of agreement between measured and target per- This difference may result from an artifact of the
cent round differs for the Type 1, Type 3, and Type 5 2-D image analyses. A single or even several 2-D
samples. This suggests that the threshold value for projections of a non-spherical object cannot fully
all glass bead types is not the same and would need capture its 3-D shape, which would tend to bias the
adjustment according to the glass bead type. Specifi- percent round results. This is also an indication that
Table 17 Statistics of percent round of Type 1 samples using b/l parameter
of COM-A, target 70%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#30 8 76.8 2.5 3.2 6.1 8.0
#50 6 78.6 1.2 1.6 1.7 2.1
#100 7 80.9 3.1 3.8 3.5 4.3
10
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Table 18 Statistics of percent round of Type 3 samples using b/l parameter
of COM-A, target 80%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#16 8 66.5 2.2 3.3 3.4 5.0
#18 8 80.1 0.9 1.1 1.1 1.4
#20 7 84.3 0.9 1.0 1.1 1.3
#25 8 76.6 4.7 6.1 9.5 12.4
the threshold value for the b/l parameter is not large of the most prevalent size classes of Type 3 glass
enough to eliminate all particles considered to be beads.
non-round by the roundometer. Similar to the obser-
vations made on the roundometer data, both the Type 5 Samples. The variability of percent round of
repeatability and reproducibility coefficients of vari- Type 5 specimens was determined after eliminating
ation of the b/l parameter are significantly smaller for the outlier data. All remaining data were re-analyzed
the #50 beads, which are the most prevalent size in the according to the E691 method to determine the
Type 1 samples. repeatability and reproducibility statistics shown in
Table 19. A review of the statistics in Table 19 indi-
Type 3 Samples. The variability of percent round of cates that the measured roundness of the #14 and
Type 3 specimens was determined after eliminating #16 glass beads, which are the most prevalent sizes,
the outlier data. All remaining data were re-analyzed agrees very well with the target roundness of 90%.
according to the E691 method to determine the The repeatability and reproducibility coefficients
repeatability and reproducibility statistics shown in of variation corresponding to the #14 and #16 size
Table 18. A review of the statistics in Table 18 indi- classes are also very small. This indicates that b/l is a
cates that the measured percent round of the #18 reliable parameter for measuring the roundness of the
glass beads (80.1%), which is the most prevalent most prevalent size classes of Type 5 glass beads.
size, agrees very well with the target roundness of
80%. The percent round of the #20 sieve is slightly Summary of Percent Round by COM-A b/l. The analy-
overestimated, which may also be due to 2-D image sis of mass percent round of COM-A b/l data indicates
analysis artifacts as noted in the previous section. The that the b/l parameter captured the roundness of
results in Table 18 further indicate that the repeata- Type 3 and Type 5 glass beads very well but over-
bility and reproducibility coefficients of variation estimated the roundness of Type 1 beads. This indi-
of percent round according to the b/l parameter for cates that the threshold value for b/l should not be the
the #18 and #20 beads, which are the most preva- same for all glass bead types. While the threshold value
lent sizes, are very small. This indicates that b/l is of 0.83 seems adequate for Type 3 and Type 5 glass
a reliable parameter for measuring the roundness beads, it may need to be increased for Type 1 beads.
Table 19 Statistics of percent round of Type 5 samples using b/l parameter
of COM-A, target 90%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#12 8 80.8 1.2 1.5 3.0 3.7
#14 8 89.2 1.1 1.2 1.5 1.7
#16 7 91.4 1.9 2.1 2.3 2.6
#18 8 89.8 1.1 1.2 1.4 1.5
11
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D10, D50, and D90 Measurements Table 21 Comparison of measured and target particle
sizes of Type 3 beads for 10%, 50%, and 90% passing
The accuracy of COM-A in measuring the size
distribution of glass beads was evaluated. For this Sieve Target Particle
purpose, the three diameters where 10%, 50%, and No. of Size Percent DiameterXcmin Percent
90% of the particles, by mass, are smaller than these Labs (mm) Passing (mm) Smaller
diameters (D10, D50, D90) were compared with 7 0.85 5 0.89 10
the sieve sizes and the mass percent passing that 7 1.00 40 1.07 50
were used to prepare the bead samples. Tables 20, 21, 7 1.18 95 1.18 90
and 22 provide the measured diameters correspond-
ing to 10%, 50%, and 90% of particles having a diam-
eter less than the given diameter. These tables also instrument has measured the size distribution of the
provide the sieve sizes and the percent passing of Type 3 samples reasonably well. The percent smaller
Types 1, 3, and 5 glass beads prepared in this study. for D90 has an expected value of 95% compared to
a measured value of 90%, but the percent smaller
Type 1 Samples. Column 4 of Table 20 shows the than D10 and D50 are reasonable. For example, 40%
values of D10, D50, and D90 of Type 1 samples of the beads were prepared to pass through a 1.0 mm
according to COM-A data. The results in Column 4 opening (#18 sieve) and the COM-A predicted that
are averages of COM-A measurements received from 50% of the beads have diameter smaller than 1.07 mm,
seven laboratories. The comparison of the measured which is reasonable agreement.
and target values of particle size with respect to per-
cent smaller and percent passing values indicates that Type 5 Samples. Column 4 of Table 22 provides the
the COM-A instrument has measured the size distri- sizes in millimeters for D10, D50, and D90, as deter-
bution of the Type 1 samples reasonably well. For mined from the COM-A results. The second and third
example, bead samples were prepared to have 95% columns provide the sieve openings and the cor-
passing a 0.6 mm sieve opening (#30 sieve) and the responding percent passing used in preparing the
COM-A data measured that 90% of the beads are Type 5 bead samples. The comparison of the mea-
smaller than 0.53 mm. The same logic is applied to sured and target values of particle size with respect to
other sieve sizes of Type 1 samples, which indicates the percent smaller and percent passing indicates that
that the COM-A device, using the width (b or Xcmin) the COM-A device has measured the size distribution
parameter, has measured the size distribution of of the Type 5 samples reasonably well. For exam-
Type 1 beads reasonably well. ple, 40% of the beads were prepared to pass through
a 1.40 mm opening (#14 sieve); the COM-A result is
Type 3 Samples. Column 4 of Table 21 provides the that 50% of the beads by mass have diameters smaller
values of D10, D50, and D90, in terms of the param- than 1.49 mm.
eter Xcmin, for the Type 3 samples; Columns 2 and 3
provide the sieve openings and the corresponding Summary of D10, D50, and D90 Measurements by
percent passing used in preparing the Type 3 sam- COM-A. The analysis of D10, D50, and D90 data
ples. The comparison of the measured and target measured by COM-A indicated that COM-A mea-
values of particle size with respect to percent smaller sured the size distribution of the three types of glass
and percent passing values indicates that the COM-A bead samples reasonably well. Only one out of nine
Table 20 Comparison of measured and target particle Table 22 Comparison of measured and target particle
sizes of Type 1 beads for 10%, 50%, and 90% passing sizes of Type 5 beads for 10%, 50%, and 90% passing
Sieve Target Particle Sieve Target Particle
No. of Size Percent DiameterXcmin Percent No. of Size Percent DiameterXcmin Percent
Labs (mm) Passing (mm) Smaller Labs (mm) Passing (mm) Smaller
7 0.15 0 0.20 10 7 1.18 5 1.21 10
7 0.30 45 0.31 50 7 1.40 40 1.49 50
7 0.60 95 0.53 90 7 1.70 95 1.66 90
12
