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uniformity ratio.pdf
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Journal of The Textile Institute
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Determination of the 50%
and 2.5% Span Lengths and
the Uniformity Ratio with the
Fibrograph
R. S. Krowicki
a
, J. M. Hemstreet
a
& K. E. Duckett
b
a
USDA, ARS, Southern Regional Research Center, New
Orleans, USA
b
The University of Tennessee, Knoxville, USA
Version of record first published: 30 Mar 2009.
To cite this article: R. S. Krowicki , J. M. Hemstreet & K. E. Duckett (1997):
Determination of the 50% and 2.5% Span Lengths and the Uniformity Ratio with the
Fibrograph, Journal of The Textile Institute, 88:3, 167-173
To link to this article: http://dx.doi.org/10.1080/00405009708658542
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7. Krowicki. Hemstreet. and Duckett
correcting tbe array data for holding length. The average ratio of the theoretical value to
the value adjusted for holding length is 1.00, indicating no difference. Additional correction
for start of scan tends to increase the UR by about 20% for these data. This increase has
been explained (Krowicki and Ramey. 1984) as primarily due to an increase in tbe 50%
span length. Adjustment due to estimated crimp changes Ibe UR sligbtly.
Consider tbe possibility of determining an estimate of ibe UR which is a better
approximation of the theoretical UR. Each span length (SL) measure is dependent upon a
lengtb to start of scan (LS). (LS is defmed as the distance from the outer edge of the comb
teeth to the centre of tbe measuring lens.) The measured 50% SL (SL^,,^^) is overestimated
by 50% of LS wbile the 2.5% SL (SL,,_J is overestimated by 2.5% of LS. Length data are
now generally presented as SL,^^ and calculated UR. Since:
• - (1)
3,,n, , , J (2)
A corrected 50% SL (SL^^^) can be determined for use in calculating a corrected UR
.u , . . (3)
and
UR =100SL,JSL^^ (4)
Assume that LS = 0.38! cm. The correction to the 50% SL is then -0.190 cm and to tbe
2.5% SL is -0.00952 cm. Corrected UR values for the five varieties are compared witb
theoretical and measured values in Table V. The UR. are a much better estimate of
theoretical UR tban the UR .
m
Table V
Comparison of Uniformity Ratios*
Cotton
ID
I
2
3
4
5
Array
39.7
36.7
40.2
37.8
38.3
Measured
45.2
43.6
48.2
44.2
48.5
Difference
+5.5
+6.9
+8.0
+6.4
+ t0.2
Corrected
Measured
38.5
36. t
39.2
37.0
40.9
Difference
-1.2
-0.6
-1.0
-0.8
+2.6
•This is a comparison of values determined from array data with values determined from
Digital Fihrograph data and with values determined by correcting Ihe Digital Fihrograph data.
4. CONCLUSIONS AND SUMMARY
The effects on span length and uniformity ratio of holding length, stan of scan, and fibre
crimp have been examined. Tbey have led lo the following conclusions.
Holding length and fibre crimp, in conjunction with start of scan, can account for the
major proportion of the shorter lengtb measured by tbe Digital Fibrograpb.
Holding length and fibre crimp shorten the measured length while tbe start of scan
increases the length.
The start of scan increases tbe 50% span length by one-balf tbe distance from the edge
of tbe clamp to the start of scan line, but only increases tbe 2.5% span lengtb by 0.025
limes tbis distance. This causes the uniformity ratio determined from measured values to
be excessive, with tbe largest increases occurring in shorter varieties.
A crimp estimate of Ihc order of 6% appears to be a good approximation for the varieties
172 J. Ten. hist.. 1997. f(S Pan I. No. J C Textile Institute
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