ASTM D2525-90(1995)
(Practice)Standard Practice for Sampling Wool for Moisture
Standard Practice for Sampling Wool for Moisture
SCOPE
1.1 This practice covers the design of a sampling plan to be used to obtain samples for the determination of the moisture content of grease wool, scoured wool, carded wool, garnetted wool, wool top and intermediate products, and rovings.
1.2 Directions are given for the designation of sampling units, calculation of the number of sampling units required to achieve a preselected precision and confidence level or, alternatively, for calculating the confidence limits for the mean based on the variability of the sample tested.
Note 1--This practice for devising a sampling plan is intended for use in connection with Test Method D1576 or Test Method D2462. The sampling of raw wool for the determination of clean wool fiber present is covered in Practice D1060.
1.3 This standard does not purport to address the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D 2525 – 90 (Reapproved 1995)
Standard Practice for
Sampling Wool for Moisture
This standard is issued under the fixed designation D 2525; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 lot, n—in acceptance sampling, that part of a consign-
ment or shipment consisting of material from one production
1.1 This practice covers the design of a sampling plan to be
lot.
used to obtain samples for the determination of the moisture
3.1.3 lot sample, n—one or more shipping units taken at
content of grease wool, scoured wool, carded wool, garnetted
random to represent an acceptance sampling lot and used as a
wool, wool top and intermediate products, and rovings.
source of laboratory samples.
1.2 Directions are given for the designation of sampling
3.1.4 sample, n—(1) a portion of a lot of material which is
units, calculation of the number of sampling units required to
taken for testing or record purposes.
achieve a preselected precision and confidence level or, alter-
(2) the group of specimens used, or observations made,
natively, for calculating the confidence limits for the mean
which provide information that can be used for making
based on the variability of the sample tested.
statistical inferences about the population from which they
NOTE 1—This practice for devising a sampling plan is intended for use
were drawn.
in connection with Test Method D 1576 or Test Method D 2462. The
3.1.5 sampling unit, n—in wool, a portion of material that is
sampling of raw wool for the determination of clean wool fiber present is
taken at one time from one physical location and that is
covered in Practice D 1060.
combined with similar portions to make up the laboratory
1.3 This standard does not purport to address all of the
sample.
safety concerns, if any, associated with its use. It is the
3.1.5.1 Discussion—A sampling unit may or may not have
responsibility of the user of this standard to establish appro-
the same physical size as a specimen. Examples of sampling
priate safety and health practices and determine the applica-
units include: (1) for bulk materials seen as scoured wool, a
bility of regulatory limitations prior to use.
handful of wool conforming to a stated mass range, (2) for
cored material, a minimum mass of material collected by one
2. Referenced Documents
insertion of a coring tool, (3) for sliver, a stated length of
2.1 ASTM Standards:
material, and (4) a single package, such as a ball of top.
D 123 Terminology Relating to Textiles
3.1.6 specimen, n—a specific portion of a material or a
D 1060 Practice for Core Sampling of Raw Wool in Pack-
laboratory sample upon which a test is performed or which is
ages for Determination of Percentage of Clean Wool Fiber
selected for that purpose.
Present
3.1.7 For definitions of moisture, moisture content, moisture
D 1576 Test Method for Moisture in Wool by Oven-Drying
regain, and other textile terms used in this practice, refer to
D 2462 Test Method for Moisture in Wool by Distillation
Terminology D 123.
with Toluene
E 122 Practice for Choice of Sample Size to Estimate a
4. Summary of Practice
Measure of Quality for a Lot or Process
4.1 Directions are given for subdividing a lot of material
into potential sampling units and for providing each potential
3. Terminology
sampling unit with its own unique identification.
3.1 Definitions:
4.2 Directions are given for calculating the number of such
3.1.1 laboratory sample, n—a portion of material taken to
sampling units required to give a preselected allowable varia-
represent the lot sample, or the original material, and used in
tion at a stated probability level, or for calculating confidence
the laboratory as a source of test specimens.
limits for the sample mean obtained for a given size of sample.
4.3 Directions are given for deciding which particular sam-
pling units should be chosen to constitute the required lot
This practice is under the jurisdiction of the ASTM Committee D-13 on
sample. These directions ensure that all potential sampling
Textiles, and is the direct responsibility of Subcommittee D13.13 on Wool and Wool
units have approximately the same chance of being selected for
Felt.
the lot sample.
Current edition approved Jan. 26, 1990. Published May 1990. Originally
published as D 2525 – 66 T. Last previous edition D 2525 – 76 (1983).
Annual Book of ASTM Standards, Vol 07.01.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 2525
5. Significance and Use sampling unit and specimen the same.
7.1.1 The designation of the sampling unit depends on the
5.1 This recommended practice furnishes directions for the
form of the material and on the method to be used for making
sampling of wool of the various forms indicated in Section 1,
measurements on the sample. The material to be sampled may
in order that correct probability statements may be made about
exist in one of three basic forms: bulk material such as scoured
the relationship between the sample mean and the population
wool or picked blends of wools, packaged material such as
mean. If these statements are to be correct, certain conditions,
baled wool, or material put up in the form of packages within
which are stated, must hold.
packages such as balls of top within cases or bales. The method
5.2 This recommended practice requires that a deliberate act
of measurement may require a specimen as large as a whole
of randomization be performed so that all potential sampling
package of material, or as small as a few grams of material.
units have approximately the same chance of being taken and
7.1.2 Where the material to be sampled exists in some bulk
no sampling unit is deprived of its chance of being taken.
form, such as scoured wool, or a blend that has been picked and
5.3 In any case where insufficient information about the
stored in a bin, the designation of a sampling unit will depend
variability of the sampling units within the lot is available,
upon the mechanics of drawing the sample. If hand sampling is
directions are given for calculating confidence limits for the
the method employed, the sampling unit will be a handful of a
sample mean so that a correct probability statement can still be
certain specified size. Whenever possible, the size of a sam-
made.
pling unit should be made to coincide with the size of the
6. Preliminary Conditions
specimen required by the method of measurement because the
6.1 If it is desired to calculate a sample size to achieve a
random variations observed in the test results are then directly
preselected precision at a preselected level of confidence,
applicable to the sampling units.
knowledge of the variation of the moisture content is neces-
7.1.3 When the material to be sampled exists in the form of
sary.
packages such as baled wool or packages within packages,
6.1.1 The test method to be used must be the same method
such as balls of wool top in cases or bales, the sampling unit
that was used to derive any prior information with respect to
can be either an entire package or some portion of a package,
the variability of the moisture content.
depending upon the size of the specimen required.
6.1.2 The sampling unit must be the fundamental unit in
7.2 Identify each potential sampling unit in the lot by
terms of which the variance is expressed. In other words, if the
numbering, coding, using geometrical coordinates, or by any
sampling unit is chosen to be a 25-g handful of bulk material
other systematic means. It is important that by some means or
or a 4-yd (3.65-m) length of sliver, then the variance used must
other, all potential sampling units must be furnished with their
be the number that expresses the variability of these units, and
own unique identification so that none is deprived of its chance
the number of sampling units which is calculated will be the
of being sampled.
number of such units required. The sampling unit is not
7.2.1 In designing a sampling plan, it is necessary to devise
necessarily the same thing as a specimen.
a method for assigning to every potential sampling unit in the
6.1.3 The lot designated for sampling must be statistically
lot a unique identification. This is a relatively simple task in
homogeneous. This is equivalent to saying that the lot shall not
those instances where the sampling units are discrete packages,
be composed of a mixture of two or more parts, the moisture
such as might be the case with balls of top if an entire ball is
content of which is distributed sufficiently differently that if the
to be the sampling unit.
moisture content of the entire lot were measured, a plot of the
7.2.2 With material in bulk form or with packaged material
moisture content versus the number of sampling units would
in which the sampling unit is to be only a portion of the
show a curve having more than one peak. (See Appendix X1.)
package, it is not as easy to identify uniquely each potential
If the test given in Appendix X1 leads to the conclusion that the
sampling unit, and some method of approximating the ideal
lot cannot be considered to be statistically homogeneous, then
situation must be devised. See, for example, the instructions
it should be subdivided into groups that are homogeneous. The
given in Practice D 1060.
pattern of runs found may indicate what the subgroups should
7.2.3 For materials in loose bulk form, considerable inge-
be.
nuity and imagination may be required to effect a proper
6.1.4 The magnitude of the variation of moisture content
identification of the potential sampling units.
within the homogeneous lot must be known. The magnitude of
7.3 Option 1—This procedure is available for those in-
the variation is usually expressed as the standard deviation,
stances where information is sufficient to enable the calculation
although the range may also be used.
of sample size required for a specified allowable variation and
6.2 If insufficient knowledge is available to ensure meeting
probability level.
the above conditions, a sample of convenient size may be
7.3.1 If the allowable variation and probability level are not
selected and confidence limits calculated for the mean using
stated in the applicable material specification or otherwise
the information in the sample results. In this case, the only
established, determine for these factors values mutually agree-
condition that applies is 6.1.3.
able to all parties interested in the test results.
7. Procedure
7.3.2 Whenever the material being tested has been produced
7.1 Designate the form and size of the sampling unit, under statisically controlled conditions and records are avail-
bearing in mind the conditions and precautions discussed in able, or information is available from prior tests on the same
Sections 5 and 6. Whenever possible, make the size of the lot, estimate the universe standard deviation from these data.
D 2525
NOTE 2—In many instances only an estimation of the variation likely to
be encountered in a lot is available, such as the limits beyond which values
s 5 standard deviation of individual observations, in units
of moisture content are not likely to occur. Practice E 122 includes
of the property being evaluated, and
formulas for estimating the standard deviation for different distributions
E 5 allowable variation of the test results expressed in units
based on the extreme range of values expected. Whenever there is no
of the property being evaluated, which in some cases
information available as to the form of the distribution, assuming a
may be a percentage.
rectangular distribution will yield a relatively conservative estimate.
NOTE 3—The arbitrarily chosen value for E refers to the allowable
7.3.3 Based on values determined as directed in 7.3.1 and
variation in a test result based on observations still to be carried out under
7.3.2, calculate the number of sampling units required, using
conditions of single-operator precision.
Eq 1 or Table 1:
7.3.4 Using a table of random numbers or any satisfactory
2 2 2
n 5 ~t 3 s !/E (1) objective randomizing procedure, decide which particular po-
tential sampling units will make up the sample of the size
where:
calculated in 7.3.3.
n 5 number of sampling units required rounded to the next
7.3.5 Acquire these particular sampling units by the method
higher whole number when the calculated value of n is
required by the designation done in 7.1, using special care to
equal to or less than 50 and rounded to the next higher
avoid gain or loss of moisture by the sampling unit in the
multiple of five when the calculated value of n is
process of being taken. Weigh these sampling units as rapidly
greater than 50,
as possible as they are selected.
t 5 constant depending on the desired probability level
7.4 Option 2—This procedure is available for those in-
and equal to Student’s t for infinite degrees of freedom
stances where enough information to apply Option 1 is not
and two-sided limits, for example,
obtainable or for those instances where all parties interested in
Probability Level, % tt
the results of the test agree to accept whatever precision may
result from an agreed upon fixed sample size and probability in
90 1.645 2.706
95 1.960 3.842
order to reduce the cost of testing.
99 2.576 6.636
7.4.1 Decide, by agreement between the parties interested in
the test results, on the number of sampling units to be taken and
the confidence level desired.
7.4.2 Proceed as directed in 7.3.4 and 7.3.5.
7.4.3 After performing the tests, calculate the confidence
limits for the sample mean by Eq 2:
Confidence limits56 ts/ n (2)
=
TABLE 1 Number of Sampling Units Required to Achieve an
Allowable Variation, E, at a Stated Probability Level, P, for
where:
Various Values of Universe Standard Deviation, s
n 5 number of sampling units in the sample,
The listed values have been calculated by Eq 1.
t 5 value of Student’s t for n − 1 degrees of freedom,
Allowable Variation to be Achieved, E
Probability
two-sided limits, and the specification probability
Level, P,.
0.25 0.5 0.75 1.0 1.25 1.5
level, and
s
s 5 sample standard deviation, defined by Eq 3:
0.25 0.80 2 1 1 1 1 1
0.90 3 1 1 1 1 1 2 1 2
/
s 5 @( ~x 2 x¯! /~n 2 1!# (3)
i i
0.95 4 1 1 1 1 1
0.50 0.80 7 2 1 1 1 1
NOTE 4—The x in the above equation are individual values for sam-
i
0.90 11 3 2 1 1 1
pling units when the sampling unit and the specimen are the same size.
0.95 16 4 2 1 1 1
When, however, more than one specimen
...
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