## YARN EVENNESS

**DIAGRAM**

The mass variations or weight per unit length variations are
recorded and printed as a Diagram by

the Evenness tester. The diagram is an extremely important part
of evenness testing. It contains a

large amount of information which cannot be provided by the
wavelength spectrum, U% value, and the

imperfections.

Diagrams help to understand the following seldom occuring events long wave-length variations periodic mass variations with wave-lengths which are longer than 40m(which can not be confimed by the spectrogram. extreme thick and thin places randomly occurring thick and thin places which tend to be available in batches.

slow changes in the mean value step changes in the mean value
with periodic faults, it can be determined whether the fault is
permanently availabe or occurs only in batches with measurements
"within a bobbin", seldom occurring events can be found and
changes in the mean

value taking place over a number of kilometers can be confirmed.
with unusual measured values, it can be proved in many cases by
means of the diagram whether these

refer to a faulty or to a correct measurement.

**RELATIVE COUNT:**

It is a measure used to calculate the count variations using
capacitance method of USTER TESTER.

It calucalates a value called "Average Value Factor AF". This
factor is proportional to the mean count

of the tested sample length.

The relative count describes the variation of count between
separate measurements within a sample. The

single values are calculated such that they are in direct
reference to the mean value of the sample

which is always considered to be 100%. The relative count is
always estimated with reference to a

test length of 100m or 100 yards.

From the single-overall report, it is possible to recognize
immediately which samples are lying above

or below the mean value. The standard deviation provides a
reference to the variation in count between

samples. As the mean value is always 100%, the standard
deviation also provides a reference to the

coefficient of variation. If the samples are from the same
bobbin this would indicate the "within bobbin"

variation and if the samples are from the same bobbin this would
indicate the "within bobbin" variation

and if the samples are from different bobbins this would
indicate "between bobbin" variation.

**VARIANCE LENGTH CURVE:**

The variance-length curve is generally regarded as the most
useful technique for expressing the

yarn irregularity data. Any fibre assembly has a TOTAL
IRREGULARITY CV(T), and this coefficient of

variation is made up of two terms. These are the coefficient of
variation within length ,CV(L) and the coefficient

of variation between lengths CB(L).

The co-efficient of variation at different cut lengths
provided by the evenness testers provide invaluable

information with regard to the variations prevalent at the
specific cut lengths. Therefore independently, the
short, medium and long term variations could be studied by
estimating the coefficient of variation of

the required length. However, such numerical values, cannot
directly provide complete information on

the source of faults.

The spectrogram provides a possibility of
localizing the source of fault but with a

spectrogram, only faults of periodic nature could be identified
and that too, in most cases, only if proceeded
by some other means of identifying the machine / processing
stage responsible for the fault. When the
variations prevailing at different cut lengths are
simultaneously represented graphically, it provides
the possibility of segregating cut lengths at which abnormal
variations occur and consequently identify
the process stage which is most likely to be responsible.

This
is made possible by the "Variance

Length Curve" which is a standard feature of most evenenss
testers.

A variance-length curve can be set out in quite a simple
manner by cutting a fibre assembly into pieces

and determining gravimetrically the mass of these pieces. The CV
value is then calculated from each of these
separate values. If this procedure is repeated for various cut
lengths and the CV value drawn out,

one obtains the variance-length curve. Uster tester can be used
to obtain the curve in a much shorter

time than is possible by manual analysis.

For constructing the
variance length, the measuring field

length is taken as the basic cut length at which the CV is
calculated and plotted. For variations at

other cut lengths, the mass of successive portion of material
are added up and the CV calculated.

Strictly speaking, the variance-length curve is only a
straight line on double logrithmic paper in the

medium length range of approx.1 cm to 100m. For cut lengths
shorter than 1 cm and longer than 100m,

the variance-length curve tends to become flatter.

One can
easily comprehend that the curve for the

same raw material and same ideal processing conditions will
always be a straight line with an unchanged
angle of inclination. Deviations from the straight line must
therefore indicate porblems due to the
machine or the raw material.

**THEORETICAL LIMIT FOR IRREGULARITY:**

The spinning process is based primarily on a procedure which
evenly mixes the fibre, separates each

fibre from its neighbour, lays the fibres parallel to each other
and draws these out to produce a

final count. The mixing leads, however, to the fact that each
single fibre has the same probability

of appearing in any chosen section of the fibre mass. The fibres
are therefore equally distributed in

the fibre assemblies. The number of fibres in any section
considered is dependent on random variations.

The fibres overlap each other and result, even under the best
conditions, in a spun material which

has a certain minimum irregularity. With the natural fibres, in
contrast to the synthetic staple fibres,

there is an additional irregularity because the single fibres
themselves have differences in their fibre

corss sectional size.

The theoretical investigations have helped to arrive at a
formula which will help us to calculate

the limiting irregularity.

CV(lim) = 100 /(sqrt(N)

where,

N = mean number of fibres in the cross section.

CALCULATION OF NUMBER OF FIBRES IN THE YARN CROSS-SECTION:

The number of fibres in the cross section of a yarn can be
calculated if the fibre fineness and yarn

count in tex are available, or can be converted into tex(gram
per 1000m)

N = T/Tf

where,

N = number of fibres in the cross section

T = count of the fibre material in TEX

Tf= Fibre fineness in TEX

**INERT TEST:**

The uster evenness testing installations offer two possible
modes of operation which are referred to

as the

**Normal test**- Inert test With the "NORMAL TEST" , a signal is obtained
from the tested masterial which is in reference to the
measuring
field length of the applied measuring slot.
In the operating mode "INERT TEST", the signal obtained from the test material is passed through an

electrical filter arrangement. Normally, the signal from the test material consists of short and long-

term variations which are superimposed on each other. By means of this filter procedure, the shorter-term

variations are suppressed in a certain manner, so that only the mean value variations, i.e the

long-term mass variations, will be traced out in the diagram. This testg serves primarily to provide, - an indication of the random mean value variations in the test material
- a means of localizing and indicating long term periodic variations in the test material
- a means of facilitating the setting of the mean value at
the yarn signal instrument.
If medium-term varitaions appear in a diagram, one can make these more distinctive by choosing a suitable

diagram feed and suitable material speed and operating with the mode Inert test.

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