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Fibre length measurement - Fibrograph

Fibre length measurement 


Fibrograph is used for measuring cotton fibre length with the help of the optical method.

Fibrograph is a more automated method than comb shorter analysis method.

Uster digital fibrograph
Digital fibrograph

Fibrograph measures the density and length of fibres from their parallel arrangement.

To measure fibre length in a fibrograph, the first sample is prepared by fibrosampler.

Fibrosampler is an instrument to prepare the sample for fibrograph with a combing arrangement in it.

Fibrosampler for fibrograph

It has a hollow cylinder drum with a circular perforated wall in half of the cylinder’s periphery and another half periphery is closed.

Before entering the tufts into the fibre sampler, clean it properly.

The tuft of fibres is inserted into this cylinder. A Rotating brush is arranged outside of this cylinder that can rotate around the cylinder.

This rotating brush has combs on its inner surface which withdraw cotton fibres from a perforated drum and deposit them on a comb. 

The outcome is that the fibres are placed on the comb in such a way that they are caught at random points along their length to form a beard. 

After repeating 2-3 times of comb movement, fibres are parallel to the rotating 


These are collected by tweezer and placed into a Fibrograph instrument.

Brush it before testing in fibrograph because the fibre beard needs to remove trash & lose fibres carefully so that light brushing will remove fewer loose fibres and heavy brushing will pull out long fibres and disturb the random arrangement. 

The fibre fringes are placed on the measuring unit in such a way that they lie over a long narrow slot behind which are mounted the photo-electric cells. 

In fibrograph, a specific space available for putting this sample takes fibres into a closed chamber.

The sample is then scanned photoelectrically by the Fibrograph from the base to the tip. 

The intensity of light that passes through the beard at a given position is used as a measure of the number of fibres that extend to that distance from the comb. 

The sample density is then plotted against the distance from the comb to give a Fibrogram.

In the fibrogram random points on the fibres are lined up on the baseline and the segments above the baseline can be conceived as arrayed in order of length and equally spaced, with the Fibrogram as the envelope of the fibre tips. 

At the start of the measurement, the fringes are scanned across the densest region.

I.e. - beginning from the comb teeth, and the light which penetrates will be a 

minimum. As the sample is traversed towards the fibre ends, more and more light will fall onto the photoelectric cells. 

The span lengths at given percentages of fibres are usually measured; the 2.5% span length is considered to correlate with the classer's staple length. 

From the 50% span length and the 2.5% span length, a uniformity index can be achieved.

For appropriate results, 600 -900 fibres are ideal as a sample.


Servo-fibrograph is the modification of conventional fibrograph.

It automatically records the change in the amount of light reaching the cells, not in terms of intensity of illumination but as a special form of frequency distribution. 

This curve is traced out on a card which is then removed from the instrument and analyzed. 


It basically constructs the tangent to the curve to cut the horizontal at N and the vertical axis at A. 

OA is then the average length of fibres longer than 1⁄4 inch. The distance along ON represents the frequency percentage of fibres longer than 1⁄4 inch.

From S, the 50 per cent mark, construct the tangent ST to cut the vertical axis at T. 

OT is then the upper half mean length of fibres longer than 1⁄4 inch, based on weight distribution. 

The ratio OA/OT x 100 per cent gives the length uniformity ratio of the fibres. 

The upper half's mean length approximates the staple length obtained by the cotton classes. 


Digital Fibrograph


Digital fibrograph is a further development of the above fibrograph instruments. It represents test results in digital or numeric value form.

Digital fibrograph have the same method for preparing the sample and the same way pass the signals by the light source.

The modification is that the signals from the measuring console are fed into a separate transistorized unit. 

The signals are electronically processed and the results are fed back to the measuring unit which has two four-digit counters facing the operator. 

One counter is for selecting % S.L. and the other counter gives ‘Length’. 

A Servo-follower system connected to the photoelectric cells indicates on the ‘Amount’ counter the relative number of fibres in the sample beards at the point where the light beam passes through them.

This Servo-computer ‘remembers’ the total number of fibres in the sample at a 0.15-inch distance from the centre of the comb teeth and computes the number of fibres corresponding to the different Span Lengths. 

When a span length is selected, the comb carrier moves until the number of fibres under the lighthouse is equal to the number of fibres corresponding to that span length.

The span length is then indicated by the ‘Length’ counter, which indicates, in mm, the movement of the comb carrier. 

Now there are two counters t set the amount and these two corresponding Length counters give two lengths of 2.5% and 50% simultaneously. 

Relationship between fibre length (mm)


Digital Fibrograph 

2.5% Span Length (x)

Y = 1.013x + 4.39

Uster Apparatus Effective Length (x)

Y = 0.933x + 9.04

Uster Apparatus

Upper half mean length (x)

Y = 0.996x + 9.12


Digital Fibrograph

Span Length (x)

Y = 1.242x + 9.78 50%

Uster Apparatus 

Mean Length (x)

Y = 0.941x + 9.45


Uster apparatus – Upper half 

Mean length (x)

Y = 0.946x + 5.64

Uster Apparatus – Effective length (x)

Y = 0.878x + 5.77


Uster Apparatus – Mean length (x)

Y = 0.672x – 1.60

Note: If the 2.5% span length of cotton as tested on a Digital fibrograph is 

30mm, then the Baer sorter effective length is estimated to be 34.8mm (1.013 x 30 + 4.39).

Questions -
  1. Why fibrograph is used?
  2. What is fibrosampler?
  3. How the sample is taken by fibrosampler?
  4. How do micrographs work?
  5. What is servo-fibrograph?
  6. How servo-fibrograph work?
  7. What is a digital fibrograph?
  8. How digital fibrograph works?
  9. Relation between fibre length among different methods?


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Fundamental textile testing: Mechanical and Physical Tests. (n.d.). Fundamental Textile Testing: Mechanical and Physical Tests. from

Handbook of textile testing and quality control - Google search. (n.d.). G.Co. from

NPTEL IIT. (n.d.). Note.Ac.In. from

Elsevier. (2016). Performance testing of textiles (1st ed.). Woodhead Publishing.

Houck, M. M. (2009). Identification of Textile Fibers (M. M. Houck, Ed.; 1st ed.). Woodhead Publishing.

Textile School. (2010, October 27). Fibre Identification - tests to identify a fibre. Textile School

Trivedi, Y. (2020, April 10). Identification of Textile Fibers. Textilesphere.com

(N.d.). from

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