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Fibre length measurement - WIRA and Shirley instrument

Fibre length measurement

 WIRA fibre diagram machine

WIRA fibre diagram machine is designed to measure the fibre length of combed wool sliver.

In this WIRA machine testing, fibre is first prepared for the sample and then the actual test takes place.

WIRA fiber length measurement
WIRA fibre length measurement

To prepare a fibre sample, fibres are sealed from one end in the strip therefore one end of the fibres is beginning from the same point. To do this combing actions is helpful.

This will be squared by withdrawing a small amount of protruding fibres carefully with a pair of wide grips.

The squared end is then heat-sealed between two lengths of polythene tape so that about 3mm of the fibre ends are held between the tapes. 

The polyethene tapes can then be pulled away from the bulk of the fibres, bringing with them a 'draw' of fibres, all of which have one of their ends sealed between the tapes and which are therefore lined up with one another. 

Once the sample is prepared it's placed in the machine. In the WIRA machine a slowly moving slot which carries a sample with it.

The machine measure capacitance of the sample as fibres passes through the slot.

The capacitance measurement is proportional to the total amount of material in the slot at a time. 

This measurement is repeated at known distances along with the 'draw' so that a graph can be constructed of the amount of material against the distance from the fibre ends. 

By this movement, a graph is a prepared parallel to the display.

The graph is made from the cumulative length in mm versus Cumulative class frequency in percentage.

WIRA fiber length measurement principle
WIRA Fiber length measurement principle

From the above graph, it can be estimated that The mean length of the fibre sample can be calculated from ten-length readings taken at 10% intervals between 5% and 95%.

Fibres less than 10mm in length are not measured by this method. As it has been estimated that for wool only 3% of fibres lie below this value, the maximum is there- foreset at 97% rather than 100% to allow for this. 

Cumulative frequency diagram for fiber length
Cumulative frequency diagram for fibre length

Shirley photoelectric stapler

Shirley photoelectric stapler is used to quickly measure staple fibre length.

In this method, the fringe of fibres is prepared for sampling manually.

Fibres are manually opened and drawn with each other, once the sample is ready place it into a black velvet pad.

Shirley's photoelectric stapler has such an arrangement that rotates this valve pad in a forwarding direction.

During this movement, a light source release lights.

Shirley photoelectric stapler for fiber length measurement
Shirley photoelectric stapler

This light is split by a small gauge and concentrates on moving fibres with the help of lenses and mirrors at a particular angle.

Light is reflected from fibres and received by photoelectric cells. The photoelectric stapler basically detects the distance between where the density gradient is maximum on either side.

Two photoelectric cells are used in this instrument and both are connected opposite to each other.

Reflation of light completely depends on fibre length and depending on the light intensity, the opposed cells pass a current, which is proportional to the difference in the intensity.

Therefore by measuring or collecting data from photoelectric cell fibre length is easily measured. This variation in cells is shown in a sensitive galvanometer.

As the fringe is advanced inside the instrument, two maximum density gradient points will be there and this distance is “staple length” (max. deflection of the galvanometer in opposite direction)

E.L. = P. E. Staple length × 1.1

Questions -

  1. Why WIRA fibre diagram is used?
  2. How is testing was done using the WIRA fibre diagram machine?
  3. Draw a graph of cumulative length(mm) vs cumulative class frequency%.
  4. What is Shirley's photoelectric stapler?
  5. How Shirley's photoelectric stapler works?
  6. Define staple length.


Cenote, M. (2015). Google Books. In The SAGE Guide to Key Issues in Mass Media Ethics and Law (pp. 847–858). SAGE Publications, Inc.

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

Further reading -

(Part-1) Fibre length -Introduction, Direct fibre length measurement

(Part-2) Fibre length measurement - Tuft, clamped and comb sorter method

(Part-3) Fibre length measurement - Bear shorter method - Instrument, and procedure

(Part-4) Fibre length measurement - Bear shorter method- Graph, and analysis

(Part-5) Fibre length measurement - Fibrograph

(Part-6) Fibre length measurement - WIRA and Shirley instrument

Writer - 

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