Fibre Testing

 Length measurement

    In general a longer average fibre length is to be preferred because it confers a number a advantages   Firstly, longer fibres are easier to process. Secondly, more even yarns can be produced form them because there are less fibre ends in a given length of yarn. Thirdly, a higher strength yarn can be produced from them for the same level of twist. Alternatively a yarn of the same strength can be produced but with a lower level of twist, thus giving a softer yarn.

Mean Length

When calculating the means length . There are in fact three possible ways of deriving the mean length:

1. Mean length based on number of fibers (unbaised mean length) L

2. Mean length based on fiber cross-section (cross-section biased mean length) Hauteur H.

3. Mean length based on fiber mass (mass-biased mean length) Barbe B.

Mean Length (L)

                                            L = l₁+l₂+l_{3  / 3}

_{In the calculation of mean length each fiber is given an equal weighting no matter how large the diameter of the fiber is} 

_{Cross-section biased mean length H (Hauteur)}

In this calculation of mean length each fiber is weighted according to its cross section, so that if a fibre has a cross-section a_{2 which is four times the of av its length will count four times that of av in the calculation of the mean :}

                                                _{H =}  a₁l₁+a₂l₂+a₃l₃  /a₁+a₂+a₃

Mass-biased mean length B (Barbe)

The Barbe is obtained when the fiber length groups from a comb sorter are each weighed and the average length calculated from the data. The Hauteur can be obtained from the data by diving the mass of each length group by its length and expressing the result as a percentage:

                                            B  = w₁l₁+w₂l₂+w₃l₃  /w₁+w₂+w₃

_{The Barbe is always greater than the Hauteur for a given sample; the two may be interchanged using the following formula}

                                        _{Barbe = Hauteur (1+}V²)

Where V is the fractional coefficient of variation of  Hauteur, that is coefficient of variation/100. The CV% of length (Hauteur) generally lies between 40% and 60% for wool so that, assuming an average value of 50% , the Barbe would be 25% greater that the Haunter.

Fiber length measurement method 

(WIRA , Fiber Sorter Method)