The Certification of Standard Deviation of Diameter of Raw Wool Measured by OFDA

Abstract

An ILRT report to the Sliver Group meeting in Christchurch recommended that

“If one were measuring raw wool, one should use the “Tops” Calibration
to obtain the Standard Deviation and the “Cores Calibration to obtain the
Mean Fibre Diameter.”

This submission recommends that one of two approaches be taken with respect to the wording in the Test Method (IWTO-47) for the measurement of Standard Deviation (SD) using OFDA:

• A “Tops” Calibration be used to obtain the Diameter Distribution Data for Raw Wool and a “Cores” Calibration used to obtain the Mean Fibre Diameter (MFD), or
• The Diameter Distribution Data to remain uncertifiable when the “Cores” Calibration is used for measurement.

It should be noted that the Standard Deviation as measured using OFDA on the “Cores” Calibration is indicative of the Standard Deviation assigned to the Interwoollabs Harmonisation Tops. However, for the “Cores” Calibration it is inherently biased due to the effects of Fibre Relaxation on the measurement
of Fibre Diameter when using the OFDA. 

Citation

"The Certification of Standard Deviation of Diameter of Raw Wool Measured by OFDA", Independent Laboratories Round Trial (ILRT) Group, Appendix No: 01, Technology & Standards Committee, Raw Wool Group, IWTO, Nice Meeting, November, 2000