The Standardisation of Mean Fibre Curvature Using the Series 14 Calibration Top as a Reference
Abstract
This report is the first in a series investigating the use of Interwoollab Tops for calibration of instruments used to measure Fibre Curvature.
Since the introduction of Fibre Curvature measurement in the 1990s, between-instrument differences (both within-type and between-type) have been a feature of the measurement. The measured result has been shown to be sensitive to the sample preparation procedures (Fish, 2000). The two instruments (Laserscan and OFDA) commonly used for Fibre Curvature measurements have different preparation requirements. For example, OFDA requires the use of a fibre spreader whereas Laserscan does not.
Baxter (2002) examined the use of graticules as a means of calibrating OFDA instruments. While further refinement of this method shows promise as a method of comparing between OFDA instruments, it does not offer a method of comparison between the two methods currently in commercial use.
Interwoollabs already provides a service to the International Wool Textile Industry by providing Fibre Diameter calibration standards. The reference values assigned to the calibration standards are derived from International Round Trials that are conducted twice per year. It is feasible that Fibre Curvature measurements could be collected during these round trials. If a procedure using assigned Mean Fibre Curvature (MFC) values to calibrate both Laserscan and OFDA 100 instruments was demonstrated to reduce the between-instruments variance, Interwoollabs would be the preferred industry organisation to provide Mean Fibre Curvature Reference material to the wool industry.
The method of calibration examined in this report investigates the potential to use the Interwoollabs IH Series 14 Calibration tops as a reference.
An international round trial was conducted across 6 core-test laboratories to investigate the potential of using the IH Series 14 Calibration Tops as a standard reference for calibrating Laserscan and OFDA instruments for the measurement of Mean Fibre Curvature.
Measurements were generated on 12 Laserscan and 10 OFDA instruments. Calibration equations based on the Geometric Mean Regression were used to calibrate raw data measurements for Mean Fibre Curvature to a standard basis.
The application of a Mean Fibre Curvature calibration to individual instruments showed potential for reducing the between-instrument variance in the measurement of Mean Fibre Curvature for guillotined sliver, but it did not provide the same improvement when samples prepared from greasy wool were measured using the calibration derived for tops.
The critical issue appears to be the difference in the linear relationships between uncalibrated data for top samples and the grand mean compared to the same relationship for samples prepared from greasy wool.
Further research is needed to explain the differences between the two relationships.
Citation
"The Standardisation of Mean Fibre Curvature Using the Series 14 Calibration Top as a Reference", V.E. Fish, Report RWG05, Technology & Standards Committee, Raw Wool Group, IWTO, Istanbul Meeting, November 2003