Diameter and Diameter Distribution Measurement

Baxter, B. P. (1991). Measurement of the mean and distribution of fibre diameter of wool using an image analyser, (first draft). Nice, France, IWTO.

Baxter, B. P., M. A. Brims and T. Taylor (1992). "Description and performance of the Optical Fibre Diameter  Analyser (OFDA)." Journal of the Textile Institute 83(8): 507-526.

            Describes the development and performance of the first commercial version of the OFDA100.

Baxter, B. P., M. A. Brims and T. Taylor (1992). Further studies on the performance of the OFDA. IWTO, Technical report 8, Punta del Este, Uruguay.

Details a number of studies undertaken with the OFDA100 to characterise its performance and response to possible interfering effects such as sample contamination, operator influences, and snippet-related factors.  Reports the results of 1300 comparisons between OFDA and airflow.  Used to move the test method from a working group draft to a draft test method.

Baxter, B. P. (1992). OFDA round trials with greasy wool cores. IWTO, Technical report 8, Nice, France.

First international round trial with 25 greasy wool samples and a number of different preparation techniques.  7 instruments were used in 4 countries to allow estimates to be made of variance components for diameter measurement.

Baxter, B. P. and M. A. Brims (1992). Linearity and focus independence of the OFDA. IWTO, Technical report 9, Nice, France.

            Describes experimental work with graticules and precision wires to examine the linearity and focus effects on the OFDA over the range 5 to 125 µm.


Baxter, B. P. and D. C. Teasdale (1992). Suitability of Interwoollabs IH tops for calibration of the OFDA. IWTO, Technical report 10, Nice, France.

Analyses the performance of OFDA when using IH tops as calibration material, to establish whether this method adds significantly to the overall variance. 

It concludes that the use of IH tops provides a satisfactory calibration method.

Baxter, B. P., M. A. Brims and D. C. Teasdale (1992). "The Optical Fibre Diameter Analyser (OFDA) - New technology for the Wool Industry." Wool Technology and Sheep Breeding 15(4): 131-134.

            Description of the OFDA100 technology.

Edmunds, A. R. (1992). Effects of snippet length on profile diameter measurements. IWTO, Nice, France.

Provides a theoretical relationship between snippet length, ellipticity, and diameter for projected image methods such as projection microscope and OFDA. 

Shows plots of mean fibre diameter and standard deviation of diameter determined by OFDA on 10 tops with snippet lengths from 0.2 to 5 mm.

Lüpke, E. E., O. E. Wright and A. C. Botes (1992). Comparative study with OFDA and airflow on core samples before and after Shirley Analyser. IWTO, Nice, France.

            Results from OFDA and airflow were compared on 408 greasy core samples, with the OFDA samples being measured before and after Shirley Analyser treatment.


Turpie, D. W. F., C. H. Steenkamp and E. E. Lüpke (1992). Differences between calibrations for wool and mohair on the FDA200 and OFDA. IWTO, Technical report 2,

Nice, France.

Describes experimental work using FDA200 and OFDA100 instruments that provides evidence that different calibrations are required for wool and mohair on both instruments.

Anon. (1993). Fineness distribution determined by digital image processing. Wool Record: 55.

            Description of the OFDA100 and its capabilities.

Brims, M. A. (1993). The theoretical comparison of OFDA and FDA class instruments for the measurement of fibre diameter distribution. IWTO, Istanbul, Turkey.

Explored the theoretical differences between the measurements of diameter at a point on a fibre snippet as compared with averaging over a length intersected by a circular beam.

Edmunds, A. R. (1993). Comparative fibre diameter measurements on NZ wools by airflow, Laserscan and OFDA. IWTO, Istanbul, Turkey.

Details the results of comparisons between measurements on two sets of NZ wools using airflow, OFDA and Laserscan.  140 samples were used ranging from 19 to 40 µm.  The work suggests that calibration methods need to reflect measurement preparation methods.

Edmunds, A. R. (1993). A comparative evaluation of the Sirolan Laserscan and OFDA for fibre diameter measurement of New Zealand wools. Christchurch, New Zealand, WRONZ: 27.

Describes the results of measurements on 3 sets of greasy wool samples (comprising 50, 90 and 13 samples respectively) on both OFDA and Laserscan, using both minicores of greasy wool (cleaned in trichloroethane), and minicores of Waring Blendor-prepared samples.  Measurements were compared against known airflow values. Some difficulties were experienced with operation and calibration of the Laserscan.  The author concluded that "especially for use on New Zealand wools, OFDA is the preferable system of the two for the measurement of fibre diameter."


Teasdale, D. C. (1993). A technical note on the bias in diameter coefficient of variation caused by the average diameter of fibre snippets. IWTO, Instanbul, Turkey.

Examines the effects on coefficient of variation of using fibre diameter measurements undertaken at a point compared with diameter measurement based on an average over a small length of snippet.  The difference, due to an additional component of variation along the snippet length, accounts for some of the observed differences between OFDA and Laserscan diameter distribution statistics.

Baxter, B. P. (1994). "Influences on the comparisons between the mean fibre diameter of wools measured by airflow and by projected image methods." Wool Technology and Sheep Breeding 42(2): 176-193.

Literature review of performance and technical issues concerned with the different physical principles used by each of the diameter measurement techniques.  Covers a wide range of possible interfering effects, such as fibre specific gravity, crimp, ellipticity, coefficient of variation, calibration errors, residual grease, snippet and specimen fibre length, preparation effects, relaxation, medullation, and animal nutritional influences.


Baxter, B. P. (1994). Review of the suitability of the 1993 series of Interwoollabs IH tops for calibration of the OFDA. IWTO, Technical report 14, New Delhi, India.

Reviews the calibration performance of the OFDA using the 1993 IH tops series, and confirms that this series is equally as capable of providing suitable calibrations as the previous series.

Baxter, B. P. (1994). Some observations on the 1993 snippet length effect - projection microscope round trial. IWTO, Technical report 4, Nice, France.

Applies OFDA measurements of curvature and Edmunds's elliptic integral theory to the 1993 snippet length round trial results, and concludes that the data is consistent with this theory.

Baxter, B. P. and M. A. Brims (1994). 1994 OFDA round trials on greasy wool core samples. IWTO, Technical report 5, Nice, France.

Outcome of an international round trial using greasy wool cores measured for mean fibre diameter by both OFDA100 and airflow.  The precision of the OFDA100 and airflow were found to be similar.

Baxter, B. P. and M. A. Brims (1994). 1994 OFDA round trials on sliver samples. IWTO, Technical report 6, Nice, France.

Reports the results of an international round trial carried out using OFDA and airflow on sliver samples and concludes that the precision of the OFDA was similar to that of airflow.

Baxter, B. P. (1994). Supplementary analyses on OFDA round trial on sliver samples. IWTO, Nice, France.

A supplementary analysis of the data from the 1994 sliver round trial.  The author concluded that 2 slides per sample were adequate to achieve the required precision, rather than the 4 slides used in the trial.


Edmunds, A. R. (1994). Effects of snippet length on profile fibre diameter measurements: additional data for recent series of Interwoollabs reference tops. IWTO, Technical report 14, Nice, France.

Repeats investigations using OFDA100 measurements on a range of snippet lengths (see report 14, IWTO Nice, Dec 1992) on 17 additional IH tops.  Concludes that the available evidence clearly indicates that the snippet length used in all profile fibre diameter measurements should be at least 2.0 mm in order to avoid serious positive bias in both mean and standard deviation.  The author also recommends that snippets should be obtained by minicoring rather than microtoming.

Edmunds, A. R. (1994). Comments on snippet length effects. IWTO, Annex to technical committee minutes, New Delhi, India.

Comments separately on recent contributions by Blankenburg and David concerning the snippet length effect and trials, and adds further data obtained using the OFDA100 on the 1991/2 and 1993 series of IH tops.  Both minicored and microtomed snippets were measured with snippet lengths ranging from 0.2 to 4.5 mm.  The author concludes that all fibre diameter values reported in the past have been positively biased.


Houillon, L. (1994). Mesure du diametre des fibres. Industrie Textile: 31-34.

In reference to the IWTO test methods for OFDA and Laserscan, or any other methods based on distribution data, the author proposes a new calibration method ("Mephisto") based on full feedback of the distribution data to the instrument. (In French)

Qi, K., C. J. Lupton, F. A. Pfeiffer, et al. (1994). "Evaluation of the Optical Fibre Diameter Analyser (OFDA) for measuring fiber diameter parameters of sheep and goats." Journal of Animal Science 72: 1675-1679.

Experiments were conducted on both wool and mohair in top, core and staple forms, in which the results obtained with the OFDA100 were compared with both the FDA200 and the ASTM projection microscope method.  The authors concluded that the OFDA results were very closely related to the PM measurements, with the OFDA overcoming one of the shortcomings of the FDA200, which is over-estimation of SD.  They suggest that the OFDA is a promising system for rapid and accurate evaluation of fiber diameter and its distribution.

Wear, J. L. (1994). An investigation into the relationship between spin fineness, OFDA MFD, SD, and airflow measurement. Wellington, NZ, SGS-WTS.

Airflow, OFDA MFD and SD, and OFDA spinning fineness were investigated to establish whether airflow could be predicted from these OFDA measurements.  Whilst the use of SD and OFDA MFD improved the prediction of airflow over the use of MFD alone, use of spinning fineness did not improve the correlation.

Anon. (1995). Digital image processing for the determination of fiber fineness and fineness distribution. Melliand Textilberichte: E83-E84, 311-314.

Describes the instrument and parameters measured by the OFDA100 - fibre diameter, diameter distribution (histogram), standard deviation, coefficient of variation, and prickle factor.

Baxter, B. P. and J. W. Marler (1995). Report of the 1995 IWTO round trial: Part 2: Wool tops - Addendum: Confidence limits for measurements made on tops. IWTO, Technical report 16 addendum, Harrogate, UK.

Analysis of precision statistics of the 1995 IWTO round trial on tops.

Brims, M. A. (1995). Bias in measuring standard deviation that would result from bias in quoted mean fibre diameter of calibration standards: experimental verification using OFDA. IWTO, Technical report 14, Harrogate, UK.

Using recent data from projection microscope round trials, the author describes the effects that measuring short snippet lengths on projection microscope would have on the subsequent calibration and measurements on instruments such as OFDA.

Harig, H. (1995). Report of the IWTO round trial part 1: raw wool. IWTO, Technical report 15, Harrogate, UK.

            Reports on an international round trial to compare mean fibre diameter and diameter distribution results on OFDA, Laserscan and airflow on greasy wool cores.

Harig, H. (1995). Report of the IWTO round trial part 2: wool tops. IWTO, Technical report 16, Harrogate, UK.

            Reports on an international round trial comparing mean fibre diameter and diameter distribution from projection microscope, airflow, OFDA and Laserscan on tops.

Harig, H. (1995). Report of the 1995 IWTO round trials: Raw wool, additional remarks and figures. IWTO, Harrogate, UK.

            Provides plots and conclusions additional to the original report, and concludes that OFDA and Laserscan have similar performance on raw wool.

Harig, H. (1995). Report of the 1995 IWTO round trials: Wool tops, additional remarks and figures. IWTO, Harrogate, UK.

            Provides additional plots and conclusions to the original report.

IWTO (1995). IWTO-47: Measurement of the mean and distribution of fibre diameter of wool using an Optical Fibre Diameter Analyser (OFDA). Ilkley, IWTO.

            Method for the measurement of fibre diameter and diameter distribution of wool using OFDA.  Applies to fibres in raw wool and in sliver/top.


Marler, J. W. and B. P. Baxter (1995). Report of the 1995 IWTO round trial: Part 1: Raw wool - Addendum: Confidence limits for measurements made on raw wool. IWTO, Technical report 15, Addendum, Harrogate, UK.

            Analysis of precision statistics for the 1995 IWTO round trial on greasy wool


van Zyle, A. (1995). Comparison of 'Wholeslide x 1' versus 'Wholeslide x 2' for mean fibre diameter and standard deviation using OFDA. IWTO, Raw wool group Appendix 7, Nice, France.

            Concludes that 'wholeslide x 1' is adequate to provide the required precision.  This work was carried out using the WTB design of spreader.


Baxter, B. P. and A. van Zyle (1996). Preliminary data on diameter distribution differences between projection microscope, OFDA and Laserscan. IWTO, Sliver group, tabled report, Nice, France.

Presents the results of histogram comparisons between diameter distribution data on 3 coarse tops obtained by OFDA100, Laserscan and projection microscope.  The OFDA and Laserscan both reported higher SD and CvD than the projection microscope.


Edmunds, A. R. (1996). Spreader effects on OFDA fibre diameter measurements. IWTO, Raw wool group, Appendix 5, Capetown, South Africa.

Reports an experimental comparison of three different spreader designs and concludes that whilst the differences between the results were small, measurements should be made with the same design as was used for calibration.

Edmunds, A. R. and S. L. Ranford (1996). Update to precision in IWTO-47 (OFDA). IWTO, Raw wool group Appendix 7, Nice, France.

            Examines changes in measurement variance due to change from 'wholeslide x 2' to 'wholeslide x 1'.

Herrmann, S. and F.-J. Wortmann (1996). Results of the EFFN round trial on cashmere diameter testing. European Fine Fibre Network Occassional Publication 4. Aberdeen, Scotland, EFFN, Macauley Land Use Research Institute: 117-133.

An interlaboratory trial was carried out using cashmere samples at various stages of dehairing.  Projection microscope was used in 8 laboratories, OFDA100 in 3 laboratories, and Laserscan and Cross Section Method in one each.  Concludes that the OFDA should be the preferred measurement technique for diameter of cashmere.

Turpie, D. W. F. (1996). Report on results of round trial on relaxation and some related investigations. IWTO, Sliver group, Appendix 5, Nice, France.

Reports the results of a round trial involving 9 laboratories on the effects of relaxation on OFDA100, projection microscope and airflow measurements of mean fibre diameter.  Relaxation methods included hot soaking as well as steaming.

Turpie, D. W. F. and C. H. Steenkamp (1996). Changes in dimensions of calibration sample snippets with changes in pre-treatment. IWTO, Technical report 16, Capetown,

S. Africa.

Examines the effects of soaking tops in hot water and detergent on the measurement of diameter by OFDA100.  The work confirms the necessity of calibrating the instrument for the preparation conditions under which it will be used for measurement, as is specified in the test method IWTO-47.

van Zyle, A. (1996). Comparison of 'wholeslide x 1' versus 'wholeslide x 2' for mean fibre diameter and standard deviation using OFDA - Part II. IWTO, Raw wool group, Appendix 4, Capetown, South Africa.

Complements earlier work, by using the circular spreader, and concludes by recommending a change to IWTO-47 to require 'wholeslide x 1' rather than 'wholeslide x 2' measurement.

Baxter, B. P. (1997). "Examination of the differences between OFDA and Laserscan on ultrafine wools." Wool Technology and Sheep Breeding 45(4): 267.

Compares the MFD results for wools of 18 microns and below on both the OFDA100 and Laserscan, and drew attention to the increasingly significant divergence between the methods as the diameter decreased.  By comparing results with projection microscope data, it was concluded that the OFDA was measuring correctly, and that the Laserscan was in error due to extrapolation effects in the calibration.  A pragmatic solution was offered to correct the Laserscan calibration by using alternative curve-fitting methods.

Blankenburg, G., J. Hahnen, K.-H. Lehmann, et al. (1997). The problem: Fibre "diameter" measurement in profile. IWTO, Sliver group Appendix 1, Nice, France.

Presents data on "wet/set" and "wet relaxed" tops to support the hypothesis that "by a wet relaxation process the curvature and or rotation of the major/minor axes along fibre length is increased, and by this increasing the probability to measure in profile a "diameter value" which is closer to the "apparent diameter" as without relaxation".


Edmunds, A. R. (1997). Relaxation, curvature and snippet length effects in profile diameter measurement. IWTO, Technical report 20, Boston, USA.

OFDA measurements of fibre diameter and radius of curvature were made on the then current set of IH calibration tops both before and after relaxation by steaming.  Two different snippet lengths were used as well as full-length fibres.  Recommends that a standard relaxation technique should be included in all fibre diameter measurement procedures.


Hoffmann, R. and J. Vogelsang (1997). Commercial implications of difference in topmaking and top trading (short version). IWTO, Fineness seminar, Boston, USA.

Reports commercial results of MFD comparisons between the three diameter measurement technologies on tops, and comments on the effective differences in

core-comb relationships when the raw wool is measured on airflow and the tops on OFDA or Laserscan.  At the fine end the two new technologies give bigger

core-comb differences than airflow.  On tops all three technologies give similar results, but with the airflow being finer at the fine end.  During QC measurements, OFDA and Laserscan agree with each other "nearly perfectly" on tops.  Similar average values are reported for CvD from OFDA and Laserscan over 4 diameter ranges.  Hercosett treatment of wool gives coarser airflow results, finer OFDA results, and no change to Laserscan results.  Conditioning of samples is required for both OFDA and Laserscan.  Spinning is affected by both MFD and diameter variation.


Lindsay, A. R. and J. W. Marler (1997). "The importance of coefficient of variation of fibre diameter of blends of wool tops when measured by airflow, Laserscan and OFDA." Wool Technology and Sheep Breeding 47(4): 291-301.

The measured fibre diameter of blends of wool top was investigated using airflow, Laserscan and OFDA.  It was found that if the individual components of the blend differed by more than 10 µm, the airflow could be in error by up to 4 µm.  The authors conclude that large differences between airflow and projection microscope techniques may be due to excessively high coefficient of variation of diameter in the sample.


Sommerville, P. J. (1997). Measurement of the fineness of superfine wool: a comparison of airflow, Laserscan and OFDA. IWTO, Technical report 15, Boston, USA.

In a study of the measurements of mean fibre diameter of fleece samples from superfine sheep using airflow, Laserscan and OFDA, significant diameter-dependent differences were found between the instruments, which tended to increase as the diameter was reduced.  Below 16 µm, it was observed that OFDA was measuring a greater number of fine fibres than Laserscan.

van Zyle, A. (1997). Alternative procedures for the handling of subsamples for OFDA - IWTO-47. IWTO, Raw wool group, Appendix 6, Nice, France.

An experiment is reported in which subsamples are prepared for OFDA measurement in the same way as for airflow in IWTO-28.  It is concluded that there were no significant differences in the results, thereby allowing streamlined preparation procedures to be used.


Baxter, B. P. (1998). An initial investigation into the effects of medullation on comparisons between Airflow, OFDA and Laserscan. IWTO, Technical report 16, Dresden, Germany.

Using measurements obtained with the medullation module on the OFDA100, a method of correcting for the effects of medullation was suggested, so that OFDA results could be used to predict airflow results on coarser wools.

Baxter, B. P. (1998). Comparison of Laserscan, OFDA and airflow on raw wool samples. IWTO, Raw wool group, Nice, France.

Results were shown of approximately 370 comparisons between OFDA100, airflow, and Laserscan on a typical range of New Zealand wools.  It was proposed that if the OFDA was operated over the same calibration range as the Laserscan (e.g. 0 to 80 µm), then the degree of agreement between them was exemplary. Similarly, if the same constraint is applied, and an additional adjustment made for the along-fibre variance, the two instruments also agreed on CVD.  On curvature, the level of agreement was again considered satisfactory, although a bias was detected.   It was demonstrated that the Laserscan and airflow give similar results, and that the OFDA and airflow relationship can be improved to the extent that airflow can be satisfactorily predicted.

Baxter, B. P. (1998). Additional comments on the measurement of superfine wools by OFDA, airflow and Laserscan. IWTO, Raw wool group, Nice, France.

This report followed from a trial carried out between OFDA100, Laserscan and airflow on a broad range of NZ wools, and reported separately.  It highlighted the diameter range below 20 µm, and confirms that the three instruments can now produce consistent results for MFD down to the range covered by the current IH tops.  Good agreement between Laserscan and OFDA was also demonstrated on CvD.  Below 16.5 µm the OFDA diverged from both the airflow and Laserscan on MFD.  Hypotheses were presented that suggested that whilst the instrument was not in error, it was measuring aspects of the fibre which may not be observed by the other instruments, and in that respect there remains a fundamental problem at that extreme end of the range.  Two options were suggested for further investigation.

Edmunds, A. R. (1998). Relaxation and snippet length effects on the 12th series of IH tops. IWTO, Raw wool group report RWG06, Nice, France.

Reports measurements of snippets under normal conditions and after relaxation, and with different snippet lengths. The author concludes that calibration of the OFDA using shorter snippets as specified in the projection microscope method would allow closer agreement between the OFDA and PM on sliver for SD when using 2mm snippets, but would give finer results for MFD.  For curvature measurements, the author notes that steaming appears to cause less relaxation than laboratory scouring.

Knowles, D. G., P. R. Greatorex and G. V. Barker (1998). Comparison of IWTO test methods for fibre diameter measurement of the New Zealand wool clip

Part 1 - Mean fibre diameter. IWTO, Technical report 12, Dresden, Germany.

            Compares test results on NZ greasy wools using airflow, OFDA and Laserscan in NZWTA's laboratory.

Knowles, D. G., P. R. Greatorex and G. V. Barker (1998). Comparison of IWTO test methods for fibre diameter measurement of the New Zealand wool clip. 

Part 2 - Fibre diameter variability. IWTO, Technical report 13, Dresden, Germany.

            Compares the results of OFDA and Laserscan for SD and CvD over a range of NZ wools tested by NZWTA.

Knowles, D. G. (1998). Investigation into mean fibre diameter instrument differences in the measurement of New Zealand superfine wool. IWTO, Technical report 14, Dresden, Germany.

            119 sale lots are compared by all 3 diameter measurement technologies in the NZWTA laboratory.

Marler, J. W. and H. Harig (1998). A comparison of diameter measurement technologies from interwoollab international round trials for wool tops. IWTO, Technical report 10, Dresden, Germany.

The Interwoollabs round trial data was used to compare the 4 diameter measurement technologies.  Some of the observed differences between airflow and the other methods were found to be related to CvD.  When this was taken into account there were still differences that might be related to medullation content.  The OFDA and Laserscan showed the least variation between methods on paired comparisons.  PM, OFDA and Laserscan showed some systematic differences in SD values.


Pinto de Andrade, L., J. Varzea Rodrigues and J. Serrano (1998). "The quality of fine wool in Portugal - preliminary results." EFFN news 4: 2-5.

The preliminary results presented show that more than 35% of the wool produced in Portugal, from 1.3 m animals classed as Merino, can be classed as fine wool with a fibre diameter less than 22.5 µm when measured with the OFDA100.


Puntila, M.-L. (1998). "Breeding program for wool traits - The Fine Finnwool Project." EFFN news 4: 14-15.

            Describes the beginning of performance recording for Finnsheep, based on OFDA measurements and BLUP evaluation.


Sommerville, P. J. (1998). Measurement of the fineness of superfine wool: Effect of the revised Laserscan calibration function on comparisons between airflow, Laserscan and OFDA. IWTO, Commercial technology forum paper CTF04, Nice, France.

Following the use of the new calibration function for the Laserscan, relationships between the diameter measurement systems have been re-examined for superfine wool fleeces.  The Laserscan was now coarser than the airflow in the 15.5 to 19 µm range, and finer than airflow below 15.5 µm.  The Laserscan is now more closely aligned with the OFDA100 for wools below 16 µm.  Previously large differences between OFDA and Laserscan on diameter distribution parameters have been significantly reduced.


Baxter, B. P. (1999). The effects of calibration errors on between-laboratory and between-instrument diameter comparisons. IWTO, Sliver group report 1, Nice, France.

Examined the Interwoollabs data on laboratory performance in blind trials immediately after calibration.  It concluded that whilst the performance of laboratories using OFDA100 and Laserscan was better than for airflow, there was still a considerable range of possible combinations of bias between different laboratories.  It was proposed that the calibration MSE criteria in the test methods should be reviewed with a view to tightening up the allowable performance.

Denney, S. I., T. J. Mahar and J. W. Marler (1999). OFDA measurements using two different snippet lengths (0.8mm and 2.0mm). IWTO, Raw wool group report RWG02, Nice, France.

            Compared the results for MFD, SD, and curvature for 0.8 mm and 2 mm snippets on the OFDA when using the WTB spreader.


Edmunds, A. R. and S. L. Ranford (1999). Conditioning effects on fibre diameter and curvature of the 12th series of IH tops. IWTO, Raw wool group report RWG03, Nice, France.

Compares the behaviour of IH tops under increasing RH values from 0 to 100% both "as-is" and after relaxation by steaming.  Reports results of OFDA100 mean fibre diameter and curvature.  Confirmed that the behaviour with respect to relative humidity was consistent with previously published data obtained using projection microscope and airflow.


Knowles, D. G. and J. W. Marler (1999). The relationship between mean fibre diameter measurements by airflow, Laserscan and OFDA for Australian and New Zealand wools. IWTO, Raw wool group report RWG02, Florence, Italy.

            Proposes baremes to convert from one measurement result to another for Australian and New Zealand wools.  Based on AWTA and NZWTA data only.


Marler, J. W., G. R. Shepherd and R. G. Barry (1999). A comparison of histograms from OFDA, projection microscope and Laserscan for wool tops. IWTO, Sliver group report SG01, Florence, Italy.

Uses Interwoollabs PM data on 9 tops to draw comparisons with OFDA100 and Laserscan results obtained in one laboratory.  Very good agreement was obtained in the middle of the diameter range but there were some significant differences evident at both extremes.  The authors comment that the different definitions of diameter used by each instrument are unlikely to mean that the observed differences can be reconciled.  However, they also conclude that the differences are small and unlikely to have any impact on processing or product performance.


Glass, M. (1999?). "A technique for generating random fibre diameter profiles using a constrained random walk." (in draft).

A random walk technique, using appropriate statistical properties of adjacent points in along-fibre diameter profiles, in conjunction with a constrained walk deviation, has been developed for generating random along-fibre wool snippet diameter profiles.  The technique finds use in Monte Carlo simulations where the variation in diameter along fibres plays a significant role in properties of interest.  Confirms agreement with data published on along-fibre variability measured using OFDA100.


ASTM (2000). ASTM D6500 Standard test method for diameter of wool and other animal fiber using an Optical Fibre Diameter Analyser. Pennsylvania, USA, ASTM.

Test method for the use of OFDA for the determination of the average fibre diameter and the fibre diameter variation in wool and other animal fibres in their various forms.


Denney, S. I. (2000). Slide preparation procedures for the OFDA - the balance between minicoring and spreading time. IWTO, Raw wool group Appendix 2, Nice, France.

Examines small biases that could arise due with different spreader designs and length of time the spreader operates for, and recommends text changes to standardise this aspect in IWTO-47.


Denney, G. D., T. J. Mahar and J. W. Marler (2000). The effect of snippet length and fibre relaxation on the mean fibre diameter, fibre diameter distribution and fibre curvature measured by Laserscan and OFDA. IWTO, Sliver group report SG03, Christchurch, New Zealand.

Study of the effects of snippet length and relaxation effects on measurement results from Laserscan and OFDA100.  The results from both instruments were confirmed to be affected by changes in snippet lengths.  The OFDA showed greater differences due to relaxation effects (as is well known, and compensated for in MFD measurement by the calibration process for greasy wool).  The Laserscan was also found to be affected by fibre relaxation, but the potential bias of 0.2 µm was considered by the authors to be "commercially unimportant".


ILRT (2000). The effect of fibre relaxation on the mean fibre diameter and fibre diameter distribution measured by Laserscan and OFDA. IWTO, Sliver group report SG04, Christchurch, New Zealand.

Examines two different relaxation procedures and the effects on MFD and SD measurement by OFDA100 and Laserscan.  The authors conclude that the effects on Laserscan measurements were small, and the effects on OFDA MFD measurements are compensated for in the calibration process, but that there remained an uncompensated effect on OFDA SD when measuring greasy wool.  (The plots which accompany the paper, however,  suggest that there is a small but significant systematic effect on Laserscan measurements caused by relaxation.)


Knowles, D. G. (2000). The effects of standardising the measurement range on the mean and standard deviation of fineness for Laserscan and OFDA. IWTO, Raw wool group report RWG02, Christchurch, New Zealand.

Because of the data transmission limitations of some wool industry systems, the report recommends that the number of 1 µm bins reported from both Laserscan and OFDA be standardised to the lowest common denominator of the Laserscan (i.e. 80).  The author concludes that for Australasian fine wools there would be only a small average change in results.  Individual wool samples could show differences of up to 0.3 and 0.9 µm in mean fibre diameter and standard deviation respectively.  No investigation is reported on the possible effects on coarse wools from other sources or for other animal fibres.


Knowles, D. G. (2000). The relationship between coretest fineness measurements by airflow, Laserscan and OFDA of New Zealand merino wool classed at NZPAC. IWTO, Raw wool group report RWG04, Christchurch, New Zealand.

Compares the results on airflow, OFDA and Laserscan for 362 lots processed at NZPAC.  At less than 15.5 µm the Laserscan and OFDA produce similar results, both measuring finer than airflow.  The opposite trend was shown above 20 µm where airflow measured approximately 0.2 µm finer than the other 2 instruments.


McLaughlin, I. (2000). Innovative wool testing - OFDA, Australian Wool Taskforce 2000.

            Description of the OFDA technology and the application of OFDA2000 to in-shed testing.


Sommerville, P. J. (2000). "Introduction of the Sirolan-Laserscan as the standard service for certification of mean fibre diameter by AWTA Ltd." Wool Technology and Sheep Breeding 48(3): 198-232.

The paper reviews the development of the projection microscope, the airflow, the Sirolan-Laserscan and the OFDA.  The precision of the instruments is discussed and the differences in the measurements that they provide are reviewed in detail.  The review shows that for Australian greasy wools, the differences between the instruments, while in some cases statistically significant, are generally quite small.  These differences, where they exist, can often be attributed to deficiencies in the airflow instrument.


Standards_Australia and N. Z. Standards (2000). AS/NZS 4492 Wool - fleece testing and measurement, Standards Australia.

            Specifies methods for sampling of individual animals for ranking purposes, and details suitable methods for measuring washing yield and mean fibre diameter.


Stobart, R. H. and A. McColl (2000). A comparison of fiber measurement methods to obtain average fiber diameter of fibers other than wool. IWTO, Commercial technology forum paper CTF04, Christchurch, New Zealand.

Reports a trial on wool, mohair, cashmere and camel hair, comprising both greasy and top forms, using OFDA, Laserscan and ASTM projection microscope methods.  The authors conclude that there is good concensus amongst the 3 methods for measuring fibers in addition to wool and that these instruments are capable of providing reliable diameter estimates of other fibres.  The individual differences between OFDA and Laserscan for all the samples fell in a consistent band between -0.5 and + 0.5 µm across the diameter range.

van Zyle, A. (2000). The relationships between mean fibre diameter measurements by airflow, OFDA and Laserscan for South African wools from different breeds. IWTO, Raw wool group report RWG05, Christchurch, New Zealand.

Diameter differences between airflow, OFDA and Laserscan on 434 greasy South African wools were found to vary with the breed of sheep.   For the bulk of the SA clip, consisting of merino fleece wool, there appears to be no difference on average between airflow and OFDA.  Mutton merino wool, above 25 µm, which is known to have varying levels of medullation, gives slightly finer results on airflow than on OFDA.


van Zyle, A. (2000). The relationship between airflow and OFDA measurements from South African greasy wool and commercial mill tops. IWTO, Sliver group report SG02, Christchurch, New Zealand.

For the better quality tops, good relationships with small predicted difference in MFD were found between airflow results of South African greasy wool and the airflow and OFDA results from processed tops.  Between 20 and 26 µm the maximum average predicted difference was 0.1 µm.  Inferior tops produced more variable results.


AWTA (2001). What are the limits to wool fibre fineness measurement. AWTA Ltd Newsletter: 14-15.

Discusses IWTO Shanghai report RWG 02 and the issue of ultrafine fibres in wool samples with respect to instrument performance, and highlights that both OFDA and Laserscan are operating in areas where calibration must be significantly extrapolated.


Baxter, B. P. (2001). Technical note: 5 micron fibres found in an ultrafine grower lot - implications for diameter distribution measurement. IWTO, Raw wool group report 2, Shanghai, China.

Historically there has been debate in IWTO Technology and Standards groups about whether ultrafine fibres reported in diameter distributions by the OFDA instrument do actually exist.  This note describes measurements made on electron microscopes in Christchurch, New Zealand, and Aachen, Germany.  These confirmed that fibres, on which valid 5 µm OFDA measurements could be made, do in fact exist in some specialty grower lots.  Such measurements do not, however, necessarily mean that fibres with a continuous diameter of 5 µm are likely to be found frequently.

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