Comparison of existing technologies

AVAILABLE TECHNOLOGIES

Fleece measurement services are now available from on-farm service providers as well as off-farm providers.

Off-farm fleece measurement services for Mean Fibre Diameter have been available for many years, initially exclusively based on the Airflow Instrument, but since the early 1990's almost all service providers are using the OFDA 100 or the Sirolan™ Laserscan. These services require the wool grower to collect his own samples, usually from the mid-side, and submit them to the laboratory. The sample preparation and measurement systems employed by these laboratories vary considerably, but almost always involve a cleaning stage, equilibration of the sample with a standard atmosphere, followed by further sub-sampling and measurement. Standards Australia has developed defined procedures but these are rarely if ever followed in their entirety.

Off-farm fleece measurement services for Mean Fibre Diameter have been available for many years, initially exclusively based on the Airflow Instrument, but since the early 1990's almost all service providers are using the OFDA 100 or the Sirolan™ Laserscan. These services require the wool grower to collect his own samples, usually from the mid-side, and submit them to the laboratory. The sample preparation and measurement systems employed by these laboratories vary considerably, but almost always involve a cleaning stage, equilibration of the sample with a standard atmosphere, followed by further sub-sampling and measurement. Standards Australia has developed defined procedures but these are rarely if ever followed in their entirety.

In recent years two on-farm technologies have become available. The first, the Sirolan-Fleecescan, is based on the Laserscan technology. It consists of equipment that can take a random sample from a whole fleece, a cleaning stage, followed by measurement using a Laserscan instrument. This system relies on sample conditioning to occur within the Laserscan instrument.

The second, the OFDA 2000 is based on the OFDA 100 technology, but measures by scanning along the length of a sub-sample drawn form a single staple, rather than fibre snippets obtained by mini-coring a sample.

This technology does not include a cleaning step and instead relies upon an average correction factor for grease, which is determined from a sample of approximately 30 staples drawn from a randomly selected group of sheep from the mob. The correction factor is derived from the difference between measurements on the same staples, greasy and clean. The OFDA 2000 attempts to correct for the effect of varying moisture content using some specimen wool fibres of known fineness that are constantly exposed the ambient atmosphere.

PRECISION INFORMATION

Round-trials between laboratories providing off-farm services indicate that the precision of these services for Mean Fibre Diameter varies between ± 0.6 to ± 1.6 microns. Some laboratories perform better than others. These precision values typically refer to a single site rather than to a whole fleece. When applied to whole fleeces the precision of these services will be less i.e. the range will be greater.

Little information was available about the precision of the on-farm measurement systems when they were first introduced. A trial conducted in late 2001, based on sampling approximately 100 sheep at 5 sites (see illustration), provides the most comprehensive comparative data to date, but more is needed. These results were derived from only one mob of sheep, and they should be viewed as indicative only at this stage until they have been validated on at least three other mobs from different wool producing areas.

The assumption of this work was that optimally, a fleece measurement system should provide an estimate of the measured characteristic for the whole fleece, because ultimately, whatever the application, it is the value for the whole fleece that determines the economic benefit that the measurement provides, either directly or indirectly. However, the work also provided comparative precision data for single site samples such as mid-side samples. These data, for Mean Fibre Diameter (MFD), Standard Deviation of Diameter (SDD), Coefficient of Variation of Diameter (CVD) and Mean Fibre Curvature (MFC) are summarised in the following tables.

These data are derived from measurements obtained using one instrument (laboratory) and therefore do not include variation between instruments (laboratories). Hence the precision limits will be lower than normal practice. Part 4 of this series considers the practical implications of the above data.

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