Magnified Metrology
Instrument for measuring the dimensions of small objects involves projecting a backlit image onto a screen at a fixed magnification. Use of an optical projection microscope remains a standard method for determining the average diameter and distribution of wool and other animal fibres. The operator views the magnified silhouettes and uses a graduated scale or digital cursor to record the width of each individual strand.
Standard Procedure
Compliance with international testing protocols such as IWTO-8 ensures that the results are accepted in global trade. When using the optical projection microscope, the laboratory must prepare a slide of short fibre snippets called a beard. This preparation allows for the random sampling of the batch to ensure the data is representative of the whole lot.
Operator Influence
Focus and selection of the fibre edge depend on human judgment.
Calibration Routine
Accuracy of the instrument is maintained by measuring certified reference materials with known diameters. Technicians adjust the optical projection microscope until the readings match the specifications of the standard wool samples. This process compensates for any drift in the magnification or alignment of the lenses.
Consistent calibration ensures that a micron measurement in one country matches the measurement in another.
