ISO 2648:2020 pdf free

ISO 2648:2020 pdf free.Wool一Determination of fibre length distribution parameters一Capacitance method
The capacitive sensor-based machine tests the length of textile fibres, using a test specimen of fibres made up with the aid of the mechanical grip.
The grip, fed with slivers or rovings, prepares a numerical specimen of fibres, where the number of fibres in each length class is represented in the same numerical proportion as in the original sliver.This test specimen is arranged in the form of a draw of fibres, with all the fibres having one of their ends (their base) situated approximately on the same line, perpendicular to the direction of the fibres.The test specimen formed in this way is then transferred from the grip to the capacitive sensor-based apparatus, where it is inserted between two thin plastic sheets.
The carriage containing the test specimen is either moved at a constant speed through a measuring condenser, or the measuring condenser moves over a stable test specimen at a constant speed. The variation in capacitance so produced is due to the partial replacement of the dielectric “air” and fibres between the dielectric plates of the condenser. Knowing the formation of the sample, it can be shown that the measured signal (proportional to this increase in capacitance) is equivalent to a cumulative Hauteur (H) diagram, which is automatically traced.
Samples shall not be taken for measurement from the disturbed outer layer, or immediately next to the core of a package. Slivers having adventitious thickness faults [especially abnormal thick or thin places) are to be discarded. Slivers taken directly from a comb, cut or chopped slivers and those containing fibre bundles are also unsuitable. In such cases, the variation in fibre length between successive samplings is likely to be very large, potentially giving rise to significant errors.
For slivers of combed wool weighing between 15 g/m and 30 g/m, a length of about 1,2 m is broken off from the homogeneous portion of the lot. Immediately after sampling, the sample held under slight tension is given 36 turns of twist (30 turns/m); held taut in this condition, it is doubled at its centre and its ends are brought together and held. See Annex A for details.ISO 2648 pdf free download.