ISO 2648:2020

ISO 2648:2020 pdf free.Wool – Determination of fibre length distribution parameters -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.
The following length distribution parameters are calculated, Hauteur (H), coefficient of variation of hauteur (CVH), Barbe (B), coefficient of variation of barbe (CVB), L values and K values.
5.1.1 Mechanical grip.
The mechanical grip works in the same way as the nip of a rectilinear comb. At each cycle, it takes from the sliver a numerical draw or sample containing all the fibres whose heads lie in a short length of the sliver, between 2 cross-sections of the sliver about 2,5 mm (automatic preparer) to 3,7 mm (manual preparer) apart. The complete testspecimen is made up of a collection of about 6 to 10 of these samples.
5.1.2 Main capacitive sensor-based instrument, consists of two parts, assembled within one chassis:
1) a device, measuring the local mass of the fibre test specimen;
2) a computer, automatically evaluating the length distribution parameters during the test.
The device for measuring the local mass is made up of a special condenser in the form of a greatly elongated rectangle, 1,8 mm x 175 mm. The small dimension (1,8 mm) of the condenser in the direction of the fibres provides for a detailed examination of the local mass from the end of the sample up to the line of the common origin of the fibres.
A carriage automatically carries the test specimen at a constant speed between the electrodes of the measuring condenser, or conversely the condenser moves over the test specimen.
5.1.3 Recorder.
In the analogue system, the record is a galvanometric recorder, which automatically traces the cumulative Hauteur diagram on squared paper during measurement.
In the digital system, the data are captured by a computer which is capable of outputting the results to either the screen or to a printer. The diagram ordinate gives the percentage of fibres (biased by crosssection) of length greater than the length indicated on the corresponding abscissa. (The percentage by cross-section is very close to the percentage by number).ISO 2648 pdf download.

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