Cotton Fiber Length Testing Methods and High Volume Instrument Span Metrics
HVI span metrics quantify cotton length through optical beard scanning, where 2.5 percent span length dictates drafting gauges and uniformity governs noil extraction.
Optical Density Curve
Density Profiling
Optical monitoring of fiber beards allows automated test systems to analyze length distribution without damaging the sample. The plot called the optical density curve shows how the density of the fiber beard decreases as the distance from the specimen clamp increases. This curve represents the light absorption at each point along the length of the combed fibers.
It provides the mathematical foundation for calculating the span lengths of the specimen.
Sensor Recording
An optoelectronic sensor moves along the parallel beard of fibers, recording the intensity of transmitted light. The raw signals are converted into density values, which are plotted against the distance from the clamp. This curve starts at the clamp where the fiber density is highest and drops to zero at the tip of the longest fiber.
The sensor’s sensitivity must be checked regularly with reference plates to prevent measurement errors.
Metric Extraction
Analyzing the slope of the curve allows the instrument to determine several quality indicators. The fifty percent and two point five percent span lengths are calculated directly from specific points on the optical density curve. This eliminates the human bias that is common in manual array measurements.
A steeper curve indicates a higher proportion of short fibers in the cotton specimen.
Sorting Application
Weaving and spinning mills use these optical plots to evaluate the quality of their raw materials. Bales that generate erratic curves are excluded from premium production runs. This sorting process ensures that the finished yarn possesses high tensile strength and a uniform diameter.