Uster Tester — Evenness and Imperfection Testing
topic
The Uster Tester measures yarn mass variation using a capacitance sensor at 400 m/min test speed, producing: CVm% (overall evenness), spectrogram (periodic faults), imperfection counts (thin −50%, thick +50%, neps +200% per 1000 m), hairiness (H value, S3), and diameter variation. Test length: 400 m minimum for statistical reliability. The Uster Statistics (published every 5 years) provide global percentile benchmarks (5%, 25%, 50% = median) for each count and system.
Role
The Uster Tester is the single most important quality instrument in spinning and the universal language of yarn quality communication between producers and buyers. Every yarn purchase contract specifies Uster percentile targets, and every lot is tested before shipment. Mastery of Uster test interpretation — reading spectrograms, understanding what each parameter means for fabric performance — is the core analytical skill of a ring spinning quality engineer.