The method of examining the quality of the synthetic material under production and the health of equipment includes the method of measuring the winding up tension. However, a conventional tension meter has the problem todegrade the yarn quality so that the tension sensor may come in contact with the yarn. Theoretical principle of non-contact tension measurement was derived and proved by analyzing the movement of the yarn in the synthetic yarn. winder. And, the non-contact tension meter was put to practical use by the technology which measured the propagate velocity of the yarn bent line shape generated by the quick turn of traverse guide with an optical sensor.The purpose of this report is to show that the online quality control of the yarn is possible with non-contact tension meter, by examining the relation between process irregularly which happens in the synthetic yarn (polyester POY) spinning process and the winding tension. We experimented with non-contact tension meter and obtained the following conclusion.(1) Irregularity in the process will change the tension as follows.·Irregularity in which only average tension changes (For example, the abnormal air temperature of under spinneret and the abnormal of IL 2 (2ndinterlace nozzle) air pressure) ·Irregularity in which only SD (standard deviation) of the tension will change (For example, the abnormal air velocity at quenching chamber, the abnormal OPU (finishing oil pick up unit), and yarn cross over) ·rregularity in which both average tension and SD (standard deviation) will changing (For example, the abnormal air pressure of IL 1 (1stinterlace nozzle), the abnormal Polymer IV (intrinsic viscosity)) (2) Our experiment shows that the average tension will change more than 20% in case where the surface temperature of spinneret is more than 12 degrees.(3) The irregularity process conditions such as the air velocity in quenching chamber (for ex. the increase of air velocity), the abnormal OPU (for ex. The decrease of OPU) and the yarn cross over can be detected easily by measuring the running yarn tensions because they will change the standard deviation of the yarn tension by more than 20%.

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