OPTICALLY BASED ON-LINE FIBER MONITORING SYSTEM WITH DRIFT COMPENSATION

摘要

Optical transmissivity-dependent parameters (90) including yarn denier (20) are monitored on-line in real-time with a preferably microprocessor-controlled high frequency modulated-demodulated optically-bas ed system. A periodically driven LED (100) outputs preferably collimated light signal (120) and is spaced-apart from an array o f preferably identical photodetector ("PD") diodes (110A-C) that will track one another. The yarn (20) is spaced between one of the PDs and yarn characteristics can affect PD-received light. A first PD (110A) output feedback to the LED driver to compensate the system against factors affecting LED driver to compensate the system against factors affecting LED transmission and PD light reception. A second PD (110B) output is coupled to a fraction of the drive signal to enhance dynamic range. This signal is amplified, AC-coupled, sample-and- held during a stable active portion of the LED drive signal to demodulate the relevant signal. The digitized sampled held magnitude enables a CPU to provide denier and other yarn characteristics measurement data. A third PD (110C) helps self-calibrate the system.