Disclosed are embodiments of a voltage controlled oscillator capable of non-volatile self-correction to compensate for process variations and to ensure that the center frequency of the oscillator is maintained within a predetermined frequency range. The thermoplastic fibers are distributed by air entertainment through tubular forming screens having rotary distribution members therein. These profiles are processed to respectively provide joint data and seam data, thereby allowing to perform said joint tracking and said seam inspection of said joint during said motion.