Patent ID: 7228245

Claim:
A method for determining fundamental oscillation frequency in an optical fibre during drawing thereof from an optical preform, the oscillation of the optical fibre being measured perpendicular to the longitudinal axis thereof for formation of a frequency spectrum using Fast Fourier Transformation (FFT), from which the fundamental oscillation frequency is determined, wherein the method comprises: i) determining the frequency spectrum, ii) mathematically processing a number of spectra as determined in operation i) to obtain a composite spectrum, iii) re-determining the spectrum, iv) removing the oldest spectrum from the composite spectrum, v) mathematical processing the spectrum according to the operation iv) and the spectrum obtained according to the operation iii) to obtain the composite spectrum, vi) determining the fundamental oscillation frequency from the composite spectrum, vii) outputting the determined fundamental oscillation frequency, and viii) repeating operations iii)–vii).