FFT Analysis
Fast Fourier Transformation
Fourier spectrum on ECOCONTROL 2000
At the cable production, particularly at the manufacture of communication cables, smallest cable parameter variations should be avoided in case they occur periodically. The manufacture of state-of-the-art cable products demands a permanent control of the cable diameter, eccentricity and/or the cable capacity regarding periodical variations. The online analysis of these measuring data in the frequency range represents a powerful controlling tool for the determination of periodically occurring irregularities at the cable extrusion.
Periodical variations of cable parameters can be caused by irregularities such as pumping of the extruder, unbalance of rotating parts, periodical variations of the line speed, cyclical change of the foaming level and/or periodical irregularities at the pre-heating of the conductor.
While the existence of periodical variations can only be taken with difficulties from the chronological sequence of the measured cable parameters, with the analysis of the measuring values in the frequency range, periodically recurrent variations can be realized at an early stage. Moreover, the calculated frequency spectrum offers helpful information for identification of the causes of cyclical irregularities in the cable production process, especially, when product parameters, such as the line speed, are changed.
Powerful digital signal processors are included in all SIKORA measuring heads. Due to the integrated computing power, a digital spectrum analyser is realized directly within the gauge head. Furthermore, in addition, a prediction of SRL (see Structural Return Loss) is implemented. That is to say, that the online calculation of the spectrum of cable parameter variations as well as the online prediction of the SRL is shown where input data, i.e. diameter, eccentricity or cable capacity measuring values, are available with high amplitude resolution and high precision at minimum measuring value noise. A problematic (normally analog) transmission of highly rated single measuring values is not necessary.
