Fast Fourier Transformation (FFT) – Reliably detect periodical variations of product parameters

Especially while producing data cables, periodical variations of diameter, eccentricity and capacitance pose a risk for data transmission features. The online Fast Fourier Transformation analysis of these measuring values is an efficient tool to detect periodical occurring irregularities during cable extrusion.

Periodical variations of cable parameters may be caused by, for example, irregularities such as an extruder “pumping”, imbalance of rotating parts, periodical variations of the line speed, cyclic changes of the degree of foaming, vibrating (oscillating) wires and/or periodical irregularities during the conductor pre-heating.

Devices with FFT functionality

While the existence of periodical variations from the chronological sequence of the measured cable parameters is usually elusive, by using an FFT analysis, periodical reoccurring variations can be detected early on. Furthermore, the calculated frequency spectrum provides useful information to identify causes of cyclic irregularities within the cable production process, especially if production parameters, such as the line speed, are altered controllably.

As a standard, all SIKORA measuring devices, such as CENTERVIEW 8000, LASER Series 2000, LASER Series 6000 as well as CAPACITANCE 2000, have efficient digital signal processors. Because of the available processing power, a digital FFT spectrum analyzer as well as a prediction of the return loss are integrated directly into the gauge. The analysis takes place where input data (meaning the diameter, eccentricity or cable capacitance measuring values) is available in high temporal and amplitude resolution and high precision at minimal measuring value noise. A mostly analog and therefore, problematic transmission of sensitive single measuring values to external analysis systems is not necessary for FFT and SRL.