Spinning machine with a drafting system for stretching a fiber structure and corresponding method

Spinning machine with a drafting system (4) for drawing a fiber structure (FB '), eg cotton, polyester or the like, with at least one drafting zone formed by two spaced drafting elements (5a, 5b, 6a, 6b, 7a, 7b) Drive system (23, 24, 25) for determining the drafting height in the at least one drafting zone, at least one inlet sensor (1) upstream of the drafting system (4) and / or at least one outlet sensor (11) downstream of the drafting arrangement (4) for determining the strip cross-section or the fiber mass per unit length of incoming or outgoing fiber strand sections (FB '), and means (28, 29) for creating at least one amplitude-frequency function (spectrogram) and / or an amplitude-time function (diagram) from the measurement signals of the inlet and / or outlet sensor (1, 11), characterized by a computing unit (30), which is designed and arranged such that it performs a comparative evaluation of the spectrograms (S E, SA, SL) and / or diagrams of measurement signals of fiber composite sections, the measurement signals originating from at least two of the following three sensors, namely the inlet sensor (1), the outlet sensor (11) and a sensor of a laboratory measuring device (27), which is designed to create a spectrogram or graph of the stretched fiber bundle in order to localize the origin of one or more band errors on the basis of the comparison.