Method, system and sensor for detecting a characteristic of a textile or metal thread fed to an operating machine

Method for detecting and monitoring a characteristic of a thread (F) fed to an operating machine (M), said method comprising optical-type detection of such monitored characteristic, said optical-type detection being performed with an illumination of the thread, the method providing for a first detection of said characteristic using means (3) of analog type and a second detection of said characteristic using means (4) of digital type, the second detection of the digital type allowing a digital value of the monitored characteristic to be determined, said digital value being used to calibrate an analog value of the monitored characteristic obtained in the first detection of the analog type to precisely identify the definitive value of said monitored characteristic, said first detection of the characteristic of analog type and said second detection of such characteristic of digital type being performed independently, separately and generating corresponding data which are sent to a monitoring unit (8), characterised in that in a first stage said monitoring unit (8) determines the digital value of the above characteristic on the basis of the data detected using the digital-type means (4) and calculates a calibration variable (C(t)) on the basis of said determined digital value, said calibration variable (C(t)) varying over time, in a second stage said monitoring unit (8) modifying the data detected by the analog-type means (3) on the basis of the calibration variable which is a function of such value of the characteristic of digital type determined in the second detection, said modification taking place in real time and allowing the detection of the characteristic of analog-type to be calibrated so to determine the definitive value of the monitored characteristic.