Measuring spindle growth in high speed milling machines 27.03.2014 In order to minimise positioning errors in machine tools, the eddy current sensor SGS 4701 measures the thermal extension of high-frequency spindles. The spindle is at the heart of a machine tool and so plays a decisive role in the dimensional accuracy and surface quality of the respective workpiece. High speeds and the heat generated result in the axial extension of the workpiece spindle and to the resultant positioning error during finishing of the workpiece. The new eddyNCDT SGS 4701 miniature eddy current sensor measures the thermal and centrifugal force extension of high-frequency spindles by measuring on the labyrinth-ring. The measured values are fed into the CNC machine tool as correction values and compensate for any positioning errors. The miniature sensor models have dimensions of 4.5 x 10 x 12 mm³ or 4 x 4 x 10 mm³ and can be integrated with the controller into the machine tool spindle. For ease of handling and in order to achieve maximum accuracy, the eddyNCDT SGS 4701 is factory calibrated for ferromagnetic and non-ferromagnetic materials used by the customer. For temperature compensation of the eddyNCDT SGS 4701, the temperature of the sensor is measured via the resistance of the eddy current coil. This signal is also available to the customer, which can eliminate the need for any additional temperature sensing technology. Due to its interchangeability with the previous model, the new mini-sensor technology can be easily upgraded at any time. This sensor is now available as a standard catalogue product and suited for OEM modifications as well.