Device for nondestructive and noncontact detection of faults in a test piece which is moving relative to the device, comprising: a transmitter coil arrangement with at least one transmitter coil for exposing the test piece to a plurality of periodic alternating electromagnetic fields a receiver coil arrangement with at least one receiver coil (12, 14, 15) for detecting a periodic electrical signal which has a carrier oscillation such that at least one of an amplitude and a phase is modulated by a fault in the test piece when a fault is detected by the receiver coil arrangement; a signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) for producing a useful signal from a receiver coil signal; an evaluation unit (50, 60, 64) for evaluating the useful signal for purposes of detection of the fault in the test piece; a self-test unit which automatically or upon an external request undertakes systematic quantitative checking of the signal processing functions of at least one of the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94), the transmitter coil arrangement, and the receiver coil arrangement, and upon external request undertakes calibration of the signal processing unit with a calibration standard which is to replace at least one of the transmitter coil arrangement and/or of the receiver coil arrangement, which self-test unit switches the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) for checking the signal processing functions such that the signal for the transmitter coil arrangement is fed directly as a periodic input signal into the signal processing unit, and is systematically varied by the self-test unit, wherein the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) comprises a plurality of amplifiers (17, 74) and a plurality of frequency filters (19, 52, 78), characterized in that the self-test unit checks whether the measured gain of at least one of the plurality of amplifiers and a measured corner frequency and steepness of the plurality of frequency filters are within a predetermined specification with a variation of a frequency and an amplitude of the signal for the transmitter coil arrangement, and outputs a corresponding fault signal if the specification is not satisfied. a transmitter coil arrangement with at least one transmitter coil for exposing the test piece to a plurality of periodic alternating electromagnetic fields a receiver coil arrangement with at least one receiver coil (12, 14, 15) for detecting a periodic electrical signal which has a carrier oscillation such that at least one of an amplitude and a phase is modulated by a fault in the test piece when a fault is detected by the receiver coil arrangement; a signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) for producing a useful signal from a receiver coil signal; an evaluation unit (50, 60, 64) for evaluating the useful signal for purposes of detection of the fault in the test piece; a self-test unit which automatically or upon an external request undertakes systematic quantitative checking of the signal processing functions of at least one of the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94), the transmitter coil arrangement, and the receiver coil arrangement, and upon external request undertakes calibration of the signal processing unit with a calibration standard which is to replace at least one of the transmitter coil arrangement and/or of the receiver coil arrangement, which self-test unit switches the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) for checking the signal processing functions such that the signal for the transmitter coil arrangement is fed directly as a periodic input signal into the signal processing unit, and is systematically varied by the self-test unit, wherein the signal processing unit (17, 19, 35, 37, 52, 60, 68, 74, 76, 78, 80, 88, 90, 94) comprises a plurality of amplifiers (17, 74) and a plurality of frequency filters (19, 52, 78), characterized in that the self-test unit checks whether the measured gain of at least one of the plurality of amplifiers and a measured corner frequency and steepness of the plurality of frequency filters are within a predetermined specification with a variation of a frequency and an amplitude of the signal for the transmitter coil arrangement, and outputs a corresponding fault signal if the specification is not satisfied.