SENSOR, AND METHOD FOR OPERATING SAID SENSOR

A sensor for checking value documents is arranged to carry out a self-test for testing its functionality. The sensor in the self-test reacts to at least one malfunction that is ascertained during the self-test and hinders the check of the value documents by the sensor automatically employing for checking the value documents, instead of the operating mode provided for checking the value documents. A modified operating mode employs at least one other measured value of the sensor for checking the value documents than is determined in the operating mode provided for checking the value documents. In contrast to the hitherto customary function failure of the sensor, the sensor can continue being operated for checking the value documents despite the malfunction.