Device, sensor circuit and method for operating a device or a sensor circuit

Apparatus for detecting a predetermined physical quantity from a source (410) of said predetermined physical size, the apparatus comprising: a first sensor element (120) and a second sensor element (220) disposed at a first and a second position with respect to the source, respectively, adapted to detect the predetermined physical quantity from the source, and responsive to the predetermined physical quantity to generate a first sensor signal (120b) and a second sensor signal (110a), respectively; a signal processing circuit (110) adapted to process the first sensor signal (120b) and the second sensor signal (110a) according to a first algorithm to obtain an output signal (110b); and an evaluation circuit (130) adapted to process the first sensor signal (120b) and the second sensor signal (110a) in accordance with a second algorithm to determine whether a predetermined normal operation criterion is met, and to obtain an indication signal indicates an abnormal operating condition if the predetermined normal operation criterion is not met.