Abstract: The invention relates to a measuring device comprising a transmitter (6) for transmitting (38, 60) a measuring signal (16) that lies within a frequency range, a sensor (8) for receiving (40, 62) an evaluation signal (20) that has been induced by the measuring signal (16) and a control unit (10) for evaluating (42, 66) the evaluation signal (20) to produce a measured result. According to the invention, the function of the control unit (10) is to check the frequency range before the transmission (38, 60) of the measuring signal (16) for the presence of a signal (28) that is independent of the measuring signal (16).