US Patent 8373961 Coupling for a fluid line

The invention relates to a coupling for a fluid line, wherein an oscillating circuit (5, 9) is present for detecting a properly closed position of an inserted part (13). A tuning device (19) is further provided, by means of which the resonant frequency of the oscillating circuit (5, 9) can be influenced such that the resonant frequency corresponds to a characteristic closure frequency only in the closed position of the insertion part (13). The proper arrangement of the insertion part (13) in the closed position can thereby be detected without contact.