structures to the wall of the vacuum vessel 2 or to the cover 4 the structure borne sound pick ups 30 1 30 2 disposed on the outer wall of the pan 6 and coupled acoustically directly to the wall of the pan the 6 are removable i e fixed releasably to the pan 6 and are only coupled to the pan 6 with quick release fastenings after insertion of the pan 6 into the vacuum vessel 2 the measurement signals m 1 m 2 m 3 or m 4 provided by the structure borne sound pick ups 30 1 30 2 30 3 and 30 4 in each case are forwarded to the control and evaluation device 40 in which they are evaluated and employed for detection of a leakage in the vacuum melting system the created measurement signals m 1 m 2 m 3 and m 4 are subjected to a signal analysis in the evaluation device 40 and with the assistance of a self learning physical model the occurrence of operating states caused by leakages for example by an incorrectly sealed cover 4 are recognized in good time and the corresponding deficiency can accordingly be rapidly rectified to do this in a learning phase before the actual commissioning different operating states are set for example operating the vacuum system with.