A method and apparatus for casting molten metal in an opaque container and for determining the level of the metal within the container. This is accomplished by locating a strain sensing transducer over the container and metal, and sending a current pulse from the transducer along a wire located in the...http://www.google.de/patents/US5577411?utm_source=gb-gplus-sharePatent US5577411 - Molten metal sensing in a closed opaque vessel
