Acoustic transit time measuring system

A method for determining a physical quantity within a measuring space by use of acoustic transit time measurement, using at least one acoustic transmitting transducer and at least one acoustic receiving transducer, comprising the steps of:

• transmitting an acoustic signal by said at least one acoustic transmitting transducer wherein said acoustic signal being reflected through the measuring space one or more times via acoustic reflection before being received by said at least one acoustic receiving transducer;
• selecting said acoustic signal at least partly on a type of signal processing and detection of at least two points in an acoustic received signal and/or a signal derived from that received signal again selected at least partly on the basis of the type of processing to be used.

A method for determining a physical quantity within a measuring space by use of acoustic transit time measurement, using at least one acoustic transmitting transducer and at least one acoustic receiving transducer, said method comprising the steps of

• using signal processing based on a comparison in a discrete manner between a) a predicted distorted acoustic signal transmitted through said space, based on models for the medium and measuring space concerning the distortion to which the signal is subjected within the measuring space and on the transmitted signal, and b) an actual measured acoustic signal transmitted through said space to determine the acoustic transit time, and
• using at least two selected points located on a slope and at a top of the received acoustic signal respectively, the at least two selected points being used for combined signal top-signal slope detection with the aid of a specially adapted signal processing technique.