Acoustic flow meter

Claim 1

APPARATUS FOR DETERMINING THE RELATIVE VELOCITY BETWEEN A BODY AND A FLUID MEDIUM, COMPRISING IN COMBINATION: INPUT SIGNAL MEANS FOR PROVIDING A MODULATED CARRIER INPUT SIGNAL HAVING ALTERNATING ON AND OFF PERIODS OF TRANSMISSION; FIRST AND SECOND TRANSDUCER MEANS COOPERATING WITH SAID BODY AND DISPOSED IN SAID FLUID MEDIUM, WITH EACH OF SAID TRANSDUCER MEANS RESPONSIVE TO SAID INPUT SIGNAL FOR PROVIDING FIRST AND SECOND ACOUSTIC SIGNALS ALONG IDENTICAL PATHS, SAID FIRST ACOUSTIC SIGNAL BEING AIDED BY SAID RELATIVE VELOCITY TO PRODUCE A FIRST OUTPUT SIGNAL FROM SAID SECOND TRANSDUCER MEANS, AND SAID SECOND ACOUSTIC SIGNAL BEING RETARDED BY SAID RELATIVE VELOCITY TO PRODUCE A SECOND OUTPUT SIGNAL FROM SAID FIRST TRANSDUCER MEANS, SAID FIRST AND SECOND OUTPUT SIGNALS HAVING A LOWER POWER LEVEL THAN SAID INPUT SIGNAL; RECEIVER MEANS HAVING A DEMODULATION REGION AND A SATURATION REGION OF OPERATION FOR RECEIVING SAID INPUT SIGNAL AND SAID FIRST AND SECOND OUTPUT SIGNALS, SAID RECEIVER MEANS BIASED SUCH THAT DURING ON PERIODS OF TRANSMISSION SAID RECEIVER MEANS IS RESPONSIVE TO SAID INPUT SIGNAL AND SAID FIRST AND SECOND OUTPUT SIGNALS, SAID RECEIVER DEMODULATION OCCURS, SAID RECEIVER MEANS ADDITIONALLY RESPONSIVE DURING OFF PERIODS OF TRANSMISSION TO SAID LOWER POWER LEVEL FIRST AND SECOND OUTPUT SIGNALS SUCH THAT OPEATION IS IN SAID DEMODULATION REGION TO PROVIDE FIRST AND SECOND DEMODULATED SIGNALS; AND PHASE COMPARISON MEANS FOR COMPARING THE RELATIVE PHASE OF SAID FIRST AND SECOND EMODULATED SIGNALS WHEREBY SAID RELATIVE VELOCITY MAY BE DETERMINED.