| CPC G01F 1/662 (2013.01) | 10 Claims |

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1. A system, comprising:
a first transducer operable to transmit a first signal having a first frequency at a first time and receive a second signal at a second time;
a second transducer operable to receive the first signal and transmit the second signal having the first frequency; and
a signal processing circuit communicatively coupled to the first transducer and the second transducer, the signal processing circuit operable to:
sample the first signal to produce a sampled first signal;
sample the second signal to produce a sampled second signal;
band pass filter the sampled first signal and the sampled second signal based on the first frequency to produce a filtered first signal and a filtered second signal;
determine a first envelope of the filtered first signal and a second envelope of the filtered second signal;
normalize the first envelope to form a normalized first envelope;
normalize the second envelope to form a normalized second envelope;
align the first normalized envelope with the second normalized envelope based on a first crossing point of the first normalized envelope with a threshold and a second crossing point of the second normalized envelope with the threshold to determine a time of flight;
determine an error based on alignment points associated with the first signal and the second signal;
determine a corrected time of flight based on the error and the time of flight; and
calculate a flow rate of a material based on the corrected time of flight.
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