Forced oscillation to reduce zero flow error and thermal drift for non-reciprocal operating liquid ultrasonic flow meters

A new method using forced oscillation excitation for transit-time difference (TTD) measurement is proposed to improve the accuracy and stability in ultrasonic flow metering under non-reciprocal operating conditions. Forced oscillation guarantees the frequencies of the received signals in both directions constant and known, thus the TTD can be measured as the phase difference. Choosing the driving frequency slightly off the resonance of the transducers can considerably decrease the long-term drift of the TTD results caused by temperature variations, and minimize the zero flow error. In the simulations and experiments, the proposed method showed good performance in the non-reciprocal metering system, the zero flow error and the thermal drift on the TTD measurement results were reduced.

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► Efforts are paid to reduce zero-flow error and thermal drift in liquid USMs.
► Forced excitation was used to convert transit-time difference to phase difference.
► Off-resonance excitation ensures the stability of phase shifts on transducers.
► Equivalent circuit model is used to analyze the frequency responses of transducers.