Abstract：A method using coded excitations combined with correlation to estimate the time-of-flight in transit time ultrasonic gas flowmeters is presented.By theoretical derivation and numrical simulation, it shows that the system with Barker coded excitation has a lower Cramer-Rao Bound of time-of-flight estimation, compared with the traditional threshold method or correlation with tone burst excitation, assuming the same signal to noise ratio (SNR).An ultrasonic gas flow metering system with Barker code binary phase-shifted keying (2PSK) excitation as well as tone burst is designed on FPGA and calibrated by a standard vortex flowmeter with 1% accuracy from 200 to 1 200 m3/h.The results, being in close agreement with the simulations, show that the measuring accuracy and repeatability of the system with Barker coded excitation is better than that of the traditional one.
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2011, Vol. 32 
