Research and realisation of reciprocal electronic circuits for gas ultrasonic flow meter

The transit-time ultrasonic flow meters often show non-zero-flow rate when the flow is stationary due to the variations between transducers, which results in a zero-flow error. Moreover, the zero-flow error may change along with the measurement environment which causes the zero-drift error. The zero-flow error and zero-drift error will lead to false flow detection and influence the measurement stability at low velocities. Reciprocal operation theory has been proven to be an effective technique to eliminate zero-flow error. Therefore, reciprocal electronic circuits for gas ultrasonic flow meter are designed in this study. The circuits are first modelled in PSpice to validate its effectiveness. It is shown that both the zero-flow error and the zero drift are reduced significantly with the reciprocal circuits. Besides, the optimum matched resistor is determined by simulation. Second, three experiments are carried out to test the reciprocal circuits including transducers paired experiment, temperature test and flow calibration. Finally, it is verified that the reciprocal circuits can improve the measurement accuracy and stability for gas ultrasonic flow meter and the calibration results show that the gas ultrasonic flow meter (USM) with reciprocal circuits can achieve 1.0% measurement accuracy in 0.3-30 m/s.