Electronic circuit design for reciprocal operation of transit-time ultrasonic flow meters

The reciprocal operation theory has been used in the circuit design of transit-time ultrasonic flow meters (USMs) to promote their zero flow performances. In this paper, the authors analyzed the transfer functions of the inter-conversion between acoustic and electric signals on each transducer, indicated that the equivalent load consistency for each transducer between the transmitting and the receiving phases would guarantee the transmitting and the receiving transfer functions equal, and thus guarantee the reciprocal operation of the USM system. In order to achieve the “load consistency” condition in practical systems with non-ideal parameters, a method of applying short pulse excitation and fixing the equivalent load in the “free oscillation period” of the transmitting transducer is proposed. Based on this method, several circuit designs are shown in the paper, the impedance preferences are also analyzed. Practical experiments done with these circuits show clear improvement in both promoting the accordance of the signals received in both directions and reducing the zero flow error in the measurement.

► We analyze the condition of reciprocal operation of USM by transfer functions.
► The “pulse and fix” method is proposed to realize reciprocal operation practically.
► Several practical transmitting and receiving circuit designs are proposed and tested.