Reciprocal circuit design to reduce zero error and thermal drift in ultrasonic flow metering

In ultrasonic flow metering system,the "zero-flow error" caused by the non-identical of signal waveforms received in both directions and the "thermal drift" caused by transducers' thermal characteristics which seriously deteriorate the accuracy and stability of the transit-time difference (TTD) measurement can be improved by promoting the reciprocity of the measurement system.In this paper,the approaches to achieve reciprocal measurement system are discussed based on the analyses of the equivalent circuit model of the ultrasonic flow meters.Measurement circuits specially designed for improving the system reciprocity by matching the equivalent impedances of transmitting and receiving circuits are proposed.In these designs,the load impedances of the transducers can be varied flexibly to meet varieties of requirements,and the designs are easy to implement in measurement instruments.Experiments performed on practical metering pipe show that,both the zero error and the thermal drift in the metering can be reduced by using proposed circuit design,the accuracy and stability of the flow rate measurement can be promoted.