| Abstract: | Clamp-on ultrasonic transit time difference meters have many benefits for use in industry such as their non-intrusive nature, portability and ability to work with corrosive fluids. However, all transit time difference meters suffer from a sensitivity to changes in the speed of sound or flow profile in the fluid during the ultrasonic measurement. Trigger time jitter in the data acquisition electronics can also contribute to fluctuations in the output of the meter, since the upstream and downstream signals jitter back and forth in time independently of one another. Both of these mechanisms are a product of the method of data acquisition used, where one transducer is used as a generator and the signal is received on the other, then the other transducer is driven to send ultrasound the other way. A new method of performing the measurement is proposed in which the transducers are both driven simultaneously and the signal is received on both transducers at the same time, with the ultrasonic waves having passed through the same volume of fluid with the same flow profile. It is shown that fluctuations in the output of a flowmeter at constant flow rate can be reduced by over an order of magnitude compared to acquisition modes where the generation pulse and the start of data acquisition are not actively synchronised. |
