Coriolis Transmitter Technology and Dynamic Response Performance

Recent research at Brunel University has demonstrated the fundamental limits on the dynamic response of Conolis meter flowtubes. Commercial meters typically exhibit much poorer dynamic response times, due to transmitter delays. Research at Oxford University into Coriolis transmitter technology has resulted in a prototype with an improved dynamic response, with a typical delay time of only 16 ms. The Oxford technology is incorporated in a commercially available transmitter. Coriolis mass flow metering is a well-established method of industrial flow measurement, with a market projected to grow from $400M currently to $520M in 2007. The basic measurement principle is that a flowtube is caused to vibrate sinusoidally at a resonant frequency by one or more drivers, while two sensors monitor the vibration. The flowtube geometry and sensor placement are arranged so that the frequency of oscillation (which may vary from 80 Hz to 800 Hz for different flowtubes) can be used to calculate the density of the process fluid, while the phase difference between the two sensor signals provides the mass flow rate. The primary benefit of Coriolis metering is the direct measurement of mass flow, which is important where commodity value is related to mass rather than volume, for example in the petrochemical industry However, Coriolis meters have other advantages, including high accuracy (to 0.1%), and turndown (100:1 or better), while their limitations include the need for a separate power supply, relative expense and vulnerability to aerated fluids. The University of Oxford, as part of its research progranune into self-validating sensors, has developed a novel mass flowmeter transmitter based entirely on digital technology, capable of driving several different commercial flowtubes. Perhaps the most significant advantage of the Oxford transmitter is an ability to maintain operation in two-phase or aerated flow, with on-line correction for mass flow errors (this issue is addressed in several of the papers in [lD. However, to achieve good two-phase flow perfonnance, the dynamic response of the transmitter needs to be rapid, in terms of both measurement and (flowtube) control. Trials have been carried out on the Oxford prototype meter to measure its dynamic response to flow step changes and pulsating flow using the test facility at BruneI University. The Oxford technology is available comrnercially through the CFT-50 Coriolis Massflow transmitter from InvensysIFoxboro.