THE 10th INTERNATIONAL SYMPOSIUM OF MEASUREMENT TECHNOLOGY AND INTELLIGENT INSTRUMENTS

A Coriolis mass flow meter (Fig. 1) consists of an (essentially mechanical) vibrating flowtube through which the process fluid passes, and an (essentially electronic) transmitter. The transmitter maintains flowtube vibration by sending a drive signal to one or more drivers (d1, d2), and performs measurement calculations based on signals from two sensors (s1, s2). The phase difference between the signals from sensors s1 and s2 is used to calculate the mass flow rate. The frequency of oscillation varies with the density of the process fluid: its value is extracted from the sensor signals so that the process density can also be calculated. The design and material selection of the flowtube determine the frequency range of the meter: the socalled “bent” tubes (as shown in Figure 1) typically oscillate between 50 150 Hz, while the “straight” flowtube geometries may oscillate at up to 1 kHz. The flowtube temperature is also monitored to provide temperature-based corrections to the mass flow and density measurements. Coriolis meters offer many benefits, including high accuracy (to 0.1% for steady flow rates), and good turndown (100:1 or better), while their limitations have included poor dynamic response and an inability to maintain operation when exposed to multi-phase flow. A user perspective on Coriolis as an “almost perfect” flowmeter is given by Reizner [1]. The exploitation of new technology, such as audio quality analogto-digital convertors and digital-to-analog convertors (ADCs and DACs) and Field Programmable Gate Arrays (FPGAs), has facilitated the development of new capabilities for Coriolis meters, such as the Fig. 1 Coriolis mass flow meter: flowtube and digital transmitter.