The large majority of currently available Coriolis flow meters have a very limited dynamic response. The dynamic characteristics of the flow tube itself provide the ultimate limit to the responsiveness of a meter. Detailed analysis of flow tubes has shown that the response time-constant cannot be faster than the period of one drive cycle. Thus, for example, a meter driven at 500 Hz has a flow tube response time of 2 ms. Flow tube response to step changes in flow rate and pulsating flows have been evaluated experimentally. The results demonstrate the potential for a high performance dynamic capability. This can be achieved, providing the necessary developments in meter drive, control and signal processing can be realised. Thus, it is the flow transmitters of current meters which are primarily responsible for their slow dynamic response. It is common for flow meters to be used to determine mean flow rates only, or totalised flow, on a timescale set by the user. There is now, however, an increasing need for flow rate measurements in flows which are required to change rapidly with time. This includes short duration batch-filling, dosing and other fast control operations. A good dynamic response is also important in the metering of intermittently aerated flows. Currently, such meters are not generally available, and there is therefore a growing need for the development of meters with a high performance dynamic response. Such meters would also open up completely new areas of application. The Coriolis flow meter is a true mass flow rate device and is known for its high accuracy (to 0.1%) in single phase flows, and its high turndown capability (100 to 1). An early report of the dynamic response of Coriolis meters (Cheesewright and Clark) and the more recent work of Wiklund and Peluso both suggest that these meters are relatively slow and, in response to flow pulsation, significant attenuation of the indicated pulsation amplitude and wave form distortion occur at frequencies as low as a few Hz.
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