In general, all types of fluid flowmeters can be classified as either direct or inference type meters.
Direct type
PD meters are the direct type since they measure volumetric flow directly by continuously separating (isolating) the flow stream into discrete volumetric segments and counting them.
Positive displacement liquid meters
Positive displacement meters have existed for over a century. Many of the designs were developed from either pumps or compressors. By the late "30s, PD meters were being used extensively for precise measurement of petroleum liquids on tank trucks, bulk loading terminals and small pipelines. With the construction of large pipelines and large ship loading facilities in the "50s and '60s, PD meters were developed which could measure flowrates over 10 000 barrels per hour. Most will agree that since its perfection in the '50s, there exists no more accurate means of petroleum measurement than the PD meter. It has become the 'Standard of measurement' for the liquid petroleum industry.
Inference type
Inference meters infer volumetric flow rate by measuring some dynamic property of the flow stream.
Turbine meters
With the development of jet engines and liquid propellant rockets in the '50s, the need arose for an accurate, quick response meter that could be used on exotic fuels and oxidisers at extreme temperatures. The turbine meter met this need. It was soon applied to many other industrial flow-measuring applications.
Turbine meters began to be applied extensively in the petroleum industry in the mid-60s. Since publication of API Standard 2534 "Measurement of liquid hydrocarbon by turbine meter systems" in March, 1970, the turbine meter has gained broad acceptance for custody transfer of petroleum liquids such as liquefied petroleum gases (LPGs), light distillates, and light crude oils, primarily at large petroleum storage and transfer terminals.
Coriolis flow meters
The S-Mass flow and density meter uses the Coriolis effect to directly measure the mass flow of virtually any liquid. Mass is independent of other physical parameters, as well as the ambient conditions in which the measurement is made. Therefore, the measurement is essentially unaffected by changes in temperature, pressure, density, viscosity and flow profile.
The S-Mass meter derives its name from the S-shaped tubes of the flow sensor. This patented geometry produces a high signal-to-noise ratio for maximum response to the generated Coriolis forces. This enables the S-Mass meter to measure accurately over a wide flow range. The meter is also a highly accurate vibrating tube densitometer for measuring process fluid density or calculating gross fluid volume.
One basic assumption of all inference meters is that the effective flow cross-sectional area at the meter sense point remains constant between meter proofings. If this effective flow area changes due to erosion, corrosion or obstructions the volume registration will change even though volumetric flow rate remains constant.
Dupleix Liquid Meters is a company that specialises in flow measurement. With more than 50 years experience, DLM says that it offers a comprehensive, technologically advanced range of products sourced from the world’s leading manufacturers. The petroleum division delivers a complete range of liquid and gas custody transfer solutions. DLM says that it is by combining the strengths, capabilities and experience acquired over five decades with a diverse product offering, that the company is able to provide a broad range of solutions for all segments of the petroleum industry.
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| www: | www.dlm.co.za |
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