Coriolis flow meters, often referred to as ‘mass’ meters, have gained a significant market share over the past 20 years and are the first choice for many flow applications. During this time, their design has been refined resulting in the evolution of a highly accurate and versatile flowmeter.
Coriolis flow meters are primarily designed to measure mass flow (kg/min, tonnes/hour etc.) with accuracy unaffected by changes in fluid density or flow profile. Offering a typical measurement accuracy in the order of 0.1% of reading over a 20:1 turndown, Coriolis flowmeters are available with MID (Custody Transfer) Approval as well as ATEX Hazardous Area Approvals. With the correct selection of tube material, the flowmeter can also work at elevated temperatures above 200 degrees C.
Coriolis flowmeters also have the capability to measure volumetrically (l/min, m3/hr etc.). Some users will opt to use this type of flowmeter for volumetric flows, rather than for mass particularly, when the process liquid is non-conductive and so precludes the use of electromagnetic flowmeters. A prime example involves ‘tanker loading’. Tankers are generally filled volumetrically to avoid over-filling and spillages. Once filled, the tanker will then be weighed on the weigh bridge to determine the actual mass of the load.
This type of flowmeter offers no obstruction to flow although the shape of the measuring tubes may create a small pressure loss. Straight tube coriolis flowmeters can be employed where pressure drop is an issue, maybe in the case of high viscosity fluids. Bi-directional flow applications can also be handled with this type of flowmeter.
A wide selection of tube materials means the coriolis flowmeter can be selected to handle ‘difficult’ liquids as well as being available with many process connection options required by specific industrial markets. Typical line sizes are available from a few millimetres up to 10” (300mm). Turbine flow meters are also commonly used for measuring liquids.
As density and viscosity of all gases are greatly affected by changes in temperature and pressure the coriolis flowmeter is the ideal choice when it comes to gas measurement. A true and accurate mass reading is provided regardless changes in gas characteristics.
Over the years the improving price competitiveness of coriolis flowmeters means that they can now compete with more traditional flow technologies, such as positive displacement flowmeters. With the very low cost of ownership (virtually maintenance free) coriolis flowmeters can often be the best economical, long-term flow solution.
Coriolis flowmeters offer a variety of signal outputs in addition to the standard 4-20mA for mass or volume flow. HART and PROFIBUS as well as pulse/frequency outputs are common requirements. In addition, analogue signals for temperature and density can also be provided.
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