Selecting the Right Flowmeter

Emerson flow measurement technologiesSelecting the right flowmeter is an expert panel session at the 2018 Emerson Exchange conference. The panel included Emerson’s Trever Ball, Karl Stappert, Dan Hackett, Jeff Foster, and Steve Ifft.

Types of flow measurement devices in the panel discussion include magnetic flowmeters, Coriolis, Ultrasonic, Vortex, Turbine and differential pressure (DP) flow. Trever described how magnetic flowmeters are known for their versatility when measuring conductive fluids. They do no work with non-conductive fluids. Magmeters have an accuracy of 0.25% the lab and 0.5% installed. He noted where any fluid where water is a carrier or very aggressive chemicals where corrosion is a concern. Sanitary versions are great for milk or juices. They are good for flow measurement but not for density measurement. Coriolis is a better technology for this application. Solids and bubbles are typically not a problem for measurement accuracy. Installation requirements are 5 internal diameters upstream and two diameters downstream.

Karl spoke about Coriolis flow meters and the only one that truly measures mass. If you can get within the range of the measurement on the high side and zero on the low side, it can work with gases, liquids and slurries. Multiphase measurements are possible. If measuring gas, it can measure the fluid up to 10% liquid. And it can measure liquids also with up to 10% gas by mass. Density of the fluid can also be measure.

Karl said one misconception is the Coriolis meters have a higher pressure drop, when in fact it’s comparable with other flow measurement technology except for the new designs for ultrasonic meters. There also is no requirement for upstream and downstream length. A problem is if there is a process disturbance at the same resonant frequency as the tubes and drive coils in the meter. Coriolis meters have a higher turndown ratio than other flow measurement technologies.

Dan discussed Ultrasonic flow measurement technology. The Daniel gas and liquid ultrasonic flowmeters where an ultrasonic sound wave is sent upstream and downstream in the flow stream. The velocity of the flow changes the transit time for the ultrasonic sound wave to travel across the meter. Their strength is highly accurate volumetric flow measurement, no moving parts and embedded diagnostic data. Ultrasonic can either clamp on to the pipes or integrated into an ultrasonic meter, which is more accurate.

Jeff discuss vortex meters that they are very high reliability and can measure any single-phase fluid, but in steam applications can handle a little water. They are known as fit and forget meters for their accuracy and reliability. They are volumetric flow measurement. Conversions are required for mass flow measurements. 10D upstream and 5D downstream are recommended for installations. Gas in liquid above 5-10% will cause affect the accuracy of the flow measurement.

Steve discussed DP and turbine meter technology. DP is the oldest and most proven measurement. Technicians widely understand DP measurements and how to troubleshoot issues. They work on the Bernoulli principle where a restriction (orifice plate, nozzle, etc.) causes an increase in the velocity in the flow and a reduction in the pressure. Pressure is measured upstream and downstream of the restriction and the differential indicates the flow rate. It is not good for pulsating flows, works with Newtonian fluids only and requires ongoing maintenance.

Although turbine meters are a part of the Daniel brand of products it was not discussed in this panel.

For more on flow measurement technologies and options, visit the Flow Measurement section of Emerson.com.

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