David W. Spitzer
David W. Spitzer

Which of the following flowmeters are not affected by their upstream velocity profile?

A.    Coriolis mass
B.    Magnetic
C.    Orifice plate
D.    Parshall flume
E.    Positive displacement

Commentary
One could opine that all flowmeters are affected by their upstream velocity profile because extreme velocity distortion, such as localized jetting, could adversely affect any flowmeter. In this case, there would be no correct answer.

Magnetic flowmeter manufacturers publish installation instructions that generally include straight-run requirements. Similarly, orifice plate flowmeter standards also specify straight-run requirements for accurate measurement and sometimes relaxed straight-run requirements for reduced accuracy. These flowmeters can be affected by velocity profile so Answers B and C are not correct.

Parshall flume level measurements can be affected by non-uniform flow such as when there is more flow in the center of the channel, the liquid has waves, or the liquid sloshes from side to side. Answer D is not correct.
 
As a practical matter, Coriolis mass flowmeters and positive-displacement flowmeters are not affected by upstream velocity profile in the overwhelming number of actual installations. Answers A and E would be correct.  

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Additional Complicating Factors
Most manufacturers publish straight-run requirements for their magnetic flowmeters. However a few magnetic flowmeters are designed to have no straight-run requirements so they would not be affected by their upstream velocity profile.

Some older Coriolis mass flowmeter designs specified installation of straight pipe upstream and downstream of the flowmeter. While having the appearance of straight run, this requirement was intended to address vibration issues by providing appropriate supports.
 
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC, offering engineering, training, strategic marketing consulting, distribution consulting, and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. Mr. Spitzer can be reached at 845 623-1830 or via www.spitzerandboyes.com.