David W. Spitzer
David W. Spitzer

Which of the following flowmeters infer the flow of fluid passing through the flowmeter?

A. Coriolis mass
B. Magnetic
C. Orifice plate
D. Oscillating piston
E. Oval gear
F.  Thermal
G. Turbine
H. Venturi
I.  Vortex shedder

Industrial Automation Insider 300x250Commentary
Positive-displacement flowmeters, such as piston and oval gear flowmeters, constantly entrap fluid to measure the actual volume.  Some flowmeters measure velocity, such as magnetic, turbine and vortex-shedding flowmeters. Coriolis and thermal flowmeters measure mass flow.
 
READ ALSO: Which Flowmeters Measure Mass?

Eliminating the above flowmeters leaves orifice plate and Venturi flowmeters—both of which are differential pressure flowmeters. These flowmeters involve a well-defined restriction in a pipe (such as an orifice plate or Venturi) that produces a differential pressure that is related to the fluid flow. Differential-pressure flowmeters do not measure volume, do not measure velocity, and do not measure mass flow—they measure inferentially.  
The correct answer is Answers C and H.  

Additional Complicating Factors
From an academic perspective, it is not clear which units of measurement inferential flowmeters should use.  In practice, inferential flow measurements of liquids are most often expressed in volumetric units such as gallons or liters per unit time.  However, mass flow units are sometimes used due to precedent, familiarity and/or when density is relatively constant.  Inferential flow measurements of gases are usually expressed in mass flow units.

David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes, LLC offering engineering, seminars, 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. David can be reached at 845 623-1830.