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| David W. Spitzer, P.E.
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Flowmeters
generally can be categorized into one of four types: flowmeters that
have wetted moving parts; flowmeters with no wetted moving parts;
flowmeters that exhibit no obstruction to the flow; and flowmeters with
no wetted parts. Which of the following groupings of flowmeters have
wetted moving parts?
A. Coriolis and vortex-shedding
B. Coriolis, vortex-shedding, and ultrasonic (wetted sensor)
C. Coriolis, vortex-shedding, and target
D. Positive-displacement and variable-area
E. None of the above
Commentary
The statement of
this problem can be interpreted and strictly parsed to allow all of
these flowmeters to be classified as flowmeters with moving parts. For
example, the tubes in a Coriolis mass flowmeter vibrate. Therefore, the
vibrating tube could be considered to be a moving part and the
flowmeter could be considered to have a wetted moving part. Forces
generated by the vortices in a vortex shedder cause the bluff body to
move (micro-inches), so this flowmeter could similarly be classified as
a flowmeter with wetted moving parts. Similarly, wetted ultrasonic
sensors also vibrate, and the obstruction in a target flowmeter will
move slightly.
That said, common
usage of the term “moving parts” refers to actual parts of the
flowmeter that physically move. In this sense, none of the parts in the
Coriolis, vortex-shedding, ultrasonic (wetted sensor), or target
flowmeters have parts that move — although they may vibrate. Therefore,
Answers A, B, and C are not correct in this context.
Positive-displacement
flowmeters have physical parts, such as gears, rotors, and other
mechanisms that physically move. The floats in variable-area flowmeters
similarly move to indicate flow. Thus, Answer D is correct.
Additional Complicating Factors
There are variants
within each technology that often limit generalizations. Note that in
this case, ultrasonic flowmeters were limited to ultrasonic flowmeters
with wetted sensors. Ultrasonic flowmeters with non-wetted sensors fall
into an entirely different category with other flowmeters with no
wetted parts.
David W. Spitzer,
P.E., is a regular contributor to Flow Control. He has more than 30
years of experience in specifying, building, installing, startup and
troubleshooting process control instrumentation. He has developed and
taught seminars for over 20 years and is a member of ISA and belongs to
the ASME MFC and ISO TC30 committees. Mr. Spitzer has written a number
of books concerning the application and use of fluid handling
technology, including the popular “Consumer Guide” series, which
compares flowmeters by supplier. Mr. Spitzer is currently a principal
in Spitzer and Boyes LLC, offering engineering, product development,
marketing and distribution consulting for manufacturing and automation
companies. He can be reached at 845 623-1830.
www.spitzerandboyes.com
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