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| David W. Spitzer, P.E.
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How do you compare
flowmeters? Which dimensions do you use? How do you weigh them? Why is
a flowmeter needed in the process? There is no one answer to these
questions, but there are some general concepts available that can help
you get the results you need.
Fundamentally
speaking, a flowmeter is a device that is used to convert resources
(time, money, materials, and the like) into measurements of how much
material is flowing. In many applications, money is the primary
resource because money buys time, materials, and the like. Therefore, a
flowmeter is a device that turns money into measurements. Money also
provides the installation and maintenance necessary for the flowmeter
to remain operating over time. In short, money is turned into flow
measurements that provide a benefit to the operation of the plant.
Flowmeters can be
compared by evaluation of the quantity of resources used, the benefit
to the plant, or both. Evaluating resources refers to a cost analysis
of the flowmeter. This has often been done based upon initial purchase
costs of the component(s). How many times have you been told to buy the
least expensive flowmeter you can find? More refined analysis
would include the cost of installation. How often has the least
expensive flowmeter been the most difficult and expensive to install?
An even more refined approach would be to include the costs of
operation/maintenance. How often has the flowmeter with the lowest
installed cost required an inordinate amount of maintenance?
The trend in
analyzing the costs associated with instruments is to consider the
initial purchase costs, installation costs, and operation/maintenance
costs. This is sometimes called the total cost of ownership or
lifecycle cost of the instrument.
The benefit
provided to the operation of the plant can depend on the quality of the
flow measurement. This benefit is often difficult to quantify. However,
in some applications, it may be readily calculable. For example,
savings can be enormous if improving the accuracy of the flow
measurement from 3 percent of the actual flowrate to 2 percent of the
actual flowrate will allow a 1 percent reduction of a raw material.
Assuming raw material that costs $1.00 per liter flows at one liter per
minute, the 1 percent raw material cost savings (assuming 24/7/365
operation) is approximately $5,000 per year. At a more realistic flow
of 10 liters per minute, raw material savings are approximately $50,000
per year. Savings of this magnitude should easily justify utilizing
more resources (money) to purchase the superior flowmeter.
Whereas the
previous example seemingly reflects a positive result, benefits for
many flowmeters involve avoiding the negative. For example, if the
cooling water is not maintained within limits, the bearings will burn
up, shut down the plant for a week, and cost $10,000 to repair. In this
application, flowmeters could be thought of as insurance against the
bad things that can happen. The benefit to the plant is clear, but it
is also more difficult to calculate than the raw material savings cited
in the above example.
The next time you
compare flowmeters, calculate or estimate the benefit the flowmeter
provides to the plant and its total cost of ownership. It is tempting
to only consider one or the other, but doing so can be shortsighted to
the point of blindness. Be sure to look at both the cost and benefit of
the flow measurement system. Evaluating the results of your
calculations may provide some interesting insights and results.
About the Author
David W. Spitzer, P.E., is a regular contributor to Flow Control.
He has more than 25 years of experience in specifying, building,
installing, start-up, and troubleshooting process control
instrumentation. He has developed and taught seminars for almost 20
years and is a member of ISA and belongs to ASME, MFC, and ISO TC30
committees. Mr. Spitzer has published a number of books concerning the
application and use of fluid handling technology, including the popular
The Consumer Guide to… 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.
For More Information: www.spitzerandboyes.com
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