David W. Spitzer, P.E.

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