QUIZ CORNER: How Flow Turndown Affects Measurement Range

Nov. 17, 2014

What is the additional measurement range in which a flowmeter can accurately measure flow if its turndown is improved from 50-to-1 to 100-to-1?

David W. Spitzer & Walt Boyes

David W. Spitzer

What is the additional measurement range in which a flowmeter can accurately measure flow if its turndown is improved from 50-to-1 to 100-to-1?

A.   0 to 1 percent of full scale
B.   1 to 2 percent of full scale
C.   2 to 4 percent of full scale
D.   50 to 100 percent of full scale

Commentary
It appears that the turndown specification of the improved flowmeter is vastly superior to that of the original flowmeter. However, the flowmeter with a 50-to-1 turndown will measure accurately from 2 to 100 percent of full scale. The improved flowmeter with a 100-to-1 turndown will measure accurately between 1 and 100 percent of full scale.

Both flowmeters measure accurately between 2 and 100 percent of full scale. The difference is that the improved flowmeter will also measure accurately between 1 and 2 percent of full scale. Answer B is correct.

Additional Complicating Factors
The performance provided by the improved flowmeter appears superior (and it is). However, the improvement is of little or no value if the process rarely (or never) operates at low flows between 1 and 2 percent of full scale.

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. Mr. Spitzer can be reached at 845 623-1830 or www.spitzerandboyes.com. Click on the “Products” tab to find his “Consumer Guides” to various flow and level measurement technologies.