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DAVID W SPITZER'S E-ZINE (November 2021)


Magnetic Flowmeters (Part 2 of 3) by David W Spitzer

The magnetic flowmeter signal is proportional to the fluid velocity. Therefore, these flowmeters measure velocity, from which the volumetric flow rate is inferred utilizing the first equation, assuming that the cross-sectional area of the conduit is known. Magnetic flowmeter performance is therefore predicated on how well the average fluid velocity is measured and how well the cross-sectional area is known. Uncertainty in the cross-sectional area can degrade the inferred volumetric flow rate measurement.

Uncovering the Unknowns: Valves (Part 1) by David W Spitzer

A few years ago, I was hired as an expert witness based on something that I did not know but turned out that I actually knew. A lawyer called and was in search of a valve expert on a case where multiple manual valves installed in a particular application failed after a short time in service. Let me emphasize that not only had the valves failed quickly but also their springs were actually broken --- sometimes, in two places. However, identical valves were reportedly in service at another location without incident.

Accuracy and Repeatability by David W Spitzer

Which of the following statements are true?
A. The repeatability of a flowmeter is important.
B. An accurate flowmeter is better than a repeatable flowmeter.
C. A flowmeter cannot be accurate unless it is repeatable.
D. An accurate flowmeter costs about the same as a repeatable flowmeter.


In addition to over 40 years of experience as an instrument user, consultant and expert witness, David W Spitzer has written over 10 books and 500 articles about flow measurement, level measurement, instrumentation and process control. David teaches his flow measurement seminars in both English and Portuguese.


Spitzer and Boyes, LLC provides engineering, technical writing, training seminars, strategic marketing consulting and expert witness services worldwide.


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