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DAVID W SPITZER'S E-ZINE (April 2023)

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FOR INSTRUMENTATION SUPPLIERS AND END-USERS

Vortex Shedding and Fluidic Flowmeter Applications (Part 4 of 4) by David W Spitzer and Walt Boyes

Plastic/Polymer Vortex Shedding and Fluidic Flowmeters
Many vortex shedding and fluidic flowmeters are metal however, many vortex shedding and fluidic flowmeters constructed of plastics and polymers. These flowmeters are often used to measure the flow of high purity water and other fluids. Many plastic/polymer vortex shedding and fluidic flowmeters are small, but they can be as large as 225 mm (9 inch).

Sanitary Vortex Shedding and Fluidic Flowmeters
Sanitary vortex shedding and fluidic flowmeters are designed and fabricated with materials and finishes that allow application to the food and pharmaceutical industries where they may be cleaned and/or steamed in place.

Two-Wire Vortex Shedding and Fluidic Flowmeters
Many vortex shedding and fluidic flowmeters are designed to require three or more wires to receive power and transmit the measurement signal. Two-wire designs implement both functions over one pair of wires. These designs are usually easier and less expensive to wire and install.

Miscellaneous
Vortex shedding and fluidic flowmeter bodies are designed to withstand outside influences, such as water and corrosive environments. The ability to withstand certain influences is typically expressed as NEMA and/or IP ratings. Installing a flowmeter body that cannot withstand its ambient environment can result in flowmeter body failure.

Vortex shedding and fluidic transmitters that are mounted integral to the flowmeter body are typically pre-wired by the manufacturer. When the flowmeter body is in a suitable environment and accessible for maintenance, this mounting method simplifies installation and is usually more economical.

Some vortex shedding and fluidic flowmeter systems are designed for installation in hazardous locations. Suitability for compliance with European standards (EEx) and the National Electric Code (NEC) are cited. Some vortex shedding and fluidic flowmeters are designed to be intrinsically safe. Intrinsically safe wiring allows the use of less restrictive wiring techniques that can reduce the cost of installation. In addition, testing and servicing of the intrinsically safe wiring can usually be performed while the transmitter is powered.

Excerpted from The Consumer Guide to Vortex Shedding and Fluidic Flowmeters.

The Verdict Is In by David W Spitzer

Previous articles described the sewage collection systems for two adjacent sewage districts where the flow measurements used to allocate expenses and bill one of the sewage districts flowmeters was questioned in court.

My testimony was strained with the first sewage district (my client) attempting to ask me questions that would reveal issues with the flowmeter installations and their accuracy, only to have the judge sustain the second sewage district's objections. In the end, some of my findings were revealed to the court and the local press. On a side note, members of the local press attended this hearing because the alleged overbilling caused contention between the people in the two sewage districts for so long that people who lived in the first sewage district reportedly avoided shopping at stores located in the second sewage district.

Orifice Plate Flowmeter Transmitter Application by David W Spitzer

An orifice plate is sized to produce a differential pressure of 0 to 100 inches of water column (WC) corresponding to zero to full-scale flow respectively to measure steam flow through a nominal 200# steam header where the flowmeter is located approximately 25 feet above grade. The differential pressure transmitter will be mounted on a pipe stand for convenient access. What is the approximate bench calibration of the differential pressure transmitter?

-2.5 to 97.5 inches of water column
0 to 100 inches of water column
2.5 to 102.5 inches of water column
240 to 340 inches of water column

The steam header is located approximately 25 feet above grade. Transmitters are typically mounted approximately 4.5 feet above grade. It was previously shown that the pressure at the transmitter is higher than the steam header pressure due to a fixed condensate leg that forms during operation. However, this increase will not affect the differential pressure measurement because the same added pressure will appear on both taps of the differential pressure transmitter and be subtracted out by the transmitter. Answer D is not correct.

Answer B would be correct if the condensate legs are of equal height and equal temperature.

Additional Complicating Factors

The differential pressure transmitter can shift if it is rotated such that its taps are not at the same elevation. A 90-degree rotation causes approximately 2.5 inches of shift as suggested by Answer A and Answer C. The direction of the shift depends on the direction of rotation.

The above analysis presumes that the height of the condensate legs is the same. However, if the steam header is vertical, the flowmeter taps will be at different elevations, thereby forming condensate legs with different condensate heights. In some installations, an inverted U-tube is used to physically make the two condensate legs of equal height and eliminate the shift.

This article originally appeared in P. I. Process Instrumentation magazine.

ABOUT SPITZER AND BOYES, LLC

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.