Defining Ultrasonic Flowmeters

English may not have been your best subject in school, but it can be the most important part of some discussions. Many engineers and technicians prefer to use equations and numbers as substitutes for words, and while this mode of communication is a superior way to describe certain phenomena and relationships, it is a poor way to describe others.

For example, consider “ultrasonic flowmeter,” which apparently refers to a device that utilizes ultrasonic energy to measure flow. Which of the following are ultrasonic flowmeters?

A. Doppler ultrasonic flowmeter
B. Transit-time ultrasonic flowmeter
C. Ultrasonic correlation flowmeter
D. Flume/weir with ultrasonic sensor

Commentary
Doppler ultrasonic flowmeters (Answer A) inject ultrasonic energy into the flowing fluid and analyze reflected ultrasonic energy to determine the flowrate. Transit-time ultrasonic flowmeters (Answer B) inject ultrasonic energy into the flowing fluid and analyze the amount of time it takes the ultrasonic energy to travel between transducers. Both of these types of flowmeters are ultrasonic flowmeters.

Correlation flowmeters sense the flowing fluid at an upstream location and at one or more downstream location(s). Fluid velocity is determined by comparing the arrival of “signatures” present in the flow stream. Different techniques, including pressure, temperature, and ultrasonic techniques, are used to sense these “signatures.” In the sense that ultrasonic energy is utilized to measure flow, an ultrasonic correlation flowmeter (Answer C) could be considered an ultrasonic flowmeter. However, the correlation flowmeter technology does not inherently utilize ultrasonic energy or ultrasonic techniques, so an ultrasonic correlation flowmeter (Answer C) might not be considered an ultrasonic flowmeter.

Flumes and weir flowmeters are restrictions to flow in open channels that cause the liquid level at a certain location to rise in relation to the flowrate through the flowmeter. Ultrasonic level sensors are commonly used to measure the liquid level and infer the flowrate through the flume or weir; however, many other techniques are also used to sense the liquid level. In the sense that ultrasonic energy is utilized to measure level, a flume or weir with an ultrasonic level sensor (Answer D) could be considered an ultrasonic flowmeter. However, open-channel flowmeter technology does not inherently utilize ultrasonic energy or ultrasonic techniques, so a flume or weir flowmeter with an ultrasonic level sensor (Answer D) might not be considered an ultrasonic flowmeter.

Whether you consider correlation and open-channel flowmeters to be ultrasonic flowmeters is your choice. But when you read about ultrasonic flowmeters, or discuss them with others, make sure that the meaning of “ultrasonic flowmeters” is clearly understood.

Additional Complicating Factors
Some articles about ultrasonic flowmeters do not contain their definition of “ultrasonic flowmeters,” so you may have to contact the author of the article for clarification. Likewise, some marketing reports on ultrasonic flowmeter technology may contain information that combines data in ways that may not be useful and/or could cause a market segment to be incorrectly portrayed.

David W. Spitzer, P.E., is a regular contributor to Flow Control. He has more than 30 years of experience in specifying, building, installing, startup, and troubleshooting process control instrumentation. He has developed and taught seminars for over 20 years and is a member of ISA and belongs to the ASME MFC and ISO TC30 committees. Mr. Spitzer has written a number of books concerning the application and use of fluid handling technology, including the popular “Consumer Guide” series, which compares flowmeters by supplier. Mr. Spitzer is currently a principal in Spitzer and Boyes LLC, offering consulting for manufacturing and automation companies. He can be reached 845 623-1830.

www.spitzerandboyes.com