David W. Spitzer, P.E.

English may not have been your best subject in school, but it can be the most important part of some discussions. In response, many engineers and technicians prefer to use equations and numbers as substitutes for words. This language is a superior way to describe certain phenomena and relationships, but 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 flow rate 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.