E-Zine June 2010
Various ultrasonic energy path geometries are used to implement the various types of ultrasonic flowmeters.
Doppler ultrasonic flowmeters transmit ultrasonic energy into the pipe and receive ultrasonic energy that is reflected by particles, bubbles, and/or eddies in the flow stream. These flowmeters can be designed to utilize dedicated transmitting and receiving sensors, or a single sensor that performs both functions. It should be noted that the flow measurement is dependent upon the penetration depth of the ultrasonic energy and the location of suitable reflectors (see figure below).
Transit time and pulse repetition ultrasonic flowmeters can have single or multiple ultrasonic paths. Single path ultrasonic flowmeters can be designed with transmitting/receiving sensors located opposite each other (see figures below).
Similarly, multiple path ultrasonic flowmeters have more than one pair of sensors oriented along more than one path through the flowing stream. Because more of the flowing stream is sampled, these designs are generally less sensitive to velocity profile distortion, and are typically more accurate than similar single path ultrasonic flowmeters (see figure below).
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Excerpted from The Consumer Guide to Ultrasonic and Correlation Flowmeters