Ultrasonic Mass Flow Meter for Industries Ultrasonic flow measurement is based on the principle of transmission and receipt of sound waves, which have a unique quality of bouncing off most objects - solid, liquid or gaseous. This technology is vastly different from traditional flow measurement technologies that use turbines or thermal sensors to measure the flow rate of fluids. Demand from industry for higher accuracy and lower costs have led to development of ultrasonic flow measurement technologies that fulfill meet the requirements of wide range of applications and processes. While there are number of different technologies in ultrasonic measurement currently available in the market, these can broadly be categorized into four types. This categorization is based on the principle on which these technologies are based. 
Transit-time Technology
This the original ultrasonic technology developed for measurement of flow rate of fluids. The technology uses the transit time of sound waves to measure velocity. An ultrasonic flow meter based on this technology has two ultrasonic transducers. These transducers act as both transmitters and receivers of ultrasonic sound waves. To measure the flow rate or velocity of fluid - either gas or liquid through the pipe, the flow meter alternates between sending and receiving bursts of ultrasonic sound waves through the transducers. The time taken by the sound waves to travel from the transmitting transducer to the receiving one gives an exact reading of the velocity of liquid in the pipe. 
Ultrasonic Doppler Technology
This technology also works by using two ultrasonic sound transducers. However, unlike the transit-time technology, Doppler utilizes one transducer as a continuous transmitter of ultrasonic sound waves. The other transducer acts as a continuous receiver. Sound waves introduced into the flow are reflected or scattered back off suspended particles or bubbles in the fluid and captured by the receiving transducer. The reflection causes a frequency shift in the sound waves, which is known as the Doppler Effect. By measuring this frequency shift it is possible to determine the flow velocity of the fluid in the pipe. This velocity, when computed with the cross-section area of the pipe gives the flow rate of pipe flow.
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Cross-correlation Measurement Technology
Cross-correlation measurement technology works on the principle that turbulent flow of a fluid is formed of eddies that have nearly consistent characteristics across a small cross-section of flow. This is known as the correlation length. A flow meter based on cross-correlation measurement technology has two ultrasonic sensors placed along the direction of flow of fluid. The first or upstream sensor picks up the signature of turbulence L/V seconds before the second or downstream sensor, where L is the distance between the two sensors and V is the velocity of flow of fluid. The velocity thus turns out to be L/T, where T is the time delay in detection between the two sensors. 
Acoustic Doppler Velocity Profiling Technology
The acoustic Doppler Velocity Profiling technology works on the same principle as the Doppler technology, with the difference that it uses three transducers instead of two. One of the transducers is a narrow-beam transducer while the other two are large angle ones. The three transducers are arranged in a straight line with the narrow angle one positioned directly above the flow while the other two ones are placed on either side of it. The middle transducer emits ultrasonic sound waves at a fixed Pulse Repetition Frequency (PRF), which get scattered from particles within the fluid. The other two transducers receive these reflected waves and provide a "pulse-to-pulse" algorithm. This in turn allows the measurement of the Doppler shift in two different directions, which can be used to create a 2D velocity profile. Take a look at other relevant information about flow meter products and applications including ultrasonic flow meter for liquids products as well as best ultrasonic flow meter manufacturers.