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 Overview Transit Time Ultrasonic Flowmeter: A pair (or pairs) of transducers, each having its own transmitter and receiver, are placed on the pipe wall, one (set) on the upstream and the other (set) on the downstream. The time for acoustic waves to travel from the upstream transducer to the downstream transducer td is shorter than the time it reqires for the same waves to travel from the downstream to the upstream tu. The larger the difference, the higher the flow velocity. td and tu can be expressed in the following forms: where c is the speed of sound in the fluid, V is the flow velocity, L is the distance between the transducers and is the angle between the flow direction and the line formed by the transducers. The difference of td and tu is where X is the projected length of the path along the pipe direction (X = L cos). To simplify, we assume that the flow velocity V is much smaller than the speed of sound c, that is, . We then have or, Note that the speed of sound c in the fluid is affected by many factors such as temperature and density. It is desirable to express c in terms of the transit times td and tu to avoid frequent calibrations: The speed of sound c becomes The flow velocity is now only a function of the transducer layout (L, X) and the measured transit times tu and td. The above formula can be further simplified by utilizing the following approximation: The flow velocity can therefore be written as
Common Specifications

Common specifications for commercially available transit time ultrasonic flowmeterss are listed below:

Fluid Phase:

 Score Phase Condition Gas Clean Liquid Clean Corrosive Dirty Gas Dirty Liquid Open Channel Viscous : Recommended : Limited applicability
Line Size: Inline model: 10 ~ 1200 mm (0.4 ~ 48 inch)
Clamped-on model: 75 mm (3 in) and up
Turndown Ratio: 100: 1
Pros and Cons

 • Pros: - No obstruction in the flow path, no pressure drop - No moving parts, low maintenance cost - Multi-path models have higher accuracy for wider ranges of Reynolds number - Can be used in corrosive or slurry fluid flow - Portable models available for field analysis and diagnosis • Cons: - Higher initial set up cost - Single path (one-beam) models may not be suitable for flow velocities that vary over a wide range of Reynolds number
Metal 3D Printing Design Guide

Direct Metal Laser Sintering (DMLS) 3D printing for parts with reduced cost and little waste.

Salary Expectation

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Essentials of Manufacturing

Information, coverage of important developments and expert commentary in manufacturing.

3D Scanners

A white paper to assist in the evaluation of 3D scanning hardware solutions.