Measurement off flow

Introduction. Basic principles of flow measurement.

Fluid flow in closed pipes. Flow in open channels. Point

velocity measurement. Flowmeter calibration methods.

References. Further reading.

Transmissive flowmeters

 Transmissive devices

differ from Doppler flowmeters in that they rely

on transmission of an ultrasonic pulse through

the flowstream and therefore do not depend on

discontinuities or entrained particles in the flowstream

for operation.

The principle of operation is based on the

transmission of an ultrasonic sound wave

between two points, first in the direction of flow

and then of opposing flow. In each case the time

of flight of the sound wave between the two

points will have been modified by the velocity of

the flowing medium and the difference between

the flight times can be shown to be directly proportional

to flow velocity.

Ultrasonic flowmeters

Ultrasonic flowmeters measure the velocity of a

flowing medium by monitoring interaction

between the flowstream and an ultrasonic sound

wave transmitted into or through it. Many techniques

exist, the two most commonly applied

being Doppler and transmissive (time of flight).

These wiil now be dealt with separately.

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