##Principle:
Optical flowmeter uses light reflection to measure the velocity of the flow stream. It measures the time of flight of light to measure the flow of a stream.
##Construction and Working:
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A dual beam laser is used as the source
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Opposite sides of the pipeline is attached with optical window to let the light into the pipeline.
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The light detecting sensors are placed at an inclination to the straight line path of the light.
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The light detected is then converted into an electrical signal and then signal processed.
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The light is let pass through the optical window and the light propagate through the fluid and comes out through the optical window at the other end.
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If there is no fluid flow in the pipeline, the light goes straight and cannot be detected by the sensors.
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If fluid flows through the pipeline. The incident light hits the particles in the fluids, the light gets scattered and deviates from the main path.
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The deviated light is getting detected by the detector. Consider this happens at the first sensor. Then the particle moves further to the second beam of light.
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The same happens for the second beam. The light beam gets deviated and detected at the second sensor. The time delay between the two successive pulse is measured.
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This time delay is proportional to the flowrate of the stream, desicribed by the equation:
V=d/t
Where, v = Velocity of particle d = Distance separating laser beams t = Time difference between sensor pulses