Although flow meters have been in use for years, up until recently were mostly mechanical devices. However, recent advances in electronic technology have given us the the Laser flowmeter , (sometimes referred to as an Ultrasonic flow meter) which uses two laser beams to determine the velocity of small particles almost always present in liquids and industrial gases as they pass through the flowmeter. The two laser beams, which are focused across the flow a short distance apart, are scattered by particles crossing the the beams with the amount of scattering indicative of the speed of the flow Their accuracy comes from their speed not being dependent on thermal conductivity of gases, composition of the gases or minor variations in gas flow. Since these factors have little effect on Laser flow meters measurements are quite accurate and repeatable.
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