TABLE OF CONTENTS The flow transducers described in this section include differential pressure elements, turbine, vortex, thermal, Doppler, transit time, and laser Doppler anemometer.
Flow can be defined as the amount of material that is moved in a given time. The amount of material can be measured in mass units such as pounds and kilograms or in volume units such as gallons and cubic feet. The flow is known as mass flow if mass units are used and volumetric flow if volume units are used. If we know the density (mass per unit volume) of the material then we can convert between mass flow and volumetric flow. Using consistent units we get:
In most cases, the material is moving in a pipe or duct whose cross-sectional area is known. In a few cases, the material is moving in an open channel or on a conveyor belt. If the pipe is completely full, we can measure the flow by determining the velocity of the moving material. Using consistent units, we get:
This relationship also requires either that the velocity be constant over the whole area or that it be possible to determine the velocity distribution (flow profile) by testing. Testing is done by dividing the area into small equal-area segments and then measuring the velocity in each segment. The average velocity is then calculated and used to determine the total flow. For similar conditions, a single velocity measurement at a known location can be adjusted to...
