Eastern Instruments - Solids Mass Flow and Air Flow Measurement Equipment

Know Your Flow Experts answering your Process Questions   The Question: Should I use a Multivariable Pressure Transmitter or DP-only Transmitter for Air Flow Measurement? The Expert: James Seagraves Senior Sales Engineer, Eastern Instruments - Over 30 years of experience in Air Flow and Solids Flow Measurement This is a question I receive all the time, as both types of transmitters measure the differential pressure (DP) of the air flow in a duct. To provide the best answer, let's first review the fundamentals of air flow measurement. Basics of Air Flow Measurement A Typical Pitot Tube in an Air Stream Typical Pitot Tube in an air stream One of the most reliable and time-tested methods of measuring the air flow in a duct is to use a differential pressure device like a pitot tube.  The pitot tube is inserted into the air stream to measure the pressure differential created between the High port and Low port on the pitot, also known as the Dynamic or Velocity Pressure. High Port (...

When measuring the flow of air or gas in a duct or pipe, accuracy is dependent on the type of device used to make the measurement, but is very dependent on the flow profile in the duct or pipe.  For example, if the flow in the duct or pipe is turbulent, many types of flow measurement devices will not even be able to measure the flow or have such an error you would be better off not having the measurement at all.  Here we will look further into turbulence and ways to minimize or eliminate it so that an accurate air flow measurement can be made. What is Turbulence? Turbulence can come in many forms, for example the flow could be spinning in the duct (cyclonic flow), or the flow could be going in the opposite direction than it is supposed to be going (reverse flow), or it can be off to one side or even angular (not parallel to the center-line of the duct or pipe).  When a flow sensor, averaging pitot tube, thermal mass sensor (thermal dispersion), venturi, or even an ori...