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 mass flow of air flow in a duct or pipe, using the correct flow element is half the battle .  After deciding that using a differential pressure device like a Velocity Averaging Pitot is the right way to go, getting the correct instrumentation to measure that differential pressure is not something that every transmitter can do. VAP³ Velocity Averaging Pitot In typical industrial, combustion, and power generation applications , the differential pressure to be measured ranges from a high of 8 to 10 inches of water column down to 0.25 inch of water column or even less.  Getting a transmitter that can measure these ranges and have a turndown that can measure the low end accurately usually requires getting a laboratory type of transmitter, rather than an industrial differential pressure transmitter.  These are typically not satisfactory for these types of applications, so most users go with an industrial transmitter that has a very large URL (upper ran...

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...

Even though it does not feel like it here in the Eastern US, it is definitely winter in many parts of the world.  And something happens every winter at process plants all around the world, namely instruments and instrumentation begin to have issues due to the temperatures, moisture, and the winds of winter.  These issues send Instrumentation Techs, Engineers, and Maintenance people scrambling to get them back online and functioning properly. One of the biggest issues is when an instrument that is crucial to the proper operation of the a plant gives erroneous readings or stops working all together.  This is especially the case with flow measurement devices and instruments.  Having a transmitter or moisture in the differential pressure lines freeze up will cause the transmitter to stop responding or give incorrect flow measurement readings.  These can be handled sometimes (depending on the temperatures) by putting the transmitters inside a building or under a...

When it comes to measuring the flow rate of air or gas in a duct, there are many different devices used.  For example, there are thermal sensors, hot wire anemometers, rotating vane anemometers, static pressure drop devices (venturi, orifice plate), and differential pressure devices (pitot, annubar, primary element).  The most widely used and considered a true measurement of the flow is the differential pressure device.  The most widely used differential pressure device is a velocity averaging pitot tube. Velocity Averaging Pitot Tube The velocity averaging pitot tube is a device that when inserted into the air or gas flow stream, provides a high pressure measurement port and a low pressure measurement port.  The high pressure port measures the total pressure created when the air or gas stream impacts the port, where the low pressure port typically measure the static pressure in the duct. VAP³ Velocity Averaging Pitot Tube from Eastern Instruments The dif...

Measuring the Air Flow in a duct can be difficult enough when the flow profile is not free from turbulence, disturbances, cyclonic flow, and reverse flow, but add to that particulate, ash, dust, or debris in the air, and it can almost be impossible.  So, how do you get accuracy when trying to measure the Air Flow in a duct that has particulate, ash, dust, or debris in the air stream? The traditional way is to use a blast purge or blow back system that will take high pressure compressed air and blow it back through the high and low ports of the air flow pitot or flow element so that any particles, ash, dust, or debris is blown out of the ports on the probe.  This not only uses a lot of compressed air, which needs to be completely dry to work properly, but it also requires a complex system of valves in order for this to be done automatically.  If the blast purge or blow back is not done on a regular basis, and if the particulate, ash, dust, or debris level is high enough ...