In an automation.com article, Emerson’s Michael Flesch explains how advances in DP flow metering technology solve measurement challenges of compressible fluids.
One of the perpetual instrumentation challenges that engineering students and working technicians face is measuring the flow of a gas, or worse, steam. The main problems emerge due to the compressible nature of such fluids, resulting in far more variables entering into the measurement. Since most compressible fluid measurement applications use differential pressure (DP) flow metering technologies, technicians sometimes find the task all the more complex due to the range of hardware options available.
Sorting through these options is the topic of my article at automation.com, Differential Flow Meter Selection for Challenging Compressible Fluid Flow Applications.
A host of new DP primary element technologies have been introduced, each having distinct advantages in specific applications. DP transmitters themselves have also been re-engineered, offering multivariable measurement, dynamic compensation capabilities, bias elimination, and exceptional accuracy. Suddenly, the flow meter selection process went from choosing an orifice bore size and DP transmitter, to evaluating a wide array of primary element and transmitter options.
Just to remind readers of the complex nature of flow measurement, in the article, I list 15 variable parameters that can affect a flow measurement.
Variations in any of these parameters, particularly fluid pressure and temperature, can significantly impact the accuracy of the flow measurement. Variable process temperatures and pressures change the fluid’s density, as well as the viscosity and Reynolds number, affecting the measurement. That is why the most accurate DP flow meters require a separate process temperature and pressure measurement, both used to compensate and correct the flow calculations as process conditions change.
The article goes into more detail on several of Emerson’s Rosemount DP measurement technologies and applications where they have particular advantages, including the following solutions:
Each of these can be used with a Rosemount 3051S MultiVariable transmitter to provide the highest accuracy and wide turndown range. This does require some homework, but Emerson has made it easy to determine the best possible solution, even in the most difficult compressible fluid applications, with its DP Flow Sizing and Selection Tool.
Given the wide variety of options, choosing the best combination of primary element and transmitter for a particular application can be a daunting task. Fortunately, there are free online tools available that take the user through a series of questions to define the application, with the answers used to provide a range of suitable solutions, including the pros and cons of each. Such tools allow users to quickly narrow their options for a primary flow element and transmitter that will satisfy their measurement requirements and meet their budget.
For more information, visit Emerson’s Flow Measurement Systems pages at Emerson.com. You can also connect and interact with other engineers at the Emerson Exchange 365 community.
