I received a call the other day and wanted to capture the question and answer for other people Googling around with similar questions. The question:
What are the required distances in pipeline inside diameters (I.D.) upstream and downstream for a differential pressure (DP) flowmeter for the pressure and temperature sensors doing pressure-temperature (PT) compensation?
I turned to my friends on the Rosemount DP Flow Specialist team. Emerson’s Vernon Binger responded:
It is common to take the line pressure (static pressure) measurement at the same port for the upstream DP measurement; a “tee” fitting can be used.
This is compliant to ASME practices per the ASME MFC-3M standard, and therefore compliant to U.S. Environmental Protection Agency (EPA) requirements.
If a separate tap location will be used for the line/static pressure measurement, then it should be at least 1 pipe diameter upstream from the tap used for the upstream DP measurement. This tap location should be offset 30 degrees radially from the upstream DP tap location.
The line/static pressure tap in the process pipe should be ≤0.50″, and <0.13 x pipe I.D.
The temperature probe/thermowell should be installed at a location between 5D to 15D downstream from the orifice plate or other primary element. That is, unless the temperature measurement is done as an integral part of the primary element, such as the integral RTD option on the 405 Compact Primary element, or the 485 Annubar.
Vernon and I received a note back from the person who asked me the question:
That was precisely what I needed. Thanks very much.
I hope this also helps you if you found this post in your search. Leave me a comment if it did… thanks!
