According to an ISA presentation given by Process Automation Hall of Fame member, Greg McMillan, the most common measurement device is the differential pressure (DP) transmitter. It is most commonly used in level and flow measurement. Measuring the differential pressure across an orifice plate is the common way to measure flow. Wikipedia provides a quick primer on orifice plates if you’re new to process automation.
Emerson’s Brian Fretschel shared with me some new, short educational videos the team managing the Rosemount brand of measurement products has put together. Today we’ll feature one of them on DP flow measurement, How Conditioning Orifice Plates Work (run time 1m 57s).
These conditioning orifice plates help condition the irregular flow profiles caused by upstream disturbances, which can result in swirling effects. Instead of a single hole in the orifice plate, the four holes reshape the flow profile across the entire pipe for a more stable measurement.
Per the ISO 5167 international standard, an orifice plate installation within a pipe requires 44 diameters of straight pipe run downstream after a 90° elbow, and an additional 7 diameters downstream of the orifice plate. For many production facilities space is limited and it is difficult to attain these distances. For the same upstream disturbance, conditioning orifice technology only requires two diameters upstream and two diameters downstream. This distance requirement reduction makes it possible to mount the conditioning orifice flowmeters in safer locations, such as grade level.
To connect and interact with Brian and other flow measurement specialists, join the Flow track in the Emerson Exchange 365 community. Greg McMillan also moderates a discussion group in the community, Mentoring Engineers, if you’re new to process automation.
