Modern multivariable transmitters have exceptional reference accuracy specifications for differential pressure measurement, but these are generally defined as a percent of calibrated span. Fluid and gas flow measurement is related to differential pressure measurement through a square root function, and thus flow measurement errors can increase dramatically at low DP readings. These errors can be glaringly present when a traditional percent of span accuracy transmitter is used in an application where flow rates vary widely, requiring a transmitter to be capable of high turndowns. Such an application is plunger lift where the normal flow rate inherently fluctuates. Missed flow at the high end or inaccurate measurement at the low end can result in lost revenue.
This problem is often approached one of two ways. Transmitters of varying span can be “stacked” to measure specific flow ranges, but more commonly orifice plates of different bore sizes are swapped to maintain the same DP range across different flow regions. Rosemount Enhanced for Flow (EFF) technology available on the Rosemount 4088 is equipped with a percent of reading accuracy specification and effectively eliminates the need for transmitter stacking or swapped orifice plates. A single EFF 4088 can capture the capture the entire flow range, including the high flow region and low flow region.
The percent of reading specification defines accuracy using the transmitter’s measured DP value as a reference. This results in decreased uncertainty across the entire flow range and significant improvements in the low flow region. Accurate measurements can be made at much lower flow rates not attainable with a percent of span transmitter.
Capturing the entire flow range is not the only benefit of a Rosemount 4088 with EFF. Standardization on a single model number is possible since accuracy is maintained across the whole DP flow measurement range, reducing the volume of required on hand inventory. Combining the EFF percent of reading specification with the versatility of the 4088 to integrate into any RTU, reduced costs can be realized through transmitter standardization, configuration tool reduction, and increased reliability. In addition to Modbus, the 4088 can communicate via MVS and BSAP protocols thus facilitating seamless integration into Emerson flow computers. Rosemount Enhanced for Flow is also backed by a 12-year warranty and 5-year stability specification, providing measurement confidence years into the future. If you would like to learn more about the Rosemount 4088 and Enhanced for Flow Technology, please contact your local Emerson Representative or visit the links below.
Rosemount 4088 MultiVariable Transmitter: https://www.emerson.com/en-us/catalog/rosemount-sku-4088-multivariable-transmitter?fetchFacets=true#facet:&facetLimit:&productBeginIndex:0&orderBy:&pageView:list&minPrice:&maxPrice:&pageSize:&
Enhanced for Flow Flyer: https://www.emerson.com/documents/automation/flyer-rosemount-enhanced-for-flow-en-5884348.pdf
9175 Natural Gas Flow Meter: https://www.emerson.com/documents/automation/flyer-rosemount-9175-natural-gas-flow-meter-en-5542884.pdf