Multivariable technology has been around for more than 2 decades now and it has made huge advances in adoption and growing leaps and bounds. There are several types of multivariable transmitters available today but the most common type is the DP Flow multivariable transmitter which replaces a pressure, differential pressure and temperature transmitter, at the least. Other types of multivariable transmitters from Emerson are Electronic Remote Sensors (which provides static pressure, differential pressure, level, volume etc in a tank) or a 3051S Advanced Diagnostics Transmitter (which provides standard deviation of the primary variable). This is like killing many birds with the same stone. What’s more – the DP Flow multivariable transmitter can also work as the flow computer and perform the flow totalization function within the transmitter. For a non HART host, the non primary variables can either be transmitted using a HART Tri-Loop or a Smart Wireless THUM Adapter.
Why Compensate?
In a compressible fluid flow, the density of fluid changes with changes in pressure and / or temperature. If the flow transmitter is not dynamically compensating for changes in density, it results in erroneous flow reading.
Recall the theoretical DP flow equation which is derived from Bernoulli’s Equation and the continuity equation. The final equation has many variables and it looks something like this:
It is often misunderstood how much a lack of compensation can affect your mass flow accuracy. The exact number will vary with application and the rangedown you are operating at but with full compensation, a 2-3% improvement in accuracy is not unheard of. A quick analysis can tell you how much accuracy you are losing out because of a lack of compensation, especially when dealing with steam and gas. Please contact your Emerson representative for an analysis for your next application need where P &/or T in a flow is changing and demands a dynamic compensation of many factors affecting your flow rate accuracy.
Achieve unprecedented flow performance, including enhanced energy management, with the Rosemount 3051S MultiVariable Mass and Energy Flow offering. The 3051S MultiVariable transmitter provides Differential Pressure, Static Pressure, and Process Temperature measurements along with advanced compensation techniques to provide faster and more accurate calculations. You can find more information regarding 3051S Multivariable Transmitter HERE.
Please share your own experience on the need to compensate and with multivariable transmitters.
Anshuman Prasad
Director of Integrated Marketing, Rosemount Measurement and Analytical
Multivariable transmitters also saves alot of time needed to install, commission and configure/set up, when compared with multiple devices and flow computers. And it becomes more cost effective now that we have lesser devices, IO points and manhours to work with. Definitely the technology that will give you an edge in a competitive market out there.