In my automation-related blogs RSS feed, I discovered a Foundation Fieldbus blog post, Good Article on Benefits of Control in the Field. The Fieldbus Foundation (FF)‘s Larry O’Brien points to an article, Control-in-the-field provides control & reliability written by Emerson’s Travis Hesketh.
The PCN [Process & Control News] Europe article describes the capability for control functions to be executed outside the control system in transmitters and final control elements, such as control valves. Travis notes:
Embedded control functionality in field devices is one of the key enablers for achieving high process availability and a stepping stone towards single loop integrity.
This ability to execute control functions such as PID loops outside the control system is unique to the FF digital communications protocol. Beyond improved availability, Travis highlights customer experience, greater reliability, and improved performance as benefits that control-in-the-field technology provides process manufacturers.
For customer experience, Travis relays a plant situation where:
…the interface card in the DCS failed, which meant communication between the devices was no longer taking place. Instead of needing to shut down the plant, the Control-in-the-Field functionality of FF enabled direct communication between measurement devices and valves.
For greater reliability, Travis cites a study [hyperlink added]:
…by safety consultant Edward Marszal that compared an analogue system with FF with Control-in-the-Field, the first thing that was noted was the use of fewer components and diagnostics when adopting Control-in-the-Field. Fewer parts means less to go wrong. Analysing the components used in each system and all of the possible issues arising with both systems, the study found that there is far more scope for failure in the analogue system, accounting for the huge difference in mean time to failure statistics: just under 16 years for the analogue system, versus 48.2 years for FOUNDATION fieldbus with Control in-the-Field.
On improved performance:
Control-in-the-Field also offers improved control performance because it is no longer necessary to communicate control-related data to the central control system. This means time delays are reduced and determinism is improved compared to using conventional fieldbus systems where control calculations are performed within the DCS.
Travis mentions the Industrial Systems and Control (ISC) study I highlighted in an earlier blog post, Operational Gains with Foundation Fieldbus. Some of work from this study was captured and summarized in an ARC whitepaper, The Business Value Proposition of Control in the Field.
He concludes the article:
Implementation of a FF with Control-in-the-Field can reduce costs associated with wiring, power supplies, panel space, and redundancy hardware. In turn, by reducing the hardware requirement there are actually fewer points of failure, thus adding to the reliability of the system. Similarly the smaller number of connections between the devices increases system reliability. The increased reliability and availability of the process has a significant affect on the number of unplanned incidents taking place. Greater plant availability has a serious positive affect on a company’s bottom line. As does greater accuracy of control, enabling operators to reduce raw material and energy use, increase output and improve final product quality.