Operational Gains with Foundation Fieldbus

Emerson’s Jonas Berge alerted me to a series of Asia Pacific region seminars on Foundation fieldbus. The Singapore Fieldbus Foundation site has links to the presentations given for the seminars held in Malaysia, Taiwan, and one in Singapore for the water/waste water industry.

Control Engineering Asia magazine described the focus of these seminars:

This year’s seminar put emphasis on Foundation fieldbus benefits in the operation phase. Improved product quality and throughput is possible due to reduced process variability, which in turn is a result of tighter control achieved from a digital loop as compared to traditional 4-20 mA analog. In addition, having access to real-time status as well as the process value distinguishes device failure from process problems, hence reducing downtime by avoiding spurious trips.

I opened up Jonas’ presentation from the Malaysian seminar detailing operational benefits achievable with Foundation fieldbus digital communications. He provides analysis in three areas: higher performing control, earlier warning of abnormal process situations, and increased availability.

On higher performing control, Jonas compared analog-based control with analog input (AI) and analog output (AO) I/O versus Foundation fieldbus (FF) digital control. AIs/AOs have asynchronous updates that lead to longer deadtimes and sampling jitter. Foundation fieldbus communication and execution is synchronized to provide precise periodic samples, no jitter and the shortest possible deadtime. For those unfamiliar with asynchronous and synchronous communications, think email or Facebook wall posts (asynchronous) versus a chat session or phone call (synchronous). It’s the difference of messages left for later viewing vs. interactive communications.

The reduced deadtime and lack of jitter leads to a shorter control response periods and reduced process variability from tighter control. Jonas cited the work of Industrial Systems and Control and a study they performed, Control in the field: analysis of performance benefits. ARC Advisory Group summed up some of their findings in a whitepaper, The Business Value Proposition of Control in the Field:

Recently, UK-based firm Industrial Systems and Control Ltd. (ISC, www.isc-ltd.com) released a study called “Control in the Field: Analysis of Performance Benefits”. In a series of illustrative simulation studies, ISC determined that control in the field has the potential to offer improved control loop performance due to its ability to offer faster sample rates and shorter latencies in the read-execute-write cycle of a control loop. ISC examined the differences in timing and sequencing associated with control in the field versus a scheme employing control in the DCS to establish typical latencies and sample rates that limit control performance. Many different scenarios and process dynamics were tested, and the results and corresponding benefits are outlined in this report. Whilst benefits of increased integrity, flexibility, and reliability can be attributed to all control in the field loops, ISC found that control loop performance benefits can be quite significant in fast process loops.

Jonas relayed another whitepaper, Fast Control Response Requirement, which describes how fast loop control is achieved by using Foundation fieldbus with control algorithms running in the FF field devices.

On the topic of earlier warning, Jonas shared how diagnostics from the Foundation fieldbus devices are integrated with the control system operator displays to provide information on device failures, communication issues, and abnormal process conditions. The status from these devices can be used in the control strategies to provide validated, quality and limit information, protection from loop windup, bumpless transfer for valves, valve fault states, and other conditions, which could otherwise increase the variability of the process or cause unplanned shutdowns.

If you visit the Singapore Foundation fieldbus page, you can find presentations from most of the automation suppliers on improvements possible with Foundation fieldbus through the entire lifecycle of a plant–from front-end engineering design (FEED) through ongoing operations and maintenance.

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