- One advantage of Foundation Fieldbus is that it’s a continuously evolving specification.
- The Fieldbus Foundation updated its specification in August 2010, to incorporate NE 107, and it’s supported in Version 6.0 of the Interoperability Test Kit.
- A series of new field diagnostic alarms correspond to the five primary diagnostic categories NAMUR outlined.
We’ve said for a long time that the real economic benefits of fieldbus come in the operational phase of the plant. Foundation Fieldbus-compatible devices can provide a wealth of data both about themselves and about the process that can be turned into useful information. Sometimes, however, turning all the data and getting it to the right people at the right time can be a challenge.
The Fieldbus Foundation realizes this, and several years ago we began cooperation with a European end user group called NAMUR (www.namur.de) to provide more information in context to operations and maintenance. For those that are not familiar, NAMUR is a group comprised solely of end users and systems integrators in the European process industries. NAMUR represents approximately 15,000 process control experts, of whom approximately 300 are active in 33 working groups. NAMUR pools their experience to create best-practice documents and other aids that help member companies fulfill their functional requirements. Member companies include names like Shell, BP, Dow and Akzo Nobel. NAMUR does not create standards, per se. Although many of its members also sit on standards committees outside of NAMUR, the purpose of the organization’s recommendation documents is to give the user some guidelines and best practices and to guide suppliers as they develop new products and applications.
Of particular concern to NAMUR is the role of the operator and maintenance technician and their impact on plant reliability and uptime. Unplanned downtime is one of the primary enemies of the process industries. According to ARC Advisory Group (www.arcweb.com), unplanned downtime accounts for the equivalent of 20% of all production in the process industries. A single unplanned shutdown can wipe out your plant profit for the year. In the same piece of ARC research, it states that 40% of unplanned downtime events can somehow be traced back to the operator or the human in the loop. We need not always blame the human in the loop, however, since that person may be working on faulty information or may not have the right information presented to them at the right time.
Today’s fieldbus device has unparalleled capability to diagnose its own state. NAMUR outlines 10 representative methods for self-diagnose field instrumentation, from signal processing tests to use of reference signals. The Foundation Fieldbus specification allows for many other methods of self-diagnosis of field instruments, including plugged impulse line detection and probe wear on electrochemical sensors.
Diagnostic data, however, is not of much use unless it is presented to those that need it in a timely fashion. It was in this same vein that NAMUR created a recommendation document called NE 107, "Self-Monitoring and Diagnosis of Field Devices," which outlines a series of recommendations on how to drive reliability and contextual presentation of fieldbus diagnostic data to the people who need it.
Figure 1. An operator needs to look at information from a wide array of systems, not just the distributed control system.
The operator and field diagnostics
The role of the operator has become more complex (Figure 1). An operator needs to look at information from a wide array of systems, not just the distributed control system. Information comes from plant asset management systems, electrical reliability systems and other sources. There also are fewer personnel in many of today’s process plants, so the operator’s job has widened in terms of the scope of the plant. NE 107 categorizes internal diagnostics into four standard status signals — failure, function check, out of specification and maintenance required (Figure 2). Each of these categories can also contain greater detail. In the case of failure, for example, is the failure related to the device or the process? Is maintenance required immediately, or is the requirement more for long term maintenance?
Figure 2. The series of new field diagnostic alarms corresponds to the primary diagnostic categories outlined by NAMUR in its document.
Information overload or information in context?
Users also might become overwhelmed by the amount of diagnostic data that is possible from fieldbus devices. It requires some intelligent planning from both a work process perspective and a data management perspective. To address this, NE 107 also stipulates that the solution should be highly configurable, depending on the user’s requirements. Plant operators, for example, should only see the information they need to see. Anything that may cause an impending unplanned downtime event would be of interest to the plant operator. A device needing long-term maintenance would likely be of little interest. A bad diagnosis can be worse than no diagnosis at all, so NAMUR recommends that data should also be reliable, allowing the operator to take action at the right time. All the relevant diagnostic parameters should be clear and readable.