Now you can learn Foundation Fieldbus Concepts at your own pace using our hightech multimedia training course on CD-ROM or with our on-line Distance Learning Program

Foundation Fieldbus has arrived
and is here to stay

Interoperability among multiple vendors is possible

The very first production installation of Foundation Fieldbus (FF) demonstrating interoperability among multiple vendors with closed-loop control distributed in the field started up on June 3, 1997, at Daishowa America in Port Angeles, Washington. The installation includes a fieldbus host and six fieldbus transmitters with two closed loops, six analog inputs, and five analog outputs. The installation controls a refiner mill's interstage hydrogen peroxide bleaching process in a mechanical pulping facility. As an end user, Daishowa has developed a taste for what fieldbus can offer today as well as a flavor for what's to come.

This article shares Daishowa's experience over the past 18 months with project engineering, start-up, and operating fieldbus instruments. It also describes why fieldbus was chosen over other technologies, project benefits, training, maintenance, and opinions the mill has formed as a result of doing the project. This is written for end users interested in the technology and discusses some issues they may face as the new fieldbus instrument revolution begins.

Technology drove selection process

Daishowa chose to use a fieldbus instead of a distributed control system (DCS) to explore new technology and save the mill some money. With the existing process area poorly automated and the DCS cabinets full, this project was a prime application for new technology.

Daishowa selected Foundation Fieldbus over other digital alternatives because it provides a comprehensive user layer that is unprecedented in the industry. From a technical perspective, the selection process was straightforward.

The Foundation Fieldbus user layer specifies a standard function-block (FB) configuration for process control applications. For example, conventional feedback control is configured by interconnecting analog input (AI), proportional-integral-derivative (PID), and analog output (AO) function blocks. The design engineer places these fieldbus function blocks into one or more field transmitters during control configuration. The Foundation Fieldbus standard defines 29 function blocks and allows suppliers and end users the freedom to define their own.

All fieldbus function blocks must include what the standard defines as a device description (DD). The device description is located in a host directory and contains all information needed to communicate over the bus with function blocks in the field. Therefore, given a new field instrument with embedded function blocks and device descriptions, the end user can engineer, operate, and maintain the new instrument from the fieldbus host with no further ado. This is beyond plug and play; it is plug and run. The specification calls it interoperability-the ability to add new instruments to the bus from one supplier and instantly establish communications with the fieldbus host and instruments from other suppliers.

In addition to the extraordinary user layer, Foundation Fieldbus provides many significant cost-saving benefits over older DCS technology. Conduit and wiring are reduced by 40% to 60% because only one twisted-pair segment is used to interconnect many field devices. System hardware costs are reduced because the control, I/O, and communications hardware are all contained in the field transmitters. Air-conditioned rack rooms with raised floors for cabling are not needed. There are no separate control cabinets, I/O cabinets, large power supply cabinets, or any control and I/O modules, communications modules, control and I/O racks, or separate termination units and associated cabling. With this considerable reduction in hardware, fieldbus equipment reliability is significantly improved while required spare parts inventory is substantially reduced.

There are many additional benefits to Foundation Fieldbus (e.g., standard fail-safe and alarm-handling methods); however, a comprehensive review is beyond the scope of this article. Those mentioned here were key in Daishowa's selection criteria.

Many features beneficial

Daishowa's fieldbus project takes advantage of many features contained in the final Foundation Fieldbus specification. The system uses AI, PID, and AO function blocks for controlling and monitoring the process. The configuration is done on a host PC and then downloaded to the field. The PC interface card serves as a fieldbus link active scheduler (LAS), which administers all communications on the bus. Interoperability is demonstrated by two different manufacturers' products operating on one Foundation Fieldbus segment.

All six fieldbus transmitters for the project were delivered by Smar International, each with multiple I/O (AI or AO) and PID function blocks. National Instruments provided the host hardware and software. This included a fieldbus configurator, their operator interface (Lookout), utility software, and a fieldbus PC interface card. Verbal communication between these suppliers before and during start-up was excellent and helped make the project a success.

The new technology presents the mill with a path forward away from old high-cost Distributed Control System technology (i.e., vendor dependence) to new low-cost standard fieldbus technology (i.e., vendor independence). The peroxide project, which included hardware, software, engineering, and installation, saved about 55% capital over using the DCS. This was critical since the project was initially rejected based on cost estimates alone.

Fieldbus instrument checkout during start-up was completed in 20 minutes using the PC host. The configurator shows all functioning devices on the fieldbus segment, eliminating the need to ring out individual fieldbus transmitters. However, any analog/fieldbus interface signals must still be rung out individually. Management was pleased with the project's benefits and supports an ongoing effort to fully automate the refiner mill using fieldbus technology in the near future.

System design important

As with any system, the design needs serious consideration when using fieldbus control. Up to 32 field devices can be placed on one Foundation Fieldbus segment; however, since H1 is non-redundant, process considerations may dictate fewer devices to ensure system robustness. The engineer must logically place control loops by process or area within a segment to ensure potential failures are localized with minimal impact on process and safety.

This is not significantly different from the Distributed Control System with its analog I/O typically non-redundant and grouped in the same way for similar reasons. There is no hardware equivalent to the DCS I/O system in a fieldbus transmitter. Likewise, the Foundation Fieldbus transmitter contains no more hardware and is no less reliable than today's smart transmitters. This makes the redundant fieldbus unnecessary for most processes. To take fail-safe and reliability one step further would require redundant transmitters for either a DCS or a fieldbus control system (FCS).

Documenting involved new symbols

Daishowa documented the fieldbus project using new symbols and a modified format for loop sheets. A new drawing called the bus diagram was also created to document fieldbus segments and higher level communications (e.g., H1, H2, and Ethernet). The process and instrument drawing (P&ID) is a more basic control drawing showing less detail and, therefore, remained largely unchanged except for the new fieldbus symbols.

The new loop sheet, shown in Figure 1, contains three sections: "field analog" to show analog termination, "fieldbus" to document function block connections and bus termination, and "operator interface" to cover the control room interface. The new loop sheet has no provisions for the DCS since Daishowa does not intend to integrate it with fieldbus. Thus, Distributed Control System loop sheets remain unchanged.

The field analog section is self-explanatory; it shows a flow element with transmitter and a variable-speed drive's analog connections. There is no junction box (JB) because all analog signals terminate directly to the fieldbus transmitters. The loop sheet's field analog section is present only to separate analog and digital instruments when there is a mix of the two. This section will be present in the loop sheet for some time to come.

The fieldbus section shows all digital hardware, including current-to-fieldbus (I/F) and fieldbus-to-current (F/I) transmitters, each depicted by an ellipse. The transmitter address assignments are not shown in the drawing since the Foundation Fieldbus standard frees the end user of this burden. All address assignments are made automatically during configuration or when a new transmitter is added to the bus.

The fieldbus transmitter tag numbers in Figure 1 are different from the loop tag number because the fieldbus instruments contain multiple I/O points and are therefore a part of two different loops. However, the fieldbus function blocks shown inside the transmitters use consistent loop numbers.

Bold solid lines interconnecting function blocks within a transmitter represent logical software connections in the configuration. Likewise, fieldbus function block connections drawn between transmitters are also logical software links, but they require a communication over the bus. The bus is shown as a line drawn with embedded squares.

The loop sheet also includes a list of all function blocks contained in each Foundation Fieldbus transmitter and an indication for those transmitters that provide fieldbus link master (LM) or link active scheduler capabilities. This is a maintenance requirement so technicians can select the appropriate replacement part when a transmitter fails.

The mill has elected not to intermix fieldbus and analog signals in any one junction box. The loop sheet identifies each fieldbus junction box, but does not show internal terminal blocks or screw numbers for connections. This is not necessary since the bus is wired in parallel. Therefore, JB termination blocks are labeled only by H1 segment number and bus polarity. All JB instrument wiring is labeled with the fieldbus segment number and the transmitter tag name. The home-run wiring is similarly labeled and includes the Foundation Fieldbus segment number and a reference to the upstream or downstream junction box.

Desktop training provided

Daishowa purchased and evaluated all hardware and software starter kits available for fieldbus prior to final vendor selection and project engineering. This ensured selection of the best available products and provided excellent hands-on desktop engineering training.

In addition, one engineer attended the Fieldbus Foundation's introductory and advanced training classes. National Instruments also provided in-mill custom training covering basic and advanced concepts for both engineers and technicians. One additional day of training for engineers covered embedded fieldbus function block coding for round card applications. Start-up week was an exceptional learning experience for both mill and supplier personnel. Operator training was done during start-up by mill personnel.

Maintenance functions enhanced

Some HART applications have implemented automatic diagnostics and service scheduling based on two-way digital communications. These maintenance functions will be further enhanced by Foundation Fieldbus providing interoperability along with event-driven reporting and status of all information. Universal fieldbus maintenance tools will be needed to handle this open system, with end users selecting the best tools for configuration and maintenance without investing in a proprietary software/hardware package.

Fieldbus technology supports online failure diagnostics and preventive or predictive maintenance (e.g., continuous valve diagnostics). Although some of this capability is available now on the DCS for a price, it will become standard with fieldbus at little or no additional cost. Fieldbus failures will alarm operations with specific detailed information so that instrument technicians can be informed during a call-in. Online troubleshooting will also significantly increase the number of control loops serviced by the technician. Most maintenance will be done with simple transmitter replacement.

The technician's duties and skills will also change as industry moves from electronic analog troubleshooting to purely digital. A bus analyzer to view protocol data units and other digital test equipment will replace the voltmeter and most analog tools used with the DCS. In addition, some maintenance documents, including the instrument index and data sheets, will be available online to update the host database at any time. It is software of this diversity that will give the supplier a competitive edge in the future using Foundation Fieldbus technology.

Power supplies redundant

The Daishowa application uses redundant Smar power supplies for the H1 fieldbus segment. These power supplies contain electronics that accommodate simple parallel wiring and bumpless transfer (fail-over). They are also isolated and contain short-circuit and overcurrent protection through power supply switching. This reduces process downtime and eliminates the need for fuse replacement when the bus is inadvertently shorted in the field.

The application also includes battery backup. Both power supplies and the batteries are connected to the fieldbus using a Relcom power multiplexer. Relcom also provided the power-conditioning electronics to maintain constant bus impedance as field devices are added or removed from the fieldbus segment. Bus termination connections at both ends of the home run and spur connections for individual field instruments are also made using products from this supplier.

The Foundation Fieldbus wiring includes a dedicated DC grounding system. The Relcom and power supply grounding lugs and all bus shields are tied to this ground at the power supply end of the home run using a 00 cable. All shields on the field instrument side are left floating to prevent ground loops. The building's AC grounding grid is tied to the DC rods for safety. This arrangement significantly simplifies power and grounding checkout during start-up.

DCS role changes

Only a fraction of the Foundation Fieldbus benefits will be realized by the end user who elects to go with a DCS for the fieldbus host. Since the host device is only partially covered in the final Foundation Fieldbus specification, it is not subject to the same interoperability and conformance testing as the field device and, therefore, is not necessarily programmed using standard fieldbus function blocks. Moreover, the host can include software for advanced control, process area and production coordination, Foundation Fieldbus segment (network) integration, control configuration, and operator interface. Placing any of these functions in the DCS for plant-wide operation can lock the end user into one supplier's host.

The alternative is to locate the advanced control, process coordination, and fieldbus segment integration (H1/H2) into a field device that has passed the rigorous Foundation Fieldbus testing and to locate the configurator and operator interface software in a PC. An industrially hardened field device with a powerful processor and a large nonvolatile memory capable of meeting these advanced demands is well within reach with today's available technology. Excellent PC-based fieldbus configurators and operator interface software are available now.

Integrating fieldbus with the Distributed Control System creates additional problems as the end user must deal with a hybrid of two entirely different systems. The Foundation Fieldbus specification contains specific detailed requirements for user layer operations that are totally different from any existing DCS. It includes specifics for fieldbus function block initialization, operating modes, and configuration parameters. The specification also defines data quality status and how it propagates through the fieldbus function block configuration. Alarming and alarm priorities are also an integral part of the Foundation Fieldbus specification. To integrate all of these differences into one system creates significant and unnecessary confusion and complexity for the end user.

Daishowa's plan for transition to Foundation Fieldbus technology uses a PC and software capable of interfacing to both fieldbus and the mill's DCS. The user interface for both systems can simultaneously exist on one PC, keeping the two systems' operation totally independent. Daishowa will engineer new unit operations and some retrofit projects using fieldbus where appropriate. Existing DCS applications will be cut over to Foundation Fieldbus in a future planned transition only when there is justification to do so (e.g., DCS obsolescence or quality, productivity, and cost incentives). Consequently, for an interim period operations, engineering, and maintenance must be trained for both Foundation Fieldbus and the Distributed Control System, but not for a complex hybrid of the two. This keeps all options open for future growth and expansion in the mill.

Past and future

It took more than a decade to develop and release an acceptable Foundation Fieldbus specification. Now, nearly two years hence, there is still very little to show in terms of available instrumentation and new industrial applications. The same politics that held up the specification also held up its implementation. Vendors delayed progress and struggled to determine how Foundation Fieldbus could be implemented without obsoleting their existing systems and without losing market share. Some recalled capital investments made and lost in preparation for manufacturing automation protocol (MAP) technology that never caught on in the process industries several years back. Fortunately, most of these delays and politics have past and things are looking up for the end user as many major manufacturers will finally release fieldbus products sometime this year.

New interoperable fieldbus instrument technology means major change for the instrument suppliers. Hardware becomes a commodity. The unsatisfied customer can simply remove an unacceptable product from one supplier and replace it with another more capable of meeting the needs (with little or no change to the control configuration). The process industries will finally achieve vendor independence with more control over quality, productivity, and manufacturing costs by selecting the best available fieldbus instruments and controls for the application.

Full utilization of fieldbus potential will take time to exploit as it is limited only by the developer's imagination. Supplier margins will shrink as wide-open competition to exploit Foundation Fieldbus's new capability heats up in an attempt to gain and maintain market share. There are new kids on the block and more will come with exceptional fieldbus configuration, diagnostic, application, and maintenance software and hardware tools. Powerful, industrially hardened fieldbus control processors with large memories, silicon disks, and standard software capable of both regulatory and advanced controls will become available for field installation. Proprietary closed systems will be replaced with standard open systems. Marketing and R&D strategies will change forever. The successful supplier will provide excellent customer service, support, and software with full Foundation Fieldbus functionality to improve all aspects of plant operation and maintenance.

A long time in coming, Foundation Fieldbus has arrived and is here to stay. It has a comprehensive user layer with capabilities that are unprecedented in the process industries. It will revolutionize process control, and the winner in all this is clearly the end user. IT

Author Information

Dan Dumdie is process and control engineering supervisor at the Port Angeles, Wash., mill of Daishowa America. He has a B.S. in chemical engineering from the University of Washington and more than 20 years of experience in process control. His career objectives have placed special emphasis on making advanced control theory practical and easily applied. He is author of "Foundation Fieldbus Concepts," a multimedia tutorial on CD-ROM that deals with both introductory and advanced fieldbus concepts. Inquire at http://www.hmtutorials.com/.

Jason M. Mangano is a process and control engineer for Daishowa America Co. Ltd. in Port Angeles, Wash. He has a B.S. in chemical engineering from the University of Idaho.