Fellowship of the Fieldbuses?
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Driven by end-users seeking more interoperability and responding to Ethernet’s accelerating emergence, the major fieldbus protocols and their trade organizations are cooperating—at least on the surface—to meet those demands.
The customer is always right, especially when they find out that their needs aren’t being met. End-users' demands, fueled more recently by Ethernet’s apparent openness, are forcing changes by suppliers and vendors of industrial networks and by the trade organizations that develop and represent their various fieldbus protocols and networking methodologies.
Present demands for interoperability persist because the fieldbus squabbles of years past, and the eight-part, non-consensus International Electrotechnical Commission (IEC) 61158 standard that followed, ultimately produced little genuine interoperabil-ity, though it did enable increased use of individual fieldbuses and alleviated some former trade barriers.
'However, you still can't reproduce the exact bit stream, for example, of Profibus or ControlNet, which means you can't take Type 1 fieldbus in the current standard and interoperate with the other types, so they can't communicate directly,' says Dick Caro, CMC Associates' CEO and principal consultant. 'IEC 61158 allows suppliers to have their unique protocols labeled as conforming to an international 'federated' standard, even though the users are still faced with non-interoperable, incompatible protocols. This made many end-users livid. They felt like they'd been cheated, that they no longer had a part in developing international standards, and that the only voice left was that of the suppliers.'
Consequently, many of the world's largest petrochemical, automotive, and other end-users of fieldbuses eventually began to call ever more loudly for interoperability from within their own fieldbus organizations and end-user groups. 'Users are tired of the former over-competitiveness. They're hammering away on suppliers that fieldbus solu-tions have to be something that the average guy can use with a minimum of labor,' says Ian Verhappen, chair of the Fieldbus Foundation's (FF) End-User Advisory Council (EUAC). 'They want to be able to swap out fieldbus components in the same way they were able to do with 4-20 mA.'
As a result, network manufacturers and organizations are trying to deliver more practical interoperability, and actually cooperate with each other to do it. All of these organizations have undertaken joint projects, formed partnerships and/or joined umbrella organizations to help them keep these promises. Most involve interoperability for data monitoring, but some have the potential to allow interoperable control and actuation between fieldbuses, rather than simply reporting back to a central Ethernet network.
The most notable of these recent cooperative efforts include:
Fieldbus Foundation (FF), HART Communication Foundation (HCF), and Profibus Nutzerorganisation e.V. (PNO) are collaborating to extend the specification for Device Description Language (DDL), a text-based language they all use to describe the characteristics of networked field devices. Proposed extensions to DDL include adding capabilities to describe display characteristics of device parameters, as well as the ability to include algorithmic relationships for complex device parameters, persistent data, and real-time trends. EDDL is international standard IEC 61804-2.
The memorandum of understanding (MoU) that established IAONA as the platform organization for IDA-Group and ODVA in 2000 was recently enlarged to include the Interest Group SERCOS (IGS), EtherCAT Technology Group (ETG), and Ethernet Powerlink Specification Group (EPSG). IAONA’s Joint Technical Working Groups, Technical Steering Committee, and its partner organizations are seeking to “commonly, homogenously and all-embracingly” elaborate technical guidelines and recommendations for areas of mutual interest and benefit to organizations that serve industrial automation users and vendors of IEEE 802.3 and/or TCP/IP technologies.
PNO and its U.S. subsidiary, Profibus Trade Organization (PTO), recently formed a joint cooperative working group with the Interbus Club to migrate Interbus fieldbus protocol to PNO's Profinet Ethernet-based protocol. The working group is preparing a specification that will adapt the Profinet 'proxy' concept to allow migration of Interbus systems into Profinet architectures, and will also include the required engineering. A draft specification of the proxy is expected by September 2004.
The Instrumentation Systems and Automation Society's (ISA) SP95 Committee, MIMOSA open systems alliance for operations and maintenance, and OPC Foundation (OPC) recently formed a Joint Working Group (JWG) to help simplify development and integration of operations and maintenance systems, equipment and software, enabling practical interoperability with each other and with other enterprise systems. To support this objective, JWG will coordinate the standards under development by ISA SP95, MIMOSA and OPC.
OLE for Process Control (OPC) and its OPC DX and OPC XML software aid interoperability by serving as a between devices on fieldbuses, according to Tom Burke, president of the OPC Foundation.
Because it functions in the software layers above the fieldbuses, Caro adds that OPC can accomplish some added interoperability between dissimilar systems and protocols. “For example, I can have a refinery with lots of existing HART devices, a new area with FOUNDATION fieldbus, and a package boiler with Profibus-PA, and OPC can integrate all of these at the operator console,” he says.” For example, OPC’s object-oriented software can work with a HART-based server to translate data, and pull in secondary HART variables.
Only 10 months after inception, the Ethernet Powerlink Standardization Group (ESPG) exhibited its Ethernet Powerlink real-time networking solution at Hannover Fair 2004. EPSG’s multi-vendor installation at the fair included 10 members of the group, who believe that Ethernet Powerlink is the ideal technology for real-time networking in industrial automation. Devices from these vendors were connected in one Ethernet Powerlink network. In parallel to the exchange of real-time data with sub-microsecond jitter, the network transparently handled regular IP-based traffic without disturbing real-time behavior.
Besides integrating drives, I/O systems, network components, controls and sensors, the group demonstrated that an Ethernet Powerlink network can be analyzed with standard test, measurement, and analysis equipment from the IT world. 'This is the beauty of open standards-based systems, such as Ethnernet Powerlink,' says Dr. Edwin Kiel, ESPG’s board chairman and Lenze Drives Systems’ GM. 'Other real-time Ethernet approaches cripple Ethernet frames in order to achieve similar performance. With Ethernet Powerlink, the whole range of standard Ethernet tools and software remains applicable.'
In addition to the multi-vendor installation, EPSG introduced the basics of Ethernet Powerlink technology and a roadmap for future extensions. Experts discussed details of the protocol, and showed that it can be easily integrated with existing devices.
Field Device Tool/Device Type Manager (FDT/DTM) technology reportedly allows end-users to leave an entire system's field equipment assets in place and integrate them into one operations, maintenance and lifecycle management environment.
The essential parts of FDT technology are the frame application (FDT Frame) and the so-called Device Type Managers (DeviceDTM and CommDTM), which are available for field devices and communication equipment. The two components could be likened to the Print Manager in a Windows Office program and the Print Drivers that must be installed to make printers work and which contain a graphical user interface for their configuration.
The FDT frame communicates with the hosting or stand-alone application and the device drivers via a set of standardized interfaces. All data are exchanged through these interfaces, including those generated within the application for engineering, DTM management and device configuration. It is no longer necessary to use proprietary interfaces to operate devices or build up communication paths. Frame applications can be device configuration tools, control system-engineering tools, operator consoles or asset management tools. The frame application is also reportedly open to all communication technologies, including HART, Profibus, and F OUNDATION fieldbus. Proprietary service bus protocols can also be integrated simply into the frame application because of the standardized interface.
The device DTM is a software driver developed by the device manufacturer for each of his devices or group of devices. The DTM encapsulates all the device-specific data, functions and management rules such as the device functions, its communication capabilities, internal data structure and dependencies as well as the user interface elements. It provides functions for accessing device parameters, configuring and operating the devices, calibrating, and diagnosing problems. DTMs can range from a simple user interface for setting device parameters to a highly sophisticated application. They may perform complex calculations for diagnosis and maintenance purposes or display results in the form of curves, trends and other graphical elements.
For communication equipment, such as gateways, multiplexers and other hardware interfaces a CommDTM is required. Like any communication driver, this converts data from one protocol to another, but with the difference that the integration into the system is via a standardised FDT rather than a proprietary interface. This means that users wishing to integrate existing communication equipment into a FDT frame application require only the corresponding CommDTMs. Similarly, vendors need only modify their existing drivers to include a FDT interface and their equipment can be integrated into any FDT frame application.
Many device description language (DDL) proponents disagree with the FDT method because they say promoting device type manager (DTMs) for every device adds too much costand complexityfor manufacturers.& /p>
Besides their cooperative efforts, the most active fieldbus protocols and their organizations are growing steadily and implementing efficiencies in a variety of new industries. Most also recently marked their 10th birthdays.
“The fieldbus wars are pretty much over. If you’re going to do a traditional control system, then you’re probably going to use Profibus in Europe and DeviceNet in the U.S. or Japan,” says Mike Justice, president of Grid Connect. “If you’re going to start fresh and you haven’t built a system previously, then you’re probably going to take a serious look at Ethernet or one of the other versions of it, such as DeviceNet’s Ethernet/IP, Modbus’ Modbus TCP, or Profibus’ Profinet. However, when you try to manipulate Ethernet too much, to the point that you essentially get rid of TCP/IP, then you have to ask is it really Ethernet?
“All of this may mean that battles over fieldbus will start again, but this time on Ethernet’s application layer. However, this time it would only mean a software change for the user, which is easier to support. Basically, today’s Ethernet switches allow very decent performance, and, if you want sub-10-millisecond performance, then you’ll probably want traditional Profibus or De-viceNet anyway.”
Here are brief technical profiles of each fieldbus and a look at their recent notable achievements and applications:
While fewer of the 236 respondents in “Control Engineering/Reed Research Group Industrial Networking Product Focus Study, 2003” are connecting devices to networks or plan to use some of the well-known fieldbus protocols, some plan to use more of other protocols in the near future.
AS-interface (AS-i) International reports that AS-i is the simplest electromechanical networking solution and connection system carrying data and power for actuators and sensors in manufacturing systems. Using its well-known flat, yellow, two-wire cable,
AS-i is supported by more than 200 vendors worldwide. AS-i offers a cost-efficient alternative to conventional cabling at the lowest level of the automation hierarchy, where it can operate stand-alone or with a controller. AS-i can also link to higher-level fieldbuses for low-cost remote I/O connections.
For example, Essex and Suffolk Water recently implemented an AS-i package from Tyco Valves and Controls to provide digital control of valve systems at its refurbished filter system at the Layer de la Haye water treatment works near Colchester, U.K. This plant uses Tyco’s Keystone double-acting pneumatic actuators fitted with AS-i modules and mounted onto existing butterfly valves. AS-i connects these actuators with a two-wire cable, and links the modules via a Profibus gateway to a local PLC, which is connected via a Modbus link to the central SCADA system.
Essex and Suffolk reports that its new two-wire AS-i system dramatically reduced cabling requirements, time and costs of installation, and required capacity of the PLC system. AS-i also allowed proximity sensors to communicate positions of the actuated valves, ensuring that a clean, “bounceless” signal is provided to the PLC.
DeviceNet, ControlNet, EtherNet/IP
Global adoption of all CIP networks continues to grow quickly with approximately 300 combined members reporting double-digit growth in node sales year after year, according to Katherine Voss, executive director of ODVA and CI.
ODVA and CI recently formed two new joint Special Interest Groups (jSIGs). The first group, the CIP Safety jSIG, will complete safety enhancements to CIP and the DeviceNet specification. The second group, Distributed Motion jSIG, will define, the axis data structure need to coordinate multiple axes of motion over CIP networks and a commissioning gateway for reading and writing to SERCOS drive configuration IDNs.
CIP networks also have advanced in several vertical markets. In April 2003, EtherNet/IP was added to the SEMI E54 sensorbus standard, allowing use of EtherNet/IP in semiconductor tools. More recently, General Motors Corp. (GM) an-nounced plans to standardize on EtherNet/IP at its plant-level Ethernet network for ve-hicle manufacturing.
In the mining industry, EtherNet/IP was picked by CSIRO Exploration and Mining at Australia’s Queensland Centre for Advanced Technologies to achieve control system standardization for a coal shearer. The shearer’s military-grade, inertial navigation system and wireless Ethernet gear must be located on the mining machinery itself, and EtherNet/IP is providing a common communication interface for them. EtherNet/IP will help the navigation system track shearer position in three dimensions as it moves to stay within a given coal seam. According to Dave Reid, senior research engineer for CSIRO, EtherNet/IP provides the bandwidth necessary for on-machine cameras; condition monitoring to collect vibration data; and improved wireless Ethernet for broadband communications.
F OUNDATION fieldbus
Interest in and implementation of F OUNDATION fieldbus appears to be snowballing, growing by 50% annually from 175 interoperable devices a year ago to 300 at present, and increasing from 205,000 installed devices 14 months ago to about 300,000 now in more than 5,000 host sys-tems worldwide.
“We’re winning!” exclaimed John Pittman, FF’s former president and CEO, at the organization’s recent general assembly in New Orleans. In fact, FF now has 200 members, while there are now 250 devices registered as F OUNDATION fieldbus-compliant from 20 suppliers.
One of the main reasons for this accelerating acceptance is that F OUNDATION fieldbus allows logic and control functions to run in field devices, such as a PID loop occurring in its valve, which no other technology is able to do, according to David Glanzer, FF’s technology development di-rector. “We’re moving from centralized to fully distributed control in the field, so instead the traditional DCS, we now have flexible function blocks (FFBs) running in an HSE field device,” says Glanzer.
FF’s latest milestones include:
Release of the final specification for a standard pressure transducer block (TB). Similar to function blocks, TBs are key components of F OUNDATION fieldbus that reside at the fieldbus’ user layer, and are used to make sensor-related parameters needed for calibration and diagnostics visible to the fieldbus network.
Registration of the first F OUNDATION fieldbus-compliant power supplies and conditioners. Manufactured by MTL, Relcom, and Pepperl+Fuchs, these nine registered devices were tested according to specifications that exceed the IEC 61158-2 standard for use in a fieldbus installation.
Infraserv Höchst Technik, an independent consultancy located in Frankfurt, Germany, that grew out of the former Hoechst engineering division, will host Fieldbus Foundation Safety In-strumented Systems (FF-SIS) laboratory specification validation testing during 2004.
In addition, F OUNDATION fieldbus was recently implemented as part of Emerson Process Management’s installation of PlantWeb, DeltaV, AMA Suite software, and an Ethernet LAN at Repsol YPF’s Loma la Lata natural gas field in Neuquen Province, Argentina. PlantWeb helps the company manage 4,000 field inputs and outputs, both continuous (analog) and discrete (switched), as well as three control rooms, which oversee 196 wells, field separators, and compressors with a collective average daily gas production of 40 million standard cubic meters.
FOUNDATION fieldbus H1 handles power and digital communications for as many as 16 instruments at Loma la Lata with one multi-drop cable. HART superimposes bi-directional digital pulses on a 4-20 mA signal from a transmitter or to a control valve.
Besides generating material and labor savings and other efficiencies, Repsol’s PlantWeb system helps minimize the plant’s environmental impact on the sensitive Patagonian desert around it.
Similar to other fieldbuses, HART is also more than 10 years old. However, HART is a comparatively simpler, lower-level protocol that was always supposedly about to stop growing and be overtaken by those other fieldbuses. However, this never happens, and HART keeps right on growing, as users realize the intelligent capabilities of installed devices with real-time, HART-enabled I/O system connections. In fact, recent research indicates that HART will likely grow at approximately 5% per year from 2002 to 2010.
“4-20 mA analog signaling is still the fastest, safest way to move I/O data and control variables from a process connection to the control room and back,” says Ron Helson, PE, HCF’s executive director. HART-enabled devices have the unique ability to support both 4-20 mA analog and HART digital communication simultaneously on the same wire. HART-enabled systems use both communication channels to continuously validate loop in-tegrity, and provide early warning of problems that could disrupt or shutdown process operations.
However, HCF reports that HART’s most recent milestone is that the IEC recently approved DDL in a unanimous vote as its International Standard 61804-2. DDL has been a key element of HART technology since 1990. HART was the first communication technology to implement DDL as its standard. HCF endorses only DDL for configuring HART devices.
In the trenches, Detroit Water and Sewerage Department (DWSD) uses HART to eliminate metering disputes, improve system reliability, and streamline operations. “HART minimized the additional investment we had to make, since most of the existing instrumentation was HART-capable and could use existing wiring,” says Dennis Green, DWSD’s head engineer. “HART allowed us to digitally extract secondary variables and diagnostic infor-mation, while the intelligence built into the HART instruments enabled them to perform calculations, freeing computing power in higher-level platforms for other tasks.”
DWSD used HART to help develop and implement an extensive automatic meter reading/supervisory control and data acquisition (AMR/SCADA) system, which was a $10-million piece of the utility’s major infrastructure upgrade project. This system uses HART to deliver consistent, reliable performance data. DWSD integrated many diverse field devices and technologies onto one networked system that took advantage of HART's digital communication capabilities.
Demand for Interbus interface products rose considerably in 2003 with sales of protocol chips and masterboards growing more than 25% compared to the previous year, while sales of master products for high-end applications increased more than 40%.
Interbus is maintained and developed by 600 member companies in 16 worldwide Interbus Clubs. For example, the clubs will jointly complete development of the Interbus Safety system in 2004.
Dave Skelton, director of Phoenix Contact’s Automation Systems Group, adds that Interbus Safety can function on a single or dual cable, which means it can be retro-fitted into existing applications, but still have its own independent network. This means that Interbus Safety’s safe controller and safe I/O points are intermixed with regular I/O points. However, the two contacts in each module allow I/O statuses to be compared, which means that Interbus Safety can interrupt power to the safe I/O and affected devices if an invalid reading occurs or if a safety interlock is open.
In addition, the clubs are adapting the Interbus protocol chip to handle new field communication requirements. This new SUPI 4 chip will be available in 2005, and will have a higher transmission speed, integrated fiber-optic control, and will support PCP.
To move Modbus from being a longtime de facto standard to a formal standard, Schneider Electric recently transferred its copyright of the protocol to Modbus-IDA, a nonprofit organization formed in 2002. Modbus-IDA will manage the protocol’s future evolution. Modbus was originally developed by Modicon, which became part of Schneider Automation in 1979.
Next, Modbus-IDA will begin testing and certifying devices, and will eventually compile a catalog of interoperable Modbus devices. Modbus doesn’t presently allow multicasting, and so Modbus-IDA reports that its members also will help it improve how it broadcasts data.
Modbus-IDA adds that it offers a toolkit that allows users to develop Modbus devices without paying the fee required by some other organizations. The kit includes software for developing devices, as well as a method for testing them.
Profibus marked its 10-year anniversary by achieving more than 10 million total installed nodes by the end of 2003. This included selling approximately 1.3 million slave devices worldwide in 2003, with most of this new growth occurring in the U.S.
Ron Mitchell, head of PTO's Profibus Interface Center (PIC), reports another gauge of Profibus' growth is that the organization also tested more new Profibus-compliant devices in 2003 than in any year since the previous peak in 1998. He adds that 90% of these device vendors were also based in the U.S.
'I think we're finally reaching people,' says Mitchell. 'I think they're finally realizing that a fieldbus is really better than parallel wiring, and that our recent economic upturn is making it possible for them to implement it.'
One recent convert is John Young, Roberts PolyPro’s chief electrical engineer, who worked with Control Corp. of America (CCA) to find a more efficient solution for a new high-speed French fry scoop (carton) folder/gluer that would run at 1,800 ft/min or 260,000 cartons per hour. Young and CCA decided to use a Siemens S7-300 PLC and MM440 ac drives networked with Profibus.
“By replacing the costly, former blushless dc motors and drives with standard, off-the-shelf motors and vector drives, we lowered costs, significantly improved machine performance, simplified maintenance, eliminated costly and troublesome wiring, and improved machine setup by using recipe capabilities over the Profibus network,” says Young.
For more information on the fieldbus protocols and other networking methodologies covered in this article, please visit:
For a comprehensive technical view of all the fieldbuses, visit “Grid Connect Fieldbus Comparison Chart” .