Fellowship of the Fieldbuses?
This article contains an online expanded version.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 represent them. Present demands for interoperability persist because the fieldbus squabbles of years past, and the eight-par...
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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 represent them.
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 interoperability, though it did enable increased use of individual fieldbuses and alleviated some former trade barriers.
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 solutions 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. 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 Electronic Device Description Language (EDDL), 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) with IDA-Group and ODVA that established IAONA in 2000 as a platform organization for the advancement of IEEE 802.3 and/or TCP/IP communication technology for industrial automation was expanded in 2004 to include Interest Group SERCOS (IGS), EtherCAT Technology Group (ETG), and Ethernet Powerlink Specification Group (EPSG). IAONA's Joint Technical Working Groups, its 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.
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 10thbirthdays. Here are brief technical profiles of each fieldbus and a look at their recent notable achievements and applications:
DeviceNet, ControlNet, EtherNet/IP
DeviceNet, ControlNet, Ethernet/IP, which are based on Common Industrial Protocol (CIP) upper-layer protocol
Developer/support organizations: ODVA (Open DeviceNet Vendor Association) and ControlNet International (CI), which co-manage EtherNet/IP
Installed base: approximately 3.5 million nodes, total for all CIP networks
Topology: linear (trunkline/dropline) for DeviceNet; linear, tree, star or combination (ControlNet); active star with devices connected to an Ethernet switch (Ethernet/IP)
Physical media: twisted-pair for signal and power (DeviceNet); coaxial or fiber (ControlNet); 10/100-base T twisted-pair Cat 5E (Ethernet/IP)
Max. devices: 64 nodes (DeviceNet); 99 nodes (ControlNet), no limit (EtherNet/IP)
Max. distance: 500 meters at 125 kbps, depending on data rate (DeviceNet); 1 km via coax with two nodes, 3 km over fiber with 99 nodes, 30 km over fiber or coax with repeaters up to 99 nodes (ControlNet); no limit (EtherNet/IP)
Communication method: producer/consumer with peer-to-peer and master/slave option for DeviceNet and ControlNet
Data Rate: 500 kbps, 250 kbps or 125 kbps (DeviceNet); 5 Mbps (ControlNet); 10/100 Mbps (Ethernet/IP)
Data packet size: 0-8 bytes variable (DeviceNet); 0-510 bytes variable (ControlNet); 0 to 65,511 bytes variable (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.
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.
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) announced plans to standardize on EtherNet/IP at its plant-level Ethernet network for vehicle 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.
FOUNDATION fieldbus H1 and High-Speed Ethernet (HSE)
Developer/support organization: The Fieldbus Foundation (FF)
Installed base: more than 300,000 nodes in 5,000 systems; growing by approximately 125,000 nodes per year
Topology: star or bus (H1); star(HSE)
Physical media: twisted-pair, fiber
Max devices: 240 nodes per segment, and up to 65,000 segments (H1); unlimited due to IP addressing (HSE)
Max distance: 1,900 meters on 31.25 kbps wire (H1); 100 meters on 100 Mbps twisted-pair and 2 km on 100Mbps full-duplex fiber (HSE)
Communication method: client/server, publisher/subscriber, event notification
Data packet size: 128 octets (H1); varies with TCP/IP (HSE)
Cycle time: less than 500 msec (H1); less than 100 msec (HSE)
Interest in and implementation of FOUNDATION 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 systems 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 FOUNDATION fieldbus-compliant from 20 suppliers.
One of the main reasons for this accelerating acceptance is that FOUNDATION 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 director. "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 H1 and HSE field devices," says Glanzer.
In addition, FOUNDATION 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.
HART (Highway-Addressable Remote Transducer)
Developer/support organization: HART Communication Foundation (HCF)
Installed base: more than 14 million HART-enabled devices, which may be only 25% of the total potential base worldwide
Topology: typically uses existing wiring
Physical media: same as 4-20 mA wiring, no terminators needed
Max devices: point-to-point recommended, but can multi-drop up to 15 devices for some applications
Max distance: 3,000 meters, but can use repeaters
Communication method: analog 4-20 mA, plus two-way digital master/slave
Transmission speed: analog 4-20 mA, which is instantaneous, always present, with no transport lags or synchronization time
Data packet size: four process variables in IEEE floating point values, plus engineering units for them, plus device status in one packet
Cycle time: 500 msec for digital
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, adopted by users realizing that many already-installed I/O devices are HART-enabled and able to interpret intelligent I/O signals. 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 a control room and back," says Ron Helson, PE, HCF's executive director. To aid users seeking increasingly sophisticated diagnostic capabilities, such as process deviations, HART recently developed a digital communication channel. This allows users to access both signals in real-time, detect device problems in seconds, and take appropriate action.
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 is the standard on which HART is based, and 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. 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.
Profibus-PA, Profibus-DP, Profinet, ProfiSafe
Developer/support organization: Profibus Nutzerorganisation e.V. (PNO) and the Profibus Trade Organization (PTO)
Installed base: more than 10 million nodes
Topology: line, star, ring, or bus
Physical media: twisted-pair or fiber
Max devices: 127 nodes in four segments with three repeaters, plus three masters
Max distance: 100 meters between segments at 12 Mbps, or 12 km with fiber
Communication method: master/ slave, peer-to-peer
Transmission properties: 500 kbps, 1.5, 12 Mbps for Profibus DP; 31.25 kbps for Profibus PA
Data packet size: 256 bytes
Cycle time: configuration dependent, less than 2 msec
PTO 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 brushless 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.