What's the Best Fieldbus for Your Process Plant?

EtherNet/IP, a newcomer to the fieldbus technology that offers fast and easy way connections.

Industry 4.0 and the Internet of Things are influencing the choice of fieldbus technology for process plants. Previously, the primary thing most instrument and control engineers worried about was how to connect hundreds, if not thousands, of process instruments to the distributed control system (DCS) in their plant.

Connecting the old-fashioned way—via 4-20mA “loops”—was getting too expensive because of the cost of running thousands of wires. Foundation Fieldbus and Profibus PA were initially developed 25 years ago to address this and other issues.

Today, engineers have another concern: How do they route data from process instruments to higher-level information technology software? Software platforms such as enterprise resource planning (ERP), computerized maintenance management system (CMMS), asset management, batch analysis and similar systems need real-time data. Here, a newcomer to the fieldbus scene, EtherNet/IP, offers a fast and easy way to make those connections.

Foundation Fieldbus and Profibus PA—How Do They Work?

Foundation Fieldbus and Profibus PA were developed in the 1980s as replacements for the 4-20mA standard and have gone on to dominate the process control world. Today, virtually every manufacturer of flow meters, pressure transmitters and similar instrumentation offers Foundation Fieldbus and Profibus PA interfaces, and every major control system supplier supports both.

Both fieldbuses save wiring costs because they allow multiple instruments to send and receive data using a single cable called a trunk or segment. A trunk or segment begins at an interface device located at the control system.

On a Foundation Fieldbus system, the interface is called an H1 card; on a Profibus PA system, it’s a DP/PA segment coupler. In terms of signal wiring and power requirements for the segment, they are similar as the dc power needed for instruments on the segment is provided by a power supply.

A typical segment includes an interface device, power supply, a cable to a device coupler and individual cables from the coupler to the instruments.

But because of the high cost of licensing fieldbus and the technical complexity, only the major DCS suppliers—ABB, Emerson, Honeywell, Siemens, Yokogawa and a few others—have fieldbus interface devices. In other words, this makes it difficult to connect Foundation Fieldbus or Profibus PA segments to a PLC or a PAC, or to an industrial computer running software not directly associated with the DCS.

EtherNet/IP—How Does It Work?

EtherNet/IP was originally introduced by ODVA in 2001, primarily to support machine automation. It was later adopted by Endress+Hauser, Rockwell Automation and others to support process applications.

An EtherNet/IP instrument typically offers a choice of Foundation Fieldbus, Profibus PA and EtherNet/IP interfaces. The major difference between the three interfaces is that EtherNet/IP can communicate directly via Ethernet IEEE 802.3, allowing connection to any virtually any controller or PC with an Ethernet port.

Cabling distances are up to 100 meters when deploying over copper, and up to 2,000 meters when using fiber. Power over Ethernet (PoE) is available, so power supplies may not be needed in the field. EtherNet/IP uses standard Ethernet switches, routers and wireless devices.

Foundation Fieldbus and Profibus PA can be used in hazardous areas as can EtherNet/IP. Ethernet switches are available that use Intrinsically Safe Power over Ethernet (PoEX) for connecting to field instruments in Zones 1 and 2.

Foundation Fieldbus and Profibus PA can be set up in redundant configurations to allow for failure of a power supply, short circuits or a damaged segment cable. For EtherNet/IP, redundancy can be achieved through appropriate network architecture.

Foundation Fieldbus and Profibus PA both provide extensive instrument data and diagnostic information via their digital communications, so does EtherNet/IP. In fact, Ethernet IEEE 802.3 provides a larger data packet—up to 1500 bytes— enabling device suppliers to provide much more data.

Getting to the Data

Foundation Fieldbus, Profibus PA and EtherNet/IP have similar capabilities, features and functions (see the table, “Fieldbus Comparison”). The biggest difference is how instrument data can be acquired by Industry 4.0, Internet of Things and other software.

Because EtherNet/IP is a standard interface, connection is relatively simple. For example, devices can be polled by any condition monitoring system with an Ethernet port for diagnostic and other data. Also, an industrial PC equipped with asset management, maintenance or HMI/SCADA software can access all the I/O and diagnostic information it needs directly from the devices via an Ethernet interface.

With Foundation Fieldbus and Profibus PA, instrument data typically first goes to the interface device, then travels to the DCS. At the DCS, the data is processed and placed into a database or process historian for access by other software platforms and systems.

Because Ethernet is the interface, many EtherNet/IP instruments have a built-in web server, allowing access to the device over the Internet.

Availability

Virtually every process instrument is available with Foundation Fieldbus and Profibus PA interfaces. By contrast, fewer EtherNet/IP instruments are currently available. Endress+Hauser is the primary source of such devices. However, other instrument suppliers are entering the scene. For example, EtherNet/IP flow meters are now available from Emerson, Badger Meter, Dynasonics, Spirax Sarco, Burkert and Anderson.

In addition, thanks to the initial emphasis on machine automation by ODVA, a large number of motor controls, actuators, motion controllers, vision systems, bar code readers, safety systems, process controllers and I/O systems are EtherNet/IP compatible. This makes EtherNet/IP a good fit for hybrid manufacturing applications such as food and beverage which typically encompass both process and machine automation.

ODVA recently announced the formation of a special interest group for EtherNet/IP in the process industries to address field device to industrial control system integration; field device to plant asset management integration; and a field-to-enterprise communication architecture.

But despite recent advances by EtherNet/IP, it trails by a substantial margin. According to Tom Moore, an Industrial Automation Analyst with IHS, Profibus DP and PA combined had about 806,000 new nodes installed in 2014. This overstates the case for Profibus PA alone somewhat, but is still instructive.

Approximately 462,000 Foundation Fieldbus nodes were put into service in 2014, while EtherNet/IP trailed the pack at around 209,000 nodes installed in 2014. More promising for EtherNet/IP were 2014 compound annual growth rates (CAGRs) at 6.8% for Profibus, 8.6% for Foundation Fieldbus and 9.8% for EtherNet/IP.

Based on this data, all three options remain viable going forward, with selection of the proper fieldbus driving by application requirements.