Protocol independence, Ethernet speed, power and intrinsic safety, on a twisted pair

Oct. 29, 2018

Networking professionals to speak in terms of layers—application layer, transport layer, presentation layer, etc.—all of which can be rather abstract to the uninitiated. But one layer, the physical layer, actually seems tangible. The physical layer is where the rubber meets the road in automation and IT systems, or perhaps better stated, where the bits or waveforms meet the wire—or, in some cases, the air.

In process automation, we’re all familiar with physical layers. A two-wire twisted pair that transports a 4-20 mA analog signal with a superimposed digital signal at 1,200 bps is the physical layer for HART. The wire pairs in an H1 cable carrying a 31.25 kbps bitstream is the physical layer for FOUNDATION Fieldbus.

In the IT world, we look at Ethernet cabling and think it’s all the same. But if you need 10 Gbps Ethernet, you’d better use the Cat-6 cable, because Cat-5 or Cat-5e won’t work, even if the cable jacks are the same. Note that these physical layers use four-wire communication. Twice the copper means more cost. And to get the highest speeds, cable lengths are limited to 100 meters, which means more switches, routers, extenders, infrastructure, etc., and more cost.

Standard path to IP

In the process industries, domain-specific concepts like the NAMUR Open Architecture (NOA) or Open Process Automation (OPA) by the Open Process Automation Forum (OPAF) are presently attempting to simplify the efficient construction, commissioning and operation of process plants. Broader use of wireless solutions, simplified field device integration and Ethernet to the field represent integral components of these concepts.

And certainly information and operations technology (IT/OT) integration, Industrie 4.0, and the Industrial Internet of Things (IIoT) are the buzzwords of the past few years. Embedded in all of those ideas is the belief that adopting Internet protocol (IP) networking technology is the way of the future.

FieldComm Group has been, and will remain, a leader in the development and support of standards for the process automation world. The foundation of a path to IP technology was laid in 2007 with the release of WirelessHART. The release of HART-IP in 2012 defined HART at the speed of Ethernet.

“IT protocols are already used at the I/O level. TCP/IP-based HART-IP is a good example. The next logical step is to do this in field devices directly,” says Andreas Hennecke, product marketing manager at Pepperl+Fuchs. “This dramatically enhances functionality in field instruments and seamless integration in automation infrastructures. Such services can include browser-based diagnostics, FTP-based download of manuals or OPC/UA based cloud integration.”

Advanced Physical Layer (APL)
  • Ethernet-based, for any protocol or application 
  • Power and data over a shielded twisted-pair line
  • Any method of hazardous area protection, especially intrinsic safety, including simple validation
  • Transparent connection to any IT network
  • Re-use of existing two-wire cable
  • Supports the familiar trunk-and-spur topology 
  • Device access anytime and anywhere
  • Fast and efficient communications for automation and other application 

Now in 2018, FieldComm Group along with Profibus, ODVA and leading automation companies, including ABB, Endress+Hauser, Krohne, Pepperl+Fuchs, Phoenix Contact, Rockwell Automation, Samson, Siemens, Stahl, Vega and Yokogawa, are working together on an Ethernet-to-the-field project that uses a two-wire, powered, intrinsically safe (IS) physical layer for IP-enabled instruments and infrastructure. Currently referred to as Advanced Physical Layer (APL), the project focuses on an extension of 10BASE-T1L—an Ethernet physical layer for process automation and instrumentation, which can be deployed in hazardous areas (Zones 0 and 1, Division 1), allows long-reach connectivity, and includes an option for device powering over the line. Products are projected to be available in late 2021.

The realization of the APL vision began in 2011, when a group of solution suppliers at the urging of several end user groups began a technical investigation of a protocol-neutral, advanced physical layer that could solve the longtime problem of a long-reach Ethernet for use in hazardous locations. The results of this five-year investigation proved the feasibility of a solution for this problem, and also generated interest in an industry-wide solution based on IEEE’s Ethernet standards.

“APL brings Ethernet into the field of process automation,” explains Hennecke. “APL is in development, incorporating important lessons learned in cooperation with all stakeholders of the process automation lifecycle. It’s based on the same two-wire cable as FOUNDATION Fieldbus H1, thus offering continuity to users.”

Where will APL be used?

APL parameters and specs

Parameter

Specification

Standards IEE 802.3 (10BASE-T1L), IEC 60079
Power supply output (Ethernet APL power switch) Up to 60 W
Switched network Yes
Redundant cable and switches  Optional 
Cable type for intrinsic safety IEC 61158-2, Type A
Maximum trunk length 1000 m
Maximum spur length  200 m
Speed 10 Mbps, full-duplex
Hazardous area protection For all zones and divisions with intrinsic safety at the device

“Connectivity to IP-style Internet is one purpose,” says Ted Masters, president and CEO, FieldComm Group. “But there’s a need in the field today for a faster solution. Higher-use devices such as drives and motors need higher data speeds. Valves need to send signatures, and analyzers also can use more bandwidth. We need to move more data during operations, and especially during startups, configurations and commissioning. Will everything become high-speed Ethernet? Will it be all wireless? No, we’ll see different things—Ethernet, HART, 4-20 mA, even different protocols. The key is at the integration layer, where different physical layers and protocols are integrated. FDI and information models become important. Users want a standard way to reliably bring things together and display data.”

Seiichiro Takahashi, general manager, marketing at Yokogawa, and member of the System Integration and Maintenance Working Group at FieldComm Group, adds that, “At the early stages, four-wire devices such as magnetic or Coriolis flowmeters will be released, because upgrading from existing Ethernet-type flowmeters is not difficult. However, the majority of devices in process automation are two-wire devices, such as pressure/temperature transmitters. To disseminate APL technology, it is mandatory to adopt two-wire, intrinsically safe and powered field devices.”

Hennecke adds, “For simple signals, such as NAMUR-switches or pilot valves, an IP-layer may not be reasonable or necessary for functionality. Here, data concentrator devices can act as process interfaces to multiple, simple analog, or discrete signals to Ethernet while offering an IP-stack for higher-level services.”

This new Ethernet physical layer, together with the automation protocols that define the structure and meaning of information being transmitted to and from field devices, are the enabling factors of the IIoT. It will provide the prerequisite to extend the digitized world to process automation and instrumentation.

The leading standards development organizations participating in the project are working to ensure that all technologies and standards will be compatible to their respective protocols, such as EtherNet/IP, HART-IP and Profinet. They will also contribute to protocol-neutral conformance standards for their respective industrial Ethernet networks.

“No one is ripping out field devices. Fifty million HART devices are not going away,” adds Masters. “We’re not going to replace everything with Ethernet, but as suppliers make devices with Ethernet, it will come along. People want devices to fit the plant network.” 

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