The growing volume of data in process automation requires higher bandwidths and faster transmission rates in order to monitor and control processes in real time wherever possible. Additional requirements arise from the increasing demand for diagnostic data and device information. This increases the importance of integrated Ethernet networking of entire industrial plants. With EtherNet/IP, HART-IP and Profinet, various standards for IP communication have become established in process technology. Industrial Ethernet is characterized, among other things, by deterministic data transmission and robust components with extended temperature resistance and increased IP protection. In the process industry, the use of Ethernet is subject to additional conditions. In addition to long operating cycles of process control systems, field devices and installed infrastructure, this also includes practicable explosion protection in order to implement networking down to field level, including areas designated as potentially explosive atmospheres.

For networking even remote hazardous areas via Ethernet, the connection via fiber optic cable (FO) is the ideal solution. The interference-free fiber optic cabling requires neither complex earthing nor shielding and enables data exchange between sensors and actuators, remote I/O systems, control and monitoring cameras over distances of several kilometers. Potential ignition hazards are prevented in accordance with the "op is" type of protection to DIN EN 60079-28 by limiting the optical energy of the light beam to a non-ignitable level. Installations protected in this way also allow optical rings with convenient diagnostic and signaling functions to be set up in hazardous areas. Corresponding media converters and switches for Zone 1 and 2 are available for this purpose.

Intrinsically safe Ethernet sets new standards

Although fiber optic cables with "op is" have been used for a long time, applications and users often require the use of copper cables in potentially explosive atmospheres. For example, the NAMUR recommendation NE168 "Requirements for an Ethernet communication system for the field level" specifies the use of two-core cables for connecting field devices. The "intrinsically safe" type of protection has proven itself in the process industry and has become globally established. Standards for interoperable intrinsically safe Ethernet networking of field devices and systems open up new possibilities for digital process automation. According to DIN EN 60079-11, device protection through intrinsic safety requires the amount of energy in a circuit to be limited to a non-incendive level so that sparks and thermal effects cannot act as ignition sources. Intrinsically safe fieldbus systems such as Profibus DP via RS485-IS have long been used for networking remote I/Os, operating terminals and analysis devices. Today, intrinsically safe 2-wire fieldbus installations with Profibus PA and Foundation fieldbus H1 are often used for digital communication up to the field device.

The decisive advantages of the intrinsic safety type of protection lie in the uncomplicated and convenient handling of intrinsically safe devices, as conversion and maintenance work can be carried out on intrinsically safe circuits or devices in potentially explosive atmospheres. As there is no need for enclosure encapsulation, there is no need for more complex protective measures such as the use of d or p enclosures. Extensions or repairs can be carried out under voltage (hot work) and devices can be added or disconnected (hot swap) without completely switching off systems or system components. The high level of flexibility also makes the intrinsic safety type of protection attractive for Ethernet networking in hazardous areas. In order to develop future-proof solutions for interoperable and intrinsically safe Ethernet, R. Stahl has joined forces with other manufacturers in two working groups. Both working groups - the Advanced Physical Layer (APL) Project and the Intrinsically Safe Ethernet Working Group - are currently developing international standards for intrinsically safe Ethernet based on 10BASE-T1L and 100BASE-TX technology.

Field networking up to zone 0

Ethernet-APL will be available at Achema 2021 as a dedicated solution for the use of intrinsically safe 2-wire field devices in process automation. The technology is based on the physical layer of Single Pair Ethernet (SPE) 10BASE T1L in accordance with the IEEE Std 802.3cg-2019 specification. SPE uses 2-wire cables to bridge distances of up to 1,000 m at transmission rates of 10 Mbit/s and optionally supply connected devices via PoDL (Power over Data Line). Ethernet-APL is compatible with SPE, but uses a supply concept for field devices that differs from PoDL in order to enable the use of the intrinsic safety type of protection. Other connectors and terminal connections are also expected to be used in order to meet the requirements of process automation. In addition to manufacturers, leading industry organizations are also involved in the development of Ethernet-APL in order to ensure compatibility with the communication protocols HART-IP (FieldComm Group, FCG), EtherNet/IP (ODVA) and Profinet (Profibus and Profinet International, PI).

Based on the FISCO concept (Fieldbus Intrinsically Safe Concept, see IEC 60079-11 and -25) and designed together with Dekra Exam, the 2-WISE explosion protection (2-Wire Intrinsically Safe Ethernet) for intrinsically safe 2-wire fieldbus systems enables field use up to Zone 0 in accordance with ATEX and IECEx as well as DIV 1 for installations in the NEC area of application. Thanks to standardized Ex i parameters, Ethernet-APL devices from different manufacturers can be interconnected within the specified boundary conditions of Ethernet-APL or 2-WISE without an intrinsic safety verification calculation and without taking cable parameters into account. In order to make the migration of existing fieldbus installations as simple as possible, Ex i parameters compatible with FISCO are specified for 2-WISE and type A fieldbus cables can still be used. The 2-WISE concept is currently being prepared for standardization by the IEC project team PT 60079-47. A technical specification as IEC TS 60079-47 "Equipment protection by 2-Wire Intrinsically Safe Ethernet concept (2-WISE)" should be available by 2021 so that Ethernet-APL devices can be certified as soon as possible.

Ethernet APL allows different installation concepts. For example, an APL power switch supplies the network (trunk) with up to 60 W of power. APL Field Switches installed in the field and fed by the trunk convert the supplied energy into intrinsically safe energy and distribute it to several outgoing circuits (spurs). The field devices, which can be installed as ia, ib or ic circuits in zones 0, 1 or 2 depending on their configuration, are operated on these Ex i tracks, which can be up to 200 m long. By cascading the APL field switches, a total of around 50 Ex i field devices can be operated per APL network. Externally powered Ethernet APL switches with a connection to other Ethernet networks such as 100BASE-TX are also possible. Without the "hot-swap" or "hot-work" properties of intrinsic safety, Ethernet-APL also supports field devices with types of protection such as flameproof enclosure "d" or encapsulation "m".

High bandwidths with great compatibility

For IP networking of operating terminals, analysis devices or remote I/O systems that require higher bandwidths and more energy, R. Stahl is working in the Intrinsically Safe Ethernet Working Group on an intrinsically safe variant of the widely used 100BASE-TX Ethernet, also known as Fast Ethernet. The new 100BASE-TX-IS standard provides high data rates of 100 Mbit/s for process control, data acquisition and evaluation. The explosion-proof 4-wire Ethernet is fully interoperable with the IEEE 802.3 industry standard and, in conjunction with an intrinsically safe front end and galvanic isolation where necessary, enables the connection of conventional industrial electronics with the continued use of Media Access Control (MAC) and PHY. In contrast to Ethernet-APL, 100BASE-TX IS does not offer power supply via the network. In addition, the transmission path via CAT cable is limited to the standard Ethernet distance of 100 m. For significantly greater distances of up to 30 km, 100BASE-TX IS switches and media converters with additional fiber optic interfaces, for example with "op is" type of protection, are currently being developed. Similar to Ethernet-APL, 100BASE-TX-IS does not require complex verification of intrinsic safety. A comparison of the participants for conformity with the underlying standard is sufficient. As the boundary parameters of a 100BASE-TX-IS installation are known - exactly two subscribers (thus two energy sources) in a point-to-point connection via CAT 5/6/7 cable and a maximum distance of 100 m - a generally valid intrinsic safety verification can be carried out on the basis of IEC 60079-25 "Intrinsically safe systems". This has already been carried out and documented as an example by PTB using the ISpark tool. This means that no calculations by the planner are required and the proof of intrinsic safety is limited to the documentation or the required explosion protection document for the installation.