The Physical Layer and Installation

IEEE standardizes communication of Single Pair Ethernet (SPE) at different speeds and cable lengths, which meet the requirements of a variety of applications such as in-vehicle communication, discrete manufacturing, data centers, building, discrete manufacturing and process automation. In addition to communication, the entire physical layer from cable to connectors and from power supply to installation rules must be designed for the purpose of the application. Ethernet-APL deploys one standard from SPE (10BASE-T1L) and adds definitions for physical layer attributes that meet the needs of process users. The vast attention that Ethernet-APL has received is due to the fact that its standardization is exhaustive and complete from power to connectors to cables to hazardous area protection to conformance testing. Add to this a comprehensive engineering guide providing best practices, and Ethernet-APL is ready for deployment by all users of and vendors to the process industries.

Additionally, Ethernet-APL standardizes screw / spring terminals in conjunction with glands and connectors. Even for terminals the order of connections is defined making installation as simple as possible.

Likely! The cable must be shielded for reliable communication. The reference cable is type ‘A’, which is widely used in process industries, e.g. in fieldbus installations. Many users can re-use this installed cable base. Because of the higher frequency range, which is not explicitly specified for most cable installed today, the experts highly recommend testing the installed cable. This is even more important if shielded cable other than type ‘A’ is considered for re-use. A reduction in usable cable length should be expected. For conformance information, refer to the Ethernet-APL engineering guideline.

No! Plus and minus leads require proper isolation to ground. In addition, planners and installers need to design and implement functional bonding and shielding, which serves two purposes. First, to avoid potential differences that could ignite an explosive atmosphere. Second, to improve the electromagnetic compliance of the plant’s installation. As with all communication, proper isolation, grounding and shielding is required to ensure reliability of the communication.

A common and preferably meshed bonding network provides the best protection from stray currents, which can be a dangerous nuisance. Other techniques such as capacitive grounding of the shield, are permitted and subject to local installation standards.

The field switch provides point-to-point connections to the instrument. Field switches with fast Ethernet or Gigabit interfaces support redundancy of the infrastructure with parallel redundancy, the media redundancy protocol, (MRP) or device level ring (DLR). The switches are easily configured for redundant logical connections since the data just passes through the infrastructure, e.g. an instrument can maintain multiple communications paths to controllers to enable controller redundancy.

Point-to-point connections resulting from the switched infrastructure eliminate the risk of cross talk between instruments, e.g. during connect and disconnect operations. The network is protected from negative influences when work is performed on an instrument during operations. Thus, the designers gave the terminator a place inside the device’s port as an integral part of the communication circuit. Users and installers do not need to worry about proper termination anymore. It is always ensured.

The spur definition specifies a lower signal strength compared to the trunk. The reduced signal power allows for more power available to the instrument while still enabling a cable length of up to 200 meters between field junction box and instrument. The two signal specifications provide a simple engineered system that ensures interoperability. Field switches installed in a junction box provide connectivity in a convenient place, which is common and well known to work crews.

General System Considerations

No! You don’t need to worry about isolation with Ethernet-APL. The ground loop issues associated with 4-20 mA signals normally exist due to longer than usual cable lengths of several hundred meters, or as a result of exposure of the unshielded wire pair to EMC and EMI since power is being supplied over a line as well. With the shielded pair of Ethernet-APL we have already proved in the lab and our demonstrator that this cannot occur if the correct cable type, length, shielding and installation guidelines, as specified in the Engineering Guideline, are followed.

Technology has come such a long way, and with the same user experience we already know from Ethernet networks, an Ethernet-APL instrument can announce itself via the same native tools that computers and hardware use to connect to the network in the office environment. So you can expect more user-friendly attributes in the protocols used in the Ethernet-APL physical layer as they align with market and industry needs.

Security must be considered from the system perspective. Like any other physical layer, Ethernet-APL transports application-layer safety and security services from the leading industrial automation standards bodies, which utilize standards such as IEC 61508 and ISA/IEC 62443. Network architects which design the infrastructure for the entire plant can deploy the same techniques and working procedures for the field of process plants.

The APL Power Switches and APL Field Switches, together with the APL Field Devices, are downstream of the overall Ethernet network. The techniques and ideas of a data diode will be able to find their place in switches and infrastructure devices higher up in the Automation Pyramid.

From the Field-Switch to the field instrument it’s a 1:1 connection (<200m). If you need redundancy there, you could implement it in your application. Examples include installing Homogeneous Redundancy (two transmitters of same type) or Diverse Redundancy (two transmitters of different types to avoid systematic failures in a device).

Redundancy on the north side of the Field-Switch or the Power-Switch (if installed) would use the Redundancy technology, which depends on the protocol. For example, you could use MRP for PROFINET or DLR in an EtherNet/IP network.

Explosion protection for Ethernet-APL

Ethernet-APL definitions enable application and installation in any hazardous area. The possible installation of field devices and field switches depends on the manufacturer’s design of the product and is not related to Ethernet-APL technology. The new intrinsic safety concept for the Ethernet-APL spurs, called 2-WISE (2-Wire Intrinsically Safe Ethernet, IEC TS 60079-47) and the port profiles allow for intrinsically safe circuits corresponding to “ia” type of protection – which is suitable even for Zone 0, Zone 20 or DIV 1 installations.

While both technologies could be used either for the one or the other or for both applications, Ethernet-APL is optimized to meet the needs of process plants and specifically for hazardous areas with various options for explosion protection, including intrinsic safety. It is not impossible to use it in standard industrial applications as well – but therefore at a higher cost and with some restrictions on connectors and cables. SPE could be used in explosive atmospheres as well but not with intrinsically safe field devices. Other types of protection like flameproof “d” or pressurized “p” enclosures work with SPE but offer less flexibility for installation and maintenance. The choice of technology should be based on practical and economical requirements.

The Ethernet-APL field switch can be understood as the intrinsically safe barrier or isolator for intrinsically safe Ethernet-APL field devices. The energy at the field switch ports is limited to values conforming to intrinsic safety (see ignition curves from IEC 60079-11). However, the device that can be connected to such a port also needs to comply to the intrinsic safety standard to make sure that device internal temperatures and energy storage are well below the acceptable intrinsic safety values. This means that Ethernet-APL field devices need to get their intrinsic safety parameters and behavior certified for the respective place of installation.

Yes, there are. To simplify engineering work and the required verification of intrinsically safe loops, a new technical specification (TS) standard was developed, the IEC TS 60079-47 “2-WISE, 2-Wire Intrinsically Safe Ethernet”. This extends the IEC 60079-11 and is based on IEC 60079-25 “Intrinsically safe systems” and the FISCO (Fieldbus Intrinsically Safe Concept, part of IEC60079-11 and -25). A field switch port that is (additionally) certified according to 2-WISE can be connected to 2-WISE field devices without calculation of intrinsic safety / entity parameters. In addition, the field switch may be certified to other types of protection as well, depending on the place of installation and required explosion protection.

Actually neither of these. While Ethernet-APL is based on a 2-wire cable with intrinsically safe supply for field devices, 1000 m cable run, and 10 Mbit/second bandwidth, 100BASE-TX-IS focuses on other applications. It is based on a standard 4-wire Ethernet network with 100 Mbit/second bandwidth with only 100 m distance and without integrated supply for devices. 100BASE-TX-IS is based on the IEEE 100BASE-TX specification and just adds an intrinsically safe front end to it, enabling 100BASE-TX devices (with external power supply) to be connected to such intrinsically safe networks. Even a combination of 100BASE-TX-IS as a fast backbone with Ethernet-APL as the field device interface may make sense.

The IEC TS 60079-47 allows an intrinsically safe load of up to 5.32 W for power input Pi of field devices. This value is identical to the FISCO value and allows the use of Ethernet-APL and FISCO field devices on a field switch from an intrinsic safety design point of view. The defined Power Classes 0.54 W or 1.11 W are based on minimum nominal values. It was decided to limit the available energy per port to make product design, intrinsic safety certification, and engineering easy with a limited set of well-standardized field device parameters, as well as to not require any cable calculations (due to voltage drops etc.) while allowing as many field devices as possible in one network. Any field device that complies to the described power classes will be interoperable to appropriate field switch ports without the need to do any calculations.

Conformance Tests Ensure Interoperability

Ethernet-APL defines various types of ports such as Trunk/Spur, Source/Load, and so on. Each port type has its own specification and port match that must be adhered to. The conformance test ensures interoperability of valid combinations of port types across all vendors by testing the behavior of the port across different types of instruments and infrastructure components based on the Ethernet-APL port profile specification. This ensures plug-and-play interoperability. It is important to note that since Ethernet-APL specifies the physical layer only, that the complete connection includes conformance testing for the communication protocol as well.

Four standards development organizations (SDOs), inclusive of FieldCommGroup, ODVA, OPC Foundation, and PROFINET/PROFIBUS International, are involved in Ethernet-APL. The SDOs will provide Ethernet-APL conformance testing as part of their protocol certification process. Members of the SDOs have access to the Ethernet-APL specifications.

There are many different types of Ethernet-APL devices that can have multiple types of ports. The basic concept for device testing is to test port specifications one at a time. Every single port is tested, proving that the device in total is conformant. Checks include testing interference of different ports on the same device or interruption from external power. Test case design incorporates worst case conditions to ensure an optimal and interoperable device.

Since Ethernet-APL is a physical layer specification, the conformance test only covers the physical layer. Conformance testing is split into two parts: data tests based on IEEE, 10BASE-T1L and power tests based on Ethernet-APL port profiles. Specifications for EMC testing align with IEC/EN 61326 and with NAMUR recommendation NE 21. Intrinsic safety or functional safety certification are approved by the notified body. Any protocol functions defined above layer 2 of the OSI model are subject to testing by the respective standards development organizations. For physical layer testing, the four standards development organizations deploy the same tests and mutually accept test results reducing efforts for product development.