Ethernet-APL for Process Automation

Summary

Ethernet-APL (Advanced Physical Layer) is the new standard for the process industry. It is based on the 10BASE-T1L specification as per IEEE 802.3cg and facilitates two-wire Ethernet to the field. The primary advantage of Ethernet-APL is the interoperability and flexibility achieved by the seamless connection of field devices with rapid data transmission on the information layer, in both small networks at short distances as well as in large networks covering long distances. Importantly for the process industry, Ethernet-APL also supports the intrinsically safe ignition protection type “i” in Ex Zones 0, 1 and 2. With the Ethernet-APL technology, the future digitalization of automation networks is relatively easy to implement, assuming several preconditions concerning network topology are considered as part of the equation.  

For end users, Ethernet-APL creates new layout opportunities when building high-performance automation networks. Field devices can be integrated seamlessly into the network—and we’re not talking about a few pieces of equipment but millions of installed devices, such as small sensors, control units, or highly complex analytical instruments. Every year, a similar volume of new devices is added, with most of these still using 4–20 mA technology, potentially supplemented by digital point-to-point communication over the HART protocol.  

Formally adopted in 2021, Ethernet-APL is a new standard for end-to-end Ethernet communication. The standard accounts for the specific requirements of the process industry, like the bridging of large distances with a simple, two-wire conductor that not only handles data communications but also supplies power to the connected field device. Another significant step was taken by increasing transmission rates to 10 Mbps compared to HART and field buses.  

APL limits itself to defining a new data exchange standard for Ethernet at the lowest layer, ensuring that it retains compatibility with any Ethernet-based protocols at higher layers. For the first time, this makes transparent communication possible between production and company networks down to field devices, while removing the need for expensive gateways. Automation protocols can be deployed as required, as can web servers, OPC UA and cloud/edge connectivity.  

Network typology variants 

Looking at the huge number and diversity of plant types, the various models involved and the range of sizes, a network system should be easy and inexpensive to expand and should offer redundancy while being able to handle the specific requirements of the process industry, including harsh environments or operation in potentially explosive atmospheres. The Ethernet-APL Engineering Guideline outlines a number of network topologies for Ethernet-APL networks, although the circumstances for the Ethernet-APL spurs are the same for all topologies. Ethernet-APL devices can be connected to a switch by a Category IV cable (no longer than 200 m) and can communicate at a transmission rate of 10 Mbps. Let's take a closer look at three of these variants.  

Variant 1: APL field switches are connected directly to a standard Industrial Ethernet network, with the configuration of the installation environment largely determining the location – i.e. whether these are installed in the control cabinet or out in the field (Figure 1). In this version, the APL switch is connected directly to the control network using normal Ethernet copper cables or fiber-optic cables. The typical transmission rate in this section of the network will be 100 Mbps. This is equivalent to today’s Fieldbus structures and is intended to accommodate the brownfield plants that were installed at a time when the rapid pace of digitalization was not yet foreseeable and process control fell far short of today's requirements—but is now being asked to keep step with 21st-century developments.  

Network stability  

To ensure that a PROFINET network can be operated to be both stable and fail-safe, it is essential to monitor the load that Ethernet-APL devices are exposed to. Continuous control of load peaks works to prevent sporadic outages affecting individual devices due to overloading. This is achieved by limiting the ingress and egress data traffic at switch ports—as also envisaged by the IEEE (Institute of Electrical and Electronics Engineers)—because where networks transition in the switch from 100 Mbps to 10 Mbps, a higher network load in the 100 Mbps control network is especially critical for the Ethernet-APL devices on the 10 Mbps spurs. This 10 Mbps is, after all, only 10% of the data throughput compared with the control network. 

As already mentioned, the net load is a critical factor that needs to be effectively countered. Accordingly, vendors have developed special Ethernet-APL switches that set the respective net load rate limits to ensure stable network operation without overloading, and which support both copper and fiber-optic connections. These are especially suited to the Variant 1 network topology mentioned above.  

One way to implement new Ethernet-APL-compatible devices within a short time-to-market is to use an electronics module providing all the hardware and software components needed for communications, such as the Softing commModule APL. This SMD hardware module with a pre-installed PROFINET stack offers a configurable application data model as well as command mapping that can be used to migrate existing HART and Modbus devices to Ethernet-APL without code having to be written. Assignments to HART or Modbus commands are made using the corresponding commScripter tool.  

Ethernet-APL offers a wealth of flexibility and options for individual network structures and a level of maturity permitting the deployment of corresponding devices in production environments. It has other obvious benefits too as it avoids hardware costs, no dedicated gateway components need to be purchased and no expert-level configuration tasks are required to integrate with the upstream Ethernet infrastructure of the equipment responsible for these gateways. An implementation should nonetheless be planned and structured properly to exploit all the advantages of this new standard—and Ethernet-APL should certainly be considered as a candidate for any future planning work. 

<sub>All images courtesy of Softing

This feature originally appeared in the April 2024 isue of InTech digital magazine.</sub>