What Is Ethernet-APL?

Ethernet-APL, short for Ethernet Advanced Physical Layer, is the physical layer the process industries chose to take Ethernet all the way to field instruments. It is a defined use of 10BASE-T1L single pair Ethernet from IEEE 802.3cg, with the extra rules for power, wiring and explosion protection that process plants need.

Until now, plants have reached transmitters, valves and analysers with 4–20 mA current loops, HART, PROFIBUS PA or FOUNDATION Fieldbus H1. Those signals are slow, and each needs gateways before its data reaches an IP network. Ethernet-APL keeps the two-wire, long-cable, loop-powered style that instrument engineers know but carries 10 Mb/s Ethernet, so every instrument gets an IP address and can be configured and diagnosed over the network.

It was developed jointly by the main process automation standards organisations (FieldComm Group, ODVA, the OPC Foundation and PROFIBUS & PROFINET International) together with instrument and system vendors. The relevant specifications are IEEE 802.3cg for the physical layer, IEC TS 63444 for the APL port profiles and IEC TS 60079-47, known as 2-WISE, for intrinsic safety.

APL networks usually follow the trunk and spur layout familiar from fieldbus.

Many process instruments sit where flammable gas or dust can be present, so the energy on their cables must be too low to ignite it. Ethernet-APL handles this with 2-WISE, the two-wire intrinsically safe Ethernet concept in IEC TS 60079-47. Like the FISCO model used for fieldbus, it lets engineers verify intrinsic safety by comparing port parameters, without calculating every cable and device combination. Each APL switch and instrument still carries its own hazardous-area certificate, issued by a notified body, stating the zones and gas groups it is approved for.

The intrinsic safety barrier sits in the switch and instrument ports, separate from the Ethernet PHY. That means the same chips serve safe-area and hazardous-area designs, and live work on spurs is possible without a hot-work permit, which is a real gain during maintenance. Our FAQs on ATEX and ATEX zones explain the zone system APL is designed around.

APL does not have to replace everything at once. Plants commonly run it alongside existing loops, starting with new plant areas or the instruments that gain most from rich diagnostics.

Above the power switch, an APL network is ordinary Ethernet. Instrument data reaches the distributed control system, asset management tools and historians over the plant network, and it can also be read directly by edge computers for analytics and condition monitoring, often through OPC UA. That is the main promise of APL: the same IP data the control system uses is open to maintenance and analytics without extra gateways.

Our white paper on single pair Ethernet in industrial and edge AI computing sets APL alongside the other SPE variants and their connectors. On the control-room side, our industrial PCs can host the software that collects and analyses that data.

Planning an APL installation starts with a few practical checks: whether the instruments you need are available with APL ports, the power budget of each field switch, whether existing trunk cable passes testing, and how the control system will address and secure several hundred new IP devices. Treating the field network as its own zone, with controlled routes to the rest of the plant, is the usual starting point for security.

When APL data reaches the control room, we build the industrial computers that collect and analyse it as standard, with the operating system and protocol software set up before the system ships.