Ethernet-APL

What is Ethernet-APL?

Ethernet-APL (Ethernet Advanced Physical Layer) is a physical layer for Ethernet that supplies field instruments in the process industry with both data and power over a single twisted pair, running at 10 Mbit/s over cable lengths of up to 1,000 metres and with intrinsic safety for hazardous areas. Ethernet-APL builds on 10BASE-T1L from IEEE 802.3cg-2019 and adds what process automation needs: long cable runs, power over the line and explosion protection. In the long run it replaces the classic 4-20 mA loop and fieldbuses such as PROFIBUS PA and FOUNDATION Fieldbus H1. Since its launch in June 2021, Ethernet can run from the enterprise network all the way to a transmitter or valve.

🔧 How does Ethernet-APL work?

Ethernet-APL uses the 10BASE-T1L PHY: full-duplex Ethernet at 10 Mbit/s over a single shielded two-wire cable. The same two conductors also carry power to the field instrument. Every connection is point-to-point; instead of a shared bus as with a fieldbus, you get a switched network.

The network has two kinds of segments and two kinds of switches:

• Trunk — the backbone between switches, up to 1,000 m, with a higher signal amplitude (2.4 V peak-to-peak) and a power budget of up to about 60 W; it can extend into Zone 1
• Spur — the branch to a single instrument, up to 200 m, with lower power (1.0 V peak-to-peak) and optionally intrinsically safe; it can extend into Zone 0
• Power switch — feeds power into the trunk and connects to ordinary Ethernet in the rack room
• Field switch — sits in the field, is powered via the trunk or externally, and provides spurs to the instruments

Because the reference cable is the same as for PROFIBUS PA and FOUNDATION Fieldbus, existing fieldbus cabling can often be reused.

🧱 Who is behind Ethernet-APL?

Ethernet-APL is not a single vendor’s product. After an evaluation project by device manufacturers (2011–2016), the official APL Project started in 2018, backed by four standards development organisations: FieldComm Group (HART, FOUNDATION Fieldbus), ODVA (EtherNet/IP), the OPC Foundation (OPC UA) and PI – PROFIBUS & PROFINET International. Twelve suppliers took part, including ABB, Emerson, Endress+Hauser, Krohne, Pepperl+Fuchs, Phoenix Contact, R. Stahl, Rockwell Automation, Samson, Siemens, Vega and Yokogawa.

Ethernet-APL is also a building block of NAMUR Open Architecture and Open Process Automation, both of which assume open, Ethernet-based access to field data.

🔥 How does intrinsic safety work with 2-WISE?

In an hazardous area, an electrical circuit must never hold enough energy to ignite an explosive mixture. That principle is called intrinsic safety (Ex i) and comes from the IEC 60079 series. Fieldbuses used FISCO for this; for Ethernet-APL the equivalent is 2-WISE (2-Wire Intrinsically Safe Ethernet), defined in IEC TS 60079-47.

2-WISE works with predefined parameters per port. You no longer need to calculate cable capacitance and inductance for each circuit: if the port markings of switch and instrument match, the combination is intrinsically safe. A spur in power class A (Ex ia, suitable for Zone 0) delivers about 0.54 W to the instrument; class C (Ex ic, Zone 2) about 1.1 W. That is considerably more than a 4-20 mA loop and leaves room for smarter sensors. For installations in the EU, the ATEX certification of equipment still applies as usual.

🏭 Where does Ethernet-APL sit in the OSI and Purdue models?

Ethernet-APL is purely layer 1 of the OSI model. Everything above it is standard Ethernet and IP, so any Ethernet protocol can run over it:

• PROFINET — with the PA profile as the successor to PROFIBUS PA
• IP — ODVA’s route into the process industry
• HART-IP — the IP variant of HART, preserving existing device know-how
• OPC UA — for direct, information-centric access to instrument data

In the Purdue Model, Ethernet thereby moves down to levels 0 and 1: the sensor itself gets an IP address. A controller and an asset management system can talk to the same instrument at the same time, without a gateway or multiplexer.

🔄 How does it differ from 4-20 mA, HART and fieldbuses?

That makes Ethernet-APL more than 300 times faster than PROFIBUS PA and Foundation Fieldbus. More importantly, the translation step between fieldbus and Ethernet disappears: one network technology from the field to the enterprise network.

🔐 How secure is Ethernet-APL?

Ethernet-APL itself adds no security: it is a physical layer. The flip side of “IP all the way to the sensor” is that every instrument becomes a network device with an attack surface. A 4-20 mA signal is hard to manipulate remotely; an Ethernet instrument with a web server or an open configuration port is not. Security therefore has to come from the architecture and the protocols:

• Network segmentation — place APL networks in their own zones following the zones and conduits model of IEC 62443, with controlled conduits to control systems and asset management
• Managed field switches — use management features such as VLANs, disabling unused ports and logging
• Protocol security — PROFINET security classes, CIP Security (TLS/DTLS) for EtherNet/IP and the security modes of OPC UA
• Device hardening — choose instruments whose vendor develops according to IEC 62443-4-1 and that meet IEC 62443-4-2

🛠️ How do you approach an Ethernet-APL project?

1. Take stock — determine which instruments are new and where existing type A fieldbus cable can be reused.
2. Choose the topology — trunk-and-spur for spread-out plants, or a compact star with field switches close to the rack room.
3. Determine the hazardous zones — trunk into Zone 1, intrinsically safe spurs into Zone 0; check the port profiles according to 2-WISE.
4. Check the power budget — add up the consumption of the instruments per field switch against the trunk budget.
5. Design the security zones — define zones, conduits and permitted protocols before installation.
6. Test and document — use the built-in switch diagnostics for signal quality and record the network topology.

For brownfield plants a mixed approach is common: new units on Ethernet-APL, existing loops on 4-20 mA with HART until the end of their service life.

❓ Frequently asked questions

Is Ethernet-APL the same as Single Pair Ethernet?

Ethernet-APL is a specific application of Single Pair Ethernet. It uses the 10BASE-T1L variant from IEEE 802.3cg and adds process industry requirements on top, such as port profiles, power over the line and intrinsic safety through 2-WISE.

Can I use existing fieldbus cable for Ethernet-APL?

Ethernet-APL uses type A fieldbus cable according to IEC 61158-2 as its reference cable, the same cable used for PROFIBUS PA and FOUNDATION Fieldbus. Existing cabling can therefore often be reused, provided the cable is in good condition and the lengths stay within the trunk and spur limits.

How far can an Ethernet-APL connection reach?

An Ethernet-APL trunk between switches can be up to 1,000 metres long, and a spur from a field switch to an instrument up to 200 metres. Every switch starts a new segment, so you bridge longer distances with an additional switch or with fibre run close to the field.

Can Ethernet-APL be used in Zone 0?

Ethernet-APL spurs can be made intrinsically safe according to 2-WISE (IEC TS 60079-47) and can therefore reach into Zone 0. The trunk may run into Zone 1, with field switches in a suitable type of protection.

Which protocols run over Ethernet-APL?

Ethernet-APL is a physical layer and therefore carries any Ethernet protocol. In practice these are PROFINET, EtherNet/IP, HART-IP and OPC UA, the protocols of the four organisations behind the APL Project.

Will Ethernet-APL replace the 4-20 mA loop?

Ethernet-APL is intended as the successor to 4-20 mA, HART and fieldbuses, but the replacement is gradual. Existing installations often stay analogue for many years, while new plants and extensions are increasingly built on Ethernet-APL.

📌 In summary

Ethernet-APL brings standard Ethernet at 10 Mbit/s, with power over two wires, right into the process field, including Zone 0, and is gradually replacing 4-20 mA and fieldbuses. Every sensor thereby becomes a network device, so segmentation and security in line with IEC 62443 belong in an Ethernet-APL project from the very first design.