Chemical Engineering August 2022 - 32

Fieldbus technologies also have a
slow data-transfer rate, although it is
faster than the HART protocol. However,
fieldbus systems are complex
in terms of their protocol conversions
for remote access, engineering
of segments, and troubleshooting.
There is some industry resistance
to widespread adoption of fieldbus
technology due to the complexity
associated with its use.
Existing industrial architecture has
an electronic or fieldbus layer for field
devices, a plant Ethernet network
for supervisory and control layers,
and an enterprise Ethernet for management
and planning. However, to
enable the seamless data access
across all layers, a single network
technology is required. Making vast
quantities of data available in real
time for optimization and analytical
models, while meeting the requirements
of the harsh environments in
process plants, has been one of the
primary drivers leading to the development
of Ethernet-APL. (Figure 1).
Standard Ethernet limitations
Standard Ethernet seems to offer
many of the features needed for the
next generation of industrial field instrumentation.
However, there are
some drawbacks that make it impossible
to implement directly into industrial
settings. For example, 100BASETX
Ethernet has a data rate of 100
Mbit/s full duplex, but cable lengths
are limited to 100 m.
Standard Ethernet uses CAT5/6
cables that have four internal wires.
This is incompatible with industrial installations,
which require a two-wire
solution for field instrumentation. It
is vital for an industrial Ethernet solution
to integrate with the existing
two-wire infrastructure to prevent the
need for rewiring whole plants, which
would not be financially justifiable.
Many field instruments are looppowered,
meaning that they receive
the power supply from the same pair
of wires that transmits their data.
Standard Ethernet is not designed
to supply power at this scale, and
therefore cannot be used on many
field instrument installations.
One of the most critical features
of industrial field instrumentation in
process plants is compliance to in32
FIGURE
2. Several examples of potential network topologies are possible with Ethernet-APL
trinsic safety requirements. Devices,
switches, wiring and terminals found
in hazardous areas must be certified
as explosion proof or non-sparking
depending on the area classification.
Standard Ethernet does not meet
these intrinsic-safety requirements
for industrial applications.
Ethernet-APL is designed to overcome
these limitations without losing
the benefits of Ethernet technology
for industrial use.
Field connectivity
Major user organizations and leading
manufacturers worked together
over the last years to develop an
Advanced Physical Layer for Ethernet
that meets the requirements of
process plants. The requirements
for this new technology were aligned
with the NAMUR organization (User
Association for Automation Technology
in the Process Industries;
Leverkusen, Germany; namur.net)
and noted in an official NAMUR
recommendation [2]. The following
standards and guidelines are the
most important documents in the
context of Ethernet-APL:
IEEE 802.3cg-2019. This new IEEE
standard 10BASE-T1L defines the
full duplex 10 Mbit/s data transmission
via a two-wire cable for long
cable runs. It is mainly relevant for
the PHYs (the PHY layer defines the
physical and electrical characteristics),
which are integrated in the
APL devices.
IEC TS 60079-47. This technical
specification for a two-wire, intrinsically
safe Ethernet ensures the installation
of two-wire Ethernet devices
in hazardous areas. The concept is
derived from the well-known FISCO
(Fieldbus Intrinsically Safe Concept)
and provides a simple installation
without Ex calculations.
APL Port Profiles. This specification
defines the power supply via the
same two-wire cable with different
power profiles. In addition, the preferred
cables and connection technology
is defined.
APL Engineering Guideline. This
user-centric document supports end
users during planning, installing and
commissioning of APL networks. It
provides many useful information in
terms of topologies, shielding, cables
and so on.
APL Conformance Tests. Via these
mandatory conformance tests, it is
ensured that APL components are
interoperable with each other.
Ethernet-APL topologies
Ethernet-APL
can
be
designed
using different topologies to match
the requirements of each process
plant. " Star " topologies suit plants
with a compact layout, while " trunkand-spur "
topologies are similar to
fieldbus architectures (Figure 2). Depending
on the switch variant, it is
possible to mount APL field switches
in Zone 2 or Zone 1 areas and to
connect APL field devices in different
Ex zones, including intrinsic safety
(Ex ia).
Star topologies require externally
powered APL field switches. These
switches supply power to each APL
field device connected on the spur
line in a point-to-point configuration.
Several APL field switches can be
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Chemical Engineering August 2022

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