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Introduction and Overview
WL Circuit Breaker
Ethernet
The Industrial Ethernet is a high-
performance network that conforms
to IEE 802.3 (ETHERNET). The highly
successful 10Mbit/s technology,
which has been used for over a
decade, and the new 100Mbit/s
technology (Fast Ethernet to IEEE
802.3u) in conjunction with Switching
Full Duplex and Autosensing enable
the required network performance to
be adapted to different requirements.
The appropriate data rates are
selected as required because
complete compatibility enables the
technology to be implemented on
a step-by-step basis.
Used in 80% of networks, Ethernet
is currently the best of its kind in
LAN environments.
SIMATIC NET is based on this tried-
and-tested technology. Siemens
has supplied well over 500,000
connections all over the world,
many of which are in harsh
industrial environments with high
EMC requirements.
In addition, Internet technology
opens up considerable scope for
worldwide networking. With
Industrial Ethernet, SIMATIC NET
provides a tool that can be
seamlessly integrated in the new
media landscape. The enormous
potential offered by intranets,
extranets, and the Internet, which
are already available in offices of
all kinds, can also be implemented
in production and process
automation environments.
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Unlike PROFIBUS-DP, ethernet does
not function according to a master-
slave principle. All the stations have
equal priority on the bus, which
means that any station can be the
sender or receiver. A sender can only
send on the bus if no other station is
sending at that time. This is due to
the fact that the stations are always
"listening in" to find out whether any
messages are being sent to them or
any senders are currently active. If a
sender has started sending, it checks
that the message it has sent is not
corrupt. If the message is not changed,
the send operation continues.
If the sender detects that its data
is corrupt, another sender must
have already started sending data.
In this case, both senders abort their
respective send operations.
After a random time has elapsed, the
sender restarts the send operation.
This is known as CSMA/CD and, as
a "random" access procedure, does
not guarantee a response within
a certain time frame. This largely
depends on the bus load, which
means that real-time applications
cannot yet be implemented with
Ethernet.
WL PROFIBUS Communication and Electronic Accessories • July 2004
LON (Local Operting Network)
This bus system is based on VLSI
circuits, which control communication
between up to 32,385 network
nodes. The nodes are arranged in
subnetworks, each with a maximum
of 64 stations. Routers, which are
also based on these circuits
(neuron chips), are responsible for
connecting the subnetworks. The
specifications are available from
the manufacturer, ECHELON.
Depending on the data rates, a wide
range of transmission media can be
used, including current leads, radio
and infrared channels, coaxial cables,
and optical fibers.
The LON bus is a highly distributed
bus system in which each field
device features integrated on-site
intelligence. LONs are mainly used
for building system automation and
are often implemented in the
production industry.
One disadvantage of gateways,
however, is that there is always an
additional time delay in the system
when data is passed from one bus
system to another. This is because
the data must be buffered on one
side, converted, and then output
on the other side. In addition, not
all functions provided by the
PROFIBUS-DP can be used when
they are implemented on the
PROFIBUS-DP (e.g. event-driven
diagnostic messages).
One or more PROFIBUS-DP-capable
circuit breakers can be integrated
in an existing LON bus system. To
do this, a gateway is required
beween the two different bus
systems, enabling communication
with PROFIBUS-DP devices via the
LON bus.
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