Page 343 - Programmable Logic Controllers, Fifth Edition - Mobile version

(reaction to events). Two different types of objects are de-
The field devices that are connected to the network
fined in the CIP specification: communication objects and contain intelligence in the form of microprocessors or
application-specific objects. A DeviceNet network can other circuits. These devices can communicate not only
support up to 64 nodes and the network end-to-end dis- the on/off status of field devices but also diagnostic
tance is variable, based on network speed. Figure 14-40 information about their operating state. For example,
shows an example of a typical layout of the trunk wiring you can detect via the network that a photoelectric
for a DeviceNet network. Communications data is carried sensor is losing reliability because of a dirty lens, and
over two wires with a second pair of wires carrying power. you can correct the situation before the sensor fails to

Terminatorerminator
T T
Generic
sealed device
T-port tap
DC
power DevicePort tap
supply (8-port)

Thick cable
PowerT
PowerTapap
PowerT
tap
Generic
Generic sealed device
open-style device
Generic
sealed
device Thin cable

DeviceBox
tap Terminatorerminator
T T
(4-port)
Thick cable
Open-style T-port tap
tap

Figure 14-40 Layout of a DeviceNet network.
Source: Images Courtesy of Rockwell Automation, Inc.

324 Chapter 14 Process Control, Network Systems, and SCADA

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