Digital Field Bus Communication
Networks
systems. In today’s manufacturing
environment, however, automated
systems are expected to help
manage the process, not merely
monitor it. With the advent of
digital field bus communication
networks such as CC-Link,
DeviceNet, PROFIBUS, and Smart
Distributed Systems (SDS), gone
are the days of constrained
CONTROLLER
To date, despite its many draw-
backs, the 4 - 20 mA analog
current loop has been the most
widely accepted standard for
implementing process control
BUS
INTERFACE
OPTICAL
ISOLATION
TRANSCEIVER
FIELD BUS
information. Controllers can now
receive multiple readings from
field devices (sensors, actuators,
etc.) in addition to diagnostic
information.
TRANSCEIVER
TRANSCEIVER
TRANSCEIVER
TRANSCEIVER
OPTICAL
ISOLATION
OPTICAL
ISOLATION
OPTICAL
ISOLATION
OPTICAL
ISOLATION
BUS
INTERFACE
BUS
INTERFACE
BUS
INTERFACE
BUS
INTERFACE
XXXXXX
YYY
SENSOR
The physical model for each of
these digital field bus communica-
tion networks is very similar as
shown in Figure 15. Each includes
one or more buses, an interface
unit, optical isolation, transceiver,
and sensing and/or actuating
devices.
DEVICE
CONFIGURATION
MOTOR
CONTROLLER
MOTOR
STARTER
Figure 15. Typical field bus communication physical model.
Optical Isolation for Field Bus
Networks
data from and transmitting data
onto the network), two Agilent
optocouplers are needed. By
providing galvanic isolation, data
integrity is retained via noise
reduction and the elimination of
false signals. In addition, the
network receives maximum
protection from power system
faults and ground loops.
To recognize the full benefits of
these networks, each recommends
providing galvanic isolation using
Agilent optocouplers. Since
network communication is bi-
directional (involving receiving
Within an isolated node, such as
the DeviceNet Node shown in
Figure 16, some of the node’s
components are referenced to a
ground other than V- of the
network. These components could
include such things as devices with
serial ports, parallel ports, RS232
and RS485 type ports. As shown in
Figure 16, power from the network
is used only for the transceiver and
input (network) side of the
AC LINE
NODE/APP SPECIFIC
uP/CAN
LOCAL
NODE
SUPPLY
optocouplers.
GALVANIC
ISOLATION
BOUNDARY
HCPL
772x/072x
HCPL
772x/072x
Isolation of nodes connected to any
of the three types of digital field
bus networks is best achieved by
using the HCPL-772X/072X
optocouplers. For each network,
the HCPL-772X/072X satisify the
critical propagation delay and
pulse width distortion require-
ments over the temperature range
of 0°C to +85°C, and power supply
voltage range of 4.5 V to 5.5 V.
5 V REG.
TRANSCEIVER
DRAIN/SHIELD
SIGNAL
V+ (SIGNAL)
V– (SIGNAL)
V+ (POWER)
V– (POWER)
POWER
NETWORK
POWER
SUPPLY
Figure 16. Typical DeviceNet Node.
12
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
