YASKAWA SGD7S Product Manual page 140

4.7 DeviceNet System Configuration
4.7.3 Precautions for Connecting DeviceNet Communications Cables
 Configuration Example
The following diagram shows the suggested configuration if the baud rate is 500 Kbps.
T (with terminating resistance)
The above example must satisfy the following conditions.
• a ≤ 6 m
• b ≤ 6 m
• c ≤ 6 m
• d ≤ 6 m
• d + f ≤ 6 m
• d + e + g ≤ 6 m
• d + e + h ≤ 6 m
The total drop line length must satisfy the following condition.
• Total drop line length= ±a + b + c + d + e + f + g + h ≤ 39 m
Basic Precautions
Observe the following basic precautions.
• The communications power supply for the DeviceNet network must be 24 VDC.
• The communications power supply must have sufficient capacity to handle the device load.
• The communications power supply must be connected to the trunk line.
• If many nodes are provided with power from a single power supply, the power supply must be
placed as close as possible to the middle of the trunk line.
• The allowable current flow in a thick cable is 8 A. The allowable current flow in a thin cable is
3 A.
• The power supply capacity for a drop line depends on the length of the drop line.
• The maximum current capacity of the drop line will become lower as the drop line becomes
longer regardless of the thickness of the drop line. To calculate the current (I) that flows to the
drop line (i.e., the total current consumption on the drop line), use the following equation:
I = 4.57 / L
I: Allowable current in amperes, L: Drop length in meters
• If only the communications power supply is turned OFF while the network is operating, errors
may occur at the nodes that are communicating at that time.
4-44
T
b
a
Node Node Node
g
T
Node
c
d
f
T
Node
e
h
T
Node Node
Terminating resistance
Node
: Trunk line
: Drop line
: T-branch adapter
T