Emerson SI-DeviceNet, Руководство пользователя

Страница: 14 / 78

14
SI-DeviceNet User Guide
Issue Number: 2
4.4 DeviceNet network termination
It is very important in high-speed communications networks that the network
communications cable is installed with the specified termination resistor network at each
end of the cable segment. This prevents signals from being reflected back down the
cable and causing interference.
During installation of a DeviceNet network, 120
Ω
0.25 W termination resistors should
be installed across the CAN-H and CAN-L lines at both ends of the network segment, as
shown in Figure 4-3 below.
Figure 4-3 DeviceNet network termination
If too many termination resistors are installed on a DeviceNet network, the network will
be over-loaded, resulting in reduced signal levels. This may cause nodes to miss some
bits of information, resulting in potential transmission errors.
4.5 SI-DeviceNet cable shield connections
The SI-DeviceNet should be wired with the cable shields isolated from ground at each
drive. The cable shields should be linked together at the point where they emerge from
the cable, and formed into a short pigtail to be connected to pin 3 on the DeviceNet
connector.
Failure to terminate a network correctly can seriously affect the operation of the network.
If the correct termination resistors are not installed, the noise immunity of the network is
greatly reduced.
Cable
SI-DeviceNet
2125576532
1 2 3 4 5
120
0.25 W
Ω
NOTE
The DeviceNet cable can be tie-wrapped to the grounding bar or local convenient mount-
ing that is not live to provide strain relief, but the DeviceNet cable shield must be kept
isolated from ground at each node. The only exception to this is the DeviceNet ground
point. Refer to section 4.6
DeviceNet ground point on page 15.
NOTE