GE VersaPoint IC220PBI002, Руководство пользователя

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5-8 VersaPoint™ I/O System Profibus-DP NIU User’s Manual – August 2005 GFK-1911B
5
Electrical Isolation
The Profibus-DP NIU and the VersaPoint system have a defined voltage and
grounding concept. This avoids an undesirable effect on I/O devices in the logic
area, suppresses undesirable compensating currents and increases noise
immunity.
Electrical Isolation: Profibus
The Profibus interface is electrically isolated from the station electronics. The
shield of the Profibus cable is directly connected with the function earth ground
spring (FE spring), which is located on the bottom of the NIU. This spring has no
connection with the second FE spring in the module, which can also be found on
the bottom of the NIU, directly under the terminal points. This spring is directly
connected with both terminal points of the power connector. When the two
functional earth ground springs have been snapped on, they have contact to the
DIN rail and are used to lead off interference, rather than as a protective earth
ground. To ensure discharge of interference, even for dirty DIN rails, connect the
functional earth ground directly to terminal points 1.4 or 2.4. This also sufficiently
grounds the I/O Station up to the first segment terminal.
To avoid the flow of compensating currents, which may affect data transmission
quality, connect a suitably-sized equipotential bonding cable parallel to the
Profibus cable.
Electrical Isolation: I/O
The NIU does not provide electrical isolation between the main circuit, U
M
, and the
VersaPoint module communications power. U
M
(24V) is not electrically isolated
from U
L
(7.5V) or U
ANA
(24V).
It is only possible to isolate both voltages separately using isolated power options
for the main power U
M
and the I/O voltage U
S
on the NIU, because both voltages
have the same ground reference.
If isolation of these voltages is required, a separate power terminal with a separate
isolated power supply must be used. Providing isolated power supplies for U
M
and
U
S
on the same power terminal is insufficient as the two circuits share a ground.