Schlage PIB300 User Manual page 220

Planning An Installation
Master
GND T+ T-
Connect the Cable
Shield to the
Master's Ground
Figure 2-3: Communication Shielding with All Units Earth Grounded
All units are connected to the same earth ground. Each shield ground is
connected to only one unit, then interrupted to prevent the formation of ground
loops. Two sets of lines are wired as shown in Figure 2-3. It does not matter
significantly which unit's GND is used for a particular shield, as long as the
path is broken from unit to unit.
Carry a
The second method of establishing a ground reference in a system with
Ground Line
floating power supplies is to use the ground line in the RS-422 cable to
to Each Unit
establish a common reference voltage for the communication signals. This line
should be connected to the negative power terminal on the data converter or
the ground line in the RS-232 port from the host PC system. It should then be
carried to one of the ground terminals on the back of each unit in the network.
An example of this method of grounding is shown in Figure 2-4.
Master
GND T+ T-
Connect the Cable
Shield to the
Master's Ground
: Communication Shielding Carrying a Single Ground to Each Unit
If no earth ground is available at the units, this is the only possible method of
connecting the grounds. Even if an earth ground is available, depending on
the building's power wiring and other environmental issues, this method may
be superior to the previous one, since it establishes the ground of each unit
independently of the building power lines. Local variations in grounds between
buildings, or from one point to another in a very large building, (perhaps due to
16
Remote 1
GND R+ R-
Do Not Connect
the Cable Shield
at this End
Remote 1
GND R+ R-
Connect Both Shields
to Remote 1 Ground
Remote 2
GND R+
Connect the
Cable Shield to
Remote 1's
Ground
Do Not Connect
the Cable Shield
at this End
Remote 2
GND R+
Connect Both Shields
to Remote 2 Ground
R-
Connect the
Cable Shield to
Remote 2's
Ground
Do Not Connect
the Cable Shield
at this End
R-
Connect Shield
to Next Remote
To Next
Remote
To Next
Remote