User manual

Digital Monitor AMC-1DBx Series User Manual
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4.1.2.4 Shield Termination
The RS-485 cable is a shielded cable. The cable shield is terminated on the terminal block.
How this shield is handled varies based upon the system wiring. A strap allows the user to
select different among three options to select the best solution that works in their site.
The cable shield is shorted to chassis ground at only one point, in order to avoid ground loops
with large currents. Typically, the Digital Monitor connects the cable shield of the MODBUS
channel to chassis ground. The cable shield of the interface to the Build Automation System is
typically not connected to chassis ground at the Digital Monitor; the Building Automation System
would provide this connection.
The Digital Monitor provides interface strapping options for connecting the cable shield to
ground;
• No connection to chassis ground
• Connected directly (shorted) to chassis ground
• Connected through a parallel resistor-capacitor network to chassis ground
Table 4-6: Cable Shield Termination
Strap Position Interface Strap
Location
No Connection
To Chassis Gnd
Shorted
To Chassis Gnd
RC Network
To Chassis Gnd
To Building Automation J19 Remove (Typical) 2-3 1-2
To MODBUS 1 J21 remove 2-3 (Typical) 1-2
To MODBUS 2 J20 remove 2-3 (Typical) 1-2
To MODBUS 3 J18 remove 2-3 (Typical) 1-2
To MODBUS 4 J13 remove 2-3 (Typical) 1-2
4.1.2.5 Bias
For each of the downstream RS-485 interfaces, resistors are provided to pull the idle (un-driven)
lines to the mark level.
4.1.2.6 Ethernet
A 10/100 Base-T Ethernet connection is provided by the monitor. The Ethernet cable is
terminated in an RJ-45 connector which is provided. The connector is mounted so that the cable
is parallel to the PCB assembly. The connector is mounted along the bottom edge of the
printed circuit board.
Refer to
Figure 4-3: Digital Monitor Components for the location of the Ethernet connector. It is a hybrid
connector and has the USB interface integrated into it.