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In order for the Control Link ACC to communi-
cate with each other on the MODBUS network, they
must all be set to communicate at the same baud rate
and parity.
Switch/jumper 7 determines the baud rate at which
the controllers communicate. When switch/jumper 7
is ON, the Control Link ACC will operate at 9600
baud. If switch/jumper 7 is OFF (default), the Control
Link ACC will operate at 19200 baud. Switch/jumper
8 determines the MODBUS network parity. Some
MODBUS-enabled site controllers require even
network parity; to enable even parity, set switch/
jumper 8 to the ON position. For site controllers that
require no parity, set switch/jumper 8 to the OFF
(default) position.
7.4.5. Step 5: Terminate the End
Devices
Control Link ACC Network Termination
Figure 7-16 -
Once all Control Link ACCs are networked, you
must terminate the end devices on the network.
7.4.5.1.
Termination Block Network
Because the Control Link ACC has no on-board
means of termination, use the MODBUS termination
block (P/N 535-2711) for termination that can be
18 • Control Link ACC I&O Manual
wired to the end of the cable segment using the three-
pin connector. Wire the two signal wires to the outside
terminals, and connect the shield to Earth Ground:
FROM LAST
DEVICE
AT END OF
DAISY-CHAIN
SHIELD
WIRE
(CONNECT
TO EARTH
GROUND)
MODBUS Termination Block
Figure 7-17 -
7.4.6. Step 6 - Connect a Dewpoint
Sensor to Control Link ACC(s)
on the Network
Once the Control Link ACCs are networked and
properly terminated, the only step remaining to allow
the Control Link ACCs to share a dewpoint sensor is
to connect at least one dewpoint sensor to one Control
Link ACC on the network. Any Control Link ACC on
the network can be configured with the dewpoint
sensor.
Each Control Link ACC first looks for a dewpoint
sensor connected to itself. If a dewpoint sensor is
directly connected to a Control Link ACC, it will use
that sensor for its dewpoint value and broadcast the
sensor's value on the MODBUS network. If no sensor
is directly connected to a Control Link ACC, it will
automatically look on the MODBUS network and use
the sensor value broadcast by another Control Link
ACC that has a sensor.
For fail-safe purposes, you may have multiple
dewpoint sensors connected to different Control Link
ACCs on the network. The Control Link ACCs
automatically select a primary sensor to use, and will
switch to another dewpoint sensor on the network if
the primary sensor fails or is disconnected.
For dewpoint sensor wiring instructions, refer to
Figure 6-3 and Figure 6-4.
TB
026-4704 Rev 6
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