ADS Environmental Services ADS TRITON+ QR 775027 A3 - Manual (Page 307)

9-2 ADS TRITON+ Manual
Establishing a Modbus Connection
The SCADA or process control system connects to the TRITON+
either through a serial connection using the ADS ExPAC (which
may be housed within the ADS XBUS
™ or a customer-supplied
enclosure) or through a cellular wireless modem in the monitor
using Modbus TCP.
Setting Up a Serial Connection
Two Modbus ports are available on the ExPAC through which to
communicate: RS-232 and RS-485.
Note: When both connections are available, ADS
recommends using the RS-485 connection. It has a greater
immunity to noise, supports longer cable runs without
signal degradation, and is easier to wire.
The required port settings are 19200 baud rate, 8 data bits, no
parity, 1 stop bit, and no flow control.
Connecting through the RS-485 Port
When using an RS-485 connection for Modbus communications,
choose a cable that is no longer than 4000 feet (1219 m) in length
with 24-gauge wiring. The cable must include at least one twisted
pair and one ground wire. If the cable extends beyond 1000 feet
(305 m), ADS recommends using 120 ohm termination resistors at
each end of the cable.
Connect the cable to the ExPAC in the following way:
1. Disconnect (i.e., unplug) the green terminal connector from the
RS-485 port on the top, left side of the ExPAC.