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V: 1.0 Revised: Jan. 2018
Chapter 2: Installation
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2.3.6 Communication
The AcuRev 1310 supports Modbus-RTU protocol through its built-in RS485 port. The RS485
terminals are denoted as 'A', 'B' and 'S'. 'A' is the positive differential terminal, 'B' is the negative
differential terminal and 'S' is for connecting the shield of the shielded twisted pair cable.
The maximum distance of the cable should not exceed 1200m. This distance should be shorter
if more devices are connected to the same communication link or if using a higher baud rate.
If the master device does not have a RS485 port but a RS232 port then a RS232-RS485 converter
should be utilized.
In order to improve communication quality, use the following:
• A High-quality Shielded Twisted Pair cable is very important, AWG22 (0.6mm2) or lower is
recommended.
• Pay attention to "single point earthing". This means that there is only one side for the
shield to be connected to the ground in a communication link.
• Every A (+) should be connected to A (+), B (-) to B (-), or it will influence the network, even
damage the communication interface.
• “T” type connection topology should be avoided. This means no new branches except
from the starting point.
• Keep communication cables away as far as possible from sources of electrical noise.
When several devices are connected in daisy chain to the same long communication line,
a resistor (typical value 120- 300 Ohm, 0.25W) should be used at the end of the circuit (the
last device of the chain).
• Use RS232/RS485 or USB/RS485 converter with optical isolated output and surge
protection.