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2.3.6 Communication
Acuvim II series meter uses RS485 serial communication and the Modbus-
RTU protocol. The terminals of communication are A, B, and S (14, 15, 16). A is
dierential signal +, B is dierential signal - and S is connected to the shield of
the twisted pair cables. Up to 32 devices can be connnected on a RS485 bus.
Use good quality shielded twisted pair cable, AWG22 (0.5mm
2
) or higher. The
overall length of the RS485 cable connecting all devices should not exceed
1200m (4000ft). The Acuvim II series meter is used as a slave device of masters
such as a PC, PLC, Data Collector or RTU.
If the master does not have RS485 communication port, a converter (such as a
RS232/RS485 or a USB/RS485 converter) will be required. Typical RS485 network
topologies include line, circle and star (wye).The shield of each segment of the
RS485 cable must be connected to the ground at one end only.
Every A(+) should be connected to A(+), B(-) to B(-), or it will influence the
network, or even damage the communication interface.
The connection topology should avoid “T” type which means there is a new
branch and it does not begin from the beginning point.
Keep communication cables away from sources of electrical noise whenever
possible.
When using a long communication cable to connect several devices, an anti
signal reflecting resistor (typical value 120Ω-300Ω/0.25W) is normally added
to the end of the cable beside the last meter if the communication quality is
distorted.
Use RS232/RS485 or USB/RS485 converter with optical isolated output and
surge protection.
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