AccuEnergy AcuDC 241, User Manual

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15
Note:The load's negative must be connected to meter's current input terminal.Cur-
rent output terminal should be connected to the system's negative. The load is serially
connected to the meter or the shunt.
The current input wire size is AWG15-16 or 1.5-2.5mm
2
or equivalent resistance wire.
Communication
AcuDC 240 series meter uses RS485 serial communication and the Modbus-RTU protocol.
The terminals of communication are A, B, and S (14, 15 and 16). A is diferential , B is
diferential signal - and S is connected to the shield of twisted pair cable. The overall length
of the RS485 cable connecting all devices can not exceed 1200m (4000ft). Utilizing a large
number of RS485 devices and utilizing a high baud rate will make the communication
range shorter. AcuDC 240 works as Slave device. Maser device can be PC, PLC, Data
Acquisition Device, or RTU.
In order to improve communcation quality, please pay attention to the following:

A high-quality Shielded Twisted Pair cable is very important, AWG22 (0.6mm²) or
lower is recommended. Two cables should be different colors.

Pay attention to "single point earthing". It means there is only one point of the shield-
ing connected to ground in a single communication link.

Every A(+) should be connected to A(+), B(-) to B(-), or it will infuence the network and
possibly 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 much as possible from sources of electrical noise.

When several devices are connected to the same long communication line, an anti
signal reflecting resistor (typical value 120-300Ohm 0.25W) is often used at the end of the