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2.
ELECTRICAL CONNECTIONS
Image 1 Electrical Connection
Note: some manufacturers assign for the RS-485 port the “A” connection as a “+”, and “B” as a “-“,
while others reverses this nomenclature. The Lumiplus uses the “A” as “+”, and the “B” as “-”. Mind
this aspect when connecting to the bus devices coming from different manufacturers.
3.
CABLE CHARACTERISTICS
The recommended wiring for a MODBUS-RTU Communication is based in a linear structure, active
bus with termination at both ends. Is possible coupling and uncoupling of devices during operation
without affecting other devices. The wire shall be twisted and shielded according to EN 50 170.
The values of transmission rate supported for the device, allow maximum cable length of 1,200 m
without repeaters, or up to 10 km using repeaters, when installation is according to the standard.
For the balanced pairs used in an RS485-system, a Characteristic Impedance with a value higher than
100 Ohms may be preferred, especially for 19200 and higher baud rates.
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