Astraada AS24DRV4075, Operation Manual

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Astraada DRV-24 frequency inverters Communication protocol
93
It is recommended to use shield cables and make the shield layer as the grounding wires during
RS485 remote communication.
In the cases with less devices and shorter distance, it is recommended to use 120Ω terminal resistor
as the performance will be weakened if the distance increase even though the network can perform
well without load resistor.
7.2.1.1 Single application
Figure 1 is the site Modbus connection figure of single inverter and PC. Generally, the computer
does not have RS485 interface, the RS232 or USB interface of the computer should be converted
into RS485 by converter. Connect the A terminal of RS485 to the 485+ terminal of the inverter and B
to the 485- terminal. It is recommended to use the shield twisted pairs. When applying
RS232-RS485 converter, if the RS232 interface of the computer is connected to the RS232 interface
of the converter, the wire length should be as short as possible within the length of 15m. It is
recommended to connect the RS232-RS485 converter to the computer directly. If using USB-RS485
converter, the wire should be as short as possible, too.
Select a right interface to the upper monitor of the computer (select the interface of RS232-RS485
converter, such as COM1) after the wiring and set the basic parameters such as communication
baud rate and digital check bit to the same as the inverter.
Figure 1 RS485 physical connection in single application
7.2.1.2 Multi-applications
In real multi-applications, the chrysanthemum connection and star connection are commonly used.
Chrysanthemum chain connection is required in the RS485 industrial fieldbus standards. The two
ends are connected to terminal resistors of 120Ω which is shown as figure 2.
Figure 2 Chrysanthemum connection applications
Figure 3 is the star connection. Terminal resistor should be connected to the two devices which
have the longest distance. (1# and 15#device)