INVT Goodrive3000 Series Operation Manual page 252

Goodrive3000 series medium voltage VFD
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.
8.3.1.1 Single application
Figure 8.1 is the site Modbus connection figure of single VFD 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 VFD 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 computer 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 VFD.
Figure 8.1 RS485 physical connection in single application
8.3.1.2 Multi-application
In the real multi-application, 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 8.2. Figure 8.3 is the simply
connection figure and Figure 8.4 is the real application figure.
120Ω
1 #
Shielded twisted pair
RS485 line
A B
Ground
RS232-RS485 converter
Computer
2 # 3 #
Figure 8.2 Chrysanthemum connection
-247-
B
A
485- 485+
Ground
VFD
120Ω
4 # 32 #
MODBUS protocol