Fuji Electric FRENIC-AQUA series, User Manual

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8-6
8.1.4 Communications support devices
This section describes the devices required for connecting the inverter to a PC having no RS-485
interface or for connecting two or more inverters in multi-drop network.
[ 1 ] Communications level converters
Usually PCs are not equipped with an RS-485 communications port but with an RS-232C port. To
connect inverters to a PC, therefore, you need an RS-232C–RS-485 converter or a USB–RS-485
converter. To run the FRENIC-AQUA correctly, use a converter satisfying the requirements given
below.
Requirements for recommended communications level converters
Send/receive switching: Auto-switching by monitoring of send/receive data status at the PC
(RS-232C)
Electric isolation: Electrically isolated from the RS-485 port
Fail-safe: Fail-safe facility*
Other requirements: Superior noise immunity
* The fail-safe facility refers to a feature that ensures the RS-485 receiver's output at "High" (logical
value = 0) even if the RS-485 receiver's input is opened or short-circuited or all the RS-485 drivers
are inactive. Refer to Figure 8.3.
Recommended converters
System Sacom Sales Corporation (Japan) : KS-485PTI (RS-232C
−
RS-485 converter)
: USB-485I RJ45-T4P (USB
−
RS-485 converter)
Send/receive switching system
The RS-485 communications system of the inverter acts in half-duplex mode (2-wire) so the converter
must feature a send/receive switching circuitry. Generally, the switching system may be either one of
the following.
(1) Auto-switching by monitoring of send/receive data
(2) Switching by RS-232C control signal of RTS or DTR (hardware flow control system)
Figure 8.3 Communications Level Conversion
FRENIC-AQUA (two-wire system) RS-232C — RS-485 converter
RS-485
Computer
送受信切換
Level
conversi
on
Driver
Receiver
Transmission/
receiving
switching
Driver input
Receiver enable
Receiver
Receiver output
Driver input
Driver
Driver enable
Receiver enable
Driver
enable
Receiver output
RS-232C