Communications Support Devices - Fuji Electric FRENIC-HVAC User Manual

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-HVAC correctly, use a converter satisfying the requirements given
below.
Requirements for recommended communications level converters
Send/receive switching:
Electric isolation:
Fail-safe:
Other requirements:
* 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)
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)
Computer
Transmission/
RS-232C
RS-232C
Auto-switching by monitoring of send/receive data status at the PC
(RS-232C)
Electrically isolated from the RS-485 port
Fail-safe facility*
Superior noise immunity
Driver
Driver input
Driver
enable
receiving
switching
Receiver output
Receiver enable
Receiver
RS-485 converter
—
Figure 8.3 Communications Level Conversion
: KS-485PTI (RS-232C−RS-485 converter)
: USB-485I RJ45-T4P (USB−RS-485 converter)
RS-485
FRENIC-HVAC (two-wire system)
8-6
Driver
Driver input
Driver enable
Receiver output
Receiver enable
Receiver