Its simplicity and robustness for long distance travel makes RS485 the IC preferred than the RS232. It is simpler because it uses only single pair wire to carry out data in bidirectional manner. While if RS232 is used, we need 3 wires minimum to carry data bidirectionally. The cable length comparison : RS232 about 25 meters only, while RS485 can be up to 1.2 km in length.
The RS232 to RS485 converter is needed because if your PC doesn’t have RS485 port and only have RS232 port, you need the converter or adapter. Below is the schematic diagram :
RS232 DB9 is used as the RS232 port, and a terminal block used as RS485 connector. For cabling, twisted pair cable is ideal for RS485 cause it makes both positive and negative wires exposed to an identical noise figure, therefore cancelling the noise itself when received at the interface port.
Dangerous signal, e.g lighting or other high voltage induction is potentially carried over a long outdoor wires. This high voltage induction can give great damage to your personal computer. However, the circuit above uses optical insulation (opto coupler) to isolate the RS232 port from the RS485 cables.