The most convenient method is to use a Sealevel Interface Converter to convert the electrical interface from RS-232 to RS-422 or RS-485. Use one of our interface converters at each end, with standard twisted pair cable in between, and you can communicate with your RS-232 device up to 4,000 feet away from your computer. Sealevel Interface Converters handle the electrical interface conversion in hardware so it is completely transparent to your software application.
You may also consider using a Sealevel Ethernet Serial Server. The RS-232 ports on the serial server are recognized as virtual COM ports by your computer. This allows you to communicate with your RS-232 device, anywhere on your Ethernet network, as though it were connected directly to your computer.