An RS-232 serial port was once a standard feature of a personal computer, used for connections to modems, printers, and other peripheral devices.
In modern personal computers, USB has displaced RS-232 from most of its peripheral interface roles due to the low transmission speed, however USB was designed for desktop usage and not robust enough for industrial uses - due to the problems operating in noisy environments, and being especially susceptible to inductive noise. In addition connectors for the USB devices are not fastened securely with a locking mechanism, and have a limitation of 16 feet.
Therefore RS-232 devices are still widely used, especially in industrial machines, networking equipment, and scientific instruments, due to their ability to operate in noisy industrial environments. The RS232 device specification is 50 feet minimum, however they will work many times this distance in mild noisy environments.
Many computers do not come equipped with RS-232 ports and must use either an external USB-to-RS-232 converter or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. In high noise environments, one of our Isolated USB to RS232 converters can be used to help limit the inductive noise that affects the USB devices, these units connect directly to the modular cables that we use on the RS232 relay boards.