Key Facts about RS-485 Industrial Network

RS-485 network is used in many industrial applications to gather data and control addressable motor drives, PLCs, cameras, time clocks, barcode scanners for process control and other factory automatic apparatus.

RS-485 devices can be connected to a computer and multi-dropped at various locations in a network style configuration. The devices can be up to 4000 feet (1220 meters) feet away before a repeater is required and up to 32 nodes (devices) can be connected. More nodes can be connected using repeaters, up to the addressability limit (typically 256) of the devices used.

To connect a computer to RS-485 device, you can use an RS-485 converter or USB to RS-485 converter or install an RS-485 interface card in your computer. You may use PCI bus, PCMCIA/CardBus or ISA bus cards.

You also need to know how many wires are used on the RS-485 port of the device you need to connect. A Data (A) and Data (B) line and ground is a ‘2-wire’ 485 connection, if there are more connections and they are labelled TD(A) & TD(B) as well as RD(A) & RD(B) and ground, then you need a ‘4-wire’ converter.

The RS-485 standard doesn’t specify the type of connector or pinouts. RS-485 connectors can be DB9, DB25, Terminal Blocks, RJ11, RJ45 or one of the round DIN connectors, etc. The maximum distance of RS-485 without using a repeater is 4000 feet (1200 meters) at baud rates of up to 90 kbps. You can extend the distance by adding an RS-485 repeater or optically isolated repeater every 4000 feet.

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John Mulindi

John Mulindi is an Industrial Instrumentation and Control Professional with a wide range of experience in electrical and electronics, process measurement, control systems and automation. In free time he spends time reading, taking adventure walks and watching football.