A very often asked question is: “how far can Profibus networks communicate, and how fast can it communicate?” Answer: Profibus Distance & Baud Rate affect each other. Baud rate affects distance, and distance affects baud rate in electrical Profibus networks. Repeaters can extend your distance, and the type of media (cable vs fiber-optic) have different distances that they can extend to. The following information is taken from the Siemens perspective, but is applicable to Profibus networks in general.
First a brief descrpition of Profibus segments: a Profibus segment is a part of the Profibus network, simply speaking. If you have devices connected together without a Profibus repeater in your network, you have only 1 Profibus segment. If you have 1 repeater, then on each side of the repeater you have one segment: 2 segments total. And for each repeater you add, you add one more segment. A segment can have a maximum of 32 devices connected, including the repeater(s), and including your programming device if you connect it.
Baud Rates & Distances for Profibus (RS-485)
|Transmission Speed||Segment Length|
|9.6 kbps||1000 m|
|19.2 kbps||1000 m|
|45.45 kbps||1000 m|
|93.75 kbps||1000 m|
|187.5 kbps||1000 m|
|500 kbps||400 m|
|1.5 Mbps||200 m|
|3 Mbps||100 m|
|6 Mbps||100 m|
|12 Mbps||100 m|
Fiber Optic Profibus Networks
The maximum distance for optical Profibus networks depends on the type of cable used (plastic vs. glass cable, for example) and the transmission power of the device or optical link module (OLM) used. There is no real chart that can be created as in the electrical segments, because different cables and different devices have different specifications. Generally, fiber optic segments are for very long distance or electrical noise immunity requirements.
The above information is a guideline to baud rates and distances.
More detailed information can be found in the SIMATIC NET PROFIBUS Network Manual