# PLCs & Distances

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#### Ion Voinea

Please tell me if it is possible to have a Master PLC controlling 3-4 I/O modules located on about 4 km(1km between each). Can I do it with Profibus modules? Is it possible on 2 wires(RS485) because Optical fiber is expansive. Please help !

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#### Gilles Allard

According to my Profibus documentation, there is no problem with such a distance. You can have up to 187Kbps data rate for a segment of 1km. Using repeaters, you can cover up to 12km. Profibus is not designed for very small stations so the cost per I/O will not be negligeable in your case. The least expensive solutions may be the ET200S product family from Siemens. I suppose your network will be installed outdoor. Be sure your cable is adequately protected (surge protectors). Also, because of Earth ground voltage differences, you will probably need repeaters with isolation feature (the Siemens model has such a feature). I hope this help Gilles

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#### Ralphsnyder, Grayg

Actually, you can have relays/repeaters to do comms any distance that you want. The only big problem is when you have to be concerned about signal propagation delays. Grayg Ralphsnyder

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