dear all,

which cable is best for remote I/Os(distance 20m) 

Hello Prasa;

A Profibus-DP cable (copper, standard) will carry Profibus-DP signals for 100m, at maximum speed of 12 MB, on a single segment. With repeaters you can extend this to 1000 m. At lower speeds, less than187,5 kB, your Profibus segment can have a length of 1000 m, with copper cable; again, with repeaters the network could extend to 10 km..

The only reason you would need F.O. cabling (including the cost of the OLMs) for such a short distance in your network would be that the area where you are laying the Profibus copper cable makes it impossible to avoid EMC (Profibus cabling parallel to power cables in a conduit, or near high magnetic fields in an aluminium plant, for example), Fiber optic is not susceptible to induction problems, so it will isolate the signals properly.

Hope this helps,

Daniel Chartier

Edit: To complete the information above, you will find the part number for the Standard Profibus-DP (copper) cable from Siemens and Belden in the following links:

Profibus networks manual:

https://support.industry.siemens.com/cs/ww/en/view/35222591

Belden Profibus-DP cable:

https://catalog.belden.com/techdata/EN/3079A_techdata.pdf

Thank you Mr.Daniel for giving me difference between FO and DP cable.

lot of thanks,

prasa