Why we used rs-485 only twisted wires with out shield and pvc cover like profibus and there is no lost by signal ?

PROFIBUS DP It runs over two core screened cable that is violet sheathed and its speed varies from9.6Kbps to12Mbps. A particular speed can be chosen for a network to give enough time for communication with all the devices present in the network. If systems change slowly then lower communication speed is suitable and if the systems change quickly then effective communication will happen through faster speed. The RS485 balanced transmission that is used in PROFIBUS DP only allows32 devices to be connected at once but more devices can be connected and network can be expanded with the use of hubs or repeaters.

PROFIBUS PA It is slower than PROFIBUS DP and runs at fixed speed of31.2Kbps via blue sheathed two core screened cable. The communication may be initiated to minimise the risk of explosion or for the systems that intrinsically need safe equipment. The message formats in PROFIBUS PA are identical to PROFIBUS DP.....

extract from wikipedia.....read more on....http://en.wikipedia.org/wiki/Profibus