Profibus stands for Process field bus and DP stands for Decentralized peripherals.
In an industrial there will be a bunch of sensor installed in field area. They have to connected sensors to i/o module of PLCs, so that a automation system can take a control action. An ordinary such connection as shown below.
Problem we have to face here is distance. Each of the sensor is directly connected to the i/o module separately. Thus huge number of wires is needed to connect in parallel for long distance. This cause the installation expense to increase.
Here the idea of Profibus comes.
Unlike from the above system, i/o module is shifted from PLC module in the control room to a new enclosure, which will be less distance from sensors.
An IM or Interface Module is installed within the enclosure. Each an every sensors won't needed connect directly to PLC. But only IM alone is needed to connected to PLC with RS-485 cable. RS-485 transfer all data
From the initial condition to profibus installation we decentralized the i/o module from HMI station to this enclosure near the field area. This is why we uses decentralized peripheral/ DP as suffix in Profibus-DP.
RS-485 uses binary data so external noises won't effect the data transfer and maintenance and installation cost and work can reduced
If RS -485 fails, entire signal transmission stops. which is counted as a disadvantage.
So that main signals are connected directly to the PLC.
This method is called Hybrid method. Important signals are transferred directly to PLCs so important facilities won't lost.