Choose between Profibus PA and DP

Question

I currently try to understand a new technology: Profibus, until now I worked with HART, with which I also had some struggle in the begging but now it's clear. I try to understand why in a factory is used both PA and DP. I understand that to convert a PA Profibus to DP a coupler is needed "...The connection of PROFIBUS PA subsegments to the RS-485 PROFIBUS DP segment is carried out using segment couplers or links. Segment couplers are transparent from the standpoint of the bus protocol...", but what I don't understand is why the PA is used? and not directly DP? (only for safety reasons? "... PROFIBUS PA can be deployed in hazardous environments since its physical layer: MBP, is intrinsically safe..." in this case what does it mean intrinsically safe?)

And what is the difference between these terms:

1. PA (process automation)
2. DP (decentralized periferics)
3. MBP and RS485

I understand that MBP and RS485 are the communication protocols, but in this case what are PA and DP? Only a standard (e.g ISO)?

Answer 1

MBP and RS485 are different electrical signaling schemes. Essentially the physical layer in the OSI model. MBP supports power over the same wire as communication. RS485 supports higher bandwidth.

Profibus PA is "Profibus over MBP". It delivers power and communication over the same pair of wires, and can support intrinsically safe requirements for hazardous areas. That is, electrical power and voltages are limited to levels which cannot cause sparks or overheating regardless of any physical damage to the device or cables. This is so that you can deploy it in areas with flammable vapors, and not risk an electrical malfunction igniting your oil refinery. Disadvantage is that it is quite slow. Only 31.25kbit/s.

Profibus DP is "Profibus over RS485" It does not support power delivery over the same cable, but it does support much higher bandwidths. Up to 12Mbit/s.