PROFIBUS PA is the DP-V1 extension dedicated to process instrumentation, using the MBP (Manchester Bus Powered) physical layer specified in IEC 61158-2 at 31.25 kbps, which carries both power and data on the same twisted pair and is intrinsically safe for hazardous areas.
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PROFIBUS PA keeps DP-V1 application services but swaps the RS-485 physical layer for MBP at 31.25 kbps so that 4-20 mA-style two-wire field instruments can be powered over the bus. The Ex ia/ib intrinsic-safety rating allows installation in gas and dust hazardous zones found in chemical, pharma and oil & gas plants. A DP/PA coupler bridges the high-speed RS-485 backbone to the slower PA segment, and typical devices are pressure, temperature and flow transmitters from Endress+Hauser, Siemens SITRANS or Yokogawa. The modern evolution of this approach is Ethernet-APL for PROFINET.
Never mix up the segment budgets: a PA spur is limited by the power balance, not by the RS-485 unit-load rule, so always run the FISCO or FNICO calculation before adding instruments.
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