Profibus DP vs PA(Difference between Profibus DP vs PA)

In current automation market there is many different type of protocol used like modbus,IEC 61850,IEC 104….etc. among many of this protocol Profibus also part part of automation family .for understanding how profibus works ?.We need to understand details about what is Profibus DP vs first let’s start understand background of Profibus

Profibus Background

  • Introduced in 1989
  • Leading Open Fieldbus System in Europe
  • Profibus follow German Standard (DIN 19245), European Standard (EN 50170), IEC Standard (One of Eight Bus Networks)
  • Profibus Protocol Supported by Over 1,000 Companies

Profibus Levels

  • Profinet is Ethernet with use of Similar Profibus User Layer
  • Profibus DP (Distributed Peripherals) – Communication Between a Master (PC or PLC) and Slaves (Remote I/O, Field Devices)
  • Profibus PA (Process Automation) – Similar to DP with IEC 61158-2 Physical Layer

Profibus Networks

Post Read by our beloved Readers :

Profibus DP and PA : It’s Not as Difficult as You Think

Profibus DP vs PA

Profibus DP Physical Layer

  • Physical Layer : Profibus DP is using RS-485 media
  • Trunk Topology
  • Up to 32 Devices per Segment
  • Up to 126 Devices with 4 Repeaters
  • May Select From Various Speeds
Baud Rate (kbits/s)  9.6 – 93.75 500 1,500 12,000
Cable Length (meters) 1,200m          400m               200m 100m

Profibus DP Data Link Characteristics

Bus Access Methods

  • Masters on Same Segment – – Token Passing (Multi-Master System Possible)
  • Master to Slaves – – Cyclic Polling
  • Multicast for special Control Commands (Synchronization)
  • Peer to Peer for Asset Management & Set-up

Bus Operating States 

  • Operate: Cyclic transmission of I/O data
  • Clear: Inputs are read, Outputs remain in secure state
  • Stop: Diagnostics and Parameterization (No I/O read)

Slave may carry up to 246 bytes of I/O date with low bit overhead

Other Functions

  • Dynamic activation of individual slaves
  • Synchronization of I/O
  • Watchdog control of DP slave detects assigned master failure

Profibus vs Modbus (Difference between Profibus and Modbus)

Profibus DP System Function   

Profibus DP User Interface

  • A Direct Data Link Mapper Connects Data (Layer 2) with the User Interface (No Application Layer; Low Protocol Overhead)
  • At 12Mbit/sec may read 1024 discrete I/O bits in less than 1msec!
  • Devices have Electronic Data Sheet (GSD File Needed to Configure Device with Network)

Profibus PA vs DP

Profibus PA

  • Must be Attached to Profibus DP by a Segment Coupler or Linking Device
  • Uses Physical Layer, IEC 61158-2 which May be Used in Intrinsically Safe Applications (Same as FF)
  • Uses Function Blocks (Similar to FF but not as Advanced)

Profibus PA Physical Layer

Using Segment Coupler:

  • PA Segment Transparent to DP Segment
  • DP Segment Limited to 45Kbit/sec (PA segment runs at 31.25Kbit/sec)

Using Linking Device:

  • Slave on DP segment; Master on PA Segment
  • DP segment Speed not Limited
  • All PA Segment Parameters Established by IEC 61158-2 Standards (Same as FF H1)

Profibus PA Other Parameters

  • All Data Access Same as DP with Segment Coupler
  • Link Master Uses Cyclic Polling for Data Transfer and Acyclic Polling for Diagnostics (Similar to DP)
  • Limited Function Blocks are Used Similar to FF However:
  • Block Data Not Time Stamped (System Synchronization)
  • Functions executable Only in Master Device Not in the Field Devices

Profibus vs Profinet (Difference between Profibus and Profinet)

Profibus PA Network Communication

  • Multiple Communication Paths
  • Multiple Sampling Needed to Avoid Jitter and Aliasing
  • Result is Slow Control Speed & Increased Process Variability

Profibus Applications

  • Profibus DP is widely used in process as a communication bus for Drives, Motors, Pneumatic Valve Islands, and to connect AS-I Gateways to a DCS or PLC.
  • Profibus DP is widely used in factory automation, Very strong in Europe
  • Profibus PA is very strong in European Process Industries and is growing rapidly in North America

What is Profibus ? How Profibus Work ?

Leave a Comment