Profibus
Profibus, Process Field Bus is a digital fieldbus standard with two principal flavours. Profibus DP for fast device-level communications, drives, remote I/O, MCC integration and Profibus PA for process instrumentation. Originating from Siemens in the late 1980s and standardized as IEC 61158, Profibus dominates European and Asian discrete and process automation, particularly on Siemens-platform projects.
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Profibus is the digital fieldbus that grew out of the German automation industry in the late 1980s and became, through its adoption on Siemens control platforms, one of the two dominant process fieldbuses worldwide alongside Foundation Fieldbus. It is standardized as part of IEC 61158 and exists in two distinct forms that are easy to conflate. Profibus DP, Decentralized Peripherals is the high-speed variant that links a controller to remote I/O racks, variable-frequency drives, and motor-control centres over RS-485 at up to 12 Mbit, s. It is a device network, not an instrument bus. Profibus PA, Process Automation is the slower, intrinsically-safe variant that runs field instruments on a two-wire segment suitable for hazardous areas, bridged to the DP backbone through a DP, PA coupler. The practical relevance for documentation is that a PA device is addressed by its segment and bus address rather than by a terminal pair, so it appears on an I/O list with that segment reference and a GSD or GSDML device-description file in place of a conventional wiring entry, while its signal class is still the AI or AO that its function dictates. Profinet, the Ethernet-era protocol from the same lineage, has displaced Profibus DP on much new equipment, but Profibus PA remains common on Siemens-platform process projects because there was, until the recent Ethernet Advanced Physical Layer, no intrinsically-safe Ethernet equivalent at field scale.
Profibus DP vs Profibus PA.
Profibus DP runs at up to 12 Mbit, s on RS-485 twisted pair and serves as the backbone protocol between PLC, DCS and remote I/O, drives, and motor-control centres. Profibus PA runs at 31.25 kbit, s on intrinsically-safe segments suitable for process-instrumentation areas. A DP, PA coupler bridges between them. Profibus PA is the closest peer to Foundation Fieldbus in process-instrumentation deployment, with broadly similar segment-design economics.
Where Profibus dominates.
Siemens DCS, PCS 7 and PLC, S7 projects worldwide. European chemicals and pharma greenfield. Asian power and process plants where Siemens is the dominant supplier. North American projects with Siemens content, auto, food, packaging. The successor protocol Profinet has displaced Profibus DP in many new installations, but Profibus PA remains the favoured process-instrumentation bus on Siemens-platform projects.
Frequently asked.
Is Profinet replacing Profibus.
Profinet is replacing Profibus DP for device-level Ethernet communications. Profinet has not, and cannot directly replace Profibus PA because there is no intrinsically-safe Ethernet equivalent at full deployment scale. Profinet for process automation typically uses APL, Advanced Physical Layer Ethernet for the PA-equivalent segments.
Can I mix Profibus and other fieldbuses on the same plant.
Yes, with gateways. Plants frequently run Profibus PA in process areas, Modbus TCP from package skids, and Ethernet, IP from packaging machinery. The DCS or PLC integrates them all via gateway modules.
How is a Profibus PA device identified on an I/O list compared to a 4-20 mA device.
A Profibus PA device appears on the I/O list with its PA segment number and device address in place of a terminal-block reference. The signal class is still AI or AO based on function, but the wiring scheme column references the segment rather than a pair in a multicore cable. PA devices also carry a GSDML file reference that the DCS engineering tool imports for device configuration.