Profibus DP: The Consolidated Industrial Standard
Profibus DP (Decentralized Peripherals) is the most installed fieldbus in the world, with over 60 million active nodes. Despite the advent of industrial Ethernet, it remains the primary choice for existing plants and retrofits.
Working Principle
Profibus DP uses master-slave serial communication on a two-wire cable (RS-485):
- The master (PLC) cyclically polls each slave
- Each slave (encoder, I/O) responds with its data when polled
- The cycle repeats at regular intervals (typically 1-10 ms)
Physical Specifications
- Physical medium: shielded twisted pair RS-485 (purple Profibus cable)
- Speed: 9.6 kbit/s β 12 Mbit/s (auto-negotiated)
- Maximum distance per segment: 100 m (at 12 Mbit/s) β 1,200 m (at 93.75 kbit/s)
- Nodes per segment: max 32 (expandable to 126 with repeaters)
- Connector: standard Profibus DB9 with integrated termination switch
Encoder Profile
Profibus encoders implement the standard profile according to PNO (PROFIBUS & PROFINET International):
- Class 1: single-turn position (16 bits)
- Class 2: single-turn + multi-turn position (16+16 bits)
- Class 4: position + speed + extended diagnostics
Italsensor Profibus Encoders
The TSM60P-PRDP series supports:
- Single-turn 13-bit + multi-turn 14-bit absolute position
- Programmable position preset
- Configurable counting direction
- GSD file for STEP 7 configuration
Profibus Wiring
Profibus wiring requires attention:
- Dedicated cable: use only certified Profibus cable (purple, 150 Ξ©)
- Termination: activate termination resistors ONLY on the first and last node of the segment
- Linear topology: long stubs are not allowed (max stub 0.3 m)
- Grounding: shield grounded at one point only per segment
- Communication status: online/offline for each node
- Transmission errors: CRC error and timeout counters
- Encoder-specific diagnostics: position alarms, bearing status, temperature
Diagnostics
Profibus offers bus-level diagnostics:
Future of Profibus
Although PROFINET is the designated successor, Profibus DP remains supported long-term. For existing plants, retrofit with Profibus encoders is the most economical choice. For new plants, PROFINET is recommended for greater flexibility and bandwidth.
