What are Fieldbuses?
A fieldbus is an industrial communication protocol that lets field equipment such as Sensors, Actuators, I/O modules, drives and PLCs communicate with each other within an automation system.
Fieldbuses replace traditional point-to-point cabling with a shared communication bus, making installations simpler, cheaper and more scalable.
🧠 What does a fieldbus do?
A fieldbus:
- Connects multiple devices via a single communication cable (bus structure)
- Sends data such as measurement values, commands or status information
- Enables Real-time communication between field equipment and the controller
- Simplifies cabling and maintenance
🧱 Typical characteristics of fieldbuses
| Characteristic | Description |
|---|---|
| Serial communication | Based on RS-232, RS-485 or industrial Ethernet |
| Deterministic | Responds within predictable time, important for control |
| Protocol-specific | Different protocols have their own specifications |
| Bus structure | One line for multiple devices (in contrast to point-to-point) |
📦 Commonly used fieldbus protocols
| Protocol | Description |
|---|---|
| Profibus | Widely used in factory and process automation |
| Modbus | Simple and widely supported (RTU, ASCII, TCP/IP) |
| CAN bus | Widely used in vehicles and embedded systems |
| DeviceNet | Based on CAN bus, primarily for I/O devices |
| EtherCAT | Real-time Ethernet for motion control |
| AS-Interface | Simple network for basic Sensors/Actuators |
| Foundation Fieldbus | For process automation with smart field equipment |
| ProfiNET | Industrial Ethernet variant of Profibus, very widely used in automation |
| Ethernet IP | Ethernet-based fieldbus from Rockwell/Allen-Bradley (CIP protocol) |
| HART | Hybrid digital/analogue protocol for smart instrumentation (over 4–20 mA) |
| SERCOS III | Real-time network for motion control over Ethernet |
| Powerlink | Open-source real-time Ethernet protocol (Ethernet Powerlink) |
| IO-Link | Point-to-point communication standard for smart Sensors and Actuators |
| BACnet | Widely used in building management systems, including HVAC and lighting |
| DNP3 | Widely used in energy and utilities, especially with RTUs |
| M-Bus | For metering of energy, water and gas (in buildings and the utilities sector) |
| LON (LonWorks) | Used for building and process automation |
🏭 Where are fieldbuses used?
- Production lines (PLC ↔ Sensor/Actuator)
- Process industry (tank level, pressure, temperature)
- Machine building (motion control, safety systems)
- Building management (HVAC, lighting, access control)
🔄 Fieldbus vs. industrial Ethernet
| Aspect | Fieldbus | Industrial Ethernet |
|---|---|---|
| Physical layer | Serial (e.g. RS-485) | Ethernet (IEEE 802.3) |
| Speed | Lower (kbit/s – Mbit/s) | Higher (100 Mbit/s or more) |
| Complexity | Simpler | More options and flexibility |
| New projects | Less commonly used | Preferred in modern installations (ProfiNET, Ethernet IP) |
📌 In summary
Fieldbuses are industrial communication systems that efficiently connect multiple devices via a single shared data line. They form the backbone of many automation systems and laid the foundation for modern industrial networks such as industrial Ethernet solutions.