What is Fieldbus?

  • Fieldbus is a collection of standardized protocols used in industrial environments that are principally defined by IEC61158. 
  • It is a collection of communication protocols that enable seamless data transmission across diverse devices in industrial automation systems. 
  • These protocols improve the efficiency and flexibility of industrial processes by allowing real-time control and monitoring of field equipment such as sensors and actuators. 
  • Fieldbus enhances interoperability and simplifies data transfer in complex industrial networks through providing a standard language for communication, contributing to enhanced automation, reliability, and overall system performance.
  • Fieldbus is widely utilized in industrial automation applications where real-time distributed control is required. 
  • It is used in manufacturing facilities, process industries, and other industrial settings. Fieldbus technology has mainly replaced older communication technologies such as RS232 serial communications, which were confined to two devices. 
  • Fieldbus improves communication and management in industrial processes by connecting various devices in a network, providing enhanced flexibility, efficiency, and the capacity to monitor and manage a wide range of field devices in a simplified manner.

The elements in an industrial Fieldbus can be arranged in a variety of ways. Some of the most typical industrial Fieldbus configurations are as follows:

Different Fieldbus Network Topology

Ring: In a ring topology, each node is physically connected to two other nodes—one on each side—to establish a continuous, circular data flow.

Line: A line topology, also known as a daisy chain or bus topology, consists of nodes that are connected to a host computer one by one in a line.

Star: In a star architecture, each device is linked to a central hub or node that acts as a conduit for data transmission.

Tree: A tree or branch topology is a hybrid topology that incorporates star networks connected by line topologies and resembles the branches of a tree.

  • Fieldbus is an all-digital, serial, two-way communication system used in industrial environments to connect and integrate measuring and control equipment. 
  • It allows for effective data interchange and real-time control inside an industrial automation system by facilitating the interaction of diverse devices such as sensors, actuators, and controllers. 
  • Like typical point-to-point connections, Fieldbus systems, while similar to Ethernet in some ways, include a set of protocols that specify communication rules and standards. 
  • This technology allows several field equipment to be connected to a single point, facilitating communication and contributing to increased flexibility and control in industrial processes.

Fieldbus is a collection of industrial computer networks that allow input devices such as Ethernet switches and sensors to communicate with output devices like as valves and drives without requiring each item to be connected back to a controller.

There are various instances of fieldbus networks, each customized to specific industrial uses and needs. Some of the notable Common Fieldbus protocols are:

  1. FOUNDATION Fieldbus: Used in process automation, FOUNDATION Fieldbus enables communication among field devices like sensors and actuators.
  2. DeviceNet: Part of the ODVA family, DeviceNet is commonly used for connecting industrial devices on the factory floor.
  3. ControlNet: Also part of the Allen-Bradley family, ControlNet is designed for high-speed and high-reliability applications in industrial automation.
  4. Modbus: Widely used for serial communication between devices, Modbus is a simple and robust protocol.
  5. PROFIBUS: Used in both process automation and factory automation, PROFIBUS supports various communication profiles for different applications.
  6. EtherCAT: Known for its high-speed communication capabilities, EtherCAT is often used in applications where rapid data exchange is crucial.
  7. CANopen: Commonly used in embedded systems and automation, CANopen is based on the Controller Area Network (CAN) protocol.
  8. Ethernet/IP: This is an industrial Ethernet protocol widely used in manufacturing and process control.
  9. Profinet: A real-time Ethernet standard used for industrial automation, Profinet supports both TCP/IP and real-time communication.
  10. IO-Link: Designed for point-to-point communication between sensors/actuators and controllers, IO-Link is used for connecting industrial sensors and devices.
  11. HART (Highway Addressable Remote Transducer): While not a fieldbus in the traditional sense, HART is a digital communication protocol used in process automation.

These examples highlight the variety of fieldbus networks, each adjusted for different industrial applications, and show the range of communication options accessible in the field of industrial automation.

What is an example of a fieldbus?

Fieldbus operates through providing an all-digital, serial communication system that supports the interaction of numerous field devices in an industrial setting, such as sensors, actuators, and controllers. The following are the major aspects of how Fieldbus works:

Fieldbus allows several field devices to connect to a single central point that acts as a communication hub. The central point is then connected to the controller, creating a networked communication system.

In a Fieldbus system, information is exchanged in the form of small data packets. These packets are sent sequentially and multiplexed over time to efficiently transport data between devices and the controller.

Fieldbus uses a sequential system for transferring data packets rather than parallel transfers. This sequential transmission, in conjunction with multiplexing, enhances communication channel utilization and assures effective data interchange.

Fieldbus enables the connection of a large number of devices to a single controller by establishing a single connection point through which all information is exchanged. This scalability enables the automation system to incorporate hundreds of devices.

Levels of a Fieldbus System

Fieldbus systems are divided into four levels, with each level increasing in complexity.

 This foundational level involves basic field devices like limit switches connected to a single network cable. It transmits output signals from the controller to actuator devices, such as alarms or indicator lamps.

 Operating on a larger scale, this level connects numerous sensors, actuators, variable speed drives, and motor control centers. It enables control over individual elements within the network.

Among the most complex on the factory floor, control bus networks facilitate high-level data communication. Programmable logic controllers (PLCs) and smart instruments are interconnected, linked to human interface panels (HIPs) for comprehensive configuration and control.

The highest and most intricate level in a Fieldbus system, the enterprise bus network, also known as the information level network, interconnects all computers and departments. It is computer-driven, involving extensive data collection, file transfers, and computer monitoring.

 Fieldbus allows hundreds of devices to connect to a single point, drastically reducing the number of cables needed compared to parallel wiring configurations. This simplifies the network infrastructure and minimizes cable lengths.

The reduction in cabling requirements not only simplifies the system but also leads to cost savings. Fieldbus significantly cuts the expenses associated with setting up and maintaining a network by eliminating the need for extensive individual device connections.

 Fieldbus systems are easier to install compared to parallel wiring due to their streamlined cabling structure. With fewer cables to manage, the planning, installation, and organization of Fieldbus systems require less time and effort.

 Fieldbus systems often exhibit higher reliability than parallel wiring. Short signal pathways enhance system availability, and the technology provides better protection against interference, particularly in the case of analog values. This contributes to a more stable and dependable industrial network.

The structure of Fieldbus standards is organized under the International Electrotechnical Commission (IEC) framework, specifically IEC 61158 and IEC 61784, which define the specifications and profiles for industrial communication networks. Here’s an overview of their structure:

  1. IEC 61158-1 Part 1:  IEC 61158 and IEC 61784 series overview and guidelines.
  2. IEC 61158-2 PhL: Part 2: describes the physical layer and defines services.
  3. IEC 61158-3-x DLL: Part 3-x: Definition of a data-link layer service – Type x elements.
  4. IEC 61158-4-x DLL: Part 4-x: The specifics about the data-link layer protocol – Type x parts.
  5. IEC 61158-5-x AL: Part 5-x: Definition of an application layer service – Type x elements.
  6. IEC 61158-6-x AL: Part 6-x: Protocol definition for the application layer- Type x elements.

The IEC 61158 standard is divided into different layers, each further categorized into services and protocols. The fieldbuses are incorporated as different types, and each part is subdivided into subparts, with each protocol type having its own subpart.

  1. IEC 61784-1: profiles for fieldbus application in industrial control systems for both discrete and continuous manufacturing.
  2. IEC 61784-2: Additional profiles for ISO/IEC 8802 3 based communication networks in real-time applications.
  3. IEC 61784-3: Functional safety fieldbuses – Definitions of profiles and general guidelines.
  4. IEC 61784-3-n: Functional safety fieldbuses – Additional specifications for CPF n.
  5. IEC 61784-5-n: Installation profiles for CPF n during fieldbus installation.

The IEC 61784 series complements IEC 61158 by providing instructions for the use of different parts of IEC 61158 to assemble a functioning system. It includes profiles for continuous and discrete manufacturing, additional profiles for real-time applications, and profiles for functional safety.

To address the diverse requirements of fieldbus networks in process automation and discrete manufacturing, IEC 62026 specifies controller-device interfaces (CDIs). As of 2019, it includes parts such as:

  1. IEC 62026-1: General rules.
  2. IEC 62026-2: Actuator sensor interface (AS-i).
  3. IEC 62026-3: DeviceNet.
  4. IEC 62026-7: CompoNet.

These standards cover different aspects of device networks, offering rules and interfaces specific to various types of fieldbus systems.

The table below provides a comprehensive overview of various fieldbus protocols, highlighting key parameters such as speed, maximum distance, maximum nodes, topology, and use cases. Understanding the characteristics of these protocols is essential for engineers and professionals involved in designing and implementing industrial automation solutions.

Fieldbus ProtocolSpeedMaximum DistanceMax NodesTopologyUse Cases
Modbus31.25 kbit/s to 1 Mbit/s1.2 km (RS485), Variable (TCP/IP)247 (RS485), 253 (TCP/IP)100 m to 9.6 km (speed-dependent)Broad spectrum of industrial control systems
Profibus9.6 kbit/s to 12 Mbit/s100 m to 9.6 km (speed-dependent)127Tree, StarApplied in factory and process automation
DeviceNet125 kbit/s to 500 kbit/s500 m (at 125 kbit/s)64Trunk/DropUtilized in the automotive industry and industrial automation
EtherCAT100 Mbit/s100 m (between devices)65535LineFacilitates real-time industrial control systems
Ethernet/IP10 Mbit/s to 1 Gbit/s100 m (Copper Ethernet), Distance up to 40 km (Fiber Optic type)UnlimitedStar, Tree, LineVaried applications in automation and process control
CAN (Control Area Network)50 kbit/s to 1 Mbit/sFrom 40 m (at speed 1 Mbit/s) to 1 km (at speed 50 kbit/s)127Bus, StarWidely adopted in automotive and industrial control systems
Profinet100 Mbit/s to 1 Gbit/s100 m (Copper Ethernet), up to distance 40 km (Fiber Optic Type )UnlimitedLine, Star, RingKey role in industrial automation and process control
AS-Interface (AS-i)167 kbit/s100 m (extendable with repeaters)62Line, Tree, StarSimple or binary device integration, e.g., switches and sensors
CC-Link10 Mbit/s100 m (extendable to 1.2 km with repeaters)64Line, Star, RingPredominantly used in Mitsubishi PLCs and Asian markets
Foundation Fieldbus H131.25 kbit/s1900 m32Bus, Star, TreeApplied in process automation and intelligent devices
SERCOS III100 Mbit/s100 m (Copper Ethernet), Distance up to 80 km (Fiber Optic type)511RingPrimarily employed in servo drives and machine tools
POWERLINK100 Mbit/s100 m (Copper Ethernet), Distance up to 40 km (Fiber Optic type )240Line, RingReal-time I/O and drives integration
Modbus-Plus1 Mbit/s1.6 km64Peer to PeerTailored for Modicon PLCs

This comprehensive comparison aids in selecting the most suitable fieldbus protocol based on specific industrial automation requirements, ensuring optimal performance and reliability in diverse applications.

Sundareswaran Iyalunaidu

With over 24 years of dedicated experience, I am a seasoned professional specializing in the commissioning, maintenance, and installation of Electrical, Instrumentation and Control systems. My expertise extends across a spectrum of industries, including Power stations, Oil and Gas, Aluminium, Utilities, Steel and Continuous process industries. Tweet me @sundareshinfohe

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