Fieldbus

Fieldbus technologies mark a significant change in industrial automation, allowing devices and systems to communicate digitally and move away from traditional control methods relying on individual connections for each field device. Originating in the 1980s, fieldbus technology's development was spearheaded by the ISA's SP50 committee, dedicating years to define technical requirements and establish a consensus for a digital fieldbus. An early implementation, Bitbus, introduced by Intel Corporation in 1983, aimed to enhance Multibus systems in industrial settings by separating slow input/output functions from faster memory access.

Fieldbus technology facilitates a shift from centralized to distributed process control, placing control in field devices like transmitters and valves. This transition allows concurrent control processing, reducing the reliance on centralized controllers. Characterized by bidirectional communication, this technology enables real-time, closed-loop control between intelligent field instruments and host systems, ranging from handheld devices to complex plant control systems. Implemented through networks like DeviceNet, ControlNet, Modbus, PROFIBUS and FOUNDATION Fieldbus, these protocols operate on different layers of the OSI model, offering services from the physical and data link layers to the application layer.

Fieldbus technology laid the foundation for today's modern automation in the sense of Industry 4.0, offering a reliable and cost-effective means of communication between various components within a distributed control system. Its ability to streamline processes and facilitate diagnostics and maintenance makes it an indispensable tool for industries looking to optimize their control systems and maintain a competitive edge.

Fieldbus technology is a crucial part of industrial automation, acting as a real-time distributed control network. It's a serial bus system linking components like sensors and actuators to controller devices such as industrial PCs or PLCs. Fieldbus facilitates data exchange between system components over long distances and high external load conditions. The key components comprising a Fieldbus network are:

• Programmable Logic Controllers (PLCs)

  These are industrial digital computers that have been ruggedized to control various processes within a manufacturing environment. PLCs act as the central controller in a fieldbus system, interpreting data from sensors and making decisions on actuator control.

• Sensors

  Devices that detect and measure changes in physical properties like temperature, pressure, or flow, and translate these signals into a readable form to the PLC or other devices in the network.

• Actuators

  Components that act under command from a control system to move or control a mechanism or system. This could be opening a valve, starting a motor, or adjusting a damper.

• Human Machine Interface (HMI)

  Graphical Interface through which operators can monitor and control various processes and equipment within an industrial system.

• Industrial Communication Interfaces

  Interfaces for industrial communication, which are integrated into the above components via a communication controller, embedded module or PC card/fieldbus card, enable data exchange between the various field devices and thus form the basis for fieldbus networks.

In the intricate web of industrial networks, the seamless transfer of digital data plays a pivotal role in ensuring the efficient communication of vital information. Among the array of encoding methods employed in fieldbus technology one stands out for its reliability and effectiveness – Manchester encoding. This method encodes the data to ensure that it can be transmitted reliably over the network, facilitating communication between various industrial devices such as sensors and actuators Manchester encoding in fieldbus communication is a method of digital data transfer where a logical '1' is represented by a low-to-high transition and a logical '0' by a high-to-low transition. This encoding technique is self-clocking, which means that the receiver can synchronize its clock with the transmitter's clock, minimizing error rates and providing a more reliable mechanism for transmitting data.

Delving deeper into the realm of fieldbus communication, another critical aspect comes to light – time synchronization, which is crucial for coordinating actions and correlating data between sensor nodes and communication scheduling. It ensures that all nodes in a distributed system maintain a common notion of time. In fieldbus systems, each passive station synchronizes its clock in every communication cycle, calibrating after receiving the data frame from the controller station. This prevents the accumulation of synchronization errors.

Fieldbus networks are bi-directional, digital serial networks that facilitate the exchange of data across different components, ensuring real-time control and monitoring within manufacturing plants. At the core of their operation lies the Open Systems Interconnection (OSI) model, which is a conceptual framework that defines industrial communication in seven distinct layers.

The physical layer (Layer 1) in Fieldbus communication encompasses wiring, connectors, and transmission media, responsible for carrying power and signals between devices. It ensures hardware is configured for data transmission. The data link layer (Layer 2) handles protocols and addressing, facilitating node-to-node data transfer and error detection/correction. At the Network Layer, Fieldbus supports various topologies (bus, star, etc.) for flexible network installation and expansion. 

Data exchange in fieldbus systems involves two primary methods: cyclic and acyclic communication. Cyclic communication is a scheduled data transmission where the Link Active Scheduler (LAS) compels field instruments to transmit critical process control data at regular intervals. This ensures determinism in the industrial communication network, providing a guaranteed maximum response time for critical control functions, essential for stability in feedback control systems. On the other hand, acyclic communication takes place during unscheduled periods, allowing devices to broadcast less critical data such as operator setpoints, alarm acknowledgments, and diagnostic messages. LAS sequentially permits devices to transmit this information during these times, which doesn't require the strict timing of cyclic communications.

Fieldbus communication protocols are integral to modern factory automation these protocols facilitate the exchange of data between various devices such as sensors, actuators, controllers, and instruments, enabling them to operate cohesively and efficiently. Some of the core protocols for the fieldbus communication are as follow:

• PROFIBUS (Process Field Bus)

  Operates on a controller-device model, with a controller orchestrating communication cycle by sending outputs and receiving inputs from all connected devices. PROFIBUS DP (Decentralized Periphery) facilitates high-speed serial communication, employing a multi-controller token network for coordinated system communication. PROFIBUS PA (Process Automation) is designed for hazardous environments, using MBP technology (Manchester bus powered) for both data transmission and power supply over the same two wires, ensuring intrinsic safety. Within the OSI model, PROFIBUS employs layers 1, 2, and 7. Layer 1 defines transmission characteristics, including copper-wire options like RS-485 and MBP, as well as optical and wireless. Layer 2, the data link layer, utilizes a hybrid access method of token passing with controller-device communication for data security and bus access. Layer 7, the application layer, facilitates communication between industrial devices.

• FOUNDATION Fieldbus

  Enables communication between input devices (e.g., Ethernet switches, sensors) and output devices (e.g., valves, drives) without requiring a direct connection to a controller for each device. FOUNDATION Fieldbus supports diverse network topologies, including point-to-point, bus, tree, or mixed configurations. It utilizes two bus systems, H1 with Manchester Coding (MBP) and HSE with Highspeed Ethernet, providing parallel connections and efficient energy distribution. The technology is suitable for hazardous and explosive areas, featuring interoperable, bi-directional, digital, serial, publisher-subscriber communication networks. FOUNDATION Fieldbus operates on layers 1, 2, and 7 of the OSI model.

• CANopen

  CANopen is an open and standardized industrial communication protocol based on the CAN bus. It defines the application layer and communication profile for embedded systems and devices. CANopen supports various network topologies, including bus, star, and ring configurations. It utilizes the lower layers of the OSI model, specifically the physical and data link layers, while defining its own application layer. CANopen enables flexible and modular combinations of manufacturing cell units through standardized device profiles and object dictionaries. It was initially developed under the Esprit research program of the European Community and is now maintained by the CAN in Automation (CiA) organization.

• Modbus

  The Modbus protocol, widely used in Fieldbus systems, employs a controller-device model where a controller device initiates requests, and devices respond. Its simple design transmits data as voltage-represented bits over serial lines, with a basic setup involving just two devices connected by a single cable, contributing to its reliability. Modbus, supporting interfaces like RS485 and RS232, is adaptable to various setups, with RS485 Two-Wire being popular for multiple devices on a network. Operating at both the application and data link layers, Modbus ensures error-free communications with a 16-bit frame structure and a Cyclic-Redundant Checksum. It accommodates different network topologies like star, and bus, enabling comprehensive control and status information exchange. This flexibility allows for efficient parameter management, particularly in devices like soft starters, ensuring smooth motor starts crucial for industrial applications.

Fieldbus technology has revolutionized industrial automation by offering a myriad of advantages over traditional wiring systems. The primary benefits are:

• Reduced wiring complexity

  In a conventional setup, each device requires a direct connection to the control system, leading to extensive and complicated wiring networks. This approach is resource-intensive and prone to errors during installation and maintenance, with each added wire introducing potential failure points. Fieldbus systems streamline this by creating a communication network where multiple devices share the same physical wire to communicate with the main controller. This method, known as multidrop or bus topology, significantly simplifies the physical layout of connections, often requiring only two wires for both power and data signals, depending on the specific Fieldbus standard used.

• Advanced diagnostic capabilities

  Enables real-time monitoring, data logging, and remote device configuration with a bidirectional communication protocol for closed-loop control. Connecting sensors and actuators on the same cable simplifies network complexity, allowing specific instruments to offer diagnostics and calibration. Fieldbus networks execute control functions directly between field instruments, reducing the load on plant computers. Its all-digital nature eliminates the need for I/O conversion subsystems, ensuring interoperability among products from multiple vendors. This interoperability is critical for adopting Control-in-the-Field (CiF) strategies, ensuring continued safe operations during host system failures.

• Scalability and flexibility

  Fieldbus networks enable the seamless addition or removal of devices without causing disruptions, which is particularly advantageous for industries that require constant adaptation to new technologies or changes in production processes. The inherent design of Fieldbus systems allows for long-distance data exchange and operation under high external loads, making them suitable for a wide range of industrial environments.

• Enhanced data transmission

  Fieldbus systems operating at 31.25 kbit/s, efficiently transmit process variables and diagnostic information, ideal for scenarios not requiring high bandwidths. This optimized protocol outperforms Ethernet for small data packets. The lower data rate is crucial in hazardous environments, ensuring safety by minimizing ignition risk in places like chemical plants and oil refineries. Fieldbus technology's versatility is evident in supporting various topologies (bus, star, etc.), enhancing communication, efficiency, and productivity by connecting and coordinating devices within manufacturing plants.

Hilscher offers a wide range of products for industrial communication in fieldbus networks. The netX technology, based on multiprotocol-capable SoCs (System on Chips) and accompanying protocol software, is at the forefront. netX can be integrated into industrial components - such as controllers, sensors or actuators - as highly integrated communication interfaces. Thanks to the associated firmware, which can be loaded onto the chip as needed for the required protocol stack, Hilscher supports component manufacturers and automation specialists in the development of flexible solutions for use in a wide variety of fieldbus networks - whether for PROFIBUS, CANopen, DeviceNet, CC-Link or other fieldbuses.

Based on the netX communication controllers, Hilscher developed different embedded modules and the PC cards of the cifX family (which are available in all common form factors - from PCI and PCIe to the smallest multiprotocol-capable PC cards on the automation market in M.2 format). These communication interfaces already include the necessary chip peripherals and are therefore faster to integrate.

In addition, gateways, switches and network and communication diagnostic devices support the smooth operation of fieldbus networks.

Next to conventional fieldbus systems, Hilscher's components for industrial communication networks also support the most common protocols for Industrial Ethernet - such as CC-Link IE, EtherCAT, EtherNet/IP, Modbus TCP or PROFINET.