Powering industrial connectivity: wired solutions

Introduction

Industrial networks interconnect intelligent devices and provide essential data to all network nodes, such as controllers, HMIs, or field devices. Industrial facilities optimise efficiency, improve productivity and operations, and prevent downtime by gathering, processing, and transmitting data in real-time. These networks form the infrastructural bedrock that supports the transition to smart factories and wide-scale alignment with Industry 4.0.

Industrial networks use a range of dedicated protocols for specific purposes and environments. The combination of greater adoption of the Industrial Internet of Things (IIoT) and the continual increase in the device population that connects to the network demands the creation of new mechanisms for connectivity revolving around wireless and wired protocols.

This article discusses the networking protocols used in industrial installations, focusing on wired industrial network protocols.

Types of industrial networks

Designing an Industrial Automation system whereby machines, field devices, and industrial computers communicate with each other is tedious. The design involves several factors on each side of the scale to determine the best possible option. At present, industrial network designs are based on wired and wireless technologies. Table 1 represents some of the commonly used industrial communication protocols.

Table 1: Types of industrial communication protocols

Hard-wired industrial networks

In industrial automation systems, engineers prefer wired communication as the preferred connectivity method among different hierarchy levels. Wired communication provides a secure, robust, and reliable exchange of real-time information between field devices to an industrial control system or high-level communication to or from a cloud using different protocols. Industries use several hard-wired communication protocols. The popular protocols are:

ControlNet: The control network is an open network used for real-time data transfer of time-critical network or non-critical data between processors and I/Os on the same link. The ControlNet data transfer rate is 5 million bits/second, and up to 99 nodes can be connected on a control network depending on how much data needs to be transferred and how efficiently the network bandwidth is set up. ControlNet is a combination of Data Highway Plus and Remote I/O. This network provides peer-to-peer information exchange and I/O networking on the same platform. It can handle time-critical (scheduled) I/O data, non-time-critical programming, program uploading and downloading, and messaging.

KeyLink: The KeyLink communications protocol allows fast and easy integration into an existing bus system such as CANOpen or Profibus. It features a point-to-point connection without setting an address for each connection. KeyLink protocol connects Inputs and outputs using a serial half- or full-duplex interface. There can be up to 128 I/O points. KeyLink allows for the separation of the power and control units. The switching load is defined by the relay in the master power unit instead of the KeyLink switch. The basic configuration of the master and slave is done automatically. Keylink also has two selectable transmission speeds.

CANOpen: This is a communication standard developed for embedded systems used in various industries, including automation and motion applications. It is built upon CAN and combines higher-level communication protocols and profile specifications. CANOpen covers a network programming framework, device descriptions, interface definitions, and application profiles. It is designed for a maximum of 110 nodes with a maximum wire length of 500 m at 125 kBaud with twisted pair cable available for higher rates. CANOpen supports flow control, device addressing, and transporting data blocks larger than one message. CANOpen is typically used as a slave device to collect data from switches and send information to digital outputs.

Figure 1: CANOpen protocol

DeviceNet: It is a digital, multidrop network that connects and serves as a communication network between industrial controllers and I/O devices. Each device/or controller is a node on the network. DeviceNet uses a trunk line/drop line topology that provides twisted layer buses for signal and power distribution. Thin cables can be used for trunk lines and drop lines. The maximum end-to-end network varies with data rates and cable thickness. DeviceNet allows the transmission of the necessary power on the network. This allows devices with limited power requirements to be powered directly from the network, reducing connection points and physical sizes. It also provides for up to 64 node addresses on a single network. DeviceNet can be configured to operate in a master-slave or distributed architecture using peer-to-peer configuration.

HART: The HART or Highway addressable remote transducer is a two-way communication path with twisted pair. It retains the popular 4-20 mA analogue functionality with the addition of a digital signal which is superimposed on top of this. The digital signal is a frequency shift keying (FSK) modulated carrier that uses frequencies of 200Hz for 0 and 1200Hz for 1. The data rate is 1200 bits/sec. Additional information about other variables, parameters, device configuration, calibration, and diagnostics are transmitted digitally simultaneously.

Figure 2: HART protocol

PROFIBUS: This is widely deployed in industrial automation systems, including those working for factory and process automation. It is based on network communication over bus lines between the master controller(host)and an intelligent device(slave). Several slave devices can communicate with one another. Slave devices are typically remote I/O devices, master control centers, control valves, variable frequency drives, and transmitters. The Profibus network requires a separate controller or computer to perform closed loop on-off and PID operations. Profibus encompasses several industrial products like Profibus-DP, Profibus-PA, and ProfiNet.

• Profibus-DP: It is a device-level bus that supports both analog and digital. It was developed to replace conventional I/O systems that require separate wires between a controller and field devices that carry 4-20 mA,24 V DC signals. It is designed to handle time-critical signals in which each device is assigned a predetermined time to communicate. Profibus DP communicates over RS 485 at speeds of 9.8 Kbps to 12Mbps at distances up to 100-1200 meters. The field devices receive power separately from the communication bus.
• Profibus-PA: This version of Profibus DP is designed to support process automation applications. Profibus PA has a device description and functional block capabilities. It can manage smart process instrumentation. The bus carries the communication data and supplies power to the field devices. Data is supplied at 19.25Kbps and has a maximum length of 19 meters per segment.

PROFINET: It is an open Industrial Ethernet standard developed by the PROFIBUS Organization (PI). PROFINET communicates across Ethernet networks with TCP/IP protocols and IP services. It eases vertical integration of field level with Enterprise level based on Ethernet versatility. PROFINET is real-time automation and covers all requirements of the Automation Industry. It fits factory automation, process automation, safety applications, motion control applications, etc. There are two versions of Profinet: PROFINET CBA and Profinet IO.

• PROFINET CBA: It is suitable for component-based machine-to-machine communication via TCP/IP and for real-time communication to meet real-time requirements in modular plant manufacturing. The CBA enables a simple modular design of plants and production lines based on distributed intelligence using graphics-based communication configuration between intelligent modules. PROFINET IO describes an I/O data view on distributed I/O.
• PROFINET IO: It features real-time (RT) communication and isochronous real-time (IRT) communication with the distributed I/O. The designations RT and IRT are used solely to describe the real-time properties of communication.

Figure 3: Profibus hierarchy

MODBUS: The MODBUS is a data exchange protocol for field bus networks. Modbus devices use a master-slave technique to communicate, in which only one device (the master) can initiate transactions (called ‘queries’). The other devices (the slaves) supply the requested data to the master as a response or take the action requested in the query. The master can address individual slaves or can initiate broadcast messages to all slaves. Slaves return queries that are addressed to them individually. Responses are not returned to broadcast queries from the master. The three most common Modbus versions are MODBUS ASCII, MODBUS RTU, and MODBUS/TCP.

• MODBUS ASCII/RTU: It is a master-slave communication protocol that supports up to 247 slaves connected in a bus or a star network. The protocol uses a simplex connection on a single line. In this way, the communication messages move on a single line in two opposite directions.
• MODBUS TCP/IP: This Modbus variant uses an “Intranet” or “Internet” environment for communications using the TCP/IP protocol on a fixed port 502. Modbus TCP/IP does not require a checksum calculation, as lower layers provide checksum protection.

Figure 4: Ethernet, ControlNet, Fieldbus, and DeviceNet

Powerlink: This is a real-time open protocol managed by Ethernet POWERLINK Standardisation Group (EPSG). It uses both mixed polling and time slice mechanism for deterministic data transmission. Data that is less critical, like maintenance or configuration of a device, can also be sent in asynchronous mode. A gateway uses this mode to transmit non-Powerlink fieldbus data. The protocol enables integration of different networks-i.e., it is an industrial Ethernet solution designed to give single or users single and integrated means for handling all the communication tasks in today’s automation systems. Hubs and switches are used to limit EPL jitters. It can be applied in process industries as well as machine and plant engineering. Ethernet Powerlink can integrate all the components in the industrial automation systems, viz., PLCs, HMIs, motion control, and safety sensors.

Figure 5: Ethernet powerlink

SERCOS III: The SERCOS or Serial-Real Time Serial Communications System is a Fieldbus specialised for digital motion control. It is a real-time Ethernet communication protocol specifically designed for serial communication between PLCs and Intelligent electronic devices (IEDs) operating at high speeds within a control loop.

SERCOS III, an IEC-compliant third-generation SERCOS, is a Master/slave protocol that operates cyclically using a mechanism in which a single master synchronisation Telegram is used to communicate to slaves, and the slave nodes are given a predetermined time (again synchronised by the master node) during which data can be placed on the bus. All messages for the nodes are packaged into a Master Data Telegram.

Figure 6: SERCOS and EtherCAT

EtherCAT: Ethernet for Control Automation Technology or EtherCAT is an open, high-performance Ethernet-based field bus system. EtherCAT is based on the summation frame method: The EtherCAT master transmits an Ethernet frame containing data for all nodes on the network. That frame passes through all nodes in sequence. When it arrives at the last node on a trunk, the frame is turned back again. The nodes process the information in the frame as it passes in one direction. Each node reads out data addressed to it on the fly and inserts response data back into the frame. To support the bandwidth of 100 Mbit/s, special hardware based upon ASICs or FPGAs is required for fast processing as data passes through. In effect, the topology of an EtherCAT network always constitutes a logical ring. The trunks that branch out can be hooked up to nodes especially designed for such connections. This is executed by adding a two-way junction where the summation frame telegram travels up and back down the branching line.

CC-Link: Control & Communication Link, or CC-Link, is an integrated family of open networks originally developed by Mitsubishi Electric. CC-Link IE is a family of integrated Industrial Ethernet-based networks designed for high-performance deterministic control. It integrates networks from the controller level to field and motion networks over Ethernet for a seamless data transfer without being aware of the hierarchy or boundary of the network. This also extends to the existing non-Ethernet-based CC-Link control networks.

The CC-Link IE controller network is a high-reliability trunk network for large-scale controller-distributed control. It operates over a 1Gbps deterministic network using full duplex optical fiber. It has a ‘floating’ network master to maintain stable operations, automatic cable error detection, and many other features.

INTERBUS has been designed as a fast sensor/actuator bus for transmitting process data in industrial environments and is standardised in the IEC-61158. It presents several peculiarities mainly related to the topology and the protocol, providing fast, cyclic, and time-equidistant process data transmission, diagnostics to minimise downtime, and easy operation and installation. The first important feature refers to the topology. INTERBUS is a ring system, i.e., all devices are actively integrated into a closed transmission path. In a ring, each device amplifies the incoming signal and forwards it, thus providing a better signal quality which, in turn, reduces the noise and enables higher transmission speeds over longer distances. Unlike other ring systems, the data forward and return lines in the INTERBUS system continues to all devices via a single cable. This means that the general physical appearance of the system is an “open” tree structure. A mainline exits the bus master and can form seamless subnetworks up to 16 levels deep. This removes one big limit of ring-based topologies that require the communication line to round back to the starting point to close the ring. With an open tree structure, the bus system can be quickly adapted to changing applications, and it is easy to add new branches to expand the system.

Moreover, the unidirectional communication in the ring makes it well-suited for fiber optic technology. The INTERBUS master/slave system connects up to 512 devices across 16 network levels. The ring is automatically closed by the last device. Countless topologies can be created. Branch terminals create branches, which enable the connection and disconnection of devices.

Foundation Fieldbus: It is an open networking standard that provides an open specification for both the control application and the communication on the bus. Foundation Fieldbus communication protocol is an industry-proven international standard (IEC 61158-2) designed for use in the process industry and complies with the ISA-SP50 recommendation for Fieldbus devices. There are two versions of Foundation Fieldbus: H1 and HSE.

• Foundation Fieldbus H1: Foundation Fieldbus H1 is intended primarily for process control, field-level interface, and device integration. This technology interconnects devices such as transmitters and actuators on a field network at the speed of 31.25 kbit/s.H1 is designed to operate on existing twisted pair instrument cabling with power and signal on the same wire. Fiber optic media is optional. It also supports Intrinsic Safety (IS) applications. Foundation H1 devices comprise a function block application, act as a publisher and subscriber of process variables, transmit alarms and trends, and provide server functionality for host access and management functions. Devices can act as a scheduler and time masters for regulating communication on a Fieldbus segment. They are also used for bus interfaces in process control systems or linking devices. They can control bus communications and many connections to multiple devices and support client and server applications. H1 technology enables field instruments and other devices to execute control functions reducing the load on plant computers and workstations. Since the H1 network is digital, I/O conversion subsystems are eliminated. The Fieldbus Foundation tests and registers the devices to ensure the interoperability of registered instruments from multiple vendors.
• Foundation Fieldbus HSE: Foundation Fieldbus High-Speed Ethernet (HSE) is ideally suited as a control backbone. HSE enables tight integration and a free exchange of information needed for the plant enterprise. It is a superior solution to proprietary, Ethernet-based technologies since it provides end users with interoperable devices from multiple suppliers. It is designed for device, subsystem, and enterprise integration and transfers data at 100 Mbit/s. It supports the complete range of Fieldbus capabilities, including standard function blocks and Device Descriptions (DDs) and application-specific Flexible Function Blocks (FFBs) for advanced process and discrete/hybrid/batch applications. HSE supports complex logic functions, such as those performed by Programmable Logic Controllers (PLCs), or data-intensive process devices, such as analysers and gateways to other networks.

Figure 7: Foundation fieldbus

Conclusion

The use of network communication increases versatility in industrial automation. Such flexibility is essential to satisfying the demands of adapting machines or plants. However, this process requires an informed selection of communication networks from diverse options. It is crucial to apply specific criteria during this selection process, such as ensuring that the chosen products are open, standardised, and suitable. An open network is superior to a proprietary one as the former provides unrestricted freedom to choose automation device suppliers. On the other hand, an internationally standardised network ensures long-term durability and the ability to upgrade as needed. By adhering to these simple criteria, one can make informed choices that empower them to adapt to changing needs whilst maximising their investment.

Farnell has partnered with many different suppliers catering to a wide range of components portfolio supporting the above protocols, such as CAN bus devices,CAN interfaces,input / output modules,sensor cables,motor drives,evaluation boards,network gateways,controllers,HMIs,sensor connectors & components, etc.