by Chris Vitale, Senior Product Manager, Networks, TURCK
Connectivity is turning into the foundation for enterprise efficiency and productivity, as the demand for constant communication grows. Advanced protocol capabilities can help manufacturers achieve fast, secure and reliable data transfer, factory wide.
Manufacturers are faced with the constant demand to increase productivity and reduce operating costs. A powerful industrial tool available today to streamline production is reliable, enterprise-wide connectivity with its ability to deliver high levels of visibility, control, and flexibility. To accommodate evolving networking requirements—such as decentralization of control, integrated diagnostics and simplified maintenance—network protocols integrate with industrial equipment and control systems to communicate crucial status updates and production data.
With the migration away from point-to-point connection, networking architecture such as end to-end ensures connectivity, collaboration and integration from the device level to enterprise business systems. By examining the performance capabilities and application suitability of Ethernet, DeviceNet, and PROFIBUS, manufacturers can select the right network for their application needs for continuous, complete control over all production components.
Proactively enhancing networking capabilities provides advantages ranging from: Complete process efficiency and remote access to system controls, faster response times to factor floor events, and reduced downtime, to name a few. By maximizing production control, enterprise connectivity can improve product quality, customer satisfaction, and company profitability.
Ethernet was developed with the primary purpose of conveying large amounts of information. It was originally relegated to office level networks, where multiple clients use the network to share information. Ethernet has expanded beyond traditional usage, and with the advent of EtherNet/IP, it has moved onto the plant floor. Ethernet is a solid solution for data collection, transmission and monitoring.
With EtherNet/IP, the exchange of data is based on the producer/consumer model. A transmitting device produces data on the network and multiple receiving devices consume this data simultaneously. Traffic generated during this data exchange can include input/output data and status updates produced by a remote device for consumption by one or more programmable controllers. Data collected and controlled through EtherNet/IP can use an unacknowledged method of sending information between devices on a network, which means that data delivery is not guaranteed. Therefore, to ensure delivery, a higher layer must be implemented prior to data transfer.
For enhanced industrial communication, Transmission Control Protocol/Internet Protocol (TCP/IP) provides a set of services so devices may communicate over an Ethernet network. With the increased prevalence of the Internet and intranets for internal information distribution, TCP/IP has grown, and has been transported to all major computer operating systems. A typical example of when a manufacturer would implement an Ethernet TCP/IP network would be to extend communication plant-wide to connect to a corporation’s worldwide network through the Internet. Ethernet TCP/IP can take advantage of Ethernet’s high capacity for data management to perform a variety of tasks, without requiring a high level of determinism or repeatability for message response time. Common TCP/IP applications include program maintenance, data transfer, web page retrieval, supervisory control, connectivity for operator interfaces and events and alarm recording.
DeviceNet is a low-cost communication protocol that connects and serves as a communication network between industrial controllers and I/O devices, with each device serving as a node on the network. The protocol is used for connecting and networking a variety of industrial devices, including limit switches, sensors, valve manifolds, motor starters, process sensors, bar code readers, variable frequency drives, panel displays and operator interfaces. DeviceNet is based on the Controller Area Network (CAN) broadcast-oriented communication architecture, which ensures that the highest priority messages always have access to the bus in the event of a data collision. With DeviceNet, these priorities are further defined, giving top priority to I/O messages and lower priority to configuration messages.
Capable of operating on both a client/server and a master/slave basis, DeviceNet accommodates diverse communication needs. With client/server, the network provides a convenient way to interconnect programs that are distributed efficiently across different locations. It also allows peer-to-peer data exchange, where a node can initiate communication with other nodes or peers. Through master/slave operation, the master node initiates all communication with all other nodes responding to the master’s request. DeviceNet is suited for collecting and managing I/O data that machine and process control systems rely on.
Supporting up to 64 nodes, DeviceNet networks offer nearly unlimited amounts of I/O. The bus uses a trunkline-dropline topology, which allows bus power and communication to be supplied on a single cable. This protocol is compatible with a range of industrial manufacturing products, enabling it to connect to nearly any device and allow stations to be easily added to existing operations. Further, by permitting direct connections to control devices, it eliminates point-to-point wiring, which improves communication between devices, as well as provides critical device-level diagnostics not easily accessible through point-to-point I/O interfaces.
DeviceNet is connected to programmable logic controllers (PLCs) to obtain and transmit messages to the network through these PLCs and is typically programmed with PCs. These stations are designed to transfer data from industrial devices to the controllers, as well as perform different control functions, such as PID loops, start/stop motors, turn indicators ON and OFF, position valves and more. Plus, for more flexibility, devices connected to DeviceNet stations can also be hot swapped—removed and replaced without affecting other operations connected to the station.
PROFIBUS is an industrial network protocol that connects field I/O devices, eliminating hard wiring. It is designed to increase device-level diagnostic capabilities while maintaining high-speed communication between devices. PROFIBUS-DP, a version of PROFIBUS based on the RS-485 serial data transfer standard, is for use in factory automation and machine control solutions. RS-485 allows multiple devices (up to 32) to communicate on a single pair of wires, at distances up to 1200 meters (4000 feet).
A PROFIBUS-DP network supports up to 126 nodes with almost unlimited I/O, with power and communication provided through separate cables, allowing easy segmentation of the power structure to avoid overloading. Plus, network length and the number of nodes can easily be extended using a variety of repeater products. This capability enables control of manufacturing and other processes over a wide area—such as the factory floor—from a central computer control station.
When selecting a network protocol, speed is a critical factor. This protocol is capable of running data rates as high as 12 Mbaud. However when it is used at high speeds, the cable drop length from the trunk to a node is limited. For example, when manufacturers are using it at 12 Mbaud, nodes must be directly connected to the trunk, with no drop length allowed.
In addition to providing the communication capabilities required for machine control applications, this protocol is also well suited for process applications and hazardous area locations. For communication in challenging industrial environments, PROFIBUS-DP can be directly connected to I/O devices in classified areas, resulting in a significant savings on barriers and wiring. Further, PROFIBUS-PA, another version of PROFIBUS, operates as an extension from the PROFIBUS-DP system that allows network communication directly in hazardous areas.
Benefits of Enterprise Connectivity
As plants expand and information is required to move across greater distances, at faster speeds and in larger quantities, maintaining reliable enterprise connectivity is necessary for continued overall production. Since network protocols connect the office with the plant floor, providing secure, seamless interoperability among manufacturing enterprise networks enables constant Internet and enterprise connectivity. Implementing a complete, end-to-end networking solution provides a range of benefits, including a lower overall Total Cost of Ownership (TCO), a higher return on investment (ROI) due to real-time visibility and flexibility, reduced network maintenance, and decreased labor costs.
Connectorized networks allow for modularity, which traditional wiring methods cannot provide, as an electronic control system cannot be easily modified using conduit and individual wires. In contrast, modular networks can be engineered and modified quickly and easily—significantly reducing both design and manufacturing time.
One immediate advantage to enterprise connectivity is the reduced cost of installation and maintenance. With their plug-and-play simplicity, implementing facility wide networks is accomplished faster than traditional wired connections. The time required to strip the jacket, prepare the conductors, feed the cable through a gland, insert the wires into the terminals and tighten the cable gland can be as much as 5 to 10 minutes per connection. This process can become even more complex and time-consuming when traditional wiring is installed in physically demanding locations. Plus, with the elimination of wiring errors, manufacturers experience greater savings by limiting production downtime and maintenance to ensure continued performance.
Further, one of the most beneficial features of connectorized networks is the minimal repair time, completed in minutes rather than hours, as any section of a network or I/O cable can be replaced in seconds. Fully connectorized networks essentially eliminate signal wire troubleshooting and repair. Providing constant access to real-time data improves plant operations by providing diagnostic information of any problem faster, improving uptime with corrective action capabilities. Additionally, by delivering faster, less costly plant upgrades, expansions and changeouts, connectivity promotes enterprise growth and plant efficiency.
Filed Under: Design World articles, Networks • connectivity • fieldbuses