The use of fiber optics in local area networks (LANs), such as Ethernet, has increased due to the inherent advantages of using fiber. High data rates can be maintained without electromagnetic or radio frequency interference (EMI/RFI). Longer distances can be achieved over that of copper wiring. For the industrial/commercial user, fiber offers high-voltage isolation, intrinsic safety and elimination of ground loops in geographically large installations. Ethernet will function with no difficulty over fiber optics as long as some simple rules are followed.
When cascading switches, a reduction in performance can occur if the backbone connection is not properly designed. This lesson addresses the concerns involved when cascading switches.
To protect against a network failure while using Industrial Ethernet, users are seeking cabling topologies that remain functional under a single cable loss. There are four popular redundancy schemes for Ethernet: Link Aggregation (Trunking), Proprietary Ring, Spanning Tree Protocol (STP), and Rapid Spanning Tree Protocol (RSTP). Each of these approaches has a set of benefits and tradeoffs, however, the industry seems to focus only on one aspect of redundancy and that is performance. How quickly does the network repair itself? This recovery time depends upon the industrial protocols being used. Protocols such as Modbus/TCP and EtherNet/IP™ rely upon the TCP/IP suite of transport-layer protocols, and they play a major role in how a network recovers from a single cable fault. A test was conducted using the various redundancy schemes to determine typical recovery times and the results were tabulated.
Real-time electronic distributed control systems are an important development of the technological evolution. Electronics are employed to control and monitor the most safety-critical applications from flight decks to hospital operating rooms. As these real-time systems become increasingly prevalent and advanced, so does the demand to physically distribute the control in strict real-time. Thus there is a need for control network protocols that can support the application's stringent real-time requirements. Real-time networks must provide a guarantee of service so that they will consistently operate deterministically and correctly.
This module introduces some of the real-time solutions available to industry today: EtherNet/IP, PROFInet, EtherCAT and ETHERNET Powerlink. This module also provides an introduction to a single standard, IEEE 1588, that is growing in popularity amongst real-time Ethernet developers to provide sub-microsecond synchronization accuracy of distributed clocks over Ethernet.
Selecting the proper Industrial Ethernet switch can be a confusing task. There are many options to consider such as auto-negotiation features, managed versus unmanaged, redundancy, environmental concerns, future-proofing, determinism issues and many more.
Industrial Ethernet, as a fieldbus replacement technology, lacks two attributes found in fieldbuses. The first is bus topology. The second is power sourced from the network cable to energize field devices. DeviceNet is a good example of a fieldbus that can accomplish both. DeviceNet can be wired in a bus topology while providing 24-volt power in the cable for powering field devices such as photo-eyes, push-button stations, and limit switches. Higher-powered actuators usually have their own power sources. Industrial Ethernet only supports star topology and, until now, could not provide power over the cable without implementing a non-standard approach. With the approval of IEEE 802.3af in 2003, the power-sourcing problem has been solved with the Power Over Ethernet (PoE) standard. PoE not only provides a safe and effective way of applying power to modern devices, but also utilizes its star topology to its advantage by controlling the amount of power each connected device receives while protecting non-powered devices from harm. DeviceNet is incapable of doing the same with its bus topology.
A local area network (LAN) is a private network usually confined to one plant. Virtual LANs (VLANs) allow a single physical LAN to be partitioned into several smaller logical LANs. VLANs limit the broacast domain, improve security and performance and are ideal for separating industrial automation systems from information technology systems.
In an industrial automation application that relies heavily on the health of the Ethernet network that attaches all the controllers and computers together, a concern exists about what would happen if the network fails. If the result is loss of production or loss of a processed batch or the endangerment of people or equipment, redundancy schemes are examined. Since cable failure is the most likely mishap, cable redundancy is suggested by configuring the network in either a ring or by carrying parallel branches. If one of the segments is lost, then communication will continue down a parallel path or around the unbroken portion of the ring. The problem with these approaches is that Ethernet supports neither of these topologies without special equipment. However, this issue is addressed in an IEEE standard numbered 802.1D that covers bridges, and in this standard the concept of the Spanning Tree Protocol (STP) is introduced.
Media converters are devices that allow for interconnecting two different cabling technologies. With Ethernet there are three types of cables — coaxial, twisted-pair and fiber optic. With modern Ethernet systems, the most common need is to connect a twisted-pair (copper) segment together with a fiber optic segment and there are media converters available to do the job. Fiber optics offer greater distances, galvanic isolation, and immunity to high levels of electromagnetic interference and lightning strikes. Product selection would seem to be easy — just make sure that connectors are compatible and select the lowest price. However, not all media converters operate the same and supplying a media converter requires some planning since an improperly installed media converter will degrade a system or simply will not function. This document reviews the issues of applying media converters to an Ethernet system.
The power for Industrial Ethernet devices is ultimately derived from mains power which can be as high as 480 V. Typically, there is a transformer or distribution system that provides mains voltages in the range of 100–240 VAC at 50–60 Hertz. This is still much too high to power the 3.3–5 VDC electronics used within the devices. What will be discussed are techniques to power these low-voltage devices.
Modern control networks such as EtherNet/IP™, Modbus/TCP and BACnet/IP® use Ethernet for communications due to its high speed, lowering cost and in some instances, the necessity to operate over structured wiring. Although the study of Ethernet does not require an understanding of application protocols, knowledge of application protocols has become increasingly important as modern networks are deployed. The latest protocols are all based upon Object Modeling which can be quite confusing to someone who has not been exposed to this abstract concept. This module introduces object modeling, object properties, and services as they pertain to a physical BACnet/IP device. Although the majority of BACnet devices support the master-slave/token-passing (MS/TP) network, newer devices now function over Ethernet.
Object Modeling a Physical BACnet Device introduced object modeling, object properties, and services as they pertain to a physical BACnet/IP device. Achieving BACnet Compliance continues the discussion by addressing the requirements for achieving BACnet compliance.