Ethernet: The Worldwide Defacto Standard for Business and PC Networking Origin: Digital Equipment Corporation, Intel and Xerox, 1976 Implemented on Multitudes of chips produced by many vendors. Based on IEEE 802.3 Formats: 10 Base 2, 10 Base T and 100 Base T, 100 Base FX, 1 Gigabit; Copper (Twisted Pair / Thin Coax) and Fiber Connectors: RJ45 or Coaxial Maximum Number of Nodes: 1024, Expandable with Routers Distance: 100M (10 Base T) to 50 KM (Mono mode, Fiber with Switches) Baudrate: 10M to 100M Bit/sec Message size: 46 to 1500 bytes Messaging format: Peer-to-Peer Supporting Trade Organization: Industrial Ethernet Association (www.IndustrialEthernet.com) and IAONA (www.iaona.com). Typical Applications: Nearly universal in office / business Local Area Networks. Widely used also in PC to PC, PLC to PLC and supervisory control applications. Gradually working its way toward the “sensor level” in plant floor applications. Advantages: Ethernet is the most widely accepted international networking standard. Nearly universal worldwide. Ethernet can handle large amounts of data at high speed and serve the needs of large installations. Disadvantages: High overhead to message ratio for small amounts of data; No power on the bus; Physically vulnerable connectors and greater susceptibility to EMI/RFI than most fieldbuses; Confusion based on multiple open and proprietary standards for process data. Ethernet: Universal, Reliable and Inexpensive The networking of millions of PC’s in offices and the proliferation of the Internet across the world has made Ethernet a universal networking standard. Ethernet hardware and related software has evolved to the point where even inexperienced users can build simple networks and connect computers together. Ethernet hardware is “dirt cheap” and can be purchased in office supply stores, computer stores and e-commerce sites everywhere. In contrast to the perception that the popular fieldbuses are expensive, difficult to use, and that there are too many of them vying for market dominance, Ethernet appears to be a panacea. Furthermore, a study by a Big Three automotive manufacturer showed that Ethernet could potentially serve up to 70% of plant floor networking applications. The Challenges of Moving Ethernet to the Plant Floor Reality may be somewhat different, however – at least right now. There are at least three major issues, which must be addressed satisfactorily for Ethernet to become a viable, popular, plant-floor Fieldbus: 1. A common “Application Layer” must be established. When your device receives a packet of data, what format is that data in? Is it a string of I/O values, a text document or a spreadsheet? Is it a series of parameters for a Variable Frequency Drive? How is that data arranged? There are several competing standards. More about this below. 2. Industrial grade connectors will be necessary for many applications. Cheap plastic “Telephone Connectors” don’t cut it on the plant floor, and the RJ45 connectors aren’t up to the task. An industrial strength connector will be a great benefit. 3. Many users desire 24 Volt power on the Bus. This is advantageous from a practical standpoint – it reduces wiring and power supply problems -- but it adds cost and introduces noise and other technical problems. 4. Some applications require determinism. Ethernet as it is typically used is not deterministic or repeatable; in other words, throughput rates are not guaranteed. However, methods exist for architecting deterministic Ethernet systems. Note that, in reality, most people who think they need determinism really just need speed. Ethernet Doesn’t Guarantee Interoperability Ethernet is just a physical layer standard, in much the same way an RS232, or for that matter, a telephone line, is. Having a physical connection means that messages can be transmitted, but it does not assure successful commun