by Perry S. Marshall, John S. Rinaldi
Industrial Automation by John RinaldiBook Description:
This book is a convenient installation, troubleshooting, and reference tool on one of the hottest topics in automation and process control. It will help you understand important Ethernet and TCP/IP terminology and provide important information about the new industrial protocols. You will quickly gain a solid grasp of Ethernet basics, the constraints of the industrial environment, and the specialized requirements of machine control. Practical reference charts and technical tips make this book an ideal quick reference source at your project meetings and on the job. New topics covered in the book include signaling types, Web services, power over Ethernet, and an expanded focus on Ethernet protocols and addressing as well as wireless Ethernet. The last part of the book provides installation, maintenance, troubleshooting, and security tips. After reading this book, you will be able to plan industrial Ethernet installations with realistic expectations, make knowledgeable purchasing decisions, and identify and prevent common causes of failure.
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Below you will find a brief intro to each of the chapters of the book. To get the full version of the book, click the “Buy Now” button above, or at the bottom of each section.
What is Industrial Ethernet?
Industrial Ethernet is the successful application of IEEE 802.3 standards with wiring, connectors, and hardware that meet the electrical noise, vibration, temperature, and durability requirements of factory equipment, and network protocols that provide interoperability and time-critical control of smart devices and machines.
Industrial Ethernet is a specialized, rigorous application of standard “office Ethernet” technology that adds any or all of the following requirements:
- Mission critical: Downtime is much less tolerable in the factory than the office. When an office network goes down, you go get a cup of coffee and check your e-mail later. When a factory goes down, you choke down your last mouthful of coffee, run into the plant, and fix the problem as fast as possible! The effects of downtime are less isolated in a manufacturing facility.
- Harsh environment: Factory equipment is not usually installed in air-conditioned hall closets. It’s more likely to be bolted to a robotic welder or oil rig. Temperature extremes and vibration threaten garden-variety hardware, cables, and connectors. Device selection, installation, and proper wiring practices are crucial.
A Brief Tutorial on Digital Communication
Digital communication is the transmission of data between two or more intelligent devices in a mutually agreed upon electronic format (e.g., binary, octal, EBSIDIC, and ASCII). The following components are necessary to accomplish this:
- Data source
- Communications channel
- Data destination
The fundamentals of communication are the same, regardless of the technology. Confusion about any aspect can usually be helped with direct analogies to more familiar modes of communication such as multiple people engaged in a conversation around the dinner table, telephones, CB radios, or Morse code.
Ethernet Hardware Basics
The many formats of Ethernet cabling are described with rather unfriendly shorthand terminology. IEEE’s Ethernet naming convention works like this:
- The first number (10, 100, 1000) indicates the transmission speed in megabits per second.
- The second term indicates transmission type: BASE = baseband; BROAD = broadband.
- The last number indicates segment length. A 5 means a 500-m segment length from original Thicknet.
Note: You might assume that the 2 in 10BASE2 indicates a 200-m segment length, but don’t be too literal. Actually 10BASE2 supports 185 m, or 300 m running point-to-point without repeaters.
- In the newer standards, the IEEE used letters rather than numbers. The T in 10BASE-T means Unshielded Twisted-Pair cables. The T4 in 100BASE-T4 indicates four pairs of Unshielded Twisted-Pair cables.
10BASE5: Thick Ethernet (Thicknet)
10BASE5 is the original 802.3 Ethernet. 10BASE5 uses thick yellow coaxial cable with a 10-mm diameter. The cable is terminated with a 50-ohm 1-W resistor. One hundred stations maximum per segment are allowed.
10BASE5 uses trunk/drop topology. Stations are connected with a single coaxial cable. The maximum length of one segment is 500 m, limited by the quality of the cable itself.
A network interface card (NIC) is attached with a 15-pin D-shell connector to a short Attachment Unit Interface (AUI) cable, which in turn connects to a Media Attachment Unit (MAU) [AU: Should this say “Media Access Unit”? The term “Media Access Unit” was used in the 10BASE-T section] and links to the coaxial cable by means of a “vampire connector,” which pierces the cable. The MAU contains the actual transceiver that connects to the coaxial cable.
For proper CSMA/CD operation, the network diameter for 10BASE5 is limited to 2500 m, consisting of five 500-m segments with four repeaters.
Ethernet Protocol & Addressing
A Little Bit of History
Did you know that the networking cable connecting your computer to the Internet dates back to 1970? In was way back in 1970 that a Harvard graduate student named Robert Metcalfe read a paper about something called Aloha Net. Aloha Net was a radio system used in the Hawaiian Islands to send small messages, also called data packets, between islands. A key feature of this network was that anyone could send messages at any time. If no acknowledgement was received, the message was not delivered and would be resent.
Dr. Metcalfe reasoned that with some mathematical enhancements to the system, the efficiency of the Aloha Net network which then hovered at between 15% and 20% could be vastly increased. Not only did the efficiency increase, all the way up to 90%, but the packet communications network he designed became the worldwide standard we know today as Ethernet. Now known as IEEE Standard 802.3, it still retains today the elegance and simplicity of the original Aloha Net.
Dr. Metcalfe later went on to found 3COM Corporation, one of the leading manufacturers of Ethernet adapter cards and a major communications company. His discovery spawned billions of dollars of in global wealth. Today Ethernet continues to gain momentum with more than half of the worlds computers linked to an Ethernet network.
Basic Ethernet Building Blocks
Even a single Ethernet network can be quite extensive, with up to 1024 nodes, hundreds of cables, and infinite possible combinations of hubs, switches, bridges, routers, network interface cards, and servers. This chapter describes these devices and their functions.
To understand the devices in this section the concept of a collision domain must be understood. Whenever two or more devices on an Ethernet segment begin transmitting at the same instant, there is a collision and neither message is transmitted. More and more collisions occur as the number of devices on a single segment increase until none of the messages can be delivered. Limiting the number of devices on a segment – the number of devices in a collision domain – solves this problem.
Hubs are the simplest method of redistributing data on Ethernet. Hubs are “dumb,” meaning that they do not interpret or sort messages that pass through them. A hub can be as simple as an electrical buffer with simple noise filtering; it isolates the impedances of multiple “spokes” in a star topology. Some hubs also have limited “store and forward” capability. In any case, hubs indiscriminately transmit data to all other devices connected to the hub. All of those devices are still on the same collision domain.
Note: Hubs are not assigned MAC addresses or IP addresses.
Network Health, Monitoring, & System Maintenance
By Mark Mullins
Reprinted with permission from the Industrial Ethernet Book, www.ethernet.industrial-networking.com ©2001 GGH Marketing Communications.
What is it that makes a network run well? Fluke Networks has profiled dozens of networks worldwide in an effort to determine the answer. In our research, the best run-networks had thirty-five times less downtime, resulting in annual savings of over $227,000. Not surprisingly, users of these networks were the most satisfied of all groups studied. One surprising conclusion is that the number of support staff per end-user of these well-run networks was actually lower than that of the poorly-performing networks.
So how does a network support group enter this desirable group? In studying this question, Fluke Networks uncovered seven “best practices” of well-run networks. They are:
- Management Involvement
- Preparation & Planning
- Problem Prevention
- Early Problem Detection
- Quick Problem Isolation and Resolution
- Invest in Tools and Training
- Quality Improvement Approach
Having the right tools for monitoring, documenting, and troubleshooting your network helps with nearly all of these areas. Let’s look at each of these three functions and discuss the tools for each.
Installation, Troubleshooting, and Maintenance Tips
The shield conductor of each coaxial cable must be grounded at one point only; otherwise you will create ground loops. On coax, this is often done at the location of a terminator. Many terminators provide screw terminals for this purpose. You should check for exposed wire at other locations since it could make contact with other conductors or ground points.
Ethernet Grounding Rules for Coaxial Cable
- 10BASE-5 (Thick Ethernet): Grounding is a requirement.
- 10BASE-2 (Thin Ethernet): You can ground if your local electrical code requires it.
Grounding coaxial cable is generally good; it dissipates static electricity and makes your network safer. Many local electrical codes require network cables to be grounded at some point.
Many Ethernet segments are not grounded though, and grounding can add complications to an otherwise working network. But always follow the electrical codes. A segment should be grounded only at one end of the coaxial segment.
Do Not Use Copper Cables to Link Buildings!
The ground potential between the two buildings may be different. This can introduce transient voltages and any number of dangerous problems.
Use fiber to connect buildings instead.
Ethernet Industrial Protocols, Fieldbuses, and Lagacy Networks
As Ethernet becomes established as a major component in automation systems, it takes its place among a collection of fieldbuses and legacy networks. An in-depth investigation of all networks shows that every attribute with respect to topology, message contention, speed, and cost represents unavoidable compromises.
From a purely technical standpoint, Ethernet is not necessarily more ideal for automation applications than other networks. Even if it were, the nature of capital equipment is still such that no one is going to rip out existing equipment and wiring just because something better exists.
Reality is that (1) Ethernet must work with other network technologies, and the real world requires integration with existing networks; (2) for some applications, other networks will deliver higher performance at a lower cost.
Basic Precautions for Network Security
The subject of protecting your data from hackers and viruses, corporate espionage, and cyber-terrorism with firewalls, security keys, passwords, and their associated organizational procedures easily occupies an entire book rack at a technical bookstore. A quick search on “network security” at www.amazon.com turned up 203 books. No book called Industrial Ethernet Made Simple can possibly do justice to this subject. The best we can do is highlight some key concerns that you should think about. From there, you can research firewalls, encryption schemes, and Virtual Private Networks to your heart’s content.
The first thing to remember is this: The most probable cause of problems is not the environmental extremist who sees your smokestack on his way to work and decides to launch a virtual terrorist attack on your factory. It’s more likely to be related to the ubiquity of PCs with Ethernet cards, the ease with which your own employees can “hang stuff on the network,” and careless or nonexistent internal security measures. Accidental problems are more common than deliberate ones. But you should be prepared for both.
The following guidelines will help you guard against the most common problems:
- Never mix your office LAN with your industrial-control LAN. They should be separated by a firewall, or at minimum, a bridge or router. That firewall also serves as a convenient boundary between the loyal, dedicated, competent automation engineer, and the egotistical control freak from the IT department whose mission in life is to discredit the engineering department and take over the planet. A control network and a business LAN have two entirely different purposes and their interaction should be closely controlled.
- Industrial Ethernet needs to be viewed in at least two categories: a control-level industrial Ethernet and an I/O-level industrial Ethernet. This means each manufacturing cell will have its own Ethernet network, possibly more than one. Ideally those networks will be isolated as well.
Power over Ethernet (PoE)
Power over Ethernet technology allows Ethernet devices to receive power and data over their existing LAN cabling without modifications to any of the existing Ethernet infrastructure. PoE radically reduces installation costs by eliminating the conduit, power wires and installation labor required to install an Ethernet device.
What is PoE?
Everyone who has ever used a standard phone line is familiar with a network powered device. Simply plug the phone into the jack and you have a network connection. Power over Ethernet, IEEE standard 802.3af, performs the same function for Ethernet devices. In fact Power over Ethernet will really enable the widespread use of IP telephones.
PoE brings the ability to connect and power devices like barcode readers, RF ID Systems, wireless access points and web-based security cameras. PoE enables a whole new generation of networked devices. Because there is no need for the device to be anywhere near a wall socket, we can expect a plethora of innovative applications, from vending and gaming machines to building access systems and retail point-of-sale systems.
Public wireless LANs are showing up everywhere. You can now find web access in Starbucks, McDonalds, in airports, convention centers and hotels. Thousands of companies are placing wireless systems in warehouses, retail stores, conference rooms and, in some cases, throughout their facilities. The radio waves that transmit data in these applications make this technology different than wired Ethernet networks. Though the contents of the base Ethernet packet is the same as a wired packet, the terms, technology, procedures and practices for operating a wireless Ethernet system are very different.
11.1 A “Very” Short Technology Primer
IEEE standard 802.11 defines the wireless communication method used in today’s wireless enterprise networks. Unfortunately there is an alphabet soup of standards within this specification for us to sort through. Before 802.11 Part a – 802.11a for short – was developed a version with less throughput, 802.11b, was adopted by some companies. After those standards, there was 802.15.1, also known as Bluetooth, the security standard 802.11i and others like 802.11g. Fortunately, most of this headache really belongs to the wireless equipment manufacturers. All we need to understand is the basic differences between the two standards most commonly used today, 802.11a and 802.11b. These two standards are summarized in Table 11-1.