Deploying Industrial Networks--A Primer

Protocols and system implementations developed within the limitations of products and technology available at the time. As technologies developed, products and equipment were developed to take advantage of the advances. Ethernet products have now been developed allowing connections over coaxial cabling, twisted pair wiring, fiber optic cables, and even wireless networking.

With relentless advances in Ethernet technology, nearly all Local Area Networks (LAN) installations being used for computer networking today use Ethernet as the fundamental base technology. As technology advances continue, Ethernet is being deployed in even more application areas; examples are Carrier Ethernet, Metro Ethernet, Ethernet in the First Mile (EFM), and Fiber to the Home (FTTH).

In much the same way, early industrial networks, that met the immediate needs of the machine control networks, were implemented using existing technologies. By using RS232, RS422, RS485 and other low speed serial connections, equipment was connected for control, configuration, monitoring, and other data exchange. Terminals were often tied directly to the equipment itself for machine control, setup or monitoring. As processes and equipment became more and more complex, the interaction and more importantly the information exchanged, increased and became more critical. Due to the need for manufacturers to have competitive production lines, automation is now critical to any industrial installation. Add to this the requirements of quality, safety, security, process and cost monitoring, and you soon have an abundance of critical inter-related issues.

In deploying any Industrial Network a great deal of planning is needed to determine the proper topology. Not only for the needs of the installation as it is, but also for how the installation will evolve as the products and business mature. Since most systems represent a significant investment, both in equipment costs, and installation costs, it is fortunate that lifecycles are often measured in years or decades. This is also the reason that many existing installations are now looking to upgrade. Many existing installations use older methods for machine or process control, with slow or inaccurate exchange of process parameters, and complex configuration of equipment, and even mechanical timing of equipment interaction. These installation upgrades, as well new ones, are looking for an "Industrial Strength" network. One that will provide fast, flexible configuration of equipment to meet the needs of today's and tomorrow's processes, while keeping up with the demands for speed, accuracy, safety and resiliency.

While no one method is perfect for all cases, there are some underlying similarities; data needs to be shared between specific locations (equipment and/or users), data needs to be accurate, communication is bidirectional, the installation's setup and maintenance needs to be efficient, with minimal down time, and the total cost (equipment and personnel) cannot be prohibitive.

During the evolution of Industrial networks, many initial proprietary technologies, with characteristics meeting the needs of the targeted application, were developed. This causes confusion in the market as to which is the best industrial network solution. Customers decided on solutions that met the present needs of their system integration, and were within their budgetary constraints. Now, a generation later, manufacturers have a myriad of networks with compatibility issues, prone to down-time and difficult to maintain and repair.

In an effort to create order out of the chaos, organizations have formed to develop standards for industrial interfaces and technologies, often referred to as field busses. The major benefit of this standardization is interoperability between multiple vendors' equipment, with minimal installation configuration tweaking. Still these organizations have developed numerous standards that are more suited to certain applications than others. Some of the more widely used field bus standards are:

• AS-Interface
• CAN
• DeviceNET
• EtherCAT
• FOUNDATION Fieldbus
• HART Protocol
• Industrial Ethernet
• Interbus
• LonWorks
• Modbus
• PROFIBUS/ProfiNet
• BITBUS
• CompuBus

The discussion of which field bus standard is best for industrial networks will never be resolved. Beyond the discussion of which field bus is best suited for an application, the particular configuration may also be unique to an installation. This is due to the dependence on a variety of factors deciding which topology is best suited for a particular installation. In one case it may be a star configuration for another it may be a redundant ring. The decision criteria weighting is based on many factors, including the communication profile characteristics, installation size, environment, equipment, safety, and cost.

Although there are variants and combinations, there are 4 basic topologies:

• Bus
• Daisy-chain
• Ring
• Star

Page 2: next page
Page 1 | 2 | 3