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Distributed Control Standard Connects Industry Regardless of Bus
Monday, April 30 2007
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In the early days of modern automation, the use of microprocessor technology addressed the need for fast and efficient configuration of control logics through graphical methods that mimic the hardwired relay logics. Over the past 30 years, the automation community has put the emphasis on simplifying and standardizing the method of programming this new breed of controllers. From these efforts came the adoption of the IEC 61131-3 standard that specifies the programming languages for automation.
Fieldbus Proliferation From the very moment that the industry started to use microprocessor-based programmable
logic controllers (PLCs), the need of having these controllers to exchange information, gather data from remote units, and set interlocks between controllers initiated a quest for a comprehensive solution. Early on, the industry focused on finding or establishing communication protocols and methodologies that would be candidates for standardization. The Modicon protocol, or Modbus, was one result of an internationally accepted standard. Derivatives of Modbus such as Modbus RTU or Modbus IP are good examples of partial solutions to meet the demand from automation engineers, but standards haven’t stopped there. Over time, associations and major automation vendors have proposed industrial fieldbus networks that eventually evolved into standards, such as PROFIBUS, DeviceNet, ControlNet, Fieldbus Foundation, CANbus, SERCOS, EtherCAT, Siemens H1, and many others.
Interoperability Realized Despite a proliferation of standards, however, interoperability still lagged among differing standards. Several organizations initiated discussion on how to achieve coherent cooperation among controllers in the same application. Fieldbus Foundation, among others, addressed the format of pertinent information to be shared on the network. Yet, although the mechanism of exchanging information could be defined, the cooperation between devices was not addressed. The International Electrotechnical Commission (IEC) came up with a conceptual view of how to have independent programmable logic controllers cooperate in a cohesive and very efficient manner. By defining the IEC 61499 standard, the IEC addressed the need for a comprehensive and familiar approach to automation controllers’ cooperation. Using function blocks as a visual representation of a control entity, the IEC committee redefined the methodology of creating modern control systems. Today, industrial networking software providers are building network control and monitoring applications that take this visual block approach to defining industrial networks comprising disparate field bus components that traditionally could not communicate.
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