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Expanding Allen-Bradley PLC Systems With Intelligent Remote I/O
Allen-Bradley ControlLogix, CompactLogix, and similar control systems have become a corporate standard for many companies. As a control engineer, you are familiar with these systems and their architecture. You appreciate their strengths and understand how to best utilize them. And you're well aware that every expansion of the PLC system, whether into new physical space or into new functionality, by necessity puts a strain on system performance.
This PLC expansion dilemma you face with each system change is more and more frequently tied to new demands on automation functionality. Today's more sophisticated automation applications often require more than the traditional scan inputs-solve logic-write to outputs approach. Incorporating connections to third-party devices, such as RFID and barcode readers, and involving more complex logic such as PID (proportional-integral-derivative) control loops, these applications place heavy, nontraditional demands on PLCs.
Of course any expansion of a PLC system means the addition of I/O for new sensors and actuators. The PLC must scan the new I/O and run logic for it, which impacts processing power. But in comparison to existing I/O, the new sensors and actuators may demand proportionally more processing power because they are simply a different type of I/O.
Analog is a good example. Applications using many analog inputs and outputs require temperature conversion, thermocouple linearization, analog scaling and Engineering Unit conversion. All these new functional demands place nontraditional burdens on the central controller.
As functional demands for industrial automation systems increase even while budgets shrink, you may be wondering if there are other ways to achieve system expansion.
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