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• Feedback loops control discrete, continuous processes
  Arguably, the most basic tool of the control engineering profession is the feedback loop, shown below. It consists of five fundamental elements: This measure-decide-actuate sequence repeats as often as necessary until the desired process condition is achieved. For a continuous process, a feedback loop attempts to maintain a process variable (or manipulated variable) at a desired value known as ... Control Engineering
• Input/output systems
  Today's I/O systems can add intelligence, broader communications, and flexibility across multiple logic platforms, central or distributed. I/O modules, installation, retrofits, and associated labor can account for half of an automation project's total cost. "Designers can now mix-and-match some I/O modules across PLC, DCS, and PC control vendor product lines," explains Connie Chick, business ma... Control Engineering
• Safety PLCs
  When is a PLC a safety PLC? Generally, a safety PLC is a programmable logic controller designed for use in mission-critical or safety-related applications; if a safety PLC fails, it does so without endangering people or processes. Actually, "safety PLC" is a bit of a misnomer. Even if a PLC achieves a specific safety integrity level (SIL) rating, it still can be applied in an unsafe way. Control Engineering