Intelligent valves like Eaton’s AxisPro proportional valves enable closed-loop control without the need for a separate motion control processor or for the PLC to close position control loops.
Distributed versus centralized control Most industrial machines utilize a PLC controller. Traditional control systems use only a centralized controller with input/output (I/O) modules. With this architecture, one PLC performs all required computing tasks for the entire machine. Take the example of a cylinder that needs to be repositioned. In a centralized control system, the PLC sends a spool position command to the valve, which in turn positions the spool to allow fluid to
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move to the cylinder. The PLC monitors the cylinder position and slowly commands the spool position back to neutral as the cylinder approaches the desired position. With this approach, the PLC needs a digitalto-analog converter to command the valve, and it needs the electronics necessary to read the cylinder position sensor. The PLC programmer has to design www.designworldonline.com  
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