PROPORTIONAL PLUS RATE CONTROL SYSTEMSProcess ControlsFigure 25 Derivative Output for a Constant Rate of Change InputFigure 26 Rate Control OutputDerivative cannot be used alone as a control mode. This is because a steady-state input producesa zero output in a differentiator. If the differentiator were used as a controller, the input signalit would receive is the error signal. As just described, a steady-state error signal corresponds toany number of necessary output signals for the positioning of the final control element.Therefore, derivative action is combined with proportional action in a manner such that theproportional section output serves as the derivative section input.IC-07 Page 38 Rev. 0
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