PROPORTIONAL PLUS RATE CONTROL SYSTEMSProcess ControlsExampleofProportionalPlusRateControlTo illustrate proportional plus rate control, we will use the same heat exchanger process that hasbeen analyzed in previous chapters (see Figure 28). For this example, however, the temperaturecontroller used is a proportional plus rate controller.As illustrated in Figure 29, the proportional only control mode responds to the decrease inFigure 28 Heat Exchanger Processdemand, but because of the inherent characteristics of proportional control, a residual offset errorremains. Adding the derivative action affects the response by allowing only one small overshootand a rapid stabilization to the new control point. Thus, derivative action provides increasedstability to the system, but does not eliminate offset error.IC-07 Page 40 Rev. 0
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