Process Controls PROPORTIONAL PLUS RATE CONTROL SYSTEMSPROPORTIONAL PLUS RATE CONTROL SYSTEMSProportional plus rate control is a control mode in which a derivative section isadded to the proportional controller.EO 1.4 DESCRIBE the characteristics of the following types ofautomatic control systems:e. Proportional plus rate controlProportional-DerivativeProportional plus rate describes a control mode in which a derivative section is added to aproportional controller. This derivative section responds to the rate of change of the error signal,not the amplitude; this derivative action responds to the rate of change the instant it starts. Thiscauses the controller output to be initially larger in direct relation with the error signal rate ofchange. The higher the error signal rate of change, the sooner the final control element ispositioned to the desired value. The added derivative action reduces initial overshoot of themeasured variable, and therefore aids in stabilizing the process sooner.This control mode is called proportional plus rate (PD) control because the derivative sectionresponds to the rate of change of the error signal.DefinitionofDerivativeControlA device that produces a derivative signal is called a differentiator. Figure 25 shows the inputversus output relationship of a differentiator.The differentiator provides an output that is directly related to the rate of change of the input anda constant that specifies the function of differentiation. The derivative constant is expressed inunits of seconds and defines the differential controller output.The differentiator acts to transform a changing signal to a constant magnitude signal as shownin Figure 26. As long as the input rate of change is constant, the magnitude of the output isconstant. A new input rate of change would give a new output magnitude.Rev. 0 Page 37 IC-07
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business