6. Function blocks6.1 Manufacturer function blocks6.1.4 Open-loop and closed-loop function blocks6.1.4.1 DC - PID controllerGeneraleasyE4 The base devices provide 32 PID controller function blocksDC01...DC32.Operating principleA closed-loop control circuit with a PID controller consists of the following com-ponents:l Setpoint (reference variable),l Actual value (controlled variable),l System deviation = (setpoint–actual value),l PID controller,l Control system (e.g. PTn system),l Disturbance variables.The PID controller operates on the basis of the equation of the PID algorithm. Accordingto this, the manipulated variable Y(t) is the result of the calculation of the proportionalcomponent, an integral component and a differential component.PID controller equation:Y(t) = YP(t) + YI(t) + YD(t)Y(t)= calculated manipulated variable with scan time tYP(t)= Value of the proportional component of the manip-ulated variable with scan time tYI(t) = Value of the integral component of the manipulatedvariable with scan time tYD(t)= Value of the differential component of the manip-ulated variable with scan time tProportional componentThe proportional component YP is the product of the gain (Kp) and the control difference(e). The control difference is the difference between the setpoint (Xs) and the actualvalue (Xi) at a specified scan time. The equation used by the device for the proportionalcomponent is as follows:272 easyE4 11/18 MN050009 EN www.eaton.com
