zn open loop method - TechTeach

Article:Ziegler-Nichols open -Loop MethodFinn HaugenTechTeach17. July 20101 IntroductionZiegler and Nichols published in 1942 a paper [1] where they described twomethods for tuning the parameters of P-, PI- and PID controllers. Thesetwo methods are theZiegler-Nichols closed loop method1, and theZiegler-Nichols open loop method2. The present article describes theopen-loop method , while the closed-loop method is described in anotherarticle (available at ).Ziegler and Nichols [1] used the following definition of acceptable stabilityas a basis for their contoller tuning rules: The ratio of the amplitudes ofsubsequent peaks in the same direction (due to a step change of thedisturbance or a step change of the setpoint in the control loop) isapproximately 1/4, see Figure 1:A2A1=14(1)However, there is no guaranty that the actual amplitude ratio of a givencontrol system becomes 1/4 after tuning with one of the

K p T i T d Pcontroller 1 LR/U ∞ 0 PIcontroller 0.9 LR/U 3.3L 0 PIDcontroller 1.2 LR/U 2L 0.5L=Ti 4 Table1: Ziegler-Nichols’ open loop method: Formulas for the ...

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