Siemens Module B3 manual General, Tu-TgApproximation, T g Approximation

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Automation and Drives - SCE

5. SETTING CONTROLLED SYSTEMS

5.1 General

Below, setting controlled systems is discussed, using a PT2 system as an example.

Tu-TgApproximation

The basis for the methods according to Ziegler-Nichols and according to Chien, Hrones and Reswick is the Tu-Tgapproximation. With it, the parameters following parameters transfer coefficient of the system KS, delay Tu und transition time Tg can be determined from the system step response. The rules for controller adjustment that are described below were found experimentally, by using analog computer simulations.

P-TNsystems can be described with sufficient accuracy with a so-called Tu-Tgapproximation; that means, through approximation by means of a P-T1-TLsystem.

Starting point is the system step response with the input step height K. The necessary parameters: transfer coefficient of the system KS, delay Tu and transition time Tg are ascertained as shown in the figure below.

This requires measuring the transition function up to the stationary upper range value (K*Ks), so that the transfer coefficient for system KS, required for the calculation, can be determined.

The essential advantage of these methods is that the approximation can also be used if the system can not be described analytically.

x / %
K*KS
		Turning Point
		Wendepunkt
	Tu	Tg	t/sec
Figure:	Tu-TgApproximation

	Preface Fundamentals	Discontinuous Action Controller Controller Block (S)FB41	Setting the System Appendix

	T I A Training Document	Page 54 of 64	Module
			B3
Issued: 02/2008			Control Engineering with STEP 7

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Contents Module B3 Automation and Drives SCE Table of Contents Automation and Drives SCE Learning Objective To 3 days Module C To 3 days Module DFrequency Converter at Simatic S7 PrerequisitesHardware and software required PLCFundamentals of Control Engineering Tasks of Control EngineeringComponents of a Control Loop Controlled VariableFeedback Variable r Comparing Element Disturbance Variable zSetpoint Value w Controlling ElementActuator Controlled SystemDead Time Characteristics For Step Function for Examining Controlled SystemsAutomation and Drives SCE Proportional Controlled System with a Time Delay Time constantProportional Controlled System with Two Time Delays Tu Delay time Tg Transition timeControllability of P-Tn systems Proportional Controlled System with n Time Delays Controlled Systems without Inherent Regulation Types of Controllers Two Position Controllers Switch-On Value Manipulated Variable Time HysteresisThree Position Controllers Basic Types of Continuous Controllers Proportional Controllers P-Controller Automation and Drives SCE With Integral Action Controllers I- ControllerPI Controllers Controller LayoutDerivative Action Controllers D-Controller PID ControllersObjectives for Controller Adjustment 450.85 Digital Controllers DAC Preface Fundamentals Structogram YESAssignment List Symbol Address Comment ExercisePossible Solution for the PLC Program NetworkD24/AIFillSetpNorm/Norm.value for level setpoint Network 10 Title Task Definition for PID Standard Controller Function Diagram of the control system with a PID controller FB 41 Contc UseDescription Exercise Example Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE SP INT PLC’ Automation and Drives SCE Automation and Drives SCE Automation and Drives SCE General Tu-TgApproximationT g Approximation Setting the PI-Controller according to Ziegler-Nichols For setpoint characteristic MAN Solution of the PLC program Setting the PI controller according to Ziegler-Nichols SetpointDiagram of the controller block AppendixInput Parameters Data Value Range Default Description Type Comrst Bool FalseParameter Data Type Value Range Default Lmnhlm Real Lmnllm Parameter Data Value Range Default Description Type Output Parameters