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

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