A Method for Estimating Process Dynamic Characteristics by Means of Undamped Cycling

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  • プロセスの動特性を限界振動から求める方法について
  • プロセス ノ ドウトクセイ オ ゲンカイ シンドウ カラ モトメル ホウホウ ニ ツイテ

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Abstract

There are several methods for estimating process dynamic characteristics by means of various responses, such as frequency response, indicial response, etc. The undamped cycling method which the author proposes here and which has been used by Ziegler and Nichols, in order to decide the optimum control conditions, can also give dynamic properties of a plant by making use of critical control conditions and its cycling period for the closed cycle system.<BR>Process characteristics may generally be assumed to be expressed by Eq. (1), and the transfer function of a controller, by Eq. (2). If the automatic control system is cycling, Eq. (3) may be suggested.<BR>Various cases supposed for each control condition are as follows:<BR>1) Proportional Action Control, (P)<BR>Eqs. (4) & (5), Fig. 2 and Table 1 are obtained. An approximate equation ωPL=1.7 and Fig. 3 are particularly recommended for practical uses. The optimum control conditions of ZieglerNichols are discussed from this standpoint.<BR>2) Integral Action Control, (I)<BR>Eqs. (8) & (9) are obtained and the ratio of critical periods of P to I action is proved to be about 2, provided T/L<1.1)<BR>3) Other Controls<BR>PI action gives Eqs. (10) & (11), and P and PI actions imply a possibility of solving both static and dynamic characteristics of the process by themselves with Eqs. (12) & (13).<BR>A special example of an oil pressure controller with a jet-pipe is given by Eqs. (14), (15) & (16). Some experimental results are also presented in Table 4. This method is convenient for obtaining dynamic properties of pressure or flow rate process without any help of special instruments, becaus their characteristic time is too short to be measured by usual records of the indicial response. The necessary requirement is that the controller should be calibrated strictly and its actions purely theoretical.

Journal

  • Chemical engineering

    Chemical engineering 22 (6), 372-376, 1958

    The Society of Chemical Engineers, Japan

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