*112893*

Anatoli M. Voronin ¹, Bekmurza H. Ajtchanov ², Janusz Partyka³,

Aitkul Aldibekova²

¹Almaty technological University, ²Kazakhstan National Technical University named after K.I.Satpayev, ³Lublin University of Technology

Elements of automatic control of hydrodynamic systems

Abstract. The paper presents data on the automated system to manage certain elements of the hydrodynamic system, relating to the production of liquid milk. Similar systems could find application in various fields of engineering, for example, to create hydroelectric power, oil production plants, the control systems of various chemical industries, in the final product containing hydrogen atoms, in the flow of propellant systems, etc., where you want to take control hydrodynamic parameters by means of nuclear magnetic resonance of atoms used in the relevant products.

Keywords. The automated control system, hydrodynamics, algorithm, magnetization of milk, flap gate, quadrupole lenses, sensor, nuclear magnetic resonance, Peltier element, controller, proportional and integral component of the signal.

Introduction

A number of studies [1, 2] examined various automated control systems of technological processes. Fundamentals of the theory of control systems incorporated in the works [3, 4]. We proposed to use as a probe of the magnetic field in the magnetization of milk nuclear magnetic resonance [5] on the hydrogen atoms. This technology can increase overall system accuracy of autoregulation.

System of automated control

For devices intended for the magnetization of milk, which changes the physico-chemical properties to the direction of improvement, it is necessary to maintain several constant parameters. To obtain stable output parameters it is necessary to have a high degree of accuracy in controlling the speed of the milk trough the pipelines and keep it constantly for a long time on one side. On the other hand a magnetic field should be monitored with its subsequent stabilization. These parameters may vary in certain amounts, depending on the type of installation.

To maintain a constant flow of fluid through the pipeline, there are various devices, such as the use of modified Mariotte vessels. In this paper we consider a more general approach to obtain a stabilized flow of fluid in the experimental installation.

Figure 1 shows a block diagram of the apparatus. The milk from the dairy farms is loaded into the reservoir (1), which trough the pipeline (2) is coming to an adjusting device (3) equipped with a system of auto regulation (4) controlled by the speed sensor of fluid flow through the pipeline (5). Then, the milk flows through a pair of quadrupole lenses (6), producing a given level of magnetic field, which is regulated by an automatic control system (7) associated with the probe-level intensity of the magnetic field (8).

Fig. 1. General block diagram of the apparatus

The temperature of entering product for the magnetizing milk system should be 3-4 ⁰С. For this purpose, the used fluid control system is based on the Peltier effect. The controller is made of flat parallel, located inside the tube, aluminum plates (12), cooled with a Peltier element (9), the heat from which is given through the radiator installed outside the pipe (14), air-cooled. In order to maintain the temperature of the milk in a tube in the aisles 3 ± 0,5 ⁰С there is used an electronic control device (13) of a temperature sensor (10,11) which is used as a thermistor incorporated into the scheme of the temperature controller. External heat is blown through the radiator air.

We propose an approach that provides a transition from hydrodynamics to the automatic control system of a flow rate of liquid.

Dynamic processes in the pipeline are characterized by two variables: by the pressure and by the flow rate ,

(1)

where , − the relative values of pressure and flow, respectively, , − basic values of , , – the speed of sound propagation in the pipeline, , g − acceleration of gravity, − cross-sectional area of the pipeline.

After the transformations we obtain the following equation for the originals:

(2)

The given equation relates the two basic quantities and at the end of the pipeline with a pressure at its beginning . In order to make the task definite, the equation of the flow rate should be added to the equation (2):

(3)

The joint solution in managing (2) and (3) determines the basic values and at the end of the pipeline with the definite values of the pressure at its beginning and in the position of the gate .

The analysis of the equation (2) shows that the length of the pipeline can be replaced (by the electric model) (while creating the automatic control systems), by the reinforcing links with delay, and by the performing a linearization of the equation (3), we can apply the methods of the analysis of linear systems with delay [6,7].

Therefore a block diagram of the model is designed to determine the value and , in order to determine the changes in pressure and flow at the point (Fig. 2), prepared on the basis of controls (2) and (3). To the input there are given the proportional signals and , which passed through the model units and converted to the desired variables and . Similar systems of diagnostics it is applied in work [8].

This conclusion about the possibility of unit recording with distributed parameters, functioning as a delay follows from the physical considerations: the object with distributed parameters can be represented as as a series-connected elementary components of the first order, and such links can be represented as a retarded unit.

Fig. 2. The block diagram of the model

ЗЗ- delay unit; УЗ- intensifying unit;

БУ- multiplying unit; ФБ- functional unit with the input h(l,t)

and output ; I, II, III, IV- composing equations (2).

Because of the transcendence of the transfer function level of delay, the characteristic equation of the closed-loop system is also transcendental, so the algebraic criteria for stability can not be directly used. However, private criteria of Mikhailov and Nyquist can be generalized for the case of delay systems, ie the system under consideration is stable [9].

For many processes the characteristic feature is a significant time lag response of the object (change of the output value ) on the change of the control action . According to the calculations for a particular value of the ratio of the delay time of the object to its time constant (for instance, at ) the effectiveness of the control laws is sharply reduced because of the large static (P, PD-laws) or dynamic (I, PI, PID - laws) errors, and in some cases, the system may become unstable. Therefore there were developed special (non-classical) laws of control: proportional-integral-differential (PIR - law) and proportional-integral of the background (PIP - law). In comparison with the classical control laws, using only the information about the deviation of the controlled quantity of a given value , here is used a priori information about the controlled object on the basis of which the classical control law is exists

,

where - coefficient of proportionality (transfer) in order to make certain corrections. In the case of a parallel transfer the correction function of the adjusted control law can be written as

(4)

where – transfer functions of the base-level control and correction unit.

In connection with the above-described process the control block diagram of the control panel-controller can be represented as it is given in Figure 3.

The analysis of this scheme shows that the control action is formed as the algebraic sum of two components: - component on the output of PI − regulator; - component unit of a parallel correction. The introduction of the component weakens the proportional and integral part of the basic component (and are less than one) at _. The latter condition is ensured by the introduction of level 4, which is a model of controlled object. Therefore, the PIP - the regulator provides a high level of control action at and gradual decline of this level at .

Fig. 3. Block diagram of automated control panel with PIP system:

1- control panel; 2- PI-regulator; 3,4- correction units; 5- PIP- regulator.

As in the case with the PIR - regulator, the implementation of PIP - control law improves the quality of transient stability process and increases the stability in amplitude and phase compared with PI-regulator. Beside this, the parameter settings of the correction level and because of their connection with linear proportional and integral components of the output signal correction level 3, is quite simple.

Therefore, the introduction of delayed units of the structure of parallel correction unit can significantly improve the quality of transient processes in the ACS objects with a significant delay, as in the system of milk magnetization.

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