Intelligent regulation of technological parameters. Typical schemes for automatic control of technological variables (flow rate, pressure, temperature, level, concentration, etc.). The principle of operation and elements of the automatic control system

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1 Ministry of General and vocational education Russian Federation Tver State Technical University V.F. Commissioner Automatic regulation technological processes Tutorial Tver

2 UDC 6.5 Automatic control of technological processes: Textbook Second edition, extended / V.F. commissioner; Tver State Technical University, Tver, 48s. Calculation methods are considered automatic systems regulation of technological processes of various types. Designed for specialty students. "Automation of technological processes and production" in the study of the discipline of the same name. Prepared at the Department of Automation of Technological Processes, Tver State Technical University.

3 3 Introduction One of the most important tasks of automation of technological processes is automatic control, which aims to maintain constancy, stabilize the set value of controlled variables or change them according to a law given in time, program control with the required accuracy, which makes it possible to obtain products of the desired quality, as well as safe and economical work technological equipment. As controlled variables, regime level, temperature, pressure, flow rate or qualitative humidity, density, viscosity, composition, etc. are usually used. indicators of the functioning of technological processes that characterize the material or energy balance in the apparatus and the properties of the product. The task of automatic regulation is realized by means of automatic control systems of ACP. The block diagram of a closed ACP is shown in Fig. F RO x OP S P - ass Fig..

4 4 In fig. marked: OR object of regulation technological process or apparatus; y is the controlled variable; х regulatory influence, with the help of which the regulation process is carried out. Regulatory influences are usually the flow rates of liquid, gaseous, granular bodies; RO is a regulating working body, with the help of which the consumption of energy substance is changed. To change the flow rates of liquid and gaseous bodies, throttling-type working bodies with a variable flow area are widely used; S is the position of the end effector, usually measured in % stroke RO, such as valve stem travel or damper rotation. Since the regulatory impact x, as a rule, is not measured, S is usually taken as the regulatory impact, thereby attributing RO to the object of regulation; F - disturbing influences that affect the value of the controlled variable; Р - automatic regulator - a set of elements designed to solve the problem of regulation; set - the set value of the controlled variable, which must be supported by the controller; - a comparing device that generates an error mismatch signal: set As an example, in fig. shows the scheme for controlling the product temperature θ pr at the outlet of the heat exchanger by changing the supply of coolant G.

5 5 G pr θ pr R G Fig.. One of the main perturbations in this system is the flow rate of the heated product G pr. The reason for regulation in a closed ACP is the occurrence of an error. When it appears, the controller changes the control action x until the error is completely eliminated in an ideal system. Thus, the ASR is designed to maintain the controlled variable at a given level with fluctuations in disturbing influences within certain limits. In other words, the main task of the regulator is to eliminate the mismatch by changing the regulatory action. The most important advantage of a closed ACS is that it responds to any disturbance that leads to a mismatch. At the same time, such systems are fundamentally inherent in the control error, since the occurrence

6 6 mismatch always precedes its elimination and, in addition, closed ACP at certain conditions may become unstable. The main tasks that arise in the calculation of the ACP are: Mathematical description of the object of regulation;. Substantiation of the structural scheme of the ASR, the type of regulator and the formation of requirements for the quality of regulation; 3. Calculation of the controller settings; 4. Analysis of the quality of regulation in the system. The purpose of calculating a closed ACP is to ensure the required quality of regulation. Under the quality of regulation, we mean the values ​​of indicators characterizing the shape of the curve of the transient process in a closed ACP with a step action at its input. An exemplary view of the transient characteristics of a closed ASR along the channels of the driving and perturbing, in a particular case, regulatory influences is shown in fig. 3. The transient response of a closed system along the channel of the driving influence, the line y fact in fig. 3a reflects the nature of the transition of the controlled variable from one steady value to another. x a y ass b y id y fact y fact y id Fig. 3.

7 7 It would be ideal if this transition was made abruptly line y id 3b reflects the process of perturbation suppression by the system. It would be ideal if the system did not react at all to the perturbation of the line y id. This manual discusses methods for solving typical tasks arising in the calculation of ASR of various types, which are used in the practice of automation of technological processes.. Mathematical description of objects of regulation [4].. Main characteristics and properties of objects of regulation The object of regulation can be in one of two states: static or dynamic. Static is a steady state in which the input and output values ​​of the object are constant in time. This definition is valid for persistent static objects. Dynamics is a change in time of the output variable of the object due to a change in the input variable or non-zero initial conditions. Static characteristics of regulated objects The behavior of a regulated object in statics is characterized by a static characteristic “input-output”, which represents the relationship between the steady values ​​of the output and input variables: fset st According to the type of static characteristics, linear and non-linear objects are distinguished. The static characteristic of a linear object is a straight line passing through the origin with the equation

8 8 K A characteristic with the equation K b, which does not pass through the origin, can be reduced to a linear one, denoting b ". Objects whose static characteristics differ from a straight line are non-linear. The tangent of the slope of the static characteristic α, equal to the derivative of the output variable with respect to the input, is called the static transfer coefficient of the object: K lim gα The coefficient K has the dimension: units of the output variable per unit of the input action Physical meaning: change of the controlled variable per unit of the input action, i.e. the transfer coefficient characterizes the steepness of the static characteristic function x For linear objects Ku / constant, for nonlinear K is When calculating the ACP, nonlinear characteristics are usually linearized. Widespread use is the linearization of the tangent by the linear approximation of the expansion into a Taylor series. Let x, y be the point in the vicinity of which the function f is linearized. Considering d d d we find d When using the linearized equation, it follows

9 9 a sufficiently small neighborhood of the point x. In addition, since the expression includes the derivative of the function f, this method of linearization is only suitable for differentiable functions. Dynamic characteristics of objects of regulation. Differential Equation The main dynamic characteristic of controlled objects is the differential equation. Objects can be described by two types of differential equations: ordinary differential equations and partial differential equations. Ordinary differential equations describe objects with lumped parameters, which can be conditionally considered as containers with ideal instantaneous mixing. Variables in such objects depend only on time and do not depend on the coordinates of the measurement point of the variable. Partial differential equations describe objects with distributed parameters. Physically, these are usually devices in which one of the coordinates is much larger than the others, for example, a “pipe in pipe” heat exchanger, column-type devices, etc. In such objects, the values ​​of variables depend not only on time, but also the coordinates of the measurement point of the variables, therefore, the differential equations include not only derivatives with respect to time, but also with respect to coordinates. Usually, in calculations, partial differential equations are approximated by a system of ordinary differential equations. In what follows, we will consider objects described by ordinary differential equations of the form: d d n n n n< n n n d d m d d L bm L b ; m, m d d

10 where n is the order of the left side and the whole equation, m is the order of the right side. Since the real objects of regulation are inertial links, always m

11 Basic properties of the Laplace transform. The delay of the argument by τ corresponds to the multiplication of the image by τ e the original displacement theorem, i.e. L e τ ( τ) 4 This property allows one to find images of differential equations with retarded argument. Differentiating the original under zero initial conditions corresponds to multiplying the image by p: d L d, so formally the variable p can be considered a symbol of differentiation. In the static In the general case, d L d 5 Since integration is the inverse of differentiation, the integration of the original corresponds to dividing the image by p: ( d) L / Property 5 allows you to write the Laplace image of the differential equation: n n n n m L bm L b represents an algebraic expression that can be resolved with respect to the image of the output variable ur and then go back from the image to the original. This operation is called the inverse Laplace transform and is denoted by the operator L ( ) L:

12 The inverse Laplace transform is determined by the integral α j π e d j α j To make it easier to find the image from the original and the original from the image, correspondence tables have been compiled between the originals and their images for the simplest functions. These tables are given in manuals on the Laplace transform and in textbooks on control theory. To find the originals of complex images, the formula for decomposing an image into simple fractions is used. see Ratio of the Laplace image of the output variable to the image of the input variable under zero initial conditions is called the transfer function W bm n m n L b L, of the form: or, since b, the transfer function can be written in b W L L m m n n B, A where Ap and Bp are polynomials from p orders n and m, respectively. What is the relationship between the transfer function and the static transfer coefficient? The transfer function is a dynamic characteristic, the transfer coefficient is a static characteristic. The static rest is a particular case of the dynamics of motion. Therefore, K is a special case of W in statics. Since p in statics, then K W 6

13 3 Time characteristics The time characteristic of an object is its response to a typical aperiodic signal. As input signals, a step function or its derivative - δ - function is most often used. The response of an object or any dynamic link to a step function of unit amplitude, a single step function, is called the transient response of the link object h. The reaction of an object to a step of arbitrary amplitude x is called the acceleration curve of the object (Fig. 4). To obtain the transient response from the acceleration curve y, divide each ordinate of the acceleration curve by the step amplitude: h / Fig. 4. Fig. 5. The reaction of the object to the δ function in real conditions on an impulse of finite duration and amplitude, for example, a rectangular one is called the impulse response of the weight function of the control object fig. 5.

14 4 Frequency characteristics Determine the behavior of an object in the frequency domain when a harmonic signal is applied to its input: m sin, where πf π / is the circular frequency of the signal, f is the frequency, is the signal repetition period, x m is the signal amplitude. At the output of a linear plant, harmonic oscillations of the same frequency also occur, but with a different amplitude and phase (Fig. 6: ϕ m ϕ; 36, j m m ϕ j 6. Fig. 7. The values ​​of m and ϕ depend on the frequency of the input signal. Since we are interested in changing two magnitudes of amplitude and phase at once, it is convenient to consider the frequency characteristics in the complex plane. The harmonic input signal is represented on the complex plane by the vector j, whose length modulus is equal to the amplitude x m, and the slope angle argument is equal to the phase of the oscillations fig. 7: j m e j The symbol in this case means "depicted".

15 5 Similarly, the output signal of the object is depicted in the complex plane by the vector j: m e j ϕ j Images j and j are called Fourier images Fourier spectra of harmonic signals and. The ratio of the Fourier images of the output harmonic signal to the input is called the frequency transfer function of the FTF or the complex frequency response W j: j m jϕ W j e j m A e jϕ frequency inputs. The transfer function is a function of the complex variable α j. The frequency transfer function is a function of the imaginary variable j. Therefore, the frequency transfer function is a special case of the transfer function, when the variable p takes on a purely imaginary value j. Therefore, formally, the expression for the frequency transfer function can be found by replacing the variable p by j in the transfer function W, i.e. assuming j: bm W j j n m j n LL b LL What is the difference between a transfer function and a frequency transfer function? The transfer function reflects the behavior of the object of regulation or any dynamic link in dynamics with an arbitrary form of input action. The frequency transfer function reflects

16 6 the behavior of the link object only in the steady state of harmonic oscillations. Thus, the frequency transfer function is a special case of the transfer function, just as the imaginary variable is a special case of the complex variable p. j is The frequency transfer function is written in algebraic form in Cartesian coordinates: W j P jq, [ W j ]; Q Jm[ W j ], P Re or in exponential form in polar coordinates: W j W j A e jϕ [ W j ] A W j; ϕ rg The hodograph of the vector W j the graph described by the end of the vector when the frequency changes from 0 to is called the amplitude-phase characteristic of the AFC. The AFC shows how the amplitude ratios and the phase shift between the output and input signals change when the frequency of the input signal changes. 8. Dependences of the ratio of the amplitudes of the output and input signals A and the phase shift between the output and input signals ϕ on frequency are called the amplitude-frequency response and the phase-frequency phase response, respectively, fig. 9. The AFC contains the same information about the link object as the AFC and PFC combined. j A ϕ ϕ A 8. Fig. 9.

17 7 Basic properties of regulated objects. Load Load is the amount of substance or energy taken from the regulated object during operation. The change in load is usually the main disturbing influence in the control system, because leads to an imbalance between the inflow and outflow of energy matter in the object, which causes a change in the controlled variable, for example, the liquid level in the tank (Fig. Q pr H Q st Fig.. In addition, a change in load leads to a change in the dynamic characteristics of the object. For example, in a container with perfect mixing, rice. the time constant is equal to the ratio of the volume of liquid stored in the container to the load, i.e. the time constant of this object is inversely proportional to the load. Capacity Capacity is the amount of energy substance that an object is able to accumulate. The capacitance characterizes the inertia of the regulated object. Objects of regulation can be single- and multi-capacity. Multi-capacity objects consist of two or more tanks separated by

18 8 transient resistances. The number of containers determines the order of the object's differential equation. For example, the liquid container in Fig. refers to the number of single-capacity objects. An example of a three-capacity object is a shell-and-tube heat exchanger in Fig., in which the heated liquid receives heat through the walls of the tubes from the coolant. The first container is the amount of heat in the heated liquid in the annulus. The second container is the amount of heat in the coolant inside the tubes. The third capacity is the amount of heat in the walls of the pipes, this capacity is usually small compared to the others, and it is neglected. Self-leveling Self-leveling is the ability of an object to restore the balance between the inflow and outflow of energy matter due to a change in the controlled variable due to internal negative feedback in the regulated object. For example, in a container with a free drain fig. when the inflow increases, the level increases and thus the runoff increases until the balance between inflow and runoff is restored. The greater the self-leveling value, the less the controlled variable deviates under the influence of disturbances. Thus, self-leveling facilitates the work of the automatic regulator. Depending on the value of self-leveling, the objects of regulation can be divided into objects with positive, zero and negative self-leveling. From a dynamic point of view, objects with positive self-alignment are stable inertial links. Their transient responses end in steady state

19 9 the section on which the controlled variable comes to a state of rest and ceases to change Fig., curve. 3 Fig. Quantitatively, the self-leveling value is characterized by the self-leveling coefficient ρ, which represents the modulus of the reciprocal of the static transfer coefficient of the object: ρ K The self-leveling coefficient shows how much the input variable of the object must change in order for the output to change by one. Linear objects have constant self-alignment ρ cons, non-linear variables ρ Vr. Objects that do not have self-alignment, objects with zero self-alignment, include the so-called neutral or astatic objects, representing integrating links from a dynamic point of view. Changes in the controlled variable in such objects can be arbitrarily large. An example of a neutral

20 of the object is a container with forced draining fig. Q pr N Q st The steady section of the transient response of an astatic object is a straight line on which the controlled variable changes at a constant speed. The curve in Fig. and has the meaning of the rate of change of the controlled variable per unit of input. There are objects in which, under certain conditions, an uncontrolled process occurs. In these objects, the rate of change of the controlled variable in the transient tends to

21 self-growth curve 3 in Fig. Such objects are called objects with negative self-alignment. From a dynamic point of view, they are unstable links. For neutral and unstable objects ρ. Delay Delay is the time interval from the moment the disturbance is applied to the beginning of the change in the controlled variable. Distinguish between pure and capacitive delay. Pure transport delay τ is the time that the flow of matter energy spends on passing the distance from the point of perturbation to the point of measurement of the controlled variable in a single-capacity object. An example of a link with a pure delay is a belt feeder conveyor fig. 3. The pure delay time is equal to the ratio of the length of the active section of the conveyor belt l to the linear speed of the belt V: τ l V Q n n V l Q П τ l nm 3. Fig. four.

22 In multicapacitive objects, several capacitances are connected in series, which causes a slowdown in the flow of energy substance from one capacitance to another and leads to capacitive delay. Figure 4 shows the transient characteristics of one n, two - n, and multicapacitive nm objects. With the number of capacitances n>, an inflection point P appears in the transient response. With an increase in n, the initial section of the transient response gravitates more and more to the abscissa axis, as a result of which a capacitive delay τ e is formed. There is a fundamental difference between pure and capacitive delays. With pure retardation, the manipulated variable is zero for the duration of the lag. With capacitive delay, it changes, although very little. In the time domain, the transport and capacitive delays appear approximately the same, while in the frequency domain, the behavior of these links differs significantly. Real objects usually contain both types of delay, as a result of which the total delay τ is equal to their sum: τ τ τ e It is almost impossible to separate the capacitive delay from the pure one on the experimental characteristic. Therefore, if the net delay is determined from the experimental acceleration curve, its value is always subjective, i.e. depends on the researcher. The delay sharply worsens the quality of regulation in the automated control system... Methods of mathematical description of objects of regulation Methods of mathematical description of objects of regulation can be divided into analytical, i. not requiring an experiment

23 3 at an industrial facility and experimental i.e. based on the results of the experiment. Analytical methods are called obtaining mathematical models objects based on the analysis of physical and chemical processes occurring in the object, taking into account its design and characteristics of the processed substances. Advantages of analytical models of objects. No on-site industrial experiments are required. Therefore, these methods are suitable for finding object models at the stage of their design or when it is impossible to experimentally study the characteristics of regulated objects. analytical models includes the design characteristics of objects and indicators of the technological mode of their operation. Therefore, such models can be used to select the optimal design of the apparatus and optimize its technological regime. 3. Analytical models can be used for similar objects. However, analytical models are quite complex. In real objects, three types of processes can occur simultaneously: chemical transformations, heat and mass transfer. Simultaneous accounting of all these processes is quite a difficult task. Experimental methods for obtaining models include obtaining time or frequency characteristics as a result of an industrial experiment and their approximation, i.e. selection of an analytical relation that describes the experimental data with the required accuracy. When taking time characteristics, the object is in a transitional mode from one steady state to another. When removing the frequency characteristics, the object is introduced into the steady state of harmonic oscillations. Therefore, obtaining frequency

24 4 characteristics, in principle, makes it possible to obtain more representative information about the object, to a much lesser extent dependent on random perturbations acting on the object. But the frequency response experiment is more time consuming compared to the time response experiment and requires special equipment. Therefore, the most accessible in real conditions is to obtain temporal characteristics. However, it should be noted that experimental models of objects can only be used for those objects and those conditions of their functioning for which the experiment was carried out..3. Obtaining and Approximation of the Time Characteristics of Regulated Objects Preparation and Conduct of the Experiment When developing the scheme of the experiment for taking the temporal characteristics of regulated objects, issues related to the measurement and registration of the test effect and the controlled variable are solved. The planning of the experiment is reduced to the choice of the type of test effect, the magnitude of its amplitude and the number of experiments. To obtain an acceleration curve, a step function is used as a test action. If the step action is unacceptable for the object of regulation without self-leveling or a long-term deviation of the controlled variable from the nominal value is unacceptable, a rectangular impulse type action is used. The impulse response thus obtained, in accordance with the principle of superposition for linear objects, can be rebuilt into an acceleration curve.

25 5 When choosing the amplitude of the test impact, a compromise is sought between the following conflicting requirements. On the one hand, the amplitude of the input action must be large enough to reliably distinguish the useful signal against the background of measurement noise. On the other hand, too large deviations of the controlled variable can lead to disturbances in the operation of the facility, leading to a decrease in product quality or the emergence of an emergency mode. In addition, with large disturbances, the nonlinearity of the static characteristics of the object affects. When determining the number of experiments, it is useful to take into account the following factors: the linearity of the static characteristics of the object, the degree of noisiness of the characteristics, the magnitude of load fluctuations, and the nonstationarity of the characteristics over time. Before the experiment, the object must be stabilized in the vicinity of the nominal mode of its operation. The time-characterization experiment continues until a new value of the controlled variable is established. When the object is noisy, the experimental characteristics are smoothed in time with high-frequency noise or in set with low-frequency noise. Approximation of transient characteristics of regulated objects. The approximation problem includes three stages. Choice of the approximating transfer function. The transient characteristics of objects with self-alignment and lumped parameters are approximated by a fractional-rational transfer function in the general case with a pure delay of the form:

26 6 W rev K rev b m n m n LL e LL For objects without self-alignment in the denominator of the transfer function 7, the Laplace transform variable p sign of the integrator is added as a multiplier. As practice shows, satisfactory approximation accuracy is achieved when using models for which n,3, and n-m in the absence of an inflection point in the acceleration curve and n-m in its presence. Determination of the coefficients of the approximating transfer function. See below 3. Estimation of approximation accuracy. To assess the approximation accuracy, it is necessary to build a calculated characteristic and determine the maximum approximation error. The expressions for the transient responses corresponding to some approximating transfer functions are given in Table. When calculating on a computer in the expressions for the transient responses, one should go to a discrete time τ 7 i sampling interval, and if there is a pure delay in the model 7, the argument at i i at i > τ to Approximation of the transient characteristics of objects with self-alignment by an inertial link of the first order with a delay

27 7 W K e τ 8 To determine τ and T to the transient characteristic of Fig. 5, a tangent AB is drawn at the inflection point C, the inflection point corresponds to the maximum angle α between the tangent and the abscissa axis set B C set O τ α A D Segment OA cut off by the tangent on the abscissa axis is taken as the time of pure delay τ : τ ОА 5. The transfer coefficient K is found as the ratio of the increments of the output and input values ​​in steady state: set K 9 set

28 8 Table. model Transfer function Roots of characteristic equation α α β β α β α α β 5 b K α j ±, sin α α α α α α b rcg e b b K α β γ 3 e e e K γ β α γ β γ α γ αβ γ β α β αγ γ α β α βγ K α j ±, γ 3 e rcg e γ α γ α α γ α α α γ γ α α γ sin 3 3 b K α β γ 3 e b e b e b K γ β α β γ α γ γ αβ γ β α β β αγ γ α β α α βγ

29 9 3 3 b K α j ±, γ 3 [ e b b b rcg e b b K γ α γ α γ α α γ α γ α α α α γ γ α α α γ sin

30 b Interpolation method The acceleration curve is preliminarily normalized from to by the formula ~ ; ~ On the normalized curve in Fig. 6, two points A and B are selected as interpolation nodes through which the calculated curve must pass. ~ B ~B ~A A A B 6. The normalized transient response of the link with transfer function 8 is equal to τ ~ e. Writing down the expression for points A and B, we obtain a system of two equations with two unknowns: ~ ~ A B e e Aτ b τ Resolving this system with respect to τ and T, we obtain:

31 3 ~ ~ B ln A A ln B τ ln ~ ln ~ A B A τ B τ ln ~ ln ~ A B or W К 4 The parameters of models 3, 4 can be easily determined by drawing the asymptote VS to the steady section of the acceleration curve Fig.6.: С А α В Fig. 6. K d / d set gα set OV OA set 5 τ OA for model 3

32 3 TOA for model 4 Approximation of transient responses of control objects by an n-th order link there are. To eliminate the component due to pure delay, all abscissas of the acceleration curve should be reduced by the amount of pure delay τ, i.e. move the origin to the right by τ. At the same time, in the transfer function of an object with a pure delay W about W e " about Section AB of the transient response without delay Fig.7 τ " corresponds to the transition function W about. B Y A C τ A Fig.7. Bα Fig.8. - When approximating the transient response of an object without self-levelling, it is represented as the difference between two characteristics Fig. 8:

33 33 To do this, we draw the asymptote VS to the steady section of the characteristic and the ray OA is parallel to VS. Subtracting from, we find. - transient response of the integrating link with the transfer function W K The coefficient K is still found by formula 5: K gα mouth is the transient response of the object with self-alignment. It corresponds to the transfer function W. Due to the linearity of the Laplace transform, the transfer function of the object corresponding to the characteristic is equal to: W К W W W о The coefficients of the transfer function W can be found using the method described below. Bringing the expression for W about to a common denominator, we obtain the desired transfer function of the object without self-alignment. Determination of the coefficients of the transfer function of an object using the Simoyu area method

34 34 In practice, as noted, n.3; m,. The transmission coefficient about K, as always, is determined by the formula 9. To simplify the calculations, we normalize the acceleration curve of the object in the range - according to the formula. For a normalized curve ~ with a single input action about K. Let's write the inverse expression of the transfer function 6 and expand it into an infinite series in powers of p: m n about S S S b W L 7 Reducing 7 to a common denominator and equating the coefficients at the same powers of p, we find: 8, S S b S b b S S b S b b S S b b S b L LLLLLLLLL in the special case with m S S S 9 equations.

35 35 So, system 8 or 9 allows you to determine the coefficients of the transfer function 6 through the yet unknown expansion coefficients S. To determine the latter, consider the Laplace image of the deviation of the normalized transient response from the steady value: L about ( ~ ) L() L( ~ ) [ W р ] From we find W rev ( L[ ~ ]), or taking into account the definition of the Laplace transform 3: W rev [ ~ ] e d Expanding the function e into a power series: e!! 3 3 L L, 3!! we can represent the integral in the expression as a sum of integrals: ~ e d ~ d d ~ d! ~! ~dL! Substituting the expansions 7 and β, multiplying the power series from and equating the coefficients at the same powers of p in the resulting relation, we obtain the following expressions for the coefficients S.

36 36 3!! ~, 6 ~ ~, ~, ~ d i S S d S S S S d S S S d S S d S i i i LLLLLLLLLLLLLL practical calculations integrals 3 are determined by numerical methods. For example, when using the trapezoidal method, the expressions for the coefficients S become: 4.5 6 ~,5 ~,5 ~,5 ~ 3 3 ` N i i N i i N i i N i i S i i S i S S S S i i S S S S i S S S discreteness of readings of the normalized transient response, N is the number of points of the transient response. From a geometric point of view, the coefficient S is the area bounded by the curve ~ and the line of steady values. S is the area weighted with the weight function S and so on. Thus,

37 37 coefficients S are some weighted areas, which determines the name of the method. If during the calculations the -th coefficient S turned out to be negative, it is necessary in model 6 to reduce n by one or increase i.e. decrease difference n-m.. Industrial regulators ASR [4].. Functional diagram of the automatic regulator An automatic regulator is a set of elements that serve to regulate technological processes. The functional diagram of a closed ASR has the form of Fig. 9 set S x H SU FU IM RO OR IE F Automatic regulator Fig. 9. Object of regulation 9 is marked: Z - the setter of the controlled variable serves to set its desired desired value; SU - comparing device, generates a mismatch signal; ass FU - forming device, serves to form the law of regulation in electrical regulators together with IM; IM - actuator, drives the RO;

38 38 RO - regulatory working body, serves to change the regulatory impact x; OR itself is the object of regulation; IE measuring element serves to measure the controlled variable y and convert it into a unified signal. The working body, together with the drive, if any, is usually attributed to the object of regulation. The measuring element can be related both to the object and to the controller. In those cases when the measuring element is used to remove the time characteristic, it is referred to the object. Thus, the automatic regulator includes a setpoint adjuster that compares the device, the forming device and the actuator ... Classification of regulators by energy consumption external source On this basis, regulators are divided into regulators of direct and indirect action. In direct action regulators, the energy of the regulated medium itself is used to rearrange the working body. For example, in a direct-acting liquid level regulator, the energy of the liquid, the level of which is regulated, is used to rearrange the working body. Direct acting regulators are simple, cheap, but do not provide High Quality regulation. Their disadvantages are also the difficulty of implementing complex regulatory laws and obtaining great efforts to rearrange the working body. In indirect action regulators, the energy of an external source is used to rearrange the working body, according to the form of which

39 39 distinguish between electric electronic, pneumatic, hydraulic, combined regulators. Electric regulators have a number of advantages. Their main disadvantage in the usual design is the inability to use in fire and explosive environments. Pneumatic regulators are deprived of this shortcoming. The main advantage of hydraulic regulators is the increased power of the actuator with relatively small dimensions. Combined controllers allow you to combine the advantages of different types of controllers. For example, electro-pneumatic systems combine the advantages of electric regulators with the ability to operate pneumatic actuators in flammable and explosive environments. In recent years, programmable controllers have found widespread use for the implementation of local automation systems. The choice of the type of regulator is dictated by various considerations: the nature environment, working conditions, special requirements..3. Classification of regulators according to the law of regulation Under the law of regulation understand the equation of the dynamics of the regulator. Five typical control laws are known: proportional P, integral I, proportional-integral PI, proportional-differential PD and proportional-integral-differential PID. Proportional static controllers Equation of the dynamics of the P-controller K 5

40 4 where is the mismatch of the controlled value, ass x is the control action more precisely, the increment of the control action relative to the constant component, therefore it is more correct to write x - x in 5 instead of x, but x is usually omitted, K is the transfer coefficient P of the regulator. As we can see from 5, the regulatory effect of the P controller is proportional to the mismatch, i.e. The P controller is a non-inertia link with the transfer function W K. Since the P controller does not introduce a negative phase shift of the PFC of the P controller into the system, the ACP with the P controller has good dynamic properties. The disadvantage of systems with a P regulator is the presence of a static error. For a single controller, the value of this error is determined from the controller equation: F K K

41 4 FK ZCF F K about Kob K p, where perturbation. К ЗCF - closed-loop system transfer coefficient according to As you can see, the static error in a system with a P controller is inversely proportional to its transfer coefficient, the limiting value of which is determined by the required stability margin of the closed ACP. Proportional controllers are used in the automation of low-inertia control objects, when the value of K can be chosen by an error. large enough to reduce the static Integral astatic regulators the control action in this case is proportional to the integral of the mismatch. The transfer coefficient of the I-controller K d / d has the meaning of the rate of change of the regulatory action per unit of mismatch. Transfer function: K W Frequency transfer function:

42 4 K K W j j e The advantage of the And controller is the zero static error. It follows from 6 that this error is equal and vanishes in statics. d / d K At the same time, since the PFC of the AND controller ϕ π, the system with the AND controller has very poor dynamic properties, because this controller introduces a negative phase shift in phase π into the system. Integral controllers can only be used in the automation of almost inertia-free objects. ACP with AND controller and plant without self-alignment is structurally unstable, π j i.e. unstable at any controller settings. Proportional integral controllers The regulation law of the PI regulator can be written in two forms: К К d К d 7 Т , K T I I

43 43 where T and isodrom time. K >> Transfer function and frequency transfer function: W W K j K K K, K e I K jrcg K From the last expression it can be seen that in the region of low frequencies at K PI the controller behaves like an AND controller. At high K frequencies, K >>, i.e. The PI controller behaves like a P controller. This allows the PI controller to combine the advantages of an AND controller in statics and a P controller in dynamics. The physical meaning of the isodrom time can be explained by the transient response of the PI controller fig. As can be seen from this figure, T I is the doubling time of the P component of the PI control action, or, equivalently, the time by which the PI control action leads the AND control action. The value of T and characterizes the speed of integration. The more T and the slower the integration speed. With T & PI, the controller becomes a P controller. K x PI I K P I Fig..

44 44 So, ASR with a PI controller has a zero static error due to the presence of an AND component in the control law. This is true for all regulators with an AND component. As can be seen from the PFC of the PI controller in Fig., in the region of operating frequencies 3 ϕ slave π Fig.. of the operating frequencies, the PI controller introduces a negative phase shift of approximately -3 into the system. This is much less than the I controller, but more than the P controller. Therefore, the dynamic properties of an ACP with a PI controller are much better than with an I controller, but worse than with a P controller. Proportional-differential controllers The law of regulation of an ideal PD controller: d d K K K P, 8 d d where K, K are the coefficients of proportionality of the P- and D- components of the control law. T P lead time. Transfer and frequency transfer functions: W W K K j K K K e P, K jrcg K

45 45 It can be seen from the last expression that at low frequencies the PD controller behaves like a P controller, and at high frequencies it behaves like a differentiator. Since an ideal differentiating link is physically unrealizable, real PD controllers use a real inertial differentiating link. The transfer function of such a controller has the form W K K The smaller the time constant T, the closer specifications ideal and real regulators. In statics, the transfer function of the PD controller coincides with the transfer function of the P-controller, therefore, ASR with a PD controller also has a static error. As can be seen from the PFC Fig.3, ϕ π ideal -3 real slave 3. In the region of operating frequencies, the PD regulator introduces a positive phase shift into the system, increasing its stability margin. Therefore, an ASR with a PD controller has the best dynamic properties. For the same reason, the value of K can be chosen larger than in the case of P

46 46 regulator. Therefore, the static error in an ASR with a PD controller is less than in a system with a P controller. However, PD regulators are practically not used, because in the presence of high-frequency interference superimposed on a low-frequency useful signal, the differentiation operation sharply worsens the signal-to-noise ratio, as a result of which the amplitude of the noise derivative can significantly exceed the amplitude of the derivative of the useful signal. Regarding the physical meaning of the lead time, we can say that T P is the time for which the regulatory action of the PD controller is ahead of the regulatory action P of the controller with a linear input action Fig.4 x PD P D p Fig. 4. Proportional - integral differential controllers Equation of dynamics: d d K K d K K d P d 9 d I Transfer functions of the ideal and real PID controllers:

47 47 W W K K K K K K K I P, The frequency transfer function of an ideal PID controller: .5 in the area of ​​operating frequencies PID controller is the same as ϕ π ideal work real π 5. and P regulator, does not introduce a negative phase shift into the system. In order to increase the noise immunity of the PID controller, in practice, the ratio of lead time/isodrome time is limited from above by the inequality / П И<,5, 3 поэтому помехоустойчивость ПИД регулятора выше, чем ПД регулятора. При выборе закона регулирования учитывают следующие соображения.

48 48 If the static error is unacceptable, the controller must contain an AND term. In the order of deterioration of the dynamic properties, the control laws are arranged in the following order: PD, PID, P, PI, I. Regulators with a D component have poor noise immunity. For this reason, PD controllers are practically not used, and PI controllers are used with a restriction of 3. In practice, PI and PID control laws are most widely used. 3. Calculation of regulator settings in linear continuous systems [4] 3. Quality of regulation 6. Main indicators of quality. Maximum dynamic deviation dyn - the largest deviation of the controlled variable from its set value in the transient process Index dyn m set In a stable ACP, the first deviation is the maximum. dyn characterizes the dynamic accuracy of regulation. Residual deviation residual unevenness ct - absolute static control error, defined as the difference between the steady value of the controlled variable and its set value:

49 49 ct set ref Static mode value. m st characterizes the accuracy of regulation in the set ass dyn 3 δ st Fig Degree of attenuation ψ - the ratio of the difference between two adjacent amplitudes of oscillations directed on one side of the steady value line, to the larger of them 3 3 ψ ;< ψ < 3 Показатель ψ характеризует колебательность переходных процессов и запас устойчивости системы. Значение ψ соответствует незатухающим колебаниям на границе устойчивости системы. При ψ имеем апериодический переходной процесс. 4. Время регулирования промежуток времени от момента нанесения возмущающего воздействия до момента, начиная с которого отклонение регулируемой переменной от установившегося значения становится и остается меньше наперёд заданного значения δ. Показатель характеризует быстродействие системы.

50 5 The considered quality indicators belong to the group of direct indicators, i.e. indicators that allow assessing the quality directly from the transient curve, for which it is necessary to solve the differential equation of the system. In addition to direct ones, there are indirect criteria that make it possible to judge the quality of regulation without having a transient curve at hand. Such criteria, in particular, include integral quality criteria representing the integrals over time from the deviation of the controlled variable from the steady state value, or from some function of this deviation and its mouth derivatives. The simplest is the linear integral criterion defined by the ratio: I lin d mouth From a geometric point of view, the criterion I lin is the area between the curve and the line mouth. The value of I lin depends on all quality indicators, except for art. In this case, with a decrease in dyn, etc. By improving the quality of regulation, the value of Ilin falls, and with an increase in the oscillatory process of the transient, Ilin also decreases, although the quality of regulation deteriorates. So, a decrease in Ilin indicates an improvement in the quality of regulation only for well-damped transients. Therefore, criterion I lin is applicable for aperiodic or weakly oscillatory processes. For such processes, such controller settings can be considered as the best, at which the value of Ilin reaches a minimum. Criterion I lin can be calculated through the coefficients of the differential equation of a closed ASR.

51 5 It can be shown that for the control object with self-leveling and PI controller I lin, 3 K i.e. the minimum I lin is achieved at the maximum of the integral component of the regulatory action, or, what is the same, the best quality of the transient process is achieved at the maximum K. For oscillatory transients, other integral criteria are used, for example, I mod set d, but this criterion cannot be calculated through the coefficients of the differential equations. This shortcoming is deprived of the quadratic integral criterion I quarter: I quarter mouth d 3. Typical optimal processes The requirements for quality indicators are contradictory. For example, a decrease in dynamic error is achieved by increasing the oscillation and duration of transient processes. On the contrary, processes with a short control time can be obtained by increasing the dynamic error. Therefore, regarding the desired values ​​of quality indicators in a closed ACP, a compromise decision has to be made. Transient processes with certain quality indicators are recommended when calculating the ASR as typical ones. In the method of extended frequency

52 5 characteristics The main indicator of quality is the degree of attenuation ψ, i.e. fluctuation of the transient process, since this indicator characterizes the stability margin of the ASR. Processes for which ψ,75,9, i.e. the third oscillation amplitude is 4 times less than the first. In those cases when the task is to select the controller settings that minimize any quality indicator, the corresponding transient process, as well as the values ​​of the controller settings, are called optimal in the sense of the specified criterion. For example, in the method of extended frequency responses, the task is to select the controller settings in such a way that, in addition to the given oscillation of the transient process, the minimum value of the criterion I lin is provided. Such a process is optimal in the sense of criterion I lin. Simplified formulas for calculating regulator settings. simplified formulas are given for determining the settings of regulators that provide a given oscillation of the transient process. The formulas are derived from the results of ACP modeling. Static objects are represented by a model of an inertial link with a pure delay 8, astatic objects by a model of an integrating link with a delay 3

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The main technological parameters subject to control and regulation in chemical-technological processes include flow rate, level, pressure, temperature, pH value and quality indicators (concentration, density, viscosity, etc.) * [Fundamentals of measuring these parameters, automatic control devices and executive devices are studied in the courses "Technological measurements and devices" and "Technical means of automation". Here, the features of regulation of these parameters are considered, taking into account the static and dynamic characteristics of control channels, control devices and automation equipment, and examples of the most common control systems for some parameters are given.]. Flow control. The need for flow control arises in the automation of almost any continuous process. Flow automated control systems, designed to stabilize disturbances in material flows, are an integral part of open-loop automation systems for technological processes. Often, flow ACPs are used as internal circuits in cascade control systems for other parameters. To ensure a given composition of the mixture or to maintain the material and heat balances in the apparatus, systems for regulating the ratio of the flow rates of several substances in single-loop or cascade ACPs are used.

Flow control systems are characterized by two features: low inertia of the regulated object itself; the presence of high-frequency components in the flow change signal due to pressure fluctuations in the pipeline (the latter are caused by the operation of pumps or compressors or random flow fluctuations when the flow is throttled through the restrictor).

On fig. 2.1 is a schematic diagram of the object when regulating the flow. Typically, such an object is a pipeline section between the flow measurement point (for example, the installation site of a restrictor 1 ) and the regulatory body 2. The length of this section is determined by the rules for installing narrowing devices and regulatory bodies and is usually several meters. The dynamics of the channel "substance flow through the valve - substance flow through the flow meter" is approximately described by a first-order aperiodic link with a pure delay. The time of pure delay is usually

Rice. 2.1. Schematic diagram of the object for flow control: /-flow meter; 2 - control valve

sets fractions of seconds for gas and several seconds for liquid; the value of the time constant is a few seconds.

Due to the small inertia of the regulated object, special requirements are imposed on the choice of automation tools and methods for calculating the ACP. In particular, in industrial installations, the inertia of flow control and regulation circuits becomes commensurate with the inertia of the object, and it should be taken into account when calculating control systems.

An approximate estimate of the net delay and time constants of individual circuit elements shows (Fig. 2.2) that modern primary flow converters, built on the principle of dynamic compensation, can be considered as amplifying links. The actuator is approximated by a first-order aperiodic link, the time constant of which is several seconds, and the speed of the actuator is significantly increased when positioners are used. The impulse lines connecting the control and regulation means are approximated by a first-order aperiodic link with a pure delay, the parameters of which are determined by the line length and lie within a few seconds. With large distances between the circuit elements, it is necessary to install additional power amplifiers along the length of the impulse line.

Due to the small inertia of the object, the operating frequency may be higher than the maximum limiting the area of ​​normal operation of the industrial regulator, within which standard control laws are implemented. Outside this range, the dynamic characteristics of the regulators differ from the standard ones, as a result of which it is necessary to introduce corrections for the operating settings, taking into account the actual laws of regulation.

Rice. 2.2. Structural diagram of the flow control system:

1 - an object; 2 - primary flow converter; 3 - regulator; 4 - impulse lines; 5 - executive device

The choice of control laws is usually dictated by the required quality of transient processes. To control the flow without static error in single-circuit ASR, PI controllers are used. If the flow ACP is an internal loop in a cascade control system, re-

Rice. 2.3. Flow control schemes after centrifugal (a) and piston ( b) pumps:

/ - flow meter; 2 - control valve; 3- regulator; 4 - pump

the flow regulator can implement the P-law of regulation. In the presence of high-frequency interference in the flow signal, the use of controllers with differential components in the control law without preliminary smoothing of the signal can lead to unstable operation of the system. Therefore, in industrial flow ACPs, the use of PD or PID controllers is not recommended.

Flow control systems use one of three ways to change flow:

throttling the flow of a substance through a regulatory body installed on the pipeline (valve, gate, damper);

changing the pressure in the pipeline using an adjustable energy source (for example, changing the speed of the pump motor or the angle of rotation of the fan blades);

bypassing, i.e. transfer of excess substance from the main pipeline to the bypass line.

Flow control after the centrifugal pump is carried out by a control valve installed on the discharge pipeline (Fig. 2.3, a). If a piston pump is used to pump liquid, the use of such an ACP is unacceptable, since when the regulator is operating, the valve may close completely, which will lead to a rupture of the pipeline (or surge if the valve is installed on the suction side of the pump). In this case, bypassing the flow is used to control the flow (Fig. 2.3, b).

The regulation of the flow of bulk solids is carried out by changing the degree of opening of the control damper at the outlet of the hopper (Fig. 2.4, a) or by changing the speed of the conveyor belt (Fig. 2.4, b). In this case, a weighing device can serve as a flow meter, which determines the mass of material on the conveyor belt.

Cost Ratio Control two substances can be carried out according to one of the three schemes described below.

1. With an unspecified total productivity, the consumption of one substance (Fig. 2.5, a) G 1 , called "leading", can change arbitrarily; the second substance is fed at a constant ratio at with the first, so that the "driven" flow is yG 1 .

Rice. 2.4. Flow control schemes for bulk solids:

a - changing the degree of opening of the control damper; b - change in the speed of the conveyor; / - bunker; 2 - conveyor; 3 - regulator; 4 - control damper; 5 - electric motor

Sometimes, instead of a ratio regulator, a ratio relay and a conventional regulator for one variable are used (Fig. 2.5.6). Relay output 6, establishing a given ratio ratio y, is given in the form of a task to the regulator 5, which ensures the maintenance of the “guided” flow rate.

For a given "leading" flow rate, in addition to the ACP ratio, the ACP of the "leading" flow rate is also used (Fig. 2.5, c). With this scheme, in case of a change in the target for consumption G\ consumption will automatically change G% (in a given ratio with Gi).

The ACP of the flow ratio is an internal loop in the cascade control system of the third process variable at(for example, the temperature in the machine). At

Rice. 2.5. Cost ratio regulation schemes:

a, b- at unspecified total load; in- at a given total load; G- at a given total load and correction of the ratio coefficient according to the third parameter; ", 2 - flow meters; 3 - ratio regulator; 4, 7 - control valves; 5 - flow regulator; 6 - ratio relay; 8 - Temperature regulator; 9 - restriction device

In this case, the given ratio factor is set by an external controller depending on this parameter, so that Gi= y{ y) G\ (Fig. 2.5, d). As noted above, the peculiarity of setting up cascade ACPs is that the internal controller is given a limit Xp ^ Rp ^ Rv. For the ACP of the flow ratio, this corresponds to the limitation Yh ^ y ^ Yb- If the output signal of the external regulator goes beyond [dg rn, x r ], then the task of the ratio controller remains at the maximum permissible value at(i.e. Yh or Yb) - Level control. The level is an indirect indicator of the hydrodynamic equilibrium in the apparatus. The constancy of the level indicates the observance of the material balance, when the inflow of liquid is equal to the flow, and the rate of level change is zero. It should be noted that "inflow" and "drain" here are generalized concepts. In the simplest case, when phase transformations do not occur in the apparatus (collectors, intermediate tanks, liquid-phase reactors), the inflow is equal to the flow rate of the liquid supplied to the apparatus, and the drain is equal to the flow rate of the liquid discharged from the apparatus. In more complex processes, accompanied by a change in the phase state of substances, the level is a characteristic of not only hydraulic, but also thermal and mass transfer processes, and the influx and flow take into account the phase transformations of substances. Such processes take place in evaporators, condensers, evaporators, distillation columns, etc.

In the general case, the level change is described by an equation of the form

(2.1)

where S is the area of ​​the horizontal (free) section of the apparatus; G B x,

Depending on the required accuracy of maintaining the level, one of the following two control methods is used:

Rice. 2.6. An example of a positional level control scheme:

/ - pump; 2 - apparatus; 3 - level indicator; 4 - level regulator; 5,6 - control valves

1) positional control, in which the level in the apparatus is maintained within a given, fairly wide range: L„^ L^. L B . Such control systems are installed on liquid collectors or intermediate containers.

Rice. 2.7. Continuous Level Control Schemes:

a- regulation "on the inflow"; b- regulation "on the drain"; in- cascade ACP; / - level controller; 2 - control valve; 3, 4 - flow meters; 5 - ratio regulator

(Fig. 2.6). When the limit value of the level is reached, the flow is automatically switched to a spare tank;

2) continuous regulation, which ensures the stabilization of the level at a given value, i.e. L = L°.

Particularly high requirements are placed on the accuracy of level control in heat exchangers, in which the liquid level significantly affects thermal processes. For example, in steam heat exchangers, the level of condensate determines the actual heat exchange surface. In such ACPs, PI controllers are used to control the level without a static error. P-regulators are used only in cases where high quality of regulation is not required and disturbances in the system do not have a constant component, which can lead to the accumulation of a static error.

In the absence of phase transformations in the apparatus, the level in it is regulated in one of three ways:

by changing the flow rate of the liquid at the inlet to the apparatus (regulation "on the inflow", Fig. 2.7, a);

change in fluid flow at the outlet of the apparatus (regulation "on the drain", Fig. 2.7.6);

regulation of the ratio of fluid flow rates at the inlet to and outlet of the apparatus with level correction (cascade ACP, Fig. 2.7, c); disabling the correction loop can lead to accumulation of errors in level control, since due to inevitable errors in setting the ratio controller, the liquid flow rates at the inlet and outlet of the apparatus will not be exactly equal to each other and due to the integrating properties of the object [see Fig. equation (2.1)] the level in the apparatus will continuously increase (or decrease).

In the case when hydrodynamic processes in the apparatus are accompanied by phase transformations, it is possible to control the level by changing the supply of the coolant (or coolant), as shown in Fig. 2.8. In such devices, the level is interconnected with other parameters (for example, pressure), so the choice of the level control method in each particular

Rice. 2.8. Level control scheme in the evaporator:

1 - evaporator; 2 - level controller; 3 - control valve

Rice. 2.9. Fluidized bed level control:

a- removal of granular material; b - change in gas flow; 1 - apparatus with a fluidized bed; 2 - level controller; 3 - regulatory body

Otherwise, it must be carried out taking into account the remaining control loops.

A special place in level control systems is occupied by level ACPs in apparatuses with a fluidized (fluidized) bed of granular material. Steady maintenance of the level of the fluidized bed is possible within rather narrow limits of the ratio of the gas flow rate and the mass of the bed. With significant fluctuations in the gas flow rate (or the flow rate of granular material), the regime of entrainment of the layer or its settling occurs. Therefore, particularly high demands are made on the accuracy of the fluidized bed level control. As regulatory influences, the flow rate of granular material at the inlet or outlet of the apparatus (Fig. 2.9, a) or the gas flow rate for liquefying the bed (Fig. 2.9, b).\

Pressure regulation. Pressure is an indicator of the ratio of the flow rates of the gas phase at the inlet to the apparatus and the outlet from it. The constancy of the pressure indicates the observance of the material balance in the gas phase. Usually, the pressure (or vacuum) in a process plant is stabilized in one apparatus, and throughout the system it is set in accordance with the hydraulic resistance of the line and apparatuses. For example, in a multi-shell evaporator (Fig. 2.10), the vacuum in the last evaporator is stabilized. In other devices, in the absence of disturbances, a rarefaction is established, which is determined from the conditions of material and thermal balances, taking into account the hydraulic resistance of the technological line.

In cases where pressure significantly affects the kinetics of the process, a pressure stabilization system is provided in individual apparatuses. An example is the distillation process, for which the phase equilibrium curve depends significantly on pressure. In addition, when regulating the process of binary distillation, often as an indirect

An indicator of the composition of a mixture is its boiling point, which is unambiguously related to the composition only at constant pressure. Therefore, in product distillation columns, special pressure stabilization systems are usually provided (Fig. 2.11).

The equation of the material balance of the apparatus for the gas phase is written as:

where V - the volume of the device; 0 V x and (Zout - the flow rate of gas, respectively, supplied to the apparatus and discharged from it; G 0 e- mass of gas formed (or consumed) "in the apparatus per unit time.

As can be seen from the comparison of equations (2.1) and (2.2), the methods of pressure control are similar to the methods of level control. In the examples of pressure ACP considered above, the control actions are the flow rate of non-condensed gases discharged from the upper part of the column (i.e. G Bb ix, Fig. 2.11) and the flow rate of cooling water into the barometric condenser, which affects the rate of condensation of the secondary vapor (t i.e. on G 0 6, Fig. 2.10).

A special place among pressure ACPs is occupied by systems for regulating the pressure drop in the apparatus, which characterizes the hydrodynamic regime, which significantly affects the course of the process. Packed columns (Fig. 2.12, a), fluidized bed apparatuses (Fig. 2.12.6), etc. can serve as examples of such apparatuses.

Temperature regulation. Temperature is an indicator of the thermodynamic state of the system and is used as you

Rice. 2.10. Vacuum control in a multi-effect evaporator:

1,2 - evaporators; 3 - barometric condenser; 4 - vacuum regulator; 5 - control valve

Rice. 2.11. ASR of pressure in the distillation column:

/ - Column; 2 - dephlegmator; 3 - phlegm capacity; 4 - pressure regulator; 5 - control valve

Rice. 2.12. Differential pressure control scheme: a- in a column apparatus with a packing; b - in the apparatus with a fluidized bed; / - apparatus; 2 - differential pressure regulator; 3 - control valve

reference coordinate in the regulation of thermal processes. The dynamic characteristics of objects in temperature control systems depend on the physicochemical parameters of the process and the design of the apparatus. Therefore, it is impossible to formulate general recommendations on the choice of temperature ACP, and an analysis of each specific process is required.

The general features of temperature ASR include significant inertia of thermal processes and industrial temperature sensors. Therefore, one of the main tasks in the design of temperature ACP is to reduce the inertia of the sensors.

Consider, for example, the dynamic characteristics of a thermometer in a protective case (Fig. 2.13, a). The structural diagram of the thermometer can be represented as a series connection of four thermal containers (Fig. 2.13.6): protective cover 1, air gap 2, thermometer wall 3 and the actual working fluid 4. If we neglect the thermal resistance of each layer, then all elements can be approximated by aperiodic links of the 1st order, the equations of which have the form:

M/- the mass of the cover, air layer, wall and liquid, respectively; c P j - specific heat capacities; al, a.c- heat transfer coefficients; ^l. Hz- heat transfer surfaces.

As can be seen from equations (2.3), the main directions for reducing the inertia of temperature sensors are:

increase in heat transfer coefficients from the medium to the case as a result of the correct choice of the sensor installation location; in this case, the velocity of the medium must be maximum; ceteris paribus, it is more preferable to install thermometers in the liquid phase (compared to gaseous), in condensing vapor (compared to condensate), etc.;

reduction of thermal resistance and thermal capacity of the protective cover as a result of the choice of its material and thickness;

reduction of the time constant of the air gap due to the use of fillers (liquid, metal chips); for thermoelectric converters (thermocouples), the working junction is soldered to the protective cover;

selection of the type of primary converter; for example, when choosing a resistance thermometer, a thermocouple or a manometric thermometer, it must be taken into account that the thermocouple in a fast-response design has the least inertia, and the manometric thermometer has the largest. pH regulation. pH control systems can be divided into two types, depending on the required control accuracy. If the rate of change in pH is low, and the permissible limits of its fluctuations are wide enough, positional control systems are used that maintain pH within the specified limits: pH H sgpH

A common feature of objects in the regulation of pH is the non-linearity of their static characteristics associated with the non-linear dependence of pH on the consumption of reagents. On fig. 2.14 shows a titration curve characterizing the

Rice. 2.13. Principal (a) and structural (b) thermometer circuits: 1 - protective case; 2 - air layer; 3 - thermometer wall; 4 - working fluid

Rice. 2.14. The dependence of the pH value on the consumption of the reagent

dependence of pH on acid consumption G\. For various given pH values, three characteristic sections can be distinguished on this curve: the first (middle), related to almost neutral media, is close to linear and is characterized by a very large amplification factor; the second and third sections, related to strongly alkaline or acidic environments, have the greatest curvature.

In the first section, the object, according to its static characteristic, approaches the relay element. In practice, this means that when calculating a linear ACP, the controller gain is so small that it goes beyond the operating settings of industrial controllers. Since the neutralization reaction itself takes place almost instantly, the dynamic characteristics of the apparatuses are determined by the mixing process and, in apparatuses with agitators, are described quite accurately by differential equations of the 1st order with a delay. At the same time, the smaller the time constant of the apparatus, the more difficult it is to ensure stable regulation of the process, since the inertia of the instruments and the controller and the delay in the impulse lines begin to affect.

To ensure stable pH regulation, special systems are used. On fig. 2.15, a shows an example of a pH control system with two control valves. Valve 1, having a large nominal diameter, it is used for rough flow control and is set to the maximum range of the regulator output signal [X pH , X rv ] (Fig. 2.15.6, curve /). Valve 2, used for precise regulation, designed for lower throughput and configured in such a way that when X R =x R °+<А it is fully open and x p = x v ° -A - completely closed (curve 2). So

Rice. 2.15. Example of a pH control system:

a - functional diagram; b - static characteristics of valves; 1, 2 - control valve; 3 - pH regulator

Rice. 2.16. Piecewise linear approximation of the static characteristic of the object when adjusting the pH.

Rice. 2.17. Structural diagram of a pH control system with two regulators

Thus, with a slight deviation of pH from pH °, when Xp°-L^AGr^lgr 0 +)A, the degree of opening of the valve / practically does not change, and the regulation is carried out by the valve 2. If a \X R-x p °| >L, valve 2 remains in the end position and the control is carried out by the valve /.

In the second and third sections of the static characteristic (Fig. 2.14), its linear approximation is valid only in a very narrow range of pH changes, and in real conditions, the control error due to linearization may turn out to be unacceptably large. In this case, more accurate results are obtained by a piecewise linear approximation (Fig. 2.16), in which the linearized object has a variable gain:

Yes rice. 2.17 shows a block diagram of such an ACP. Depending on the LRR mismatch, one of the regulators, tuned to the appropriate gain of the object, is put into operation.

Regulation of composition and quality parameters. In the processes of chemical technology, an important role is played by the precise maintenance of the quality parameters of products (the composition of the gas mixture, the concentration of a particular substance in the flow, etc.). These parameters are characterized by the complexity of measurement. In some cases, the chromatographic method is used to measure the composition. In this case, the result of the measurement is known at discrete moments of time, separated from each other by the duration of the chromatograph cycle. A similar situation arises when the only way to measure product quality is to some extent mechanized sample analysis.

Rice. 2.18. ACP Flowchart of Product Quality Parameter:

1 - an object; 2 - quality analyzer; 3 - computing device; 4 - regulator

The discreteness of the measurement can lead to significant additional delays and a decrease in the dynamic accuracy of the regulation. To reduce the undesirable influence of measurement delay, a model is used to relate product quality to variables that are measured continuously. This model can be quite simple; the coefficients of the model are refined by comparing the value of the qualitative parameter calculated from it and found as a result of the next analysis (algorithms for such refinement are described in Section 5.8). Thus, one of the rational methods of quality regulation is regulation by an indirect calculated indicator with a refinement of the algorithm for its calculation according to direct analysis data. Between measurements, the quality index of a product can be calculated by extrapolation of previously measured values.

The block diagram of the product quality parameter regulation system is shown in fig. 2.18. The computing device generally continuously calculates the quality score estimate x(t) according to the formula

in which the first term reflects the dependence X from continuously measured process variables or quantities dynamically associated with them, such as derivatives, and the second - from the output of the extrapolating filter.

To improve the accuracy of composition and quality control, instruments with an automatic calibration device are used. In this case, the control system performs periodic calibration of the composition analyzers, correcting their characteristics.

For the normal stable operation of NPP power units, it is necessary to maintain a number of thermal parameters within the specified limits. These functions are implemented by systems for automatic control of thermal parameters, on the reliable, efficient and stable operation of which the operation of the power unit as a whole largely depends.

In total, there are about 150 local automatic control systems (regulators) at one NPP power unit, of which approximately 30-35 can be classified as the most important, in the event of a failure of which the power unit, as a rule, is turned off by protections (level regulators in the SG, deaerator, BRU- CH, pressure in the primary circuit, etc.), or there is a decrease in the load of the power unit (level regulators in the HPH).

Maintaining the parameters manually for a long time is difficult, time-consuming and requires certain skills from the operating personnel. The operation and operational maintenance of regulators at the power unit requires the personnel to know the basics of the theory of automatic control, the principles of operation, the device and hardware on which the regulators are implemented.

Automatic control systems are used in cases where it is necessary to change or maintain constant for a long time any physical quantities called controlled variables (voltage, pressure, level, temperature, speed, etc.), characterizing the operation of the machine, technological process or dynamics of a moving object.

Devices that implement these functions are called automatic regulators.

The object of regulation is a machine or installation, the specified mode of operation of which must be maintained by the regulator with the help of regulatory bodies. The combination of the regulator and the object of regulation is called the automatic control system.

The automatic control system (CAP) based on the equipment "Kaskad-2" is made on the basis of microelectronics in the instrumental version.

Primary converters of the "Sapphire-22" type with strain-sensing elements, resistance thermometers and thermocouples were used as the main sources of information.

Let's consider the functional diagram of switching on block D07 with the balance of the regulator for the current value of the parameter (Figure 2.4).

Auto-regulator self-balancing to the current value is based on a change in the reference signal. When the switch is in the “P” position (manual mode), by acting on the “B” (more) or “M” (less) buttons, the regulator reference is set.

Figure 2.4 - Structural diagram of the self-balance of the autoregulator for the current value of the parameter

When the switch is in the “A” position (automatic mode), the output commands of the P27 control unit (minus 24V) are fed to the “ ” or “ ” inputs, causing changes in the output signal of the D07 unit. When the controller is switched on, the influence of the control pulses of the P27 unit on the integrator stops (normally closed contacts of the BVR relay open) and the controller reference remains equal to the value of the technological parameter at the moment of switching on.

CPS of the VVER-1000 reactor

Tasks to be solved by the NR control and protection system:

1. Ensuring a change in the power or other parameter of the reactor in the required range at the required speed and maintaining the power or other parameter at a certain predetermined level. Therefore, special CPS bodies are needed to ensure this function. They are called automatic regulation bodies (AR).

2. Compensation for changes in NR reactivity. Special KPS bodies that perform this task are called compensation bodies.

3. Ensuring the safe operation of the nuclear reactor, which can be carried out by the nuclear reactor by stopping the fission chain reaction in emergency situations

CPS is intended:

For automatic control of the NR power in accordance with the power supplied by the TG to the network, or power stabilization at a given level;

To start the NR and bring it to power in manual mode;

To compensate for changes in reactivity in manual and automatic mode;

Emergency protection of nuclear weapons;

For signaling the reasons for the operation of the AZ;

For automatic shunting of some AZ signals;

For signaling about malfunctions that occur in the CPS;

For signaling the position of the OR NR on the control room and control room, as well as calling information about the position of each OR in the SVRK IVS EB.

The reactor is controlled by influencing the course of the CRE with fuel nuclei in the core.

In the CPS NR being developed, a method for introducing solid absorbers in the form of rods is provided. Along with mechanical controls, the introduction of a solution of boric acid into the coolant of the primary circuit is used. Operational power control is carried out by mechanical movement of the executive bodies containing a solid absorber.

Requirements for the CPS:

1. To electrical parameters and modes:

CPS is designed for power supply from at least two independent power sources; when one source disappears, CPS operation is maintained;

When the power supply parameters are switched off for a long time, false operation of emergency protection (EP) does not occur and the control elements do not spontaneously move;

The KMS should ensure the exchange of information with different systems.

2. To reliability:

CPS service life not less than 10 years;

MTBF by control functions 10 5 hours;

The unavailability factor for the AZ functions, requiring the shutdown of the nuclear reactor, is not more than 10 -5 ;

Average recovery time 1 hour.

3. To the hardware:

CPS equipment provides the possibility of functional verification, as well as CPS parameters using control tools in preparation for launch, with the nuclear reactor running without stopping it, without violating the system functions and the reactor plant (RP) operability;

Communication lines are designed so that a fire in one line does not lead to the inability to perform functions.

4. To actuators:

Exclusion of spontaneous movement in the direction of increasing reactivity (in the event of a malfunction, power failure, and so on);

Working speed of movement 20 ± 2 mm per second;

The time of introduction of the working bodies into the active zone is 1.5 - 4 sec;

The time from the issuance of the AZ signal to the start of movement is 0.5 seconds;

The working stroke of the regulatory body is 3500 mm.

Composition of the CPS

PTK SGIU-M

PTK AZ-PZ

PTK ARM-ROM-UPZ

Equipment power supply.

On universal machines, the control of the parameters of the technological process and the machine is carried out by the machine operator. He also makes decisions on equipment restructuring, equipment shutdown, coolant supply, etc. Maintaining the operating parameters of the GPM equipment (flexible production module) or automatic line is carried out control system(Fig. 12.1), which includes control and diagnostic tools, which allows, when using the GPM, to refuse the personnel directly involved in the technological process. The PMG control system uses two sources of information: a program for monitoring deviations from the normal functioning of the PMG and information coming from diagnostic devices, such as feedback sensors that measure the movement parameters (speed, coordinates) of the working bodies of the machine and its auxiliary mechanisms or automation devices.

Rice. 12.1.

Additional means designed to perform the functions of an operator are combined into a system that includes control and measuring and diagnostic devices and instruments (with sensors for determining the value of controlled parameters), devices for collecting and initial processing of information and decision making.

In case of replacement of the operator, the system should: monitor the operation of the mechanisms of the GPM, the progress of the working process, the quality of the finished product, detect deviations from the normal

the functioning of the GPM, including those that have not yet led to failures and failures, but in the future may become their cause; fix failures and failures; to form the decisions necessary for the automatic continuation of the work of the GPM after a temporary stop for one reason or another; if necessary, interrupt the operation of the GPM, call the serviceman and inform him of information about the reason for the deviation from normal functioning.

The machine tool maintenance system consists of several subsystems that work together or autonomously, depending on design solutions or production conditions. These include the subsystem for monitoring the state of the cutting tool, the subsystem for quality control, the subsystem for monitoring the functioning of machine mechanisms and the subsystem for diagnosing mechanisms.

Devices subsystems for monitoring the state of the cutting tool can carry out periodic or current control (Fig. 12.2, 12.3). Small axial tools (drills, taps, end mills with a diameter of up to 6-8 mm), as well as other tools, are subject to periodic control if the current control of its condition is impossible or impractical. To implement this procedure, a command to stop the machine must be given.

The control device can be located in the working area of ​​the machine, on the node that carries the tool, in the tool magazine. The measurement method is usually direct, using inductive, electromechanical or photoelectric sensors. On fig. 12.2 shows the scheme for monitoring the state of tool 2 on a multi-purpose machine 6. After processing workpiece 1 and retracting the tool, probe 3 comes into contact with the drill. When the tool breaks, the position of the probe changes, as a result of which lever 4 turns and ceases to act on the electric contact sensor (limit switch) 5. At the signal of the latter, the control system gives a command to stop processing and replace the tool with an understudy or call the adjuster. As a sensor, a BVK type sensor or a Hall sensor can be used, which significantly increases its service life and trouble-free operation.

For status monitoring cutting tool on the lathe use the method of measuring the coordinate of the vertex of the cutter. After

of the next pass, the cutter moves to the control position, and in the event that there is no electrical contact between the cutter tip and a special contact plate, a signal is given to interrupt the technological process of processing, followed by a tool change or a call for an adjuster.

head; 3- tool; 4 - machine spindle

Rice. 12.2. Scheme of control of the cutting tool on a multi-purpose machine

Rice. 12.3. Placement of the measuring head on a multi-purpose machine: 1 - table; 2- measuring

For control the tool located in the magazine of the multi-purpose machine, television cameras made on the basis of CCD matrices are used, which, with satisfactory image quality, can significantly reduce the cost of equipment. The image of the instrument is projected onto the screen, and the electronic system sequentially "reads" the image and transfers it to the computer's memory. Due to the low quality of the image, special mathematical methods are used to restore it. To identify a breakdown, the reference image recorded in the computer's memory after installing a new tool is compared with the image of the same tool, but already working. The time required to transfer the image to the computer's memory is quite short, which allows the measurement to be carried out without stopping. Regardless of the tool size, the camera is always in the same position.

Periodic control is carried out and if necessary, enter a correction into the control program in case of replacing a worn or broken tool with an understudy. To do this, by means of a measuring head with a touch sensor on turning

machine tools measure the reach of cutters, on multi-purpose ones (see Fig. 12.3) - the length and diameter of the tool.

The measuring head occupies a certain position in the working area of ​​the machine: on the multi-purpose table or on the headstock of a lathe. Such measurements make it possible to "bind" the tool to the machine's coordinate system, obtain information about the presence of the tool in the spindle, control its wear and integrity.

The current state control is subjected to axial tool with a diameter of more than 8... 12 mm, as well as cutters and cutters different kind. Control is carried out in the cutting process; its purpose is to prevent emergency situations that occur when a tool breaks suddenly. The monitoring method is mainly indirect (by torque, main drive motor current, load, acceleration, etc.).

So, when the tool becomes blunt, the cutting force increases, and, consequently, the load (torque) on the motor and the current flowing through its windings. The sensitivity of a torque sensor operating according to this principle depends on the type of engine, its power and the value of the gear ratio of the kinematic chain between the engine and the spindle assembly. Before the start of each cutting cycle, the idle load must be measured and stored.

Measurement of the axial load on the lead screw of the machine using strain gauge, the screw built into the support allows you to monitor the wear of the tool, as well as the change in the mode of its operation in the process of processing a batch of workpieces (for example, a change of 0.2 ... 0.3 mm is recorded on a lathe). The signal of such a sensor is practically free from interference. The sensor is of low inertia, i.e. can register fast-changing loads caused, for example, by uneven rotation of the lead screw within one revolution.

To measure the load experienced by turrets, spindle boxes and spindle assemblies, strain gauges are built into them, made in the form of strain bearings. The rotation of each bearing ball under the appropriate load causes local deformation of the outer ring, perceived by strain gauges placed in a groove on the outer surface of the ring. When processing the output signal of the sensor, one should take into account its pulsation, the frequency of which is directly related to the spindle speed.

To measure the load acting on various nodes, it is widely used overhead piezo sensors(Fig. 12.4). Their sensitivity is higher than that of thermistors, and the bandwidth allows you to fix fairly fast changes in the load acting on the tool.

Structural solutions implemented when using such sensors are different. For example, they are built into a slab placed under

Rice. 12.4. Piezo sensors for measuring cutting force: a

concept of measurement; b - its constructive implementation; (1 - elastic element; 2 - piezoelectric sensor; 3 - machine part; 4 - contact surfaces, / - measuring base of the sensor; R,- tension-compression force;

R, - pressing force

under the turret head of a lathe. For creating

preload, the piezoelectric sensor should protrude above the surface by 10 ... 15 microns.

Tool wear can be determined by the magnitude of the elastic wave acceleration, which

propagates from the cutting zone to the sensor installation site

(1accelerometer), fixing

vibroacoustic emission. If the tool is rotating, the sensor

installed on the machine table; if

the tool is stationary, and the workpiece rotates - on the tool holder or on the body of the turret. When using such sensors, it is necessary for tools

each type to pre-determine the frequency range, in

which shows the relationship between the parameters to the greatest extent

vibroacoustic emission with wear or breakage of the tool. The number of joints between the workpiece (or tool) and the sensor should be reduced as much as possible, as they have a deforming effect (weaken vibrations), which makes measurements difficult.

The operating time of the tool is measured timer, plunging and cutting time - force sensor or acceleration(the moments of the beginning and end of the cutting process are fixed), the magnitude of the components of the cutting forces - pressure sensors in hydrostatic spindle bearings or magnetoelastic sensors, measuring cutting torque, EMF - millivoltmeter, electrical resistance of the contact between the workpiece and the tool - ohmmeter.

It should be taken into account that the reliability of automatic control of the state of the cutting tool is relatively low. The reasons may be microcracks in the cutting part, heterogeneity and local fluctuations in the hardness of both the processed and tool material, and other factors that cannot be determined by automatic means. Therefore, it is recommended double control tool life resource for its timely replacement and the real state of the tool according to one of the indirect parameters (current control).

When designing equipment, the sensors used to control the tool are not developed. The designer chooses a commercially available or orders a special sensor, the characteristics of which correspond to the task, and embeds it in the appropriate area of ​​the machine.

Various devices used in the cutting tool condition monitoring subsystem are described in the literature. One such device is the Monitor system used in the GPM. Monitoring system with a contact indicator (see Fig. 12.5) is based on information coming from the machine feed drive and sensors that record the movement of the table and spindle assembly. Three arrays of data are entered into the Monitor: 1) constants that determine the device setting on a particular machine, the type of control and the signal level from the sensor (for example, current); 2) instrument questionnaires containing permanent data on the characteristics of specific instruments; 3) a control program compiled for each processed workpiece. Data is entered using the keyboard; information is displayed on a display screen or a digital display.

Rice. 12.5. Monitoring scheme with contact indicator: 1 - contact indicator; 2 - workpiece (detail); 3 - control panel; 4 - information input device; 5 - terminals; 6 - head control computer; 7-

counter; 8 - impulse lines

To quality control subsystem devices(Fig. 12.6) includes active control devices (PAK) used in mass and large-scale production, and touch sensors used in mass production.

If necessary automatic control sizes, shapes and the accuracy of setting the workpiece and (or) the machined part on different

Rice. 12.6. Typical schemes for controlling the accuracy of processing when using PAC (o) and auto-adjustment ( 6)

processing stages use PAK, which can be located both in the working area of ​​the machine (Fig. 12.6, a), and with automatic cycle control. At the same time, two information flows are organized in the machine control system. The first provides the processing process according to a given program, the second is used to adjust the level of adjustment. The operator is also involved in the management of the processing process, his task is to adjust the level of machine settings and active controls. In the second flow of information, there are two control loops: the loop / refers to the automatic control system by means of a HSS or auto-adjuster (Fig.

12.6, b), contour II- to the system of manual adjustment of the processing process using a conventional measuring

device. The schemes are conditionally marked: TO - technological operation; IO - the executive body of the machine; MP - mechanism for adjusting the machine; BUT

• - auto adjuster; E - standard; IP - measuring device; Op
• - operator.

for roughness processed

For dimensional control workpieces and (or) parts (and in some cases for the counter-surface) on CNC and GPM machines are measuring heads (MG) (sometimes

called contact indicators). The IG (Fig. 12.7), consisting of a probe complete with an electronic unit and a wireless signal transmission device (usually on infrared rays), is located in the tool magazine, from where the manipulator moves it to the spindle (on drilling-milling-boring machines) or turret head (on lathes).

Rice. 12.7. Measuring head: 1 - probe tip; 2 - probe; 3-

transmission mechanism; 4 - probe balancing mechanism; 5 - electrical contact; 6 - touch signal generator; 7 - signal sent to the electronic unit or to the transmitter

With the relative movement of the probe tip and the controlled surface, they touch. The probe deviates from its original position,

the electrical contact inside the IG opens, and the touch signal generated

by a special circuit, it enters the CNC through the electronic unit, where the received data is compared with the given values ​​of the corresponding parameter.

Similar IGs are used to control allowances and basing the workpiece, for intermediate control of workpieces on the machine during processing and output control of the machined part on the machine. At the same time, in order to determine the distance between two planes, the coordinates of three points on each of them are measured and their difference is calculated. To determine the position of the center of the hole, the coordinates of three points in the radial section are measured and then the coordinates of the center of the circle passing through these three points are calculated (all these procedures are carried out automatically.

When designing processing equipment, PAK and IG are usually not designed; their development is carried out by special design organizations. The equipment designer builds a commercially available or custom instrument into the equipment. However, he must take care of the development of algorithms for the joint functioning of the machine and the control device (measurement, calculations, decision recommendations).

The stability of the machining process on modern CNC machines makes it possible not to build measuring devices into them, but to use the coordinate measuring machine (CMM) installed in the workshop for periodic quality control of machining. In this case, the machine operator or adjuster installs the machined part on the CMM, measures the controlled parameters, and, depending on the results obtained, sends the part for additional processing or a subsequent technological operation, and, if necessary, makes adjustments to the machine.

Subsystem for monitoring the functioning of machine mechanisms(Fig. 12.8) includes a number of measuring devices that fix deviations from the norm (for example, overheating of the movement of the main drive is recorded by a temperature sensor). At the output of these devices,

Rice. 12.8. The structure of the subsystem for monitoring the functioning of mechanisms; IU, IU 2 ... IU - measuring devices; D - sensor; POS - primary signal processing; USO - device for collecting and processing information; UPR - decision making device; URR - decision implementation device

normalized signals that enter the device for collecting and processing information, from where they are transmitted to the decision-making device. Here, taking into account additional information, a certain decision is made, which is subsequently implemented in the form of appropriate commands.

In their structure, microprocessor devices are identical to modern CNCs and differ from them only in the composition of modules for communication with an external device, the presence of feedback sensors and measuring devices.

Subsystem for diagnosing the state of mechanisms must ensure the operation of the machine with minimal operator involvement. There are devices for diagnosing hydraulic drives of machine tools, rolling bearings, gearboxes, feed boxes and other similar devices.

Control and compensation of typical deformation units of the machine make it possible to ensure the accuracy of processing during long-term operation. So, due to heating, the spindle assembly is displaced, which leads to a decrease in processing accuracy. Compensation in this case is based on the periodic measurement of the actual displacements of the assembly parts in space. With the help of the IG installed on the machine spindle, the position of the reference surface on its table is measured, or with the help of the IG for tool control installed on the machine table, the position of the reference mandrel in the spindle is measured. The difference between the results of successive measurements determines the displacement of the spindle for the corresponding period of time. Entering this value into the CNC memory allows you to correct the displacements specified in the control program, and thereby compensate for the effect of thermal deformations.

Such diagnostic systems are designed by the machine designer, usually from mass-produced or special elements, although in some cases it is necessary to develop special diagnostic devices. Bellows membrane relays are often used as such devices.

Automatic regulation is the control of technological processes with the help of advanced devices with predetermined algorithms.

In everyday life, for example, automatic regulation can be carried out using a thermostat that measures and maintains the room temperature at a given level.

Once the desired temperature is set, the thermostat automatically controls the room temperature and turns the heater or air conditioner on or off as needed to maintain the set temperature.

In production, process control is usually carried out by means of instrumentation and A, which measure and maintain at the required level the technological parameters of the process, such as: temperature, pressure, level and flow. Manual control in more or less large-scale production is difficult for a number of reasons, and many processes cannot be controlled manually at all.

Technological processes and process variables

For the normal performance of technological processes, it is necessary to control the physical conditions of their flow. Physical parameters such as temperature, pressure, level and flow can change for many reasons and their changes affect the process. These changing physical conditions are called "process variables".

Some of them can reduce production efficiency and increase production costs. The task of the automatic control system is to minimize production losses and control costs associated with an arbitrary change in process variables.

In any production, the impact on raw materials and other initial components is carried out to obtain the target product. The efficiency and economic operation of any production depends on how the processes and process variables are controlled through special control systems.

In a coal-fired thermal power plant, coal is ground up and then burned to produce the heat needed to convert water into steam. Steam can be used for a variety of purposes, such as operating steam turbines, heat treating or drying raw materials. The series of operations that these materials and substances go through is called the "technological process". The word "process" is also often used in relation to individual operations. For example, the operation of grinding coal or turning water into steam could be called a process.

The principle of operation and elements of the automatic control system

In the case of an automatic control system, monitoring and control is carried out automatically using pre-configured instruments. The equipment is able to perform all actions faster and more accurately than in the case of manual control.

The action of the system can be divided into two parts: the system detects a change in the value of the process variable and then takes a corrective action to force the process variable back to the set value.

The automatic control system contains four main elements: the primary element, the measuring element, the regulating element and the final element.

The primary element takes the value of the process variable and converts it into a physical value, which is transferred to the measuring element. The measuring element converts the physical change produced by the primary element into a signal representing the value of the process variable.

The output signal from the measuring element is sent to the regulating element. The regulating element compares the signal from the measuring element with the reference signal, which is the set value, and calculates the difference between the two signals. The control element then generates a correction signal, which is the difference between the actual value of the process variable and its setpoint.

The output signal from the regulating element is sent to the final regulation element. The final control element converts the signal it receives into a corrective action that causes the process variable to return to the setpoint.

In addition to the four basic elements, process control systems may have auxiliary equipment that provides information on the magnitude of the process variable. This equipment may include instruments such as chart recorders, meters, and alarm devices.

Types of automatic control systems

There are two main types of automatic control systems: closed and open, which differ in their characteristics and, therefore, in their applicability.

Closed-loop control system

In a closed system, information about the value of the controlled process variable passes through the entire chain of instruments and devices designed to control and regulate this variable. Thus, in a closed system, the controlled variable is continuously measured, compared with the set value, and the process is influenced accordingly to bring the controlled variable in line with the set value.

For example, such a system is well suited to control and maintain the required level of liquid in the tank. The displacer perceives a change in the liquid level. The transmitter converts the level changes into a signal that it sends to the controller. Which, in turn, compares the received signal with the required level set in advance. The regulator then generates a corrective signal and sends it to the control valve, which corrects the water flow.

Open-loop control system

In an open system, there is no closed chain of measuring and signal processing instruments and devices from the output to the input of the process, and the effect of the controller on the process does not depend on the resulting value of the controlled variable. No comparison is made between the current and desired value of the process variable and no corrective action is generated.

One example of an open-loop control system is an automatic car wash. This is a technological process for car washing and all the necessary operations are clearly defined. When a car comes out of a car wash, it is supposed to be clean. If the car is not clean enough, the system does not detect this. There is no element here that would give information about this and correct the process.

In manufacturing, some open-loop systems use timers to ensure that a series of sequential operations are completed. This kind of open-loop control may be acceptable if the process is not very critical. However, if the process requires certain conditions to be checked and adjustments made if necessary, an open-loop system is not acceptable. In such situations, it is necessary to apply a closed system.

Automatic control methods

Automatic control systems can be built around two basic control methods: closed-loop control, which works by correcting process variable deviations after they have occurred; and with a disturbance action that prevents the occurrence of deviations in the process variable.

Feedback control

Closed-loop control is a method of automatic control where the measured value of a process variable is compared to its pickup setpoint and action is taken to correct any deviation of the variable from the setpoint.

The main disadvantage of a closed-loop control system is that it does not begin to control the process until the controlled process variable has deviated from its setpoint.

The temperature must change before the control system opens or closes the control valve on the steam line. In most control systems, this type of control action is acceptable and is built into the system design.

In some industrial processes, such as the manufacture of pharmaceuticals, the process variable cannot be allowed to deviate from the setpoint value. Any deviation may result in product loss. In this case, a control system is needed that would anticipate process changes. Such a proactive type of regulation is provided by the regulation system with the impact on the perturbation.

Disturbance control

Disturbance control is feedforward control because an expected change in the controlled variable is predicted and action is taken before that change occurs.

This is the fundamental difference between disturbance control and feedback control. A disturbance control loop tries to neutralize the disturbance before it changes the manipulated variable, while a feedback control loop attempts to handle the disturbance after it affects the manipulated variable.

A disturbance control system has a clear advantage over a feedback control system. In the case of disturbance control, in the ideal case, the value of the controlled variable does not change, it remains at the value of its setting. But manual disturbance control requires a more sophisticated understanding of the effect that a disturbance will have on the controlled variable, as well as the use of more complex and accurate instruments.

It is rare to find a pure disturbance control system in a plant. When a disturbance control system is used, it is usually combined with a feedback control system. Even so, disturbance control is reserved for more critical operations that require very precise control.

Single-loop and multi-loop control systems

A single-loop control system or simple control loop is a control system with a single loop, which usually contains only one primary sensing element and provides processing of only one input signal per regulator.

Some control systems have two or more primary elements and process more than one input per regulator. These automatic control systems are called "multi-loop" control systems.