Ministry of vocational education

Tomsk Polytechnic University

Skorospeshkin M.V.

Basics of automation of production processes

Lecture notes

Part 1. Theory of Automatic Control (TAU)

1. Basic terms and definitions of TAU.

1.1. Basic concepts.

Control systems for modern technological processes are characterized by a large number of technological parameters, the number of which can reach several thousand. To maintain the required operating mode, and ultimately the quality of the products, all these values ​​must be kept constant or changed according to a certain law.

The physical quantities that determine the course of the technological process are called process parameters ... For example, the parameters of the technological process can be: temperature, pressure, flow rate, voltage, etc.

The parameter of the technological process, which must be kept constant or changed according to a certain law, is called adjustable value or adjustable parameter .

The value of the controlled variable at the considered moment of time is called instantaneous value .

The value of the controlled variable obtained at the moment in time under consideration on the basis of the data of a certain measuring device is called its measured value .

Example 1. Scheme of manual regulation of the temperature of the drying cabinet.

It is required to manually maintain the temperature in the drying cabinet at the level T back.

The human operator, depending on the readings of the mercury thermometer RT, turns on or off the heating element H using the switch P. 

Based on this example, you can enter definitions:

Control object (object of regulation, OU) - a device, the required operating mode of which must be supported from the outside by specially organized control actions.

Control - the formation of control actions that ensure the required operating mode of the OS.

Regulation - a particular type of control, when the task is to ensure the constancy of any output value of the OA.

Automatic control - management carried out without direct human participation.

Input action (NS)- the impact applied to the input of the system or device.

Output impact (Y) - the impact produced at the output of a system or device.

External influence - the impact of the external environment on the system.

The block diagram of the control system for example 1 is shown in Fig. 1.2.

Example 2. Scheme of automatic temperature control of the drying cabinet.

The circuit uses a mercury thermometer with RTK contacts. When the temperature rises to a predetermined value, the contacts are closed by a column of mercury, the coil of the relay element RE is energized and the heater circuit H is opened by the contact RE. When the temperature drops, the thermometer contacts open, the relay is de-energized, resuming the supply of energy to the object (see Fig. 1.3). 

R
is. 1.3

Example 3. Temperature ACP circuit with a measuring bridge.

When the temperature of the object is equal to the specified one, the measuring bridge M (see Fig. 1.4) is balanced, the signal does not arrive at the input of the electronic amplifier EI and the system is in equilibrium. When the temperature deviates, the resistance of the thermistor R T changes and the balance of the bridge is disturbed. A voltage appears at the EU input, the phase of which depends on the sign of the temperature deviation from the set one. The voltage amplified in the EI goes to the engine D, which moves the motor of the autotransformer AT in the appropriate direction. When the set temperature is reached, the bridge will balance and the engine will shut off.

(exercise)

The value of the set temperature value is set using a resistor R set. 

Based on the described examples, it is possible to determine a typical block diagram of a single-circuit ACP (see Fig. 1.5). Accepted designations:

x is the setting action (task), e = x - y is the control error, u is the control action, f is the disturbing action (disturbance).

Definitions:

Setting effect (the same as the input action X) - the impact on the system, which determines the required law of variation of the controlled variable).

Controlling influence (u) - the influence of the control device on the control object.

Control device (UU) - a device that influences the control object in order to ensure the required mode of operation.

Disturbing impact (f) - action tending to disrupt the required functional relationship between the reference action and the controlled value.

Control error (e = x - y) is the difference between the prescribed (x) and actual (y) values ​​of the controlled variable.

Regulator (P) - a set of devices connected to a regulated object and providing automatic maintenance of a given value of its regulated value or its automatic change according to a certain law.

Automatic regulation system (ACP) is an automatic system with a closed circuit of action, in which control (u) is generated as a result of comparing the true value of y with a given value of x.

An additional connection in the structural diagram of the ACP, directed from the output to the input of the considered section of the chain of influences, is called feedback (OS). Feedback can be negative or positive.

Automation of production processes is the main direction in which production is currently moving around the world. Everything that was previously performed by a person himself, his functions, not only physical, but also intellectual, are gradually moving to technology, which itself performs technological cycles and exercises control over them. This is the mainstream of modern technologies now. The role of a person in many industries is already reduced to only a controller over an automatic controller.

In the general case, the concept of "process control" is understood as a set of operations necessary to start, stop the process, as well as maintain or change in the required direction of physical quantities (process indicators). Individual machines, units, apparatuses, devices, complexes of machines and apparatuses that need to be controlled, which carry out technological processes, are called control objects or controlled objects in automation. Managed objects are very diverse in their purpose.

Automation of technological processes- replacement of the physical labor of a person spent on controlling mechanisms and machines by the operation of special devices that ensure this control (regulation of various parameters, obtaining a given productivity and product quality without human intervention).

Automation of production processes allows many times to increase labor productivity, improve its safety, environmental friendliness, improve product quality and more efficiently use production resources, including human potential.

Any technological process is created and carried out for a specific purpose. Manufacturing of the final product, or to obtain an intermediate result. So the purpose of automated production can be sorting, transportation, packaging of the product. Production automation can be complete, complex and partial.

Partial automation takes place when one operation or a separate production cycle is carried out in an automatic mode. In this case, limited participation of a person in it is allowed. Most often, partial automation takes place when the process proceeds too quickly for a person himself to fully participate in it, while rather primitive mechanical devices, driven by electrical equipment, do an excellent job with it.

Partial automation, as a rule, is used on already operating equipment, it is an addition to it. However, it shows the greatest efficiency when it is included in the general automation system from the very beginning - it is immediately developed, manufactured and installed as an integral part of it.

Complex automation should cover a separate large production area, it can be a separate workshop, power plant. In this case, all production operates in the mode of a single interconnected automated complex. Comprehensive automation of production processes is not always advisable. Its field of application is modern highly developed production, which uses extremelyreliable equipment.

The breakdown of one of the machines or unit immediately stops the entire production cycle. Such production should have self-regulation and self-organization, which is carried out according to a previously created program. In this case, a person takes part in the production process only as a permanent controller, monitoring the state of the entire system and its individual parts, intervenes in production for start-up and start-up and in the event of emergency situations, or the threat of such occurrence.

The highest level of automation of production processes - full automation... With her, the system itself exercises not only the production process, but also full control over it, which is carried out by automatic control systems. Full automation makes sense in a cost-effective, sustainable production with well-established technological processes with a constant operating mode.

All possible deviations from the norm must be foreseen in advance, and systems of protection against them must be developed. Also, full automation is necessary for work that can threaten human life, health, or are carried out in places inaccessible to him - under water, in an aggressive environment, in space.

Each system is made up of components that perform specific functions. In an automated system, sensors take readings and transmit them to make a decision on how to control the system, the command is already executed by the drive. Most often, this is electrical equipment, since it is with the help of an electric current that it is more expedient to execute commands.

It is necessary to separate the automated control system and the automatic. At automated control system the sensors transmit the readings to the control panel to the operator, and he, having made a decision, transmits the command to the executive equipment. At automatic system- the signal is analyzed by electronic devices, they, having made a decision, give a command to the executing devices.

Human participation in automatic systems is nevertheless necessary, albeit as a controller. He has the ability to intervene in the technological process at any time, correct it or stop it.

So, the temperature sensor may fail and give incorrect readings. Electronics, in this case, will perceive its data as reliable, without questioning them.

The human mind is many times superior to the capabilities of electronic devices, although it is inferior to them in terms of response speed. The operator can understand that the sensor is defective, assess the risks, and simply turn it off without interrupting the process. At the same time, he must be completely sure that this will not lead to an accident. Experience and intuition, which are inaccessible to machines, help him to make a decision.

Such targeted intervention in automatic systems does not pose serious risks if the decision is made by a professional. However, turning off all automation and transferring the system to manual control mode is fraught with serious consequences due to the fact that a person cannot quickly respond to a change in the situation.

A classic example is the accident at the Chernobyl nuclear power plant, which became the largest man-made disaster of the last century. It happened precisely because of the shutdown of the automatic mode, when the already developed programs for the prevention of emergencies could not influence the development of the situation in the reactor of the station.

The automation of individual processes began in industry as early as the nineteenth century. Suffice it to recall the automatic centrifugal regulator for steam engines designed by Watt. But only with the beginning of the industrial use of electricity became possible more extensive automation of not individual processes, but entire technological cycles. This is due to the fact that before that the mechanical force was transmitted to the machine tools using transmissions and drives.

The centralized production of electricity and its use in industry, by and large, began only in the twentieth century - before the First World War, when each machine was equipped with its own electric motor. It is this circumstance that made it possible to mechanize not only the production process itself on the machine, but also to mechanize its control. This was the first step towards creating automatic machines... The first samples of which appeared in the early 1930s. Then the very term "automated production" arose.

In Russia, back then in the USSR, the first steps in this direction were made in the 30s and 40s of the last century. For the first time, automatic machine tools were used in the production of bearing parts. Then came the world's first fully automated production of pistons for tractor engines.

Technological cycles were combined into a single automated process, starting with the loading of raw materials and ending with the packaging of finished parts. This became possible thanks to the widespread use of modern electrical equipment at that time, various relays, remote switches, and, of course, drives.

And only the appearance of the first electronic computers made it possible to reach a new level of automation. Now the technological process has ceased to be considered as simply a collection of individual operations that must be performed in a certain sequence to obtain a result. Now the whole process has become one whole.

Currently, automatic control systems not only conduct the production process, but also control it, monitor the occurrence of emergency and emergency situations. They start and stop technological equipment, monitor overloads, and practice actions in case of accidents.

Recently, automatic control systems make it easy to rebuild equipment for the production of new products. This is already a whole system, consisting of separate automatic multi-mode systems connected to a central computer, which links them into a single network and issues tasks for execution.

Each subsystem is a separate computer with its own software designed to perform its own tasks. This is already flexible production modules. They are called flexible because they can be reconfigured for other technological processes and thereby expand production, versify it.

The pinnacle of automated production is. Automation has permeated production from top to bottom. A transport line for the delivery of raw materials for production works automatically. Management and design are automated. Human experience and intelligence are used only where electronics cannot replace it.

Introduction ( Basics of process automation)

At present, there is a rapid development of the production and use of self-acting machines and apparatus, an increase in the number of production processes carried out according to the type of unmanned technology. Various automatic devices penetrate into all spheres of human activity, including science, production and everyday life. For an engineer of any specialty, it became necessary to familiarize himself with the theoretical foundations and practical applications of automation in relation to his professional interests. This is especially important for electrical engineers specializing in the field of automated electric drives, since most of their professional activity consists in the creation of equipment for the automation of various technological processes, its adjustment and operation in a production environment.

The usual course of automation of technological processes is based on the technology of a certain production: machine-building, metallurgical, chemical, textile, etc. process equipment control systems. It is important for specialists in automated electric drive to get an idea about the general tasks solved by automation in modern highly mechanized and automated production, about the place of an electric drive in automation systems. They must study the basics of the theory of automation of technological processes and learn how to solve simple technical problems associated with design, the choice of hardware for automated systems, the development of algorithms and software for their operation in specific operating conditions.

Term automation refers to a very wide class of production processes and other systems for organizing labor and other human activities, in which a significant amount of operations related to the processes of receiving, converting, transferring and using energy, materials and especially information is transferred to specialized technical devices, mechanization and control machines ... Automated processes, including management, regulation and (partially) control over them, proceed autonomously, in accordance with a program prepared in advance and introduced on a special program carrier, so that there is no need for direct human participation in their normal functioning. The maintenance personnel are left with only the functions of general control, and, if necessary, repair and adjustment. Mechanization, which consists in replacing manual labor, physical efforts of a person with machine operations, is an indispensable element of automation. In contrast to simple mechanization, automation necessarily includes the transfer of operations to control machines to control and organize the process being automated in accordance with a goal previously formulated and, possibly, refined during the implementation of the process. The goals of automation are manifold. They can include solving problems of increasing labor productivity and efficiency, improving product quality, optimizing management, ensuring the safety of human labor activity, protecting the environment, etc.

Automation goals are achieved using automated control systems(ACS), ACS is a set of mathematical methods, technical means (the main ones are computers and other microprocessor devices), their software and organizational complexes that provide control and monitoring of the parameters of automated objects in accordance with the stated goal of their autonomous functioning. Among the objects of automation are:

technological, energy, transport and other production processes;

design of various units and machines, ships, buildings and other structures, industrial complexes;

organization, planning and management within a shop, enterprise, construction site, military unit, etc .;

scientific and technical research, medical diagnostics, accounting and processing of statistical data, programming, household appliances, security systems, etc.

Of all the listed variety of automated objects, we will consider only the technological processes of industrial production. With the automation of the latter, the control and monitoring functions previously performed by humans are transferred to automatic control devices and instrumentation. At the same time, the mechanization of individual working operations is being improved. The control devices, receiving information via feedback channels about changes in monitored parameters, such as the size of the processed products, processing speed, temperature, form, in accordance with the specified processing program, control signals that ensure the execution of the processing program in the optimal operating mode.

The first chapter discusses general issues of automation of technological processes, the main functions and structure of the process control system. Since the control of a technological process becomes possible thanks to information processes that are formed in parallel with the current technological process, the second chapter discusses the elements of information theory in relation to the formation of information management processes. Special attention is paid here to the issues of coding information in binary codes, since these codes are the basis for the functioning of all modern control devices. The chapter ends with an examination of the ways of organizing the exchange of information by means of its transmission through communication channels within the framework of the process control system.

The construction of an automated process control system is impossible without a sufficiently accurate and detailed description of the properties and characteristics of a controlled technological object (TO). Therefore, the third chapter is devoted to the presentation of analytical and experimental methods for creating a TO model that reflects the specified properties and characteristics.

The central place in the textbook is occupied by chapters 4 and 5, devoted to methods of analysis and synthesis of control algorithms for process control systems. The control algorithms display the planned ways of solving the problems of the process control system for stabilization and program control of parameters and maintenance modes, which ensures the flow of technical processes in accordance with a given criterion of optimality. Particular attention is paid to the consideration of ways to optimize the modes of operation of TO with linear and nonlinear characteristics and the creation of block diagrams of control algorithms. The latter are the basis for creating control programs in the process of programming the hardware of automation systems.

The sixth chapter covers the stages of designing an automated process control system, starting with the selection of the necessary technical means for building an automated process control system, developing a technical specification and ending with detailed design. In conclusion, in the seventh chapter, the issues of building automation systems in mechanical engineering based on the CNC and programmable logic controllers are considered as an example.

FOREWORD

INTRODUCTION

Chapter 1. GENERAL INFORMATION ABOUT AUTOMATIC CONTROL OF PRODUCTION PROCESSES, CLASSIFICATION OF AUTOMATIC REGULATION SYSTEMS (SAR)

1.1 Basic concepts and definitions of the theory of automatic control

1.1 Principles of regulation

1.3 Algorithm (law) of regulation 5

1.4 Basic requirements for automatic control systems

2 Transfer functions of a linear system. Structural diagrams and their transformations

3 Statics of automatic control systems

3.1 Static characteristics of ATS elements and links

3.2 Static characteristics of link connections

4 The concept of the stability of automatic control systems

Chapter 2. METROLOGICAL CHARACTERISTICS OF TECHNICAL MEASUREMENTS

2.1 Basic metrological terms and definitions. Measurement concept

2 Types of measuring instruments (SI)

3 Systems and units of physical quantities

4 Metrological characteristics of measuring instruments. Calibration and verification of measuring instruments

Chapter 3. ELECTRIC SENSORS OF MECHANICAL VALUES

3.1 Linear and angle encoders

2 Force sensors

3 Speed ​​sensors

Chapter 4. METHODS AND MEANS OF MEASURING BASIC TECHNOLOGICAL PARAMETERS

4.1 Electrical measurement methods

2 Methods and means of measuring temperature

3 Methods and means of level measurement

4 Methods and means of measuring pressure

4.1 Direct pressure measurement methods

4.2 Methods for indirect pressure measurement

5 Methods and means of measuring flow

5.1 Differential pressure flow meters

5.2 Constant differential pressure flowmeters

5.3 Electromagnetic flowmeters

5.4 Ultrasonic flow meters

5.5 Variable level meters

5.6 Thermal flow meters

5.7 Vortex flowmeters

5.8 Coriolis flowmeters

Chapter 5. METHODS AND EQUIPMENT FOR MEASURING VIBRATION

5.1 Vibration measurement methods

2 Vibration measuring instruments

Chapter 6. MEASUREMENT OF PHYSICAL AND CHEMICAL PROPERTIES OF LIQUIDS AND GASES

6.1 Measurement of physical and chemical properties of oil and formation waters

1.1 Measurement of physical and chemical properties of oil

1.2 Measurement of physicochemical properties of formation water

2 Measurement of physical and chemical properties of gases

Chapter 7. RELAY ELEMENTS

7.1 AC and DC electromagnetic relays

1.1 Constant electromagnetic relays (neutral)

1.2 AC electromagnetic relays

2 Magnetically operated contacts (reed switches)

Chapter 8. TRANSMISSION OF INFORMATION IN AUTOMATION SYSTEMS

8.1 Basic information about telemechanics systems

2 Data interfaces

Chapter 9. MICROPROCESSORS

9.1 Basic information about microprocessors

2 Analog-to-digital and digital-to-analog conversion of information

CONCLUSION

LITERATURE

ANNEXES

Appendix 1. Control and measuring materials

Appendix 2. List of practical and laboratory work

Appendix 3. List of topics for settlement and graphic works (abstracts)

Appendix 4. List of basic and additional literature

FOREWORD

The textbook "Fundamentals of Automation of Technological Processes of Oil and Gas Production" contains a systematic presentation of the academic discipline of the same name, fully corresponds to the curriculum, and, in fact, is the main textbook for the discipline. It reflects the basic knowledge defined by the didactic units of the Federal State Educational Standard in the field of 131000 "Oil and Gas Business", specialty "Operation and maintenance of oil production facilities". The content of the textbook includes a description of methods for obtaining and using knowledge in the field of automation of technological processes, methodological foundations of basic methods and patterns of functioning of measuring instruments and automation systems and the development of the areas of activity reflected in them, as well as key problems and major trends in the development of the oil and gas industry.

The aim of the tutorial is to provide methodological assistance to trainees in creating the necessary initial theoretical knowledge base for trainees on the basic principles of building automation systems for production processes, as well as on the technical means of automation, on the basis of which the mentioned systems are built. When studying the educational material, the student will receive information about the basics of automation of measuring processes, the types and methods of measurement, the device and features of the operation of specific sensors of the main technological parameters, secondary devices and microprocessor technology.

The purpose of the manual is to provide students with the opportunity to study the device and the principle of operation of specific equipment and automation equipment, as well as some of the rules for their operation.

In the process of studying the material, students should familiarize themselves with the basics and classification of methods and measuring instruments; to get a clear idea about the technological complex, about the points of signal pickup of the technological process parameters; to master the schematic diagrams of the equipment, the principles of operation of sensors and relays, the technical capabilities of microprocessor equipment and automation means, the rules for constructing structural diagrams, the regulation criteria, the prospects for the introduction of computers in the development and operation of wells, the rules for the technically competent operation of equipment and automation; to acquire the skills of conducting a comparative analysis of controls and automation; learn about the complexities of using automation tools and the prospects for their development.

Based on the theoretical knowledge gained, students should learn how to perform practical and laboratory work, and subsequently be able to mount simple equipment, decipher and analyze the equipment recording diagrams, evaluate the information received, correct the development and operation modes of automation systems for oil and gas production processes using specialized equipment ...

INTRODUCTION

Automation of technological processes is a decisive factor in increasing labor productivity and improving the quality of products.

Technological processes of modern industrial facilities require control of a large number of parameters and are difficult to control. In this regard, in the design and operation of industrial installations, exceptional importance is attached to the issues of professionalism of specialists working at enterprises of the fuel and energy complex.

Over the years of development of oil refining and the petrochemical industry, the processes have become more complex, which requires more precise control of them. In the first half of the XX century, devices for registration and control of parameters appeared, the so-called instrumentation - instrumentation. The origin, formation and development of measuring and control devices, the process from automatic regulation to automated control systems and control at the macro and micro levels is an integral part of the processes of oil and gas production, oil refining and petrochemistry.

Further improvement of devices for recording, monitoring and controlling parameters has led to the automation and telemechanization of oil refining and petrochemistry. The latter led to computerization and process control, that is, to automated control systems (ACS).

And, of course, progress in instrumentation and apparatus engineering in ACS is an interesting task, the solution of which is necessary to determine further development prospects based on overcoming global management problems in the oil and gas sector.

Six main modern problems of operational management of production and automation in oil and gas production are formulated:

Accounting for the production, movement and use of hydrocarbon raw materials, oil, gas, petroleum products, for the solution of which it is important to ensure the possibility of monitoring accounting operations, including from licensed areas, as well as to ensure the conduct of internal and external audits on oil accounting, which in turn requires the development of appropriate measuring instruments, as well as a software and information system.

Management of territorial assets, organization of maintenance and repair of equipment, ensuring the safety of production and personnel. To solve this problem, it is required to develop software and information tools that provide accounting, planning maintenance and repairs, monitoring the state of production assets and work performed; control of the conclusion and implementation of contracts with contractors for the performance of work; control over the presence of personnel at production facilities; the possibility of on-site training of personnel using simulators; availability at workplaces of up-to-date documentation on the use of equipment, on the technology for performing procedures and operations.

High level of energy consumption of production and the need for energy saving and energy efficiency measures. To solve this problem, software and information tools are required to provide accounting, planning maintenance and repairs, monitoring the state of energy consumption by elements of the technological process; identification of energy consumption objects with an excess of the standard level of electricity consumption; control over the implementation of energy saving measures.

Variety of means of APCS, modeling and information systems. This problem requires the development of software and information tools that provide the formation of an array of initial information for strategic (plans for the development and location of production), medium-term (annual and monthly plans) and operational (daily and shift plans) management plans; meeting the requirements for the composition and structure of documents in accordance with the internal regulations of the enterprise, the requirements of standardization of shareholders; unification of access and differentiation of powers when working with documents.

Minimizing the cost of operating the system while maximizing the level of information service provided to decision-makers. To solve the problem, the following are required: development of a methodology for performing work on the development of the MES-level, automation of previously non-automated production facilities and software and information tools that provide: keeping the databases up-to-date and the operable state of the system software; control over the functioning of the system software (for the exchange of information with the APCS systems, ERP, etc.); recording the actions of the personnel involved in the operation of the system.

The increase in funds and labor for the extraction of each ton of oil is due to the fact that the fields of cheap oil in Western Siberia, discovered in the late 1950s, are gradually depleting. In the oil-bearing region, there are mainly reserves with difficult production, requiring new technological solutions and additional capital investments. To solve this problem, it is necessary to improve the efficiency of capital investments and facilitate the management of oil recovery; increase the efficiency of capital investments and facilitate the management of oil extraction from the subsoil through an approach called “smart fields”, “smart fields”, “smart oil fields”, “smart wells”; optimize the operation of all field facilities: wells, reservoirs, pipelines and other surface facilities.

Chapter 1. GENERAL INFORMATION ABOUT AUTOMATIC CONTROL OF PRODUCTION PROCESSES, CLASSIFICATION OF AUTOMATIC REGULATION SYSTEMS (SAR)

1Basic concepts and definitions of the theory of automatic regulation

It is known that the technical process is characterized by a set of data, values, indicators. The set of operations for starting, stopping the process, maintaining the constancy of the process indicators or changing them according to a given law is called control.

Maintaining indicators at a given level or changing them according to a given law is called regulation, i.e. regulation is part of governance. And if these control processes are carried out without the participation of a person (operator), then they are called automatic.

A device that implements a technological process, the indicators of which need to be controlled or regulated, is called a controlled object, or a controlled object. The objects of control can be a mud pump, a drilling rig, a drilling rig drive, etc., or their individual units that perform certain operations of a technological process, for example, a drilling rig winch.

A technical device that carries out control in accordance with a program (algorithm) is called an automatic control device.

The combination of a control object and a control device is called an automatic control system (ACS).

We are not interested in all automatic control operations, but only in regulation, that is, those operations that relate to maintaining or changing the process parameters.

Any regulatory process can be carried out

· without result control - open-loop regulation;

· with result control - closed-loop regulation.

An example of open-loop control without control of the result (flow rate Q) is the stabilization of the supply of flushing fluid Q when the piston pump is operating at full capacity when the corresponding gearbox speed is engaged (non-variable drive and no flushing fluid discharge). Here, in case of significant (non-emergency) changes in the characteristics of the hydraulic path (due to slurrying of the bottom hole, falling out of pieces of rock from the walls of the well, etc.), the flow rate of the drilling fluid remains constant.

In the given example, the object of control is a mud pump with a fixed drive (pumping unit). The control (regulating) body, which must contain an object to control the supply of flushing fluid, is a gearbox.

Open-loop control is used much less frequently than closed-loop control due to the instability of the characteristics of the elements. The elements of the system are subject to various kinds of disturbances. In the example shown, this may be a change in the filling factor of the pump cylinders due to a change in the parameters of the flushing liquid or the suction path.

Let's consider an example of closed-loop control with control of the result - flow rate Q. In fig. 1.1 shows a block diagram of the regulator (stabilizer) of the flow rate of the flushing liquid Q. Here the flow rate Q is controlled by the flow sensor DR. Setpoint Z by means of voltage regulation U backside the required flow rate Q is set. The motor shaft speed n (hence the flow rate Q) is determined by the load and voltage U G , which depends on the value of ∆U.

∆U = U backside - U os1 , (1.1)

where U os1 - voltage at the sensor output (U d ), proportional to the flow rate Q, and is called the feedback voltage. And this relationship in this case is negative (conventionally denoted by shading the sector): decreases the value of U backside ... When the flow rate Q deviates from the set value, U also changes os1 , which leads to a change in n and thus to restore the flow rate Q.

Automatic maintenance of a given law of change in process indicators using feedback is called automatic regulation. In the considered example, one indicator is Q. And it is called the controlled variable.

So, based on the considered example, we will assume that an automatic device that performs automatic regulation is called an automatic regulator.

In turn, the object controlled by the regulator is called the regulated object.

The set of the controlled object and the automatic regulator make up the automatic control system (ACS).

By their functional purpose, automatic systems are subdivided into open-loop automatic control systems, closed-loop automatic control systems and automatic control systems.

Let's consider examples that demonstrate the operation of the considered circuits.

1.Example. Electronic tube filament current stabilizer. The diagram shows open loop regulation.

Maintaining a constant filament current I N occurs without the participation of the operator, i.e. no control is exercised.

Example Manual speed control ω electric motor shaft.

Rotation frequency ω the drive motor shaft D is a function of the voltage at the generator terminals U G , which at a constant frequency of rotation of the armature ( ω VD = const) is determined by the current in the excitation winding of the OVG generator. To regulate or keep the speed constant ω the operator monitors the readings of the voltmeter V, graduated in the dimensions of the rotational speed ω and, manually changing the rheostat P current I ovg in the excitation winding, achieves the required value ω.

Here we see a closed control system. But such a manual control system has a significant drawback: low control accuracy and undesirable presence of an operator. In addition, there are a number of disturbing influences: a changing torque on the motor shaft M WITH , changes in the temperature of the medium, wear of brushes of electrical machines, etc., hence the inaccuracy of the control system; the system is not applicable for fast processes.

The examples discussed provide a basis for considering regulatory principles.

1.1.1 Principles of regulation

During the operation of the systems considered above, the influence of external factors (disturbing influences) becomes obvious. The simplest solution to account for each disturbance is to install the appropriate sensor. However, this approach is not always feasible. As a way out of this situation, techniques are usually used, according to which the deviation from a given value is first measured with the installation of the sensor, and then an amendment is introduced according to the measured deviation (similar to the example with changing the position of the rheostat slider P).

There are the following basic principles of regulation:

· by deviation;

· outrage;

· compensation;

· combined.

Figure 1.4 shows a circuit for automatic control (stabilization) of the engine speed with the use of one sensor for monitoring the deviation of the speed from the set value, which is a tachogenerator.

This circuit, in fact, is a transformation of a manual control circuit (Figure 1.3) into an automatic control circuit (Figure 1.4). Here the operator is replaced by an electrical control system and a system for influencing the rheostat P. The rheostats P are introduced into the circuit. 1 and P 2, a reversible engine RD, an electronic amplifier EU, and a Red reducer, which is mechanically connected to the rheostat engine R.

Consider the main regulatory elements (Fig. 1.4):

· the object of regulation, which is the engine, all other elements are included in the system regulator;

· an indicator of the control process, which is the angular velocity ω , i.e. regulated value, which can be either constant or change in accordance with any law;

· a regulating body, the role of which is played by the anchor chain of the engine, changing the position or state of which, you can change the controlled value;

· regulating action - voltage in the anchor chain of the engine;

· setting value (influence) of the system - U backside ; that is, it is such a quantity that is proportional or functionally related to the controlled quantity and serves to change the level of the latter; via U backside a specific value is set ω.

If ∆U = U backside - U wasps = 0, then a state of equilibrium will come. U wasps is the feedback voltage, which is proportional to the controlled value ω. When it changes ω ( due to a change in the moment M with resistance on the motor shaft), the feedback voltage U generated by the tachogenerator changes wasps , equilibrium (∆U ≠ 0) is disturbed, which leads along the chain (EU - RD - Red - R - I ovg ) to a change in the voltage generated by the generator U G and to the restoration of the controlled value ω.

In the considered scheme, the control of the controlled variable is carried out in an active way, and the signal transmission circuit from the output to the input of the system is called the main feedback.

The principle of regulation, which is laid down in the circuit (Figure 1.4), is called the principle of control by deviation. Systems built according to this principle always contain feedback. This means that they work in a closed loop.

By an automatic control system for deviation, we mean a system in which the deviation of the controlled value from the set value is measured, and as a function of the deviation value, a certain regulating action is generated that reduces this deviation to a minimum value.

Note and remember that deviation control systems should always contain main negative feedback.

Another control principle, which is much less commonly used in automatic controllers, is the disturbance control principle or the compensation principle, as well as disturbance compensation.

In fig. 1.5 shows a circuit of a DC generator. This illustration explains the principle of disturbance control. Here the generator operates on a varying load R n ... Voltage U is an adjustable variable. The generator emf is proportional to the excitation flux Φ v E G = k Φ v .

U = E - I n R a , (1.2)

E = U + I n R a = I n R n + I n R a = I n (R a + R n ) (1.3)

Let us assume that when the current I n voltage U = U O = const. Then the condition must be satisfied

E = U O + Δ E = U O + I n R a = k ( Φ in + ΔΦ v ). (1.4)

Means, Δ E will change due to

Φ v U O = k Φ in and ΔΦ v = (R a / k) I n = c I n , (1.5)

those. controlled variable change ΔΦ must be proportional to the load current I n ... This condition is fulfilled due to the compound winding, which gives an additional excitation flux Φ add proportional to the disturbance load - current I N ... Based on this, the main winding (main excitation flux Ф main ) is intended to create an initial voltage U O. Meaning Δ E is determined by the compound winding. Both windings create a total magnetic flux Ф in.

As a result of a change in the load current I N the total flow Ф in , and the voltage U O constantly. This is an example of the implementation of the principle of compensation in control, when, when measuring the load (disturbance), as a function of the measured value, a certain control action is generated, which allows the controlled variable to remain constant. Systems operating according to this compensation principle are open-loop systems that do not have feedback.

The main advantage of such systems is performance. At the same time, the system also has a number of disadvantages:

· due to the fact that the object has several disturbing influences and for compensation systems it is necessary to measure separately each disturbing influence and, as a function of it, to develop a regulatory influence, which significantly complicates the system;

· the problem of measuring non-electrical disturbing influences;

· ambiguity and complexity of the dependence of the regulatory on the disturbing influence.

Due to these disadvantages, the considered systems are used much less often in comparison with systems that implement the principle of deviation control.

The third regulation principle is combined (combination of the first two principles). It is used even less often than the first two. The advantages and disadvantages are the same. The systems are quite complex and their study has not yet been provided.

1.2 Classification of automatic control systems

According to the law of reproduction (change) of a controlled value, closed-loop control systems are divided into three types:

· stabilization systems,

· software control systems,

· tracking systems.

They differ from each other not fundamentally, but only by the mode of operation and constructively. They have a common theory and are studied using the same methods.

The stabilization system is a system for maintaining a constant controlled value. The systems discussed above are stabilization systems.

In software control systems, the controlled value must change according to a predetermined program in time.

Tracking system. Here the controlled variable changes according to an unknown arbitrary law. The law is determined by some external setting influence (arbitrarily).

Depending on the nature of the regulatory influence on the final element, automatic control systems are subdivided into:

· continuous systems,

· pulse and

· relay regulation.

In continuous control systems, the signals at the output of all elements of the system are continuous functions of the signals at the input of the elements.

Pulse control systems are distinguished by the fact that in them, at regular intervals, the control loop is opened and closed with a special device. The regulation time is divided into pulses, during which the processes proceed in the same way as in continuous regulation systems, and into intervals during which the influence of the regulator on the system ceases. Such regulators are used to regulate slow-running processes (temperature control in industrial furnaces, temperature and pressure in boilers).

In relay control systems, the control loop is opened by one of the system elements (relay element), depending on external influences.

Depending on the results obtained with automatic regulation, two types of automatic regulation are distinguished:

· static and

· astatic.

Static is such an automatic control in which the controlled variable with various constant external influences on the control object takes on various values ​​at the end of the transient process, depending on the magnitude of the external influence (for example, load).

In fig. 1.6, and the water level regulator in the tank is presented. In the water level regulator, with an increase in the water flow q, the level decreases, the valve opens through the float and the lever, the inflow q 1 increases and vice versa.

The static control system has the following characteristic properties:

the equilibrium of the system is possible at different values ​​of the controlled variable;

each value of the controlled variable corresponds to a single defined position of the regulating body.

To implement such a connection between the sensor and the actuator, the control loop must consist of so-called static links, in which, in a state of equilibrium, the output value uniquely depends on the input:. This is due to the fact that the water flow rate q is equal to the flow rate q1 at some strictly defined level H. The flow rate will change, the level will change, the flow rate will be equal to the flow rate - and again equilibrium will come.

A regulator performing static regulation is called a static regulator.

To characterize the degree of dependence of the deviation of the controlled value on the load in the theory of regulation, the concept of unevenness, or statism of regulation, is used.

Let the graph of the dependence of the steady-state values ​​of the controlled variable x on the load q (control characteristic) has the form shown in Fig. 1.6, b (the control characteristic is given in specific coordinates for the water level regulator in the tank; below the coordinates are given in general form, for any static controllers ). The maximum value of the regulated value xmax corresponds to the idle run of the object (no load); minimum value - rated load - qnom.

To determine the statism of regulation, we will use the relative coordinates:

where φ is the relative value of the controlled variable;

The regulated value itself;

The minimum value of the controlled variable (at nominal mode);

and qnom - basic values ​​of quantities;

λ is the relative value of the load.

Then the irregularity δ (or statism) of the system in the general case is a partial derivative at a given point (or the relative steepness of the regulation characteristic at this point):

If the control characteristic is linear, then the statism will be constant for all load values. And it can be defined like this:

The static controller does not maintain a strictly constant value of the controlled variable, but with an error, which is called the static system error. Thus, the statism of regulation is a relative static error when the load changes from idle to nominal.

In some systems, a static error (even if hundredths of a percent) is undesirable, then go to regulation, in which it is equal to zero - to astatic regulation. The control characteristic of such a system is represented by a line parallel to the load axis.

Astatic is called automatic regulation, in which, at various constant values ​​of the external influence on the object, the deviation of the controlled value from the set value at the end of the transient process becomes zero.

In the astatic regulator of the H water level in the tank (Fig. 1.7), the float moves the rheostat slider to one side or the other, depending on the level change from the set value, thereby energizing the motor that controls the damper position. The engine will be turned off when the water level reaches the set value.

The astatic control system has the following characteristic features:

the equilibrium of the system takes place only with one value of the controlled variable equal to the given one;

the regulator has the ability to occupy different positions at the same value of the regulated quantity.

In real controllers, the first condition is met with some error. To fulfill the second condition, a so-called astatic link is introduced into the control loop. In the given example, a motor has the property that, in the absence of voltage, its shaft is stationary in any position, and in the presence of voltage, it rotates continuously.

Depending on the source of energy received by the regulator, a distinction is made between

· direct and

· indirect regulation.

In direct control systems, the energy for repositioning the control element is obtained from a sensor (as an example, a static water level regulator).

In indirect control systems, the energy for repositioning the control element is obtained from an external source (for example, an astatic water level regulator).

Automatic control systems with several adjustable values ​​(for example, steam pressure in the boiler, water supply to the boiler, fuel and air supply to the furnace) are subdivided into unconnected and coupled control systems.

Systems of unrelated regulation are those in which regulators designed to regulate various quantities are not connected with each other and can interact only through a common regulation object for them. If, in a system of unrelated regulation, a change in one of the regulated values ​​entails a change in other regulated values, then such a system is called dependent; and if it does not, then the system is called independent.

Coupled control systems are those in which controllers of different controlled quantities are connected to each other and in addition to the control object.

A system of coupled regulation is called autonomous if the connections between the regulators included in it are such that a change in one of the regulated values ​​during the regulation process does not cause a change in the remaining regulated values.

Closed autonomous control systems with only one (main) feedback are called single-loop. Automatic control systems that, in addition to one main feedback, have one or more main or local feedbacks, are called multi-loop.

Depending on the type of characteristics of the elements that make up the systems, all systems are divided into:

· linear and

· nonlinear.

Linear systems are called systems that consist only of elements with linear characteristics; transient processes in such elements are described by linear differential equations.

Systems that have one or more elements with non-linear characteristics are called non-linear; transient processes in such systems are described by nonlinear differential equations.

When classified by the type of energy used, all systems can be divided into:

· electric,

· hydraulic,

· pneumatic,

· electrohydraulic,

· electro-pneumatic, etc.

Depending on the number of regulated values ​​of the automatic control system (ACS):

One-dimensional,