Classification of technical automation equipment based on functionality. Technical means of automation. Automated control systems

Management, consulting and entrepreneurship

Lecture 2. General information about technical means of automation. The need to study general issues related to technical automation equipment and the state system of industrial devices and automation equipment GSP is dictated by the fact that technical means

Lecture 2.

General information about technical means of automation.

The need to study general issues relating to technical automation equipment and the state system of industrial instruments and automation equipment (GSP) is dictated by the fact that technical automation equipment is an integral part of the GSP. Technical automation equipment represents the basis for the implementation of information and control systems in the industrial and non-industrial spheres of production. The principles of organizing the GSP largely determine the content of the design stage technical support automated process control systems (APCS). In turn, the basis of GSPs are problem-oriented aggregate complexes of technical means.

Typical automation tools can be technical, hardware, software and system-wide.

TO technical means of automation(TSA) include:

• sensors;
• actuators;
• regulatory authorities (RO);
• communication lines;
• secondary instruments (displaying and recording);
• analog and digital control devices;
• programming blocks;
• logic-command control devices;
• modules for collecting and primary processing of data and monitoring the state of a technological control object (TOU);
• modules for galvanic isolation and signal normalization;
• signal converters from one form to another;
• modules for data presentation, indication, recording and generation of control signals;
• buffer storage devices;
• programmable timers;
• specialized computing devices, pre-processor preparation devices.

TO software and hardware automation tools include:

• analog-to-digital and digital-to-analog converters;
• control means;
• multi-circuit analog and analog-to-digital control blocks;
• multi-connection program logic control devices;
• programmable microcontrollers;
• local area networks.

TO system-wide automation tools include:

• interface devices and communication adapters;
• shared memory blocks;
• highways (buses);
• general system diagnostic devices;
• direct access processors for storing information;
• operator consoles.

Technical means of automation in control systems

Any system control must perform the following functions:

• collection of information about the current state of the technological control object (TOU);
• determination of quality criteria for TOU work;
• finding optimal mode functioning of the technical control system and optimal control actions that ensure the extremum of quality criteria;
• implementation of the found optimal mode at the TOU.

These functions can be performed service personnel or TCA. There are fourtype of control systems(SU):

1) informational;

2) automatic control;

3) centralized control and regulation;

4) automated process control systems.

Information ( manual) control systems(Fig. 1.1) are rarely used, only for reliably functioning, simple technological objects of TOU control.

Rice. 1.1. Management information system structure:

D - sensor (primary measuring transducer);

VP - secondary indicating device;

OPU - operator control center (boards, consoles, mnemonic diagrams, alarm devices);

Remote control remote control devices (buttons, keys, bypass control panels, etc.);

IM actuator;

RO - regulatory body;

C - alarm devices;

MS mnemonic diagrams.

In some cases, the information control system includes direct-acting regulators and regulators built into process equipment.

In automatic control systems(Fig. 1.2) all functions are performed automatically using appropriate technical means.

Operator functions include:

• technical diagnostics of the ACS condition and restoration of failed system elements;
• correction of regulatory laws;
• change of task;
• transition to manual control;
• equipment maintenance.

Rice. 1.2. Structure of the automatic control system (ACS):

KP - encoding converter;

LS - communication lines (wires, impulse tubes);

VU - computing devices

Centralized control and regulation systems(SCCR) (Fig. 1.3). ACS are used for simple technical equipment, the operating modes of which are characterized by a small number of coordinates, and the quality of work is characterized by one easily calculated criterion. A special case of ACS is the automatic control system (ASR).

A control system that automatically maintains an extreme TOC value belongs to the class of extreme control systems.

Rice. 1.3. Structure of the centralized control and regulation system:

OPU - operator control center;

D - sensor;

NP normalizing converter;

KP - encoding and decoding converters;

CR - central regulators;

MP multi-channel registration tool (print);

C - pre-emergency signaling device;

MPP - multi-channel indicating devices (displays);

MS - mnemonic diagram;

IM - actuator;

RO - regulatory body;

K controller

ASRs that support the specified value of the output adjustable coordinate of the TOU are divided into:

• stabilizing;
• software;
• followers;
• adaptive.

Extreme regulators are used extremely rarely.

Technical structures of the SCCR can be of two types:

1) with individual TCAs;

2) with collective TCAs.

In the first type of system, each channel is constructed from TCA for individual use. These include sensors, normalizing converters, regulators, secondary devices, actuators, and regulatory bodies.

Failure of one control channel does not lead to a shutdown of the process facility.

This design increases the cost of the system, but increases its reliability.

The second type system consists of TSA for individual and collective use. TSA for collective use includes: switch, CP (encoding and decoding converters), CR (central regulators), MR (multi-channel recording device (print)), MPP (multi-channel indicating devices (displays)).

The cost of a collective system is somewhat lower, but reliability largely depends on the reliability of collective TSAs.

When the communication line is long, individual encoding and decoding converters are used, located near the sensors and actuators. This increases the cost of the system, but improves the noise immunity of the communication line.

Automated process control systems(APCS) (Fig. 1.4) is a machine system in which TSA obtain information about the state of objects, calculate quality criteria, and find optimal control settings. The operator’s functions are reduced to analyzing the received information and implementing it using local automated control systems or remote control of the control room.

Distinguish following types APCS:

• centralized automated process control system (all information processing and control functions are performed by one control computer UVM) (Fig. 1.4);

Rice. 1.4. Structure of a centralized automated process control system:

USO - communication device with an object;

DU - remote control;

SOI - information display tool

• supervisory automated process control system (has a number of local automated control systems built on the basis of individual use TSA and a central computer computer (CUVM), which has an information communication line with local systems) (Fig. 1.5);

Rice. 1.5. Structure of the supervisory control system: LR - local regulators

• distributed automated process control system - characterized by the division of information processing and management control functions between several geographically distributed objects and computers (Fig. 1.6).

Rice. 1.6. Hierarchical structure of technical means of SHG

PAGE 7

Federal Agency for Education

State educational institution

higher professional education

"Omsk State Technical University"

V.N. Gudinov, A.P. Korneychuk

TECHNICAL AUTOMATION TOOLS
Lecture notes

Omsk 2006
UDC 681.5.08(075)

BBK 973.26-04ya73

G
REVIEWERS:
N.S. Galdin, Doctor of Technical Sciences, Professor of the Department of PTTM and G, SibADI,

V.V. Zakharov, head of the automation department of ZAO NOMBUS.
Gudinov V.N., Korneychuk A.P.

G Technical means of automation: Lecture notes. – Omsk: Omsk State Technical University Publishing House, 2006. – 52 p.
The lecture notes provide basic information about modern technical and software-hardware automation tools (TSA) and software-hardware complexes (STC), the principles of their construction, classification, composition, purpose, characteristics and features of application in various automated control and regulation systems of technological processes (APCS).

Lecture notes are intended for students of full-time, evening, correspondence and distance learning in specialty 220301 - “Automation of technological processes and production.”
Published by decision of the editorial and publishing council of Omsk State Technical University.
UDC 681.5.08(075)

BBK 973.26-04ya73

© V.N. Gudinov, A.P. Korneychuk 2006

© Omsk State

Technical University, 2006

1. GENERAL INFORMATION ABOUT TECHNICAL AUTOMATION TOOLS

BASIC CONCEPTS AND DEFINITIONS
The purpose of the course “Technical Automation Tools” (TSA) is to study the elemental base of automatic process control systems. First, we present the basic concepts and definitions.

Element(device) – a structurally complete technical product designed to perform certain functions in automation systems (measurement, signal transmission, information storage, processing, generation of control commands, etc.).

Automatic control system (ACS)– a set of technical devices and software and hardware that interact with each other in order to implement a certain control law (algorithm).

Automated process control system (APCS)– a system designed to develop and implement control actions on a technological control object and is a human-machine system that provides automatic collection and processing of information necessary to control this technological object in accordance with accepted criteria (technical, technological, economic).

Technological control object (TOU) - a set of technological equipment and the technological process implemented on it according to the relevant instructions and regulations.

When creating modern automated process control systems, global integration and unification of technical solutions is observed. The main requirement of modern automatic control systems is the openness of the system, when the data formats used and the procedural interface are defined and described for it, which allows connecting “external” independently developed devices and devices to it. Behind last years The TCA market has changed significantly, many domestic enterprises have been created that produce automation tools and systems, and systems integrators have appeared. Since the early 90s, leading foreign manufacturers TCA began the widespread introduction of its products into the CIS countries through trade missions, branches, joint ventures and dealer firms.

The intensive development and rapid dynamics of the market for modern control technology require the emergence of literature reflecting the current state of TCA. Currently, the latest information about automation equipment of domestic and foreign companies is scattered and is mainly presented in periodicals or on the global Internet on the websites of manufacturing companies or on specialized information portals, such as www.asutp.ru, www.mka.ru, www.industrialauto.ru. The purpose of this lecture notes is a systematic presentation of material about the elements and industrial complexes of TSA. The abstract is intended for students of the specialty “Automation of Technological Processes and Production” studying the discipline “Technical Automation Tools”.

1.1. Classification of TSA by functional purpose in ACS

In accordance with GOST 12997-84, the entire TSA complex, according to their functional purpose in the ACS, is divided into the following seven groups (Fig. 1).

Rice. 1. Classification of TSA by functional purpose in ACS:

CS – control system; OU – control object; CS – communication channels;

Memory – master devices; UPI – information processing devices;

USPU – amplifying and converting devices; UIO – information display devices; IM – actuators; RO – working bodies; KU – control devices; D – sensors; VP – secondary converters

1.2. TCA development trends
1. Magnification functionality TCA:

– in the control function (from the simplest start/stop and automatic reverse to cyclic and numerical program and adaptive control);

– in the alarm function (from the simplest light bulbs to text and graphic displays);

– in the diagnostic function (from open circuit indication to software testing of the entire automation system);

– in the function of communication with other systems (from wired communications to networked industrial facilities).

2. Complication of the element base means a transition from relay contact circuits to contactless circuits on semiconductor individual elements, and from them to integrated circuits of increasing degrees of integration (Fig. 2).

Rice. 2. Stages of development of electric vehicles
3. Transition from rigid (hardware, circuit) structures to flexible (reconfigurable, reprogrammable) structures.

4. Transition from manual (intuitive) methods of designing TSA to machine, scientifically based systems computer-aided design(CAD).

1.3. TCA imaging methods
In the process of studying this course, various methods of depicting and presenting TCA and their components. The most commonly used are the following:

1. Constructive method(Fig. 7-13) involves depicting instruments and devices using methods mechanical engineering drawing in the form of technical drawings, layouts, general views, projections (including axonometric ones), sections, sections, etc. .

2. Circuit method(Fig. 14.16-21.23) assumes, in accordance with GOST ESKD, the representation of TSA with circuits of various types (electrical, pneumatic, hydraulic, kinematic) and types (structural, functional, fundamental, installation, etc.).

3. Mathematical model is used more often for software-implemented TSA and can be represented by:

– transfer functions of typical dynamic links;

– differential equations of ongoing processes;

– logical functions for controlling outputs and transitions;

– state graphs, cyclograms, time diagrams (Fig. 14, 28);

– block diagrams of functioning algorithms (Fig. 40), etc.
1.4. Basic principles of TCA construction
To build modern automated process control systems, a variety of devices and elements are required. Satisfying the needs of control systems of such different quality and complexity for automation equipment with their individual development and production would make the problem of automation immense, and the range of instruments and automation devices almost limitless.

At the end of the 50s, the USSR formulated the problem of creating a unified State System of Industrial Instruments and Automation Equipment (GSP)– representing a rationally organized set of instruments and devices that satisfy the principles of typification, unification, aggregation, and intended for the construction of automated systems for measuring, monitoring, regulating and managing technological processes in various industries. And since the 70s, GSP has also covered non-industrial areas of human activity, such as scientific research, testing, medicine, etc.

Typing- this is a reasonable reduction of the variety of selected types, designs of machines, equipment, devices, to a small number of the best samples from any point of view, which have significant qualitative characteristics. During the typification process, standard designs are developed and installed, containing basic elements and parameters common to a number of products, including promising ones. The typification process is equivalent to grouping, classifying some initial, given set of elements into a limited number of types, taking into account actual restrictions.

Unification– this is the reduction of various types of products and means of their production to a rational minimum of standard sizes, brands, shapes, properties. It brings uniformity to the basic parameters of standard TCA solutions and eliminates the unjustified variety of means of the same purpose and the heterogeneity of their parts. Devices, their blocks and modules, identical or different in their functional purpose, but derived from one basic design, form a unified series.

Aggregation is the development and use of a limited range of standard unified modules, blocks, devices and unified standard structures (UTC) for the construction of many complex problem-oriented systems and complexes. Aggregation allows you to create various modifications of products on the same basis, produce TSA for the same purpose, but with different technical characteristics.

The principle of aggregation is widely used in many branches of technology (for example, modular machines and modular industrial robots in mechanical engineering, IBM-compatible computers in control systems and automation of information processing, etc.).

2. STATE INDUSTRIAL DEVICES SYSTEM

AND AUTOMATION MEANS

GSP is a complex developing system consisting of a number of subsystems that can be viewed and classified from different positions. Let's consider the functional-hierarchical and constructive-technological structure of technical means of GSP.
2.1. Functional-hierarchical structure of SHGs

Rice. 3. Hierarchy of SHGs
Distinctive Features modern structures building automated control systems industrial enterprises are: the penetration of computing tools and the introduction of network technologies at all levels of management.

In world practice, specialists in integrated production automation also distinguish five levels of management modern enterprise(Fig. 4), which completely coincides with the above hierarchical structure of the SHG.

At the level ER.P.– Enterprise Resource Planning (enterprise resource planning) calculations and analysis of financial and economic indicators are carried out, strategic administrative and logistics tasks are solved.

At the level MES– Manufacturing Execution Systems (production execution systems) – tasks of product quality management, planning and control of the sequence of operations of the technological process, management of production and human resources within the framework of the technological process, maintenance of production equipment.

These two levels relate to the tasks of automated control systems (automated enterprise management systems) and the technical means by which these tasks are implemented - these are office personal computers (PCs) and workstations based on them in the services of the chief specialists of the enterprise.


Rice. 4. Pyramid of modern production management.
At the next three levels, problems that belong to the class of automated process control systems (automated process control systems) are solved.

SCADA– Supervisory Control and Data Acquisition (data collection and supervisory (dispatcher) control system) is a level of tactical operational management at which problems of optimization, diagnostics, adaptation, etc. are solved.

Control- level– level of direct (local) control, which is implemented on such TCAs as: software – operator panels (remotes), PLCs – programmable logic controllers, USO – communication devices with the object.

HMI– Human-Machine Interface (human-machine communication) – visualizes (displays information) the progress of the technological process.

Input/ Output– The inputs/outputs of the control object are

sensors and actuators (S/AM) of specific technological installations and working machines.

2.2. Structural and technological structure of GSP


Rice. 5. SHG structure
UKTS(unified set of technical means) – it is a collection of different types technical products, designed to perform different functions, but built on the same principle of operation and having the same structural elements.

ACTS(aggregate complex of technical means) – This is a set of different types of technical products and devices, interconnected by functionality, design, type of power supply, level of input/output signals, created on a single design, software and hardware basis according to the block-modular principle. Examples of well-known domestic UKTS and ACTS are given in Table. 1.

PTK ( software and hardware complex ) – This is a set of microprocessor automation tools (programmable logic controllers, local regulators, communication devices with the object), display panels of operators and servers, industrial networks interconnecting the listed components, as well as industrial software of all these components, designed to create distributed automated process control systems in various industries. Examples of modern domestic and foreign hardware and software systems are given in Table. 2.

Specific complexes of technical means consist of hundreds and thousands of different types, sizes, modifications and designs of instruments and devices.

Product type- this is a set of technical products that are identical in functionality, have a single operating principle, and have the same nomenclature of the main parameter.

Standard size– products of the same type, but having their own specific values ​​of the main parameter.

Modification- is a collection of products of the same type that have certain design features.

Execution– design features that affect performance characteristics.

TCA complexes Table 1

The means of generating and primary processing of information include keyboard devices for applying data to cards, tapes or other information carriers by mechanical (punching) or magnetic methods; the accumulated information is transferred for subsequent processing or reproduction. Keyboard devices, punching or magnetic blocks and transmitters are used to make up production recorders for local and system purposes, which generate primary information in workshops, warehouses and other places of production.

Sensors (primary transducers) are used to automatically extract information. They are very diverse devices in terms of operating principles that sense changes in the controlled parameters of technological processes. Modern measuring technology can directly evaluate more than 300 different physical, chemical and other quantities, but this is not enough to automate a number of new areas of human activity. An economically feasible expansion of the range of sensors in the GPS is achieved by unifying the sensitive elements. Sensitive elements that respond to pressure, force, weight, speed, acceleration, sound, light, thermal and radioactive radiation are used in sensors to control the loading of equipment and its operating modes, the quality of processing, accounting for the release of products, monitoring their movements on conveyors, stocks and consumption of materials, workpieces, tools, etc. The output signals of all these sensors are converted into standard electrical or pneumatic signals, which are transmitted by other devices.

Devices for transmitting information include signal converters into forms of energy convenient for broadcasting, telemechanics equipment for transmitting signals via communication channels over long distances, switches for distributing signals to places where information is processed or presented. These devices connect all peripheral sources of information (keyboard devices, sensors) with the central part of the control system. Their purpose is efficient use communication channels, eliminating signal distortion and the influence of possible interference during transmission over wired and wireless lines.

Devices for logical and mathematical information processing include functional converters that change the nature, shape or combination of information signals, as well as devices for processing information according to given algorithms (including computers) in order to implement laws and control (regulation) modes.

Computers for communication with other parts of the control system are equipped with information input and output devices, as well as storage devices for temporary storage of source data, intermediate and final results of calculations, etc. (see Data input. Data output, Storage device).

Devices for presenting information show the human operator the state of production processes and record it the most important parameters. Such devices are signal boards, mnemonic diagrams with visual symbols on boards or control panels, secondary pointer and digital indicating and recording instruments, cathode ray tubes, alphabetic and digital typewriters.

Devices for generating control actions convert weak information signals into more powerful energy pulses of the required shape, necessary to activate protection, regulation or control actuators.

Ensuring high quality of products is associated with automation of control at all main stages of production. Subjective human assessments are replaced by objective indicators from automatic measuring stations linked to central points where the source of defects is determined and from where commands are sent to prevent deviations outside of tolerances. Of particular importance is automatic control using computers in the production of radio-technical and radio-electronic products due to their mass production and a significant number of controlled parameters. No less important are final reliability tests of finished products (see Reliability of technical devices). Automated stands for functional, strength, climatic, energy and specialized tests allow you to quickly and identically check the technical and economic characteristics of products (products).

Actuating devices consist of starting equipment, actuating hydraulic, pneumatic or electrical mechanisms (servomotors) and regulatory bodies that act directly on the automated process. It is important that their operation does not cause unnecessary energy losses and reduce the efficiency of the process. For example, throttling, which is usually used to regulate the flow of steam and liquids, based on an increase hydraulic resistance in pipelines, they are replaced by influencing flow-forming machines or other, more advanced methods of changing the flow speed without loss of pressure. Great importance has economical and reliable control of an AC electric drive, the use of gearless electric actuators, and contactless ballasts for controlling electric motors.

The idea of ​​constructing instruments for monitoring, regulation and control in the form of units consisting of independent blocks that perform certain functions, implemented in GSP, made it possible to various combinations using these blocks to obtain a wide range of devices for solving diverse problems using the same means. Unification of input and output signals ensures the combination of blocks with different functions and their interchangeability.

The GSP includes pneumatic, hydraulic and electrical devices and devices. Electrical devices designed to receive, transmit and reproduce information are the most versatile.

The use of a universal system of industrial pneumatic automation elements (USEPPA) made it possible to reduce the development of pneumatic devices mainly to assembling them from standard units and parts with a small number of connections. Pneumatic devices are widely used for control and regulation in many fire and explosion hazardous industries.

GSP hydraulic devices are also assembled from blocks. Hydraulic instruments and devices control equipment that requires high speeds to move control elements with significant effort and high precision, which is especially important in machine tools and automatic lines.

In order to most rationally systematize GSP facilities and to increase the efficiency of their production, as well as to simplify the design and configuration of automated control systems, GSP devices are combined into aggregate complexes during development. Aggregate complexes, thanks to the standardization of input-output parameters and block design of devices, most conveniently, reliably and economically combine various technical means in automated control systems and allow the assembly of a variety of specialized installations from general-purpose automation units.

Targeted aggregation of analytical equipment, testing machines, mass dosing mechanisms with unified measuring, computing and office equipment facilitates and accelerates the creation of basic designs of this equipment and the specialization of factories for their production.

Topic 2

1. Sensors

A sensor is a device that converts the input effect of any physical quantity into a signal convenient for further use.

The sensors used are very diverse and can be classified according to various criteria (see Table 1).

Depending on the type of input (measured) quantity, there are: mechanical displacement sensors (linear and angular), pneumatic, electrical, flow meters, speed, acceleration, force, temperature, pressure sensors, etc.

Based on the type of output value into which the input value is converted, non-electrical and electrical are distinguished: direct current sensors (emf or voltage), alternating current amplitude sensors (emf or voltage), alternating current frequency sensors (emf or voltage), resistance sensors (active, inductive or capacitive) etc.

Most sensors are electrical. This is due to the following advantages electrical measurements:

Electrical quantities it is convenient to transmit over a distance, and the transmission is carried out at high speed;

Electrical quantities are universal in the sense that any other quantities can be converted into electrical quantities and vice versa;

They are accurately converted into a digital code and allow you to achieve high accuracy, sensitivity and speed of measurement instruments.

Based on their operating principle, sensors can be divided into two classes: generator and parametric. A separate group consists of radioactive sensors. Radioactive sensors are sensors that use phenomena such as changes in parameters under the influence of g and b rays; ionization and luminescence of certain substances under the influence of radioactive irradiation. Generator sensors directly convert the input value into an electrical signal. Parametric sensors convert the input value into a change in any electrical parameter (R, L or C) of the sensor.

Based on the principle of operation, sensors can also be divided into ohmic, rheostatic, photoelectric (optoelectronic), inductive, capacitive, etc.

There are three classes of sensors:

Analog sensors, i.e. sensors that produce an analog signal proportional to the change in the input value;

Digital sensors that generate a pulse train or binary word;

Binary (binary) sensors that produce a signal of only two levels: “on/off” (0 or 1).

Figure 1 – Classification of sensors for mining machine automation systems

Requirements for sensors:

Unambiguous dependence of the output value on the input value;

Stability of characteristics over time;

High sensitivity;

Small size and weight;

No feedback on controlled process and on the controlled parameter;

Work under various operating conditions;

Various installation options.

Parametric sensors

Parametric sensors are sensors that convert input signals into a change in any parameter of the electrical circuit (R, L or C). In accordance with this, active resistance, inductive, and capacitive sensors are distinguished.

Characteristic feature of these sensors is that they are used only with an external power source.

In modern automation equipment, various parametric active resistance sensors are widely used - contact, rheostatic, potentiometric sensors.

Contact sensors. The most reliable with contact sensors Magnetically controlled sealed contacts (reed switches) are considered.

Figure 1 – Schematic diagram of a reed switch sensor

The sensor's sensing element, the reed switch, is an ampoule 1, inside of which contact springs (electrodes) 2, made of ferromagnetic material, are sealed. The glass ampoule is filled with a protective gas (argon, nitrogen, etc.). The tightness of the ampoule excludes bad influence(impact) of the environment on the contacts, increasing the reliability of their operation. The contacts of a reed switch located at a controlled point in space are closed under the influence of a magnetic field, which is created by a permanent magnet (electromagnet) installed on a moving object. When the reed switch contacts are open, it active resistance equal to infinity, and when closed - almost zero.

Sensor output signal (U out on load R1) equal to voltage U p of the power source in the presence of a magnet (object) at the control point and zero in its absence.

Reed switches are available with both make and break contacts, as well as switching and polarized contacts. Some types of reed switches - KEM, MKS, MKA.

The advantages of reed switch sensors are high reliability and mean time between failures (about 10 7 operations). The disadvantage of reed sensors is a significant change in sensitivity with a slight displacement of the magnet in the direction perpendicular to the movement of the object.

Reed sensors are used, as a rule, in the automation of lifting, drainage, ventilation and conveyor installations.

Potentiometric sensors. Potentiometric sensors are a variable resistor (potentiometer) consisting of a flat (strip), cylindrical or ring frame on which a thin wire of constantan or nichrome with high resistivity is wound. A slider moves along the frame - a sliding contact connected mechanically to the object (see Figure 2).

By moving the slider using the appropriate drive, you can change the resistance of the resistor from zero to maximum. Moreover, the resistance of the sensor can change both according to a linear law and according to other, often logarithmic, laws. Such sensors are used in cases where it is necessary to change the voltage or current in the load circuit.

Figure 2 - Potentiometric sensor

For a linear potentiometer (see Figure 2) length l the output voltage is determined by the expression:

,

where x is the movement of the brush; k=U p / l- transfer coefficient; U p – supply voltage.

Potentiometric sensors are used to measure various process parameters - pressure, level, etc., previously converted by a sensing element in motion.

The advantages of potentiometric sensors are design simplicity, small sizes, as well as the possibility of power supply with both direct and alternating current.

The disadvantage of potentiometric sensors is the presence of a sliding electrical contact, which reduces the reliability of operation.

Inductive sensors. The principle of operation of the inductive sensor is based on a change in the inductance L of the coil 1, placed on the ferromagnetic core 2, when moving x anchors 3 (see Figure 3).

Figure 3 - Inductive sensor

The sensor circuit is powered from an AC source.

The control element of the sensors is a variable reactance– throttle with variable air gap.

The sensor works as follows. Under the influence of an object, the armature, approaching the core, causes an increase in flux linkage and, consequently, inductance of the coil. With decreasing gap d to a minimum value, the inductive reactance of the coil x L = wL = 2pfL increases to a maximum, reducing the load current RL, which is usually an electromagnetic relay. The latter, with their contacts, switch control, protection, monitoring circuits, etc.

Advantages inductive sensors– simplicity of the device and reliability of operation due to the absence of a mechanical connection between the core and the armature, usually attached to a moving object, the position of which is controlled. The functions of an anchor can be performed by an object itself that has ferromagnetic parts, for example a skip when controlling its position in the shaft.

The disadvantages of inductive sensors are the nonlinearity of the characteristics and the significant electromagnetic force of attraction of the armature to the core. To reduce forces and continuously measure displacements, solenoid-type sensors are used, or they are called differential.

Capacitive sensors. Capacitive sensors are structurally variable capacitors of various designs and shapes, but always with two plates, between which there is a dielectric medium. Such sensors are used to convert mechanical linear or angular movements, as well as pressure, humidity or environmental level into a change in capacity. In this case, to control small linear movements, capacitors are used in which the air gap between the plates changes. To control angular movements, capacitors with a constant gap and variable working area of ​​the plates are used. For monitoring tank filling levels bulk materials or liquids with constant gaps and working areas of the plates - capacitors with the dielectric constant of the medium being controlled. The electrical capacity of such a capacitor is calculated by the formula

where: S - Total intersection area of ​​the plates; δ - distance between plates; ε is the dielectric constant of the medium between the plates; ε 0 is the dielectric constant.

Based on the shape of the plates, flat, cylindrical and other types of variable capacitors are distinguished.

Capacitive sensors only operate at frequencies above 1000Hz. Use at industrial frequency is practically impossible due to the high capacitance (Xc = = ).

Generator sensors

Generator sensors are sensors that directly convert various types of energy into electrical energy. They do not require external power sources because they themselves produce emf. Generator sensors use well-known physical phenomena: the occurrence of EMF in thermocouples when heated, in photocells with a barrier layer when illuminated, the piezoelectric effect and the phenomenon of electromagnetic induction.

Induction sensors. IN induction sensors conversion of an input non-electrical quantity into an induced emf. used to measure movement speed, linear or angular movements. E.m.f. in such sensors it is induced in coils or windings made of copper insulated wire and placed on magnetic cores made of electrical steel.

Small-sized microgenerators that convert the angular velocity of an object into emf, the value of which is directly proportional to the rotation speed of the output shaft of the test object, are called tachogenerators of direct and alternating currents. Circuits of tachogenerators with and without an independent excitation winding are shown in Figure 4.

Figure 4 - Schemes of tachogenerators with and without an independent excitation winding

DC tachogenerators are a commutator electric machine with an armature and an excitation winding or permanent magnet. The latter do not require an additional power source. The principle of operation of such tachogenerators is that an emf is induced in the armature, which rotates in the magnetic flux (F) of a permanent magnet or field winding. (E), the value of which is proportional to the rotation frequency (ω) of the object:

E = cФn = cФω

To maintain the linear dependence of the emf. depending on the speed of rotation of the armature, it is necessary that the load resistance of the tachogenerator always remains unchanged and is many times higher than the resistance of the armature winding. The disadvantage of DC tachogenerators is the presence of a commutator and brushes, which significantly reduces its reliability. The collector provides conversion of alternating emf. anchors in D.C..

More reliable is an alternating current tachogenerator, in which the output intrinsically safe winding is located on the stator, and the rotor is permanent magnet with a corresponding constant magnetic flux. Such a tachogenerator does not require a collector, but its variable emf. converted to direct current using bridge diode circuits. The principle of operation of a synchronous alternating current tachogenerator is that when the rotor is rotated by the control object, a variable emf is induced in its winding, the amplitude and frequency of which are directly proportional to the rotor rotation speed. Due to the fact that the magnetic flux of the rotor rotates at the same frequency as the rotor itself, such a tachogenerator is called synchronous. The disadvantage of a synchronous generator is that it has bearing units, which is not appropriate for mining conditions. The diagram for controlling the speed of a conveyor belt with a synchronous tachogenerator is shown in Figure 5. Figure 5 indicates: 1 - magnetic rotor of the tachogenerator, 2 - drive roller with tread, 3 - conveyor belt, 4 - stator winding of the tachogenerator.

Figure 5 - Scheme for synchronous conveyor belt speed control

tachogenerator

To measure the linear speed of movement of the working bodies of scraper conveyors, magnetic induction sensors are used, which have no moving parts at all. The moving part (armature) in this case is the steel scrapers of the conveyor, moving in the magnetic flux of a permanent magnet sensor with an intrinsically safe coil. When steel scrapers cross a magnetic flux in the coil, a variable emf is induced, directly proportional to the speed of movement and inversely proportional to the gap between the steel core of the coil and the scraper. The magnetic flux, which leads to the emf, in the coil in this case changes under the influence of steel scrapers, which, moving above the sensor, cause fluctuations in the magnetic resistance along the path of closing the magnetic flux formed by the permanent magnet. The diagram for monitoring the speed of movement of the working body of a scraper conveyor using a magnetic induction sensor is shown in Figure 6. Figure 6 indicates: 1 - scraper conveyor, 2 - steel core, 3 - steel washer, 4 - plastic washer, 5 - ring permanent magnet, 6 - sensor coil

Figure 6 - Scheme for controlling the speed of movement of the working body

scraper conveyor with magnetic induction sensor

Magnetoelastic sensors. The principle of operation of magnetoelastic sensors is based on the property of ferromagnetic materials to change the magnetic permeability m when they are deformed. This property is called magnetoelasticity, which is characterized by magnetoelastic sensitivity

Permallay (iron-nickel alloy) has the highest value S m = 200 H/m2. Some varieties of permallay, when elongated by 0.1%, increase the coefficient of magnetic permeability up to 20%. However, to obtain even such small elongations, a load of the order of 100 - 200 N/mm is required, which is very inconvenient and leads to the need to reduce the cross-section of the ferromagnetic material and requires a power source with a frequency of the order of kilohertz.

Structurally, the magnetoelastic sensor is a coil 1 with a closed magnetic circuit 2 (see Figure 7). The controlled force P, deforming the core, changes its magnetic permeability and, consequently, the inductive reactance of the coil. The load current RL, for example, a relay, is determined by the resistance of the coil.

Magnetoelastic sensors are used to monitor forces (for example, when loading skips and planting cages on fists), rock pressures, etc.

The advantages of magnetoelastic sensors are simplicity and reliability.

The disadvantages of magnetoelastic sensors are that expensive materials for magnetic circuits and their special processing are required.

Figure 7 – Magnetoelastic sensor

Piezoelectric sensors. The piezoelectric effect is inherent in single crystals of some dielectric substances (quartz, tourmaline, Rochelle salt, etc.). The essence of the effect is that under the action of dynamic mechanical forces on the crystal, electric charges arise on its surfaces, the magnitude of which is proportional to the elastic deformation of the crystal. The dimensions and number of crystal plates are selected based on the strength and the required amount of charge. Piezoelectric sensors in most cases are used to measure dynamic processes and shock loads, vibration, etc.

Thermoelectric sensors. To measure temperatures in a wide range of 200-2500 °C, thermoelectric sensors are used - thermocouples, which ensure the conversion of thermal energy into electrical emf. The principle of operation of a thermocouple is based on the phenomenon of the thermoelectric effect, which consists in the fact that when the junction and ends of thermoelectrodes are placed in an environment with different temperatures t 1 and t 2 in a circle formed by a thermocouple and a millivoltmeter, a thermo emf appears, proportional to the difference between these temperatures

Figure 8 - Thermocouple diagram

Conductors A and B of thermocouples are made of dissimilar metals and their alloys. The phenomenon of thermoelectric effect is given by a combination of such conductors A and B, copper-constantan (up to 300 ° C), copper - kopel (up to 600 ° C), chromel - kopel (up to 800 ° C), iron - kopel (up to 800 ° C) , chromel - alumel (up to 1300 ° C), platinum - platinum-rhodium (up to 1600 ° C), etc.

The thermo-emf value for various types of thermocouples ranges from tenths to tens of millivolts. For example, for a copper-constantan thermocouple it changes from 4.3 to –6.18 mB when the junction temperature changes from + 100 to – 260 o C.

Thermistor sensors. The operating principle of thermistor sensors is based on the property of the sensing element - the thermistor - to change resistance when the temperature changes. Thermistors are made of metals (copper, nickel, atin, etc.) and semiconductors (mixtures of metal oxides - copper, manganese, etc.). A metal thermistor is made of wire, for example, copper diameter approximately 0.1 mm, wound in a spiral on a mica, porcelain or quartz frame. Such a thermistor is enclosed in a protective tube with terminal clamps, which is located at the temperature control point of the object.

Semiconductor thermistors are manufactured in the form of small rods and disks with leads.

With increasing temperature, the resistance of metal thermistors increases, while for most semiconductor ones it decreases.

The advantage of semiconductor thermistors is their high thermal sensitivity (30 times more than metal ones).

The disadvantage of semiconductor thermistors is the large spread of resistance and low stability, which makes them difficult to use for measurements. Therefore, semiconductor thermistors in automation systems of mine process plants are mainly used to control the temperature values ​​of objects and their thermal protection. In this case, they are usually connected in series with an electromagnetic relay to the power source.

To measure temperature, the thermistor RK is included in a bridge circuit, which converts the resistance measurement into a voltage at the output Uout, used in the automatic control system or measuring system.

The bridge can be balanced or unbalanced.

A balanced bridge is used with the zero measurement method. In this case, the resistance R3 is changed (for example, by a special automatic device) following the change in the resistance of the thermistor Rt in such a way as to ensure equality of potential at points A and B. If the scale of the resistor R3 is graduated in degrees, then the temperature can be read by the position of its slider. The advantage of this method is high accuracy, but the disadvantage is the complexity of the measuring device, which is an automatic tracking system.

An unbalanced bridge produces a signal Uout, proportional to the overheating of the object. By selecting the resistances of resistors R1, R2, R3, the equilibrium of the bridge is achieved at the initial temperature value, ensuring that the condition is met

Rt / R1= R3 / R2

If the value of the controlled temperature and, accordingly, the resistance Rt changes, the balance of the bridge will be disrupted. If you connect an mV device with a scale graduated in degrees to its output, the device’s needle will show the measured temperature.

Induction flow meter

To control the supply of a drainage pumping unit, it is possible to use induction flow meters, for example, type IR-61M. The operating principle of an induction flow meter is based on Faraday's law (the law of electromagnetic induction).

The design diagram of an induction flowmeter is shown in Figure 9. When a conducting liquid flows in a pipeline between the poles of a magnet, an emf appears in the direction perpendicular to the direction of the liquid and in the direction of the main magnetic flux. U on the electrodes, proportional to the fluid velocity v:

where B is the magnetic induction in the gap between the magnet poles; d – internal diameter of the pipeline.

Figure 9 – Design diagram of an induction flow meter

If we express the speed v in terms of the volumetric flow rate Q, i.e.

Advantages of an induction flow meter:

They have a slight inertia of readings;

There are no parts inside the working pipeline (therefore they have minimal hydraulic losses).

Disadvantages of the flow meter:

The readings depend on the properties of the liquid being measured (viscosity, density) and the nature of the flow (laminar, turbulent);

Ultrasonic flow meters

The operating principle of ultrasonic flow meters is that

the speed of propagation of ultrasound in a moving medium of gas or liquid is equal to the geometric sum of the average speed of movement of the medium v ​​and the natural speed of sound in this medium.

The design diagram of the ultrasonic flow meter is shown in Figure 10.

Figure 10 - Design diagram of an ultrasonic flow meter

The emitter I creates ultrasonic vibrations with a frequency of 20 Hz and higher, which fall on the receiver P, which registers these vibrations (it is located at a distance l). Flow rate F is equal to

where S is the cross-sectional area of ​​the fluid flow; C – speed of sound in the medium (for liquid 1000-1500 m/s);

t1 is the duration of propagation of the sound wave in the direction of flow from the emitter I1 to the receiver P1;

t 2 – duration of propagation of the sound wave against the flow from the emitter I2 to the receiver P2;

l is the distance between the emitter I and the receiver P;

k – coefficient taking into account the distribution of speeds in the flow.

Advantages of an ultrasonic flow meter:

a) high reliability and speed;

b) the ability to measure non-conductive liquids.

Disadvantage: increased requirements for contamination of the controlled water flow.

2. Data transmission devices

Information is transferred from the automation object to the control device via communication lines (channels). Depending on the physical medium through which information is transmitted, communication channels can be divided into the following types:

– cable lines– electrical (symmetrical, coaxial, “ twisted pair", etc.), fiber-optic and combined electrical cables with fiber optic cores;

– power low-voltage and high-voltage electrical networks;

– infrared channels;

– radio channels.

Information transmission over communication channels can be transmitted without information compression, i.e. One information signal (analog or discrete) is transmitted over one channel, and with information compression, many information signals are transmitted over a communication channel. Information compaction is used for remote transmission of information over a considerable distance (for example, from automation equipment located on a roadway to a shearer or from a section of a mine to the surface to a dispatcher) and can be done using various types of signal coding.

Technical systems that provide transmission of information about the state of an object and control commands over a distance via communication channels can be remote control and measurement systems or telemechanical systems. In remote control and measurement systems, each signal uses its own line - a communication channel. As many signals as there are, so many communication channels are required. Therefore, when remote control and measurement, the number of controlled objects, especially at long distances, is usually limited. In telemechanical systems, only one line, or one communication channel, is used to transmit many messages to a large number of objects. Information is transmitted in encoded form, and each object “knows” its code, so the number of controlled or managed objects is practically unlimited, only the code will be more complex. Telemechanics systems are divided into discrete and analog. Discrete telecontrol systems are called telealarm systems(TS), they provide the transmission of a finite number of object states (for example, “on”, “off”). Analog television monitoring systems are called telemetering systems(TI), they provide the transmission of continuous changes in any parameters characterizing the state of the object (for example, changes in voltage, current, speed, etc.).

The elements that make up discrete signals have various qualitative characteristics: pulse amplitude, pulse polarity and duration, frequency or phase of alternating current, code in sending a series of pulses. Telemechanical systems are discussed in more detail in.

To exchange information between microprocessor controllers of various automation system devices, including control computers, special means, methods and rules of interaction are used - interfaces. Depending on the method of data transfer, a distinction is made between parallel and serial interfaces. IN parallel interface q bits of data are transmitted over q communication lines. IN serial interface Data transmission is usually carried out over two lines: one continuously transmits clock (synchronizing) pulses from the timer, and the second carries information.

In mining machine automation systems, serial interfaces of the RS232 and RS485 standards are most often used.

The RS232 interface provides communication between two computers, a control computer and a microcontroller, or communication between two microcontrollers at speeds up to 19600 bps over a distance of up to 15m.

The RS-485 interface provides data exchange between several devices over one two-wire communication line in half-duplex mode. The RS-485 interface provides data transfer at speeds up to 10 Mbit/s. The maximum transmission range depends on the speed: at a speed of 10 Mbit/s maximum length line - 120 m, at a speed of 100 kbit/s - 1200 m. The number of devices connected to one interface line depends on the type of transceivers used in the device. One transmitter is designed to control 32 standard receivers. Receivers are available with input impedances of 1/2, 1/4, 1/8 of the standard. When using such receivers, the total number of devices can be increased accordingly: 64, 128 or 256. Data transfer between controllers is carried out according to rules called protocols. Exchange protocols in most systems operate on a master-slave principle. One device on the highway is the master and initiates the exchange by sending requests to slave devices, which differ in logical addresses. One of the popular protocols is the Modbus protocol.

2. Actuators

Execution of the decision, i.e. the implementation of the control action corresponding to the generated control signal is carried out actuators (ED). In general, an actuator is a combination of an actuator (AM) and a regulatory body (RO). The location of the actuators in the block diagram of the local ACS is shown in Figure 11.

Figure 11 - Location of actuators in the block diagram of a local automatic control system

An actuator (AM) is a device designed to convert control signals generated by the control unit (PLC) into signals convenient for influencing the final link of the ACS - the regulatory body (RO).

The actuator consists of the following basic elements:

executive motor (electric motor, piston, membrane);

clutch element (coupling, hinge);

transmission-converting element (gearbox with output lever or rod);

power amplifier (electric, pneumatic, hydraulic, combined)

In a specific MI model, a number of elements (except for the actuator motor) may be missing.

The main requirement for the IM: movement of the RO with the least possible distortion of the control laws of the generated PLC, i.e. The MI must have sufficient speed and accuracy.

Main characteristics:

a) nominal and maximum torque value

on the output shaft (rotary) or forces on the output rod;

b) the rotation time of the output shaft of the IM or the stroke of its rod;

c) the maximum value of the output shaft rotation angle or stroke

d) dead zone.

Actuators are classified according to the following signs:

1) movement of the regulatory body (rotary and linear);

2) design (electric, hydraulic, pneumatic);

Electric – with electric motor and electromagnet drives;

Hydraulic – with drives: piston, plunger, from a hydraulic motor;

Pneumatic – with drives: piston, plunger, membrane, diaphragm, from an air motor.

In practice, electrical MI is most widely used. Electrical MI are classified as:

electromagnetic;

electric motor

Electromagnetic MI are divided into:

IMs with drives from electromagnetic clutches are designed to transmit rotational motion (friction and sliding clutches;

IMs with a solenoid drive are 2-position devices (i.e., designed for 2-position control) that carry out translational movement of the drive elements according to the discrete principle: “on - off.”

Electric motor MI are divided into:

single-turn - the angle of rotation of the output shaft does not exceed 360 0. Example: MEO (electric single-turn mechanism). They use single-phase and three-phase (MEOK, MEOB) asynchronous motors.

multi-turn – for remote and local control of pipeline fittings (valves).

In automation systems of mining machines, electric hydraulic distributors, for example the GSD and 1RP2 types, are widely used as actuators. The 1RP2 electric hydraulic distributor is designed to control the feed speed and cutting elements of the combine as part of the URAN.1M automatic load controllers and the SAUK02.2M automation system. The 1RP2 electrohydraulic distributor is a hydraulic spool valve with a pull-type electromagnetic drive.

Regulatory body (RO) is the final element of the ACS that exercises direct control influence on the OS. RO changes the flow of material, energy, the relative position of parts of apparatus, machines or mechanisms in the direction of the normal flow of the technological process.

The main characteristic of the RO is its static characteristic, i.e. the relationship between the output parameter Y (flow, pressure, voltage) and the stroke value of the regulator in percent.

RO provide:

a) two-position regulation - the RO gate quickly moves from one extreme position to another.

b) continuous - in this case it is necessary that the throughput characteristic of the RO be strictly defined (gate, tap, butterfly valve).

General information about process automation

Processes food production

Basic concepts and definitions of automation

Machine(Greek automatos - self-acting) is a device (a set of devices) that functions without human intervention.

Automation is a process in the development of machine production in which management and control functions previously performed by humans are transferred to instruments and automatic devices.

Goal of automation– increasing labor productivity, improving product quality, optimizing planning and management, eliminating people from working in conditions hazardous to health.

Automation is one of the main directions of scientific and technological progress.

Automation as an academic discipline, it is an area of ​​theoretical and applied knowledge about automatically operating devices and systems.

The history of automation as a branch of technology is closely connected with the development of automatic machines, automatic devices and automated complexes. In its infancy, automation relied on theoretical mechanics and theory electrical circuits and systems and solved problems related to regulating pressure in steam boilers, steam piston stroke and rotational speed of electrical machines, controlling the operation of automatic machines, automatic telephone exchanges, and relay protection devices. Accordingly, technical means of automation during this period were developed and used in relation to automatic control systems. The intensive development of all branches of science and technology at the end of the first half of the 20th century also caused the rapid growth of automatic control technology, the use of which is becoming universal.

The second half of the 20th century was marked by the further improvement of technical means of automation and the widespread, although uneven for different sectors of the national economy, spread of automatic control devices with the transition to more complex automatic systems, in particular in industry - from automation of individual units to complex automation of workshops and factories. A special feature is the use of automation at facilities that are geographically distant from each other, for example, large industrial and energy complexes, agricultural facilities for the production and processing of agricultural products, etc. For communication between individual devices in such systems, telemechanics are used, which, together with control devices and controlled objects, form teleautomatic systems. In this case, technical (including telemechanical) means of collecting and automatically processing information become of great importance, since many tasks in complex systems automatic control can only be solved with the help of computer technology. Finally, the theory of automatic control gives way to a generalized theory of automatic control, which unites all theoretical aspects of automation and forms the basis of the general theory of control.

The introduction of automation in production has significantly increased labor productivity and reduced the share of workers employed in various areas of production. Before the introduction of automation, the replacement of physical labor occurred through the mechanization of the main and auxiliary operations of the production process. Intellectual work for a long time remained unmechanized. Currently, intellectual labor operations are becoming the object of mechanization and automation.

There are different types of automation.

1. Automatic control includes automatic alarm, measurement, collection and sorting of information.

2. Automatic alarm is intended to notify about limit or emergency values ​​of any physical parameters, about the location and nature of technical violations.

3. Automatic measurement provides measurement and transmission to special recording devices of the values ​​of controlled physical quantities.

4. Automatic sorting carries out control and separation of products and raw materials by size, viscosity and other indicators.

5. Automatic protection This is a set of technical means that ensure the termination of a controlled technological process when abnormal or emergency conditions occur.

6. Automatic control includes a set of technical means and methods for managing the optimal progress of technological processes.

7. Automatic regulation maintains the values ​​of physical quantities at a certain level or changes them according to the required law without direct human participation.

These and other concepts related to automation and control are united by cybernetics– the science of managing complex developing systems and processes, studying the general mathematical laws of controlling objects of various natures (kibernetas (Greek) – manager, helmsman, helmsman).

Automatic control system(ACS) is a set of control object ( OU) and control devices ( UU), interacting with each other without human participation, the action of which is aimed at achieving a specific goal.

Automatic control system(SAR) – totality OU and an automatic controller, interacting with each other, ensures that the TP parameters are maintained at a given level or changed according to the required law, and also operates without human intervention. ATS is a type of self-propelled gun.