The scheme is the main document explaining the principle of operation and interaction various elements, devices or in general automatic control systems. The most commonly used are fundamental, functional structural (functional) and algorithmic structural (structural) types of circuits. In addition to them, when designing, installing, commissioning and operating ACS, connection and connection diagrams (mounting) are used.
PRINCIPAL, FUNCTIONAL AND STRUCTURAL DIAGRAM
On the schematic diagram, all elements of the system are depicted in accordance with the symbols in interconnection with each other. From the circuit diagram, the principle of its operation and the physical nature of the processes occurring in it should be clear. Schematic diagrams can be electrical, hydraulic, pneumatic, kinematic and combined. In Figure 1.19, as an example, fragments of the principal electrical and principal hydraulic circuits are presented.
Automation elements on circuit diagrams should be designated in accordance with the standard. The image of the elements must correspond to the off state (de-energized, in the absence of excess pressure, etc.) of all circuits of the circuit and the absence external influences. The circuit must be logical
Rice. 1.19.
a- electrical, b- hydraulic
chessically sequential and read from left to right or top to bottom. Each element of the circuit diagram is assigned an alphanumeric reference designation. The letter designation is usually an abbreviated name of the element, and the digital designation in ascending order and in a certain sequence conditionally shows the numbering of the element, counting from left to right or from top to bottom. For complex schemes, as a rule, abbreviated alphabetic and numeric designations are deciphered.
Functional block diagrams reflect the interaction of devices, blocks, nodes and elements of automation in the course of their operation. Graphically, individual automation devices are represented by rectangles corresponding to the direction of the signal. The internal content of each block is not specified. The functional purpose of the blocks is indicated by alphabetic characters. In Figure 1.20, as an example, a functional diagram of the ACS with the air temperature in the greenhouse is shown, where OU- control object (greenhouse), VE- sensing element (temperature sensor), PE- transforming
Rice. 1.20. Functional diagram of the automatic control system for the air temperature in the greenhouse element (amplifier with a relay at the output), RO- regulating body (electric heater), y - controlled value (temperature), g - setting action (required temperature); / - disturbing action (influence external factors on the air temperature in the greenhouse).
Algorithmic block diagrams show the relationship constituent parts automatic system and characterize their dynamic properties. These schemes are developed on the basis of functional or circuit diagrams of automation. Algorithmic block diagram is the most convenient graphic form of ACS representation in the process of studying its dynamic properties. This scheme does not take into account the physical nature of the impacts and the characteristics of specific equipment, but displays only mathematical model management process.
On the structural diagram, as well as on the functional one, the elements uu and OU shown as rectangles. In this case, any device can be represented by several links (rectangles) and, conversely, several devices of the same type can be shown as one link.
The division of ACS into elementary links of directional action is performed depending on the type of mathematical equation that connects the output value with the input for each link. Inside the link (rectangle) indicate the mathematical relationship between the input and output values. This dependence can be represented either by a formula, or a graph, or a table. Similarly to the functional diagram, the connections between the links are depicted as arrows indicating the direction and points of application of the influencing quantities.
The block diagram of the ACS with the air temperature in the greenhouse is shown in Figure 1.21. The general view of this diagram coincides with the functional diagram (see Fig. 1.20), however, inside the rectangles there are functions or graphs that relate the output values of each element to the input ones.
As an example, consider the principle of operation of the circuit diagram of the automatic control system with the temperature of the coolant in
Rice. 1.21.
Rice. 1.22.
/-shutter; 2- THEM; 3 ~amplifier
mine grain dryer (Fig. 1.22) and draw up a functional diagram for it. The required temperature of the heat carrier in the grain dryer is maintained by means of damper 7, which, turning, changes the ratio of hot air inflows Q r , coming from the furnace, and cold Q x , taken from the atmosphere. The temperature inside the grain dryer is measured by a thermal sensor R, included in one of the arms of the measuring bridge. Controlled variable setpoint g(temperatures) are set by moving the slider of the resistor - setter R1. Since the output signal from the measuring bridge is low power, then to control the reversible motor 2 (THEM) use amplifier 3.
When the temperature of the heat carrier inside the grain dryer deviates from the set one, an unbalance signal appears at the output of the bridge, which through the amplifier 3 and relay K1 or K2 enters the electric motor 2, including it. The damper 7 is actuated from the engine, moving in one direction or another depending on the sign of the signal.
Due to the inertia of the temperature sensor R, and its distance from damper 7, the control process can continue indefinitely, i.e., a new equilibrium mode in the system will not be established. Indeed, when the damper takes a new equilibrium position, the temperature of the thermal sensor remains the same for some time, as a result of which the actuator continues to move the damper. Further, the temperature at the place of installation of the temperature sensor will first become equal to the set one, and then deviate from it in the opposite direction, i.e., it will take on a value with the opposite sign. In other words, periodic oscillations, called self-oscillations, will arise in the system. Self-oscillations of the controlled value (temperature) in this system arise due to the fact that the engine stops not at the moment the damper reaches the required position, but with some delay.
Feedback is used to eliminate self-oscillations or reduce their amplitude. (OS) which allows you to stop the engine before the temperature of the coolant reaches the set value, since after the damper stops moving, the temperature of the object and the temperature sensor approaches the set value.
Feedback is carried out using a variable resistor Lo. s, the slider of which is mechanically connected to the rotor of the electric motor 2 and moves along with it. It is obvious that equilibrium in the system will come at the moment when the increment of resistance R os, arising as a result of the movement of the slider, and the increment of resistance R „ caused by a change in the temperature of the coolant, will become equal to each other (BP, c \u003d DL,). Thus, the electric motor 2 in this system, it stops and the transient process stops completely at the moment when the temperature deviation becomes less than the dead zone of the controller.
On the functional diagram (Fig. 1.23), the grain dryer is a control object (030, a temperature sensor - a sensing organ (50), a measuring bridge - a comparator element (CO), an amplifier - an amplifying element ( UE), electric motor - actuator (THEM), damper - regulating body (RO), between the shaft THEM and potentiometer slider - Feedback(OS). Here / is the disturbing effect (outside air temperature, humidity and initial temperature of the grain), g- setting influence (desired drying temperature), at- controlled value (actual heat carrier temperature), and - control action (heat entering the grain dryer with a heat carrier).
Rice. 1.23.
CONNECTION DIAGRAM OF BOARDS, CONTROL DESK, EXTERNAL CONNECTIONS AND CONNECTIONS
Wiring diagrams are diagrams that show the connections of component parts of a device or external connections between individual devices. Schemes for devices installed in switchboards or control panels are developed on the basis of functional diagrams, principal electrical circuits, power supply schemes, as well as general types of boards and consoles.
The general rules for executing wiring diagrams are as follows:
connection diagrams are developed for one shield, console, control station;
all types of apparatus, instruments and fittings provided for by the electrical circuit diagram must be fully reflected in the connection diagram;
the positional designation of devices and automation equipment and the marking of circuit sections, adopted on the circuit diagram, must be stored in the connection diagram.
Three methods of drawing up connection diagrams are used: graphic, address and tabular. For the address and tabular method, in addition to the listed rules, a few more should be observed:
devices and devices on the connection diagrams are depicted in a simplified way without observing the scale in the form of rectangles, over which a circle is placed, separated by a horizontal line. The numbers above the line indicate the serial number of the device (Fig. 1.24, number 8); numbers are assigned panel by panel from left to right and top to bottom), and under the line - the reference designation of this product (for example, KTZ)
if necessary, show the internal diagram of the apparatus (Fig. 1.24);
Rice. 1.24.
for several relays located in the same row, the internal circuit is shown only once if they have the same one;
the output terminals of the devices are conventionally depicted as circles, inside which their factory markings are indicated (for example, 1 ... 8 in Fig. 1.24). If the output terminals of the devices do not have factory markings, then they are conditionally marked with Arabic numerals and indicated in the explanatory entry;
the boards on which diodes, triodes, resistors, etc. are placed, are assigned only a serial number (it is put in a circle under the line);
the positional designation of the elements is placed in the immediate vicinity of their conditional graphic image (Fig. 1.25);
Rice. 1.2
if devices and automation equipment are located on several structural elements of the switchboard or control panel (lid, rear panel, door), then it is necessary to unfold these structures in one plane, observing the mutual placement of devices and automation equipment.
The graphical method lies in the fact that in the drawing, conditional lines show all the connections between the elements of the apparatus (Fig. 1.26). This method is used only for panels and consoles, relatively little saturated with equipment. Schemes of pipe wiring are performed only in a graphical way. If pipes from different material(steel, copper, plastic), then the symbols use different ones: solid lines, dashed lines, dashed-dotted lines with two dots, etc.
The address (“counter”) method consists in the fact that the communication lines between the individual elements of the devices installed on the shield or console are not depicted. Instead, at the point of connection of the wire on each device or element, a digital or alphanumeric address of the device or element with which it must be electrically connected is affixed (the reference designation corresponds to the circuit diagram or serial number of the product). With such an image
Rice. 1.26.
Rice. 1.27.
diagrams, the drawing is not cluttered with communication lines and is easy to read (Fig. 1.27). The address method for performing wiring diagrams is the main and most common.
The tabular method is used in two versions. For the first, a wiring table is compiled, where the numbers of each electrical circuit are indicated. In turn, for each circuit, the conventional alphanumeric designations of all devices, devices and their contacts, through which these circuits are connected, are sequentially listed (Table 1.1). So, for chain 7, the entry means that the clamp 6 instrument KM1 connects to clamp 4 instrument KM2, which, in turn, must be connected to the clamp 3 devices CT4.
1.1. Connection table example
|
Chain number |
Compound |
|
KM 1 KM2 KT 4 6 4 3 |
|
|
KM 4XT 1 2 293 |
|
|
XTI HL1 KH2 XT 2 328 1 12 307 |
The second option for filling out the connection table differs from the first in that conductors are entered into the table in ascending order of the marking numbers of the circuits of forced electrical circuits (Table 1.2). The direction of laying wires, as for the first option, is written as a fraction. For a clearer recognition of conductors, it is customary to use additional designations. For example, a jumper made in the device is denoted by the letter "p".
1.2. Wire connection table example
Connection diagrams serve as working drawings, according to which the installation of automation equipment is carried out, therefore they are also called installation drawings. Diagrams showing external connection devices, installations, panels, consoles, etc., are performed on the basis of functional and circuit diagrams of power supply, specifications of instruments and equipment, as well as drawings of industrial premises with the location of process equipment and pipelines.
Connection diagrams are used when installing wires, with the help of which the installation, device, device is connected to power sources, switchboards, consoles, etc.
In practice, two methods of drawing up connection diagrams are used: graphical and tabular. The most common graphics.
On the connection diagrams, using conventional graphic symbols, they show: selective devices and primary converters; boards, consoles and local control, monitoring, signaling and measurement points; off-panel devices and automation equipment; connecting, lingering and free boxes; electrical wires and cables laid outside the shields; nodes for connecting electrical wires to devices, apparatuses, boxes; locking equipment and elements for connections and branches; switching terminals located outside the shields, protective earthing. Cabinets, consoles, individual devices and devices are conventionally depicted in the form of rectangles or circles, inside which the corresponding signatures are placed.
Connections of the same purpose on the connection diagrams are shown with a solid line, and only at the points of connection to devices, actuators and other devices, the wires are separated for the purpose of marking. On communication lines denoting wires or cables, indicate the number of the wire (connection), brand, cross section and length of wires and cables (if the wiring is done in a pipe, then the characteristic of the pipe must also be given). Connection wires and cables are shown as lines 0.4 ... .1 mm thick.
Connection diagrams are made without respect to scale in a form convenient for the user. Sometimes the connection diagrams are presented in the form of tables, which are performed separately for each section (or panel) of the control panel (Table 1.3).
1.3. Connection table example
|
Cable, wire |
Wiring direction |
|||||||||
For general acquaintance with the system, a block diagram is provided (Fig. 6.2). Structural scheme - this is a diagram that defines the main functional parts of the product, their purpose and relationships.
Structure - it is a collection of parts automated system, into which it can be divided according to a certain attribute, as well as the ways of transferring the impact between them. AT general case any system can be represented by the following structures:
- ? constructive - when each part of the system is an independent constructive whole;
- ? functional - when each part of the system is designed to perform a specific function (full details of functional structure with an indication of the control loops are given on the automation diagram);
Rice. 6.2.
? algorithmic - when each part of the system is designed to perform a certain algorithm for converting the input value, which is part of the functioning algorithm.
It should be noted that block diagrams may not be given for simple automation objects.
The requirements for these schemes are established by RTM 252.40 “Automated process control systems. Structural schemes of management and control”. According to this document, constructive block diagrams contain: technological subdivisions of the automation object; points
control and management, including those not included in the project being developed, but having a connection with the system being designed; technical personnel and services that ensure the operational management and normal functioning of the technological facility; the main functions and technical means that ensure their implementation at each control and management point; relationships between parts of the automation object.
The elements of the block diagram are shown as rectangles. Separate functional services and officials may be shown as a circle. Inside the rectangles, the structure of this section is revealed. Functions of the automated control system technological process are indicated by symbols, the decoding of which is given in the table above the main inscription according to the width of the inscription. The relationship between the elements of the structural diagram is depicted by solid lines, merging and branching - by lines with a break. The line thickness is as follows: conditional images- 0.5 mm, communication lines - 1 mm, the rest - 0.2 ... 0.3 mm. The sizes of elements of block diagrams are not regulated and are chosen at discretion.
The example (Fig. 6.2) shows a fragment of the implementation of a constructive control and monitoring scheme for a water treatment plant. In the lower part, the technological divisions of the automation object are disclosed; in the rectangles of the middle part - the main functions and technical means of the points local government aggregates; in the upper part - the functions and technical means of the item centralized control station. Since the diagram occupies several sheets, the transitions of the communication lines to subsequent sheets are indicated and a broken rectangle is shown, revealing the structure of the automation object.
On the communication lines between the individual elements of the control system, the direction of the transmitted information or control actions can be indicated; if necessary, communication lines can be marked with letters of the type of communication, for example: K - control, C - signaling, remote control, AR - automatic control, DS - dispatch communication, PGS - industrial telephone (loud-speaking) communication, etc. P.
According to performance requirements greenhouse farming with convection heat exchange and an irrigation system, the scheme for automating the technological process of growing agricultural products in block stationary greenhouses can be represented as a functional diagram of automation shown in Fig. 3.1.
On the automation scheme (see Fig. 3.1), the following designations are accepted:
- 1 - Air damper for supply ventilation with electric drive;
- 2 - Circulation fan;
- 3 - heating element;
- 4 - Electric exhaust air damper;
- 5 - Solenoid valve of the irrigation circuit;
- 6 - Nozzles of the irrigation system (watering);
- 7 - Sensor for opening doors (or windows);
- 8, 9 - Soil moisture sensor;
- 10 - Humidity and air temperature meter.
Based on the developed automation scheme, it is advisable to design the architecture of the control system according to a three-level scheme. At the first (lower) level, the collection of process information from measuring transducers and the control of locally installed actuators and relay automation are provided. Signals from temperature and humidity measuring transducers are processed by a programmable logic controller (PLC).
Based on the developed automation scheme, it is advisable to design the architecture of the control system according to a three-level scheme. At the first (lower) level, the collection of process information from measuring transducers and the control of locally installed actuators and relay automation are provided. The signals from temperature and humidity measuring transducers are processed by the PLC. According to the specified microclimate mode control algorithm, it generates control signals to the actuators of the control loops. The second level provides program control according to a given technological process of growing crops from the operator's post. The software system automatically checks and controls the temperature, humidity level in the chamber and on the soil surface using sensors and a heating pipeline valve, as well as a humidification system. The equipment of this level includes the control panel and the PLC installed in the control room. The industrial computer is connected by a Profibus DP network with distributed equipment and is connected to the local greenhouse segment via an Ethernet network at the third level.
At the third (upper) level, centralized processing of information about the technological process is carried out at enterprises via an Ethernet network. Information processing includes control over the course of the technological process, coolant flow, logging, archiving and operational control.
The block diagram of the automated control system for the technological process of climate control inside the greenhouse environment is shown in fig. 3.2.
Figure 3.1 - Automated greenhouse microclimate control system
Figure 3.2 - Structural diagram of ACS MKT
Lecture 9
When developing an automation project, first of all, it is necessary to decide from which places certain sections of the object will be controlled, where control points, operator premises will be located, what should be the relationship between them, i.e. it is necessary to resolve the issues of choosing a management structure. The control structure is understood as a set of parts of an automatic system into which it can be divided according to a certain attribute, as well as ways of transferring influences between them. A graphic representation of the control structure is called a block diagram. Although the initial data for selecting the management structure and its hierarchy are specified by the customer with varying degrees of detail when issuing a design assignment, complete structure management should be developed by the design organization.
In the very general view block diagram of the automation system is shown in Figure 9.1. The automation system consists of an automation object and a control system for this object. Due to a certain interaction between the automation object and the control system, the automation system as a whole provides the required result of the object functioning, characterized by the parameters x 1 x 2 ... x n
The operation of a complex automation object is characterized by a number of auxiliary parameters y 1 , y 2 , ..., y j , which should also be controlled and regulated.
In the process of work, the object receives disturbing influences f 1 , f 2 , ..., f i , causing deviations of the parameters x 1 , x 2 , x n from their required values. Information about current values x 1 , x 2 , x n , y 1 , y 2 , y n enters the control system and is compared with the prescribed values g j , g 2 ,..., g k , resulting in the control system generating control actions E 1 , E 2 , ..., E m to compensate for deviations of the output parameters.
Figure 9.1 - Structural diagram of the automation system
The choice of the control structure of the automation object has a significant impact on the efficiency of its work, reducing the relative cost of the control system, its reliability, maintainability, etc.
In general, any system can be represented by:
constructive structure;
The functional structure
algorithmic structure.
In the structural structure of the system, each part of it is an independent constructive whole (Figure 9.1).
The design scheme contains:
object and automation system;
information and control flows.
In the algorithmic structure, each part is designed to perform a specific input signal conversion algorithm, which is part of the entire system operation algorithm.
The designer develops an algorithmic block diagram (ACS) of the automation object according to differential equations or graphical characteristics. The automation object is represented as several links with different transfer functions interconnected. In the ACC, individual links may not have physical integrity, but their connection (the circuit as a whole) in terms of static and dynamic properties, according to the functioning algorithm, should be equivalent to the automation object. Figure 9.2 gives an example of ACC ACS.
Figure 9.2 - Algorithmic block diagram, presented in the form of simple links
In a functional structure, each part is designed to perform a specific function.
In automation projects, constructive block diagrams are depicted with elements of functional features. Complete information about the functional structure, indicating local control loops, control channels and technological control, is given in functional diagrams (lecture 10).
The block diagram of the APCS is developed at the “Project” stage in a two-stage design and corresponds to the composition of the system. As an example, figure 9.3 shows a block diagram of the management of sulfuric acid production.
Figure 9.3 - A fragment of the block diagram of the management and control of sulfuric acid production:
1 - communication line with the shop chemical laboratory; 2 - communication line with the points of control and management of the acid site; 3 - communication line with the point of control and management of III and IV technological lines
The block diagram displays in a general view the main decisions of the project on the functional, organizational and technical structures of the automated process control system in compliance with the hierarchy of the system and the relationship between control and management points, operational personnel and the technological control object. The principles of organizing the operational management of a technological object adopted during the implementation of the block diagram, the composition and designations of individual elements of the block diagram must be preserved in all design documents for the process control system.
Table 9.1 - APCS functions and their symbols in Figure 9.3
| Symbol | Name |
| Parameter control Remote control technological equipment and actuating devices Measuring transformation Monitoring and signaling of the state of equipment and deviations of parameters Stabilizing control Selection of the operating mode of regulators and manual control of setters Manual input data Registration of parameters Calculation of technical and economic indicators Accounting for production and compilation of data per shift Diagnostics of technological lines (aggregates) Distribution of loads of technological lines (aggregates) Optimization of individual technological processes Analysis of the state of the technological process Forecasting of the main indicators of production Evaluation of shift work Control of the fulfillment of planned targets Control of repairs Preparation and issuance of operational information in the automated control system Receiving production restrictions and tasks from the automated control system |
The block diagram shows the following elements:
1. technological divisions (departments, sections, workshops, production);
2. points of control and management (local boards, operator and control rooms, block boards, etc.);
3. technological personnel (operational) and additional special services providing operational management;
4. the main functions and technical means that ensure their implementation at each point of control and management;
5. the relationship between departments and with the higher ACS.
The functions of the automated process control system are encrypted and denoted in the diagram as numbers. Conventions APCS functions in Figure 9.3 are given in Table 9.1.
The block diagram of the automation system is carried out by nodes and includes all elements of the system from the sensor to the regulatory body, indicating the location, showing their interconnection.
The development of automated process control systems at the present stage is associated with the widespread use of microprocessors and microcomputers for control, the cost of which is becoming lower every year compared to the total costs of creating control systems. Before the advent of microprocessors, the evolution of process control systems was accompanied by an increase in the degree of centralization. However, the capabilities of centralized systems are now already limited and do not meet modern requirements for reliability, flexibility, cost of communication systems and software.
The transition from centralized control systems to decentralized ones is also caused by an increase in the power of individual technological units, their complication, and an increase in the requirements for speed and accuracy of their work. The centralization of control systems is economically justified with a relatively small information capacity (the number of control and regulation channels) of TOU and its territorial concentration. With a large number of control, regulation and control channels, a large length of communication lines in the process control system, decentralization of the control system structure becomes a fundamental method for increasing the survivability of the process control system, reducing costs and operating costs.
The most promising direction of decentralization of APCS should be recognized automated control processes with a distributed architecture, based on the functional-target and topological decentralization of the control object.
Functionally targeted decentralization is a separation complex process or systems into smaller parts - subprocesses or subsystems on a functional basis (for example, redistribution of the technological process, operating modes of units, etc.) that have independent goals of functioning.
Topological decentralization means the possibility of territorial (spatial) division of the process into functional-target sub-processes. With optimal topological decentralization, the number of subsystems of a distributed automated process control system is chosen so as to minimize the total length of communication lines that, together with local control subsystems, form a network structure.
The technical basis of modern distributed control systems, which made it possible to implement such systems, are microprocessors and microprocessor systems.
The microprocessor system performs the functions of data collection, regulation and control, visualization of all database information, change of settings, parameters of algorithms and the algorithms themselves, optimization, etc. The use of microprocessors (including microcomputers) for solving the above tasks makes it possible to achieve the following goals:
a) to replace analog technical means with digital ones, where the transition to digital means improves the accuracy, expands the functionality and increases the flexibility of control systems;
b) replace hardware with hard logic with programmable (with the possibility of changing the program) devices, or microcontrollers;
c) replace one minicomputer with a system of several microcomputers when it is necessary to ensure decentralized production or process control with increased reliability and survivability, or when the capabilities of a minicomputer are not fully used.
Microprocessor systems can perform all typical functions of control, measurement, regulation, control, presentation of information to the operator in the subsystems of a distributed process control system.
In distributed automated process control systems, three topological structures of interaction of subsystems are generally accepted: star-shaped (radial); ring (loop); bus (main) or their combinations. The organization of communication with sensors and actuators is individual and mostly radial.
Figure 3.5 shows topologies of distributed APCS.
Figure 3.5 - Typical structures of distributed APCS:
a - radial, b - main, c - ring
The radial structure of the interaction of subsystems (Fig. 3.5, a) reflects the traditionally used method of connecting devices with dedicated communication lines and is characterized by the following features:
a) there are separate, unrelated lines that combine the central subsystem (CPU) with the local automation systems of the aircraft i ;
b) technically simple interface devices US 1 - US m local automation are implemented. The central communication device of the NSC is a set of modules of the type CS i according to the number of lines or a rather complex device for multiplexing information transmission channels;
c) provided maximum speeds exchange on separate lines with enough high performance computing devices at the CPU level;
d) the reliability of the communication subsystem largely depends on the reliability and survivability of the technical means of the CPU. The failure of the CPU practically destroys the exchange subsystem, since all information flows are closed through the upper level.
A distributed system with a radial structure is a two-level system, where at the lower level the necessary functions of control, regulation, control are implemented in the subsystems, and at the second level, in the CPU, the coordinating microcomputer (or minicomputer), in addition to coordinating the work of microcomputer satellites, optimizes the tasks of controlling the TOU, energy distribution, manages the technological process as a whole, calculates technical and economic indicators, etc. The entire database in a distributed system with a radial structure must be accessible by a coordinating microcomputer for top-level control applications. As a result, the coordinating microcomputer operates in real time and must be controlled using high-level languages.
Figure 3.5 (b, c) shows the ring and bus topologies of the level interaction. These structures have a number of advantages compared to the radial one:
a) the operability of the communication subsystem, which includes the channel and communication devices, does not depend on the serviceability technical means at the levels of automation;
b) it is possible to connect additional devices and control the entire subsystem using special tools;
c) significantly lower costs of cable products are required.
Due to the exchange of information between LA i through the communication channel and the RS (“each with each”), there is an additional possibility of dynamic redistribution of the functions of coordinating the joint operation of the LA subsystems over lower levels in the event of a CPU failure. The bus (to a lesser extent ring) structure provides a broadcast mode of exchange between subsystems, which is an important advantage in the implementation of group control commands. At the same time, the bus and ring architecture already imposes significantly higher requirements on the “intelligence” of interface devices, and, consequently, increased one-time costs for the implementation of the core network.
Comparing the ring and bus topologies of a communication subsystem, it should be noted that the organization of a ring structure is less expensive than a bus one. However, the reliability of the entire subsystem with a ring communication system is determined by the reliability of each interface device and each segment of the communication lines. To increase survivability, it is necessary to use double rings or additional communication lines with workarounds. The operability of a physical transmission channel for a bus architecture with transformer isolation does not depend on the serviceability of interface devices, however, as for a ring, the failure of any interface device in the worst case leads to completely autonomous operation of the failed subsystem node, i.e., to loss of control function from the CPU level by the automation of the failed node.
An explicit method for increasing the survivability of the entire automation system in the event of a failure of matching devices in the communication subsystem is duplication of matching devices in the nodes of the subsystem. In a ring structure, this approach is already implied in the organization of double rings and detours. If the reliability of a continuous physical channel for the lower topology is beyond doubt, then it is possible to duplicate only interface devices without using a backup trunk cable.
A cheaper way to increase the reliability of the communication subsystem is to use combined structures that combine the advantages of radial and ring (backbone) topologies. For a ring, the number of radial bonds can be limited to two or three lines, the implementation of which provides a simple and inexpensive solution.
Evaluation of such indicators of distributed industrial control systems as economic(costs for cable products, cable routing, development or acquisition of network facilities, including communication devices, etc.), functional(the use of group transfer operations, the intensity of the exchange, the possibility of exchanging "each with each"), as well as indicators of unification and the possibility of evolution networks (the ability to easily turn on additional subscriber nodes, trends towards use in automated process control systems) and indicators network reliability(failure of the communication channel and communication or interface devices), allows us to draw the following conclusions:
a) the most promising in terms of development and use is the backbone organization of the communication subsystem;
b) the functionality of the backbone topology is not inferior to the capabilities of the ring and radial;
c) the reliability indicators of the main structure are quite satisfactory;
d) the backbone topology of a distributed APCS requires large one-time costs for the creation and implementation of a communication channel and interface devices.
Largely due to these features of the backbone structure and the modular organization of hardware and software in modern automated control systems TP trunk-modular principle construction of technical support has found predominant distribution.
The use of microprocessors and microcomputers makes it possible to effectively and economically implement the principle of functional and topological decentralization of automated process control systems. Thus, it is possible to significantly increase the reliability and survivability of the system, reduce expensive communication lines, ensure the flexibility of operation and expand the scope in the national economy of complexes of technical means, the main element of which is a microcomputer or microprocessor. In such distributed control systems, it is of great importance interface standardization, i.e. the establishment and application of uniform norms, requirements and rules that guarantee the information integration of technical means in typical structures APCS.
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