ACS is an abbreviation that stands for Automated Control Systems. The answer to the question of what an automated control system is can be formulated as follows: it is a collection technical systems and processes, organizational complexes and scientific methods, which allow us to provide optimal control a complex technical process or object, as well as a team of people that has one common goal.

In contact with

ACS block diagram

The following components can be distinguished in the structure of any automated control system:

1. The main part includes mathematical and Information Support and technical part.
2. Functional part - implies specific management functions and a number of interrelated programs.

Systems can be simple or large-scale and complex.

It is customary to distinguish between two structural types of such systems - an automated technical process control system (APCS) and a system organizational management(ASOU).

The differences among these systems lie in the characteristics of the object that the system will control. Process control systems are built to control complex technical objects, mechanisms, devices, and machines. ASOUs are designed to control the functioning of groups of people. According to the use of automated control systems, the methods of transmitting information will also differ - these can be documents or various physical signals.

There is also the abbreviation SAU - system automatic control. Its peculiarity is that it can operate for some time without human intervention. Such systems are used to manage small hotel facilities.

Application and main functions of the automated control system

ACS found wide application in various fields industrial production. The main functions of the systems are as follows:

Basic principles of ACS

For the first time operating principles automated systems management, the procedure for their development and creation were formulated by V.M. Glushkov.

ACS information base

The information base of an automated control system can be called the entire set of information located on computer media and necessary for the normal functioning of the system.

As a rule, all information base is divided into three sectors – general, derivative and operational.

Technical characteristics of the automated control system

The technical base of an automated control system is usually understood as all the technical means that are used to collect, accumulate and process information, as well as to display and transmit it. This also includes the executive nodes of the system that influence the control object.

Basic technical elements and ACS equipment is electronic computing technology that ensures the accumulation and processing of all data circulating within the system. This technique allows you to simulate production processes and build proposals for management.

To build and manage an automated control system, two types of electronic computer technology are used - accounting and regulatory and information and settlement.

Information and calculation equipment is located at the highest hierarchical level in the management system. Their task is to resolve all issues related to centralized management object. Such mechanisms are characterized by high performance, the presence of an interrupt system, variable word length, and syllable processing of input data.

The lower level of the control system, as a rule, is given to accounting and regulatory mechanisms and equipment. These mechanisms, as a rule, are located directly on sites or in production workshops. Their task includes collecting input data from management objects and primary processing of this information with its subsequent transfer to the information and settlement department and receiving planned directive information. In addition, the accounting and regulatory part of the equipment is engaged in local calculations and develops control actions on control objects in the event of deviations from the calculated functions. This part of the control system has a well-developed connection with big amount sources of information and control devices.

Mechanical means of collecting and displaying information

If the system provides for the collection and processing of information with human participation, it includes various recorders that allow you to obtain initial data directly from workplaces. This also includes all kinds of temperature sensors, timers, meters for the number of parts produced and other similar equipment. Automatic deviation detectors are also installed in production process, which register and transmit to the system information about the absence of materials, tools, Vehicle for dispatch of manufactured products, as well as irregularities in the operation of machines. Such equipment is installed not only in production premises, but also in warehouses for storing raw materials and finished products.

Data display tools include all devices that allow you to display information in the most accessible form for humans. This includes all kinds of monitors, displays and screens, printing devices, terminals, indicators, etc. These devices are connected directly to the central processor of the computer and can provide information either regulated or occasionally - at the request of the operator or in the event of an emergency.

The technical base of automated control systems also includes various types of office equipment, control, measuring and accounting instruments that ensure the normal functioning of the main technical units.

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 every year becomes lower and lower compared to the total costs of creating control systems. Before the advent of microprocessors, the evolution of process control systems was accompanied by an increasing degree of centralization. However, the possibilities centralized systems now they are 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 complexity, and increased requirements for speed and accuracy of their operation. Centralization of control systems is economically justified given the relatively small information power (number of control and regulation channels) of the TOU and its territorial concentration. With a large number of monitoring, regulation and control channels, a large length of communication lines in the process control system, decentralization of the structure of the control system becomes a fundamental method of increasing the survivability of the process control system, reducing cost and operating costs.

The most promising direction of decentralization of automated process control systems should be recognized automated control processes with a distributed architecture, based on the functional-target and topological decentralization of the control object.

Functional-target decentralization- this is the division of a complex process or system into smaller parts - subprocesses or subsystems according to functional characteristics (for example, processing stages technological process, operating modes of units, etc.) having independent operational goals.

Topological decentralization means the possibility of territorial (spatial) division of the process into functional-target subprocesses. With optimal topological decentralization, the number of subsystems of a distributed automated process control system is selected 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 makes 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, changing settings, parameters of algorithms and the algorithms themselves, optimization, etc. The use of microprocessors (including microcomputers) to solve the listed problems makes it possible to achieve the following goals:

a) replace analog technical means with digital ones where the transition to digital means increases accuracy, expands functionality and increases the flexibility of control systems;

b) replace hardware with hard logic with programmable (with the ability to change the program) devices, or microcontrollers;

c) replace one minicomputer with a system of several microcomputers when it is necessary to ensure decentralized production or technological process control with increased reliability and survivability or when the capabilities of the minicomputer are not fully used.

Microprocessor systems can perform in the subsystems of a distributed automated process control system all standard functions of monitoring, measuring, regulating, managing, and presenting information to the operator.

In distributed automated process control systems, mainly three topological structures for interaction of subsystems are adopted: star-shaped (radial); ring (loop); bus (main) or combinations thereof. The organization of communication with sensors and actuators is individual and predominantly radial in nature.

Figure 3.5 shows topology options for distributed automated process control systems.

Figure 3.5 - Typical structures of distributed automated process control systems:

a - radial, b - main, c - ring

The radial structure of 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, unconnected lines that connect the central subsystem (CS) with local automation systems of the aircraft i;

b) technically, the interface devices US 1 - US m of local automation are technically simple to implement. The central communication device USC is a set of modules of type US i in terms of the number of lines or a rather complex device for multiplexing information transmission channels;

c) are provided maximum speeds exchange on separate lines with sufficiently high performance of computing devices at the CPU level;

d) the reliability of the communication subsystem largely depends on the reliability and survivability of the CPU hardware. 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 control, regulation, and management functions 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 control tasks of the TOU, energy distribution, controls 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 to the coordinating microcomputer for application control programs at the upper level. 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 level interaction. These structures have a number of advantages compared to radial ones:

a) the operability of the communication subsystem, which includes a channel and communication devices, does not depend on the serviceability of technical means at the automation levels;

b) there are possibilities for connecting additional devices and monitoring the entire subsystem using special means;

c) significantly lower costs of cable products are required.

Due to the exchange of information between aircraft i through a communication channel and the US (“each with each”), an additional opportunity appears for the dynamic redistribution of coordination functions collaboration aircraft subsystems at lower levels in case of CPU failure. The bus (to a lesser extent ring) structure provides a broadcast mode of exchange between subsystems, which is an important advantage when implementing group control commands. At the same time, bus and ring architecture presents significantly more high requirements to 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 the 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 section of communication lines. To increase survivability, it is necessary to use double rings or additional communication lines with bypass paths. The performance of the physical transmission channel for a bus architecture with transformer isolation does not depend on the serviceability of the interface devices; however, as for the ring, the failure of any interface device in the worst case leads to completely autonomous operation of the failed subsystem node, i.e., to the loss of control function from the CPU level by the automation of the failed node.

An obvious method of increasing the survivability of the entire automation system in the event of a failure of the coordination devices in the communication subsystem is the duplication of coordination devices in the nodes of the subsystem. In a ring structure, this approach is already implied by the organization of double rings and bypass paths. If the reliability of a continuous physical channel for the lower topology is not in doubt, then it is possible to duplicate only the interface devices without using a backup backbone 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 connections can be limited to two or three lines, the implementation of which provides a simple and inexpensive solution.

Evaluation of such indicators of distributed automated process control systems as economic(costs of cable products, cable routing, development or acquisition of network tools, including communication devices, etc.), functional(use of group transfer operations, intensity of exchange, possibility of exchange “everyone with everyone”), as well as indicators of unification and possibilities of evolution networks (the ability to easily include additional subscriber nodes, trends for 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 ones;

c) the reliability indicators of the main structure are quite satisfactory;

d) the backbone topology of a distributed automated process control system 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 process control systems backbone-modular principle construction of technical support has found widespread use.

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, you can significantly increase the reliability and survivability of the system, reduce expensive communication lines, provide operational flexibility and expand the scope of application in national economy complexes of technical means, the main element of which is a microcomputer or microprocessor. In such distributed control systems, it becomes very important interface standardization, i.e. establishment and application of uniform norms, requirements and rules that guarantee the information integration of technical means in typical structures APCS.

The diagram is the main document explaining the principle of operation and interaction of various elements, devices or automatic control systems in general. The most frequently used are fundamental, functional structural (functional) and algorithmic structural (structural) types of diagrams. In addition to them, when designing, installing, commissioning and operating ACS, connection and connection diagrams (assembly diagrams) are used.

PRINCIPLE, FUNCTIONAL AND STRUCTURAL DIAGRAMS

In the schematic diagram, all elements of the system are depicted in accordance with the symbols in relation to each other. The principle of its operation and the physical nature of the processes occurring in it should be clear from the circuit diagram. Schematic diagrams can be electrical, hydraulic, pneumatic, kinematic and combined. Figure 1.19 shows fragments of the electrical and hydraulic circuit diagrams as an example.

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 of external influences. The circuit must be logical

Rice. 1.19.

A- electric, b- hydraulic

logically sequential and read from left to right or top to bottom. Each element of the circuit diagram is assigned an alphanumeric positional designation. The letter designation usually represents the abbreviated name of the element, and the numerical designation, in ascending order and in a certain sequence, conventionally 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 numerical symbols are deciphered.

Functional block diagrams reflect the interaction of devices, blocks, nodes and automation elements in the process of their operation. Graphically, individual automation devices are represented by rectangles corresponding to the direction of signal passage. The internal content of each block is not specified. The functional purpose of blocks is indicated by alphabetic symbols. Figure 1.20 shows, as an example, a functional diagram of an automatic control system based on air temperature in a greenhouse, where OU- management object (greenhouse), VE- sensing element (temperature sensor), PE- transformative

Rice. 1.20. Functional diagram of an ACS based on air temperature in a greenhouse element (amplifier with relay output), RO- regulating body (electric heater), y - controlled variable (temperature), g - setting influence (required temperature); / - disturbing influence (influence external factors on the air temperature in the greenhouse).

Algorithmic block diagrams show relationships components automatic system and characterize their dynamic properties. These circuits are developed on the basis of functional or circuit diagrams of automation. An algorithmic block diagram is the most convenient graphical form of representing an automatic control system in the process of studying its dynamic properties. This diagram does not take into account the physical nature of the influences and the features of specific equipment, but displays only a mathematical model of the control process.

On the structural diagram, as well as on the functional diagram, the elements UU And OU are depicted as rectangles. In this case, any device can be represented by several links (rectangles) and, conversely, several devices of the same type can be depicted as one link.

The division of the ACS into elementary links of directional action is carried out depending on the type of mathematical equation connecting the output value with the input for each link. Inside the link (rectangle) the mathematical relationship between the input and output quantities is indicated. This relationship can be represented either by a formula, a graph, or a table. Similar to the functional diagram, the connections between the links are depicted in the form of arrows indicating the direction and points of application of the influencing quantities.

The block diagram of the automatic control system for air temperature in a greenhouse is shown in Figure 1.21. The general appearance of this diagram coincides with the functional diagram (see Fig. 1.20), however, inside the rectangles there are functions or graphs that connect the output values ​​of each element with the input ones.

As an example, let us consider the principle of operation of the electrical circuit diagram of an automatic control system with coolant temperature at

Rice. 1.21.

Rice. 1.22.

/-flap; 2- THEM; 3 ~amplifier

mine grain dryer (Fig. 1.22) and draw up a functional diagram for it. The required temperature of the coolant in the grain dryer is maintained using damper 7, which, turning, changes the ratio of hot air inflows Qr, coming from the furnace, and cold Qx, taken from the atmosphere. The temperature inside the grain dryer is measured by a temperature sensor R, included in one of the arms of the measuring bridge. Set value of the controlled variable g(temperature) is set by moving the slider of the resistor - setter R1. Since the output signal from the measuring bridge is low power, to control a reversible electric motor 2 (THEM) use an amplifier 3.

When the temperature of the coolant inside the grain dryer deviates from the set one, an imbalance signal appears at the bridge output, which is sent through an amplifier 3 and relay K1 or K2 enters electric motor 2, turning it on. The engine activates the damper 7, which moves 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 regime will not be established in the system. Indeed, when the damper takes a new equilibrium position, the temperature of the temperature sensor remains the same for some time, as a result of which the actuator will continue to move the damper. Next, the temperature at the location where the temperature sensor is installed will first become equal to the set value, 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 appear in the system. Self-oscillations of the controlled variable (temperature) in this system arise due to the fact that the engine does not stop at the moment the damper reaches the required position, but with some delay.

To eliminate self-oscillations or reduce their amplitude, feedback is used (OS), which allows you to stop the engine before the coolant temperature 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. c, the slider of which is mechanically connected to the rotor of the electric motor 2 and moves at the same time as him. It is obvious that equilibrium in the system will occur at the moment when the increment in resistance L os, arising as a result of the movement of the slider, and the increment in resistance R„ caused by a change in coolant temperature, will become equal to each other (AD, c = DL,). Thus, the electric motor 2 in this system it stops and the transient process completely stops at the moment when the temperature deviation becomes less than the controller dead zone.

In the functional diagram (Fig. 1.23), the grain dryer is a control object (030, a temperature sensor is a sensing organ (50), a measuring bridge is a comparing element (CO), an amplifier is a reinforcing element ( UE), electric motor - actuator (THEM), damper - regulating body (RO), between the shaft THEM and the potentiometer slider - feedback (OS). Here/- the disturbing influence (outside air temperature, humidity and initial grain temperature), g- setting influence (required drying temperature), at- controlled variable (actual coolant temperature), And - control action (heat entering the grain dryer with coolant).

Rice. 1.23.

CONNECTION DIAGRAMS FOR BOARDS, CONTROL PANELS, EXTERNAL CONNECTIONS AND CONNECTIONS

Connection diagrams are diagrams that show the connections of the components 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, fundamental electrical diagrams, power plans, and common types shields and consoles.

The general rules for executing connection diagrams are as follows:

connection diagrams are developed for one panel, console, control station;

all types of devices, instruments and fittings provided for in the electrical circuit diagram must be fully reflected in the connection diagram;

The positional designations of devices and automation equipment and the markings of circuit sections adopted on the electrical circuit diagram must be preserved in the connection diagram.

Three methods of drawing up connection diagrams are used: graphical, addressable and tabular. For the address and tabular method, in addition to the listed rules, several more should be followed:

devices and devices on connection diagrams are depicted in a simplified manner without observing scale in the form of rectangles, above 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 below the line is the positional designation of this product (for example, KTZ)

if necessary, show the internal diagram of the devices (Fig. 1.24);

Rice. 1.24.

for several relays located in the same row, the internal diagram is shown only once if they have the same one;

The output terminals of 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 marked conventionally with Arabic numerals and this is indicated in the explanatory note;

boards on which diodes, triodes, resistors, etc. are placed are assigned only a serial number (it is placed in a circle under the line);

the positional designation of the elements is placed in close proximity to their conventional graphic image (Fig. 1.25);

Rice. 1.2

if instruments and automation equipment are located on several structural elements of a switchboard or console (cover, back panel, door), then it is necessary to unfold these structures into one plane, observing the relative placement of instruments and automation equipment.

The graphical method is that in the drawing, conventional lines show all the connections between the elements of the devices (Fig. 1.26). This method is used only for panels and consoles that are relatively sparsely equipped with equipment. Pipe wiring diagrams are performed only graphically. If pipes from different materials(steel, copper, plastic), then 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 switchboard or console are not depicted. Instead, at the wire connection point on each device or element, a digital or alphanumeric address of the device or element with which it must be electrically connected is indicated (the position designation corresponds to the circuit diagram or serial number of the product). With this 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 of executing connection diagrams is the main and most common.

The tabular method is used in two versions. For the first, an installation table is drawn up, 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 circuit 7, the entry means that the clamp 6 device KM1 connects to clamp 4 device KM2, which in turn must be connected to the clamp 3 devices KT4.

1.1. Connection table example

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 the wires, as for the first option, is written in the form of a fraction. To more clearly identify conductors, it is customary to use additional designations. For example, a jumper made in the device is designated by the letter “p”.

1.2. Example of wire connection table

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 carried out on the basis of functional and circuit diagrams of power supply, specifications of devices and equipment, as well as drawings production premises with the location of process equipment and pipelines.

Connection diagrams are used when installing wires, with the help of which the installation, device, apparatus 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 is graphic.

The connection diagrams show with the help of conventional graphic symbols: selecting devices and primary converters; switchboards, consoles and local control, monitoring, alarm and measurement points; off-panel devices and automation equipment; connecting, broaching and free boxes; electrical wires and cables laid outside the switchboards; nodes for connecting electrical wires to devices, devices, boxes; shut-off equipment and elements for connections and branches; switching terminals located outside the switchboards, protective grounding. 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 one purpose in 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 indicating wires or cables, indicate the wire number (connection), brand, cross-section and length of wires and cables (if the wiring is made in a pipe, then the characteristics 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 adherence to scale in a form convenient for the user. Sometimes 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

BLOCK DIAGRAM AND PRINCIPLE OF OPERATION OF THE ACS

A block diagram of the margarine preparation line, which shows its composition, including actuators and functionally important structural elements, is shown in Fig. 1.

Rice. 1.

The process begins with the selection of product onto fat scales from deodorized fat tanks along 12 lines and onto water-milk scales along 4 lines. The operator enters recipes for both scales, that is, indicates which line and how much product should be added to the scales. After the set on the scales is completed, the fat and water-milk components are sequentially pumped into the mixer. Pumping is only possible when the receiving tank is empty. Pumping continues until the scales are empty. After this, another batch of components begins to be loaded onto the scales. In the mixers, heating occurs, uniform mixing of the product and pumping it into the working tank. If during pumping the product level in the working tank reaches 95%, the pumping process is suspended. Product from the working tank using a pump high pressure It is fed through a cooler, where margarine crystallizes, and a decrystallizer to the filling machine.

DRAFTING A FUNCTIONAL DIAGRAM AND DESCRIPTION OF THE MAIN FUNCTIONAL UNITS OF THE ACS

Rice. 2.

Using the block diagrams (Fig. 1, 2), we will draw up a functional diagram of the automated control system.

Rice. 3.

MP - microprocessor; DAC - digital-to-analog converter; K - valve; N - pump; SM - mixer; RB - working tank; DU - level sensor; DD - pressure sensor; DT - temperature sensor; DV - weight sensor; DVL - humidity sensor; KM - switch; ADC - analog-to-digital converter.

Rice. 4.

Used as a TP monitoring device.

CPU:

AMD Athlon 64 X2 6000+ BOX, Windsor core, frequency 3000 MHz, Socket AM2, L2 cache 2048 KB. Average service life - 100,000 hours.

Motherboard:

Gigabyte GA-MA790X-DS4, AMD 790X, PCIe, PCI, 4x DDR2533/667/800, SLI/CrossFire. Average service life - 70080 hours.

Hard drive: Seagate Barracuda ST3500320AS 500 GB, SATA II, 7200 rpm, 16MB. Average service life - 70080 hours.

LCD monitor:

Monitor 18.5" LCD Acer E-Machines E190HQVB, 16:9 HD, 5ms, 5000:1. Average service life - 60,000 hours.

2) Microprocessor SIMATIC S7-300 - CPU 315-2 DP - PROFIBUS

Used as a central processing unit.

Company: Siemens

Rice. 5. Microprocessor SIMATIC S7-300 - CPU 315-2 DP - PROFIBUS

Characteristics:

1. Central processor for executing medium and large programs.

2. High performance.

3. Built-in PROFIBUS DP master/slave interface, servicing distributed I/O systems based on PROFIBUS DP; MPI interface support.

4. Working built-in memory with a capacity of 128 KB, RAM (approximately 43 K instructions); Loadable memory - MMC 8 MB.

5. Flexible expansion options; connection of up to 32 S7-300 modules (4-row configuration).

6. Input voltage: 20.4 - 28.8 V; current consumption: from power supply - 800 mA, power consumption - 2.5 W.

7. CPU/execution time: logical operations - 0.1 μs, word operations - 0.2 μs, fixed-point arithmetic - 2 μs, floating point arithmetic - 3 μs.

8. Built-in communication functions: PG/OP communication functions, global data exchange via MPI, standard S7 communication functions, S7 communication functions (server only)

9. System functions: CPU supports wide range diagnostic functions, parameter settings, synchronization, alarms, time interval measurement, etc.

10. Average service life - 70080 hours.

3) High-speed DAC/ADC with support for SM 321

Used as a signal converter from analog to digital and vice versa.

Company: Siemens

Rice. 6. High speed DAC/ADC

Characteristics:

1. Number of inputs - 32

2. Rated input voltage - DC 24V

3. Channel programmable gain

4. Auto calibration

5. Total current consumption - 35 mA

6. Power consumption - 5.5W

7. Programmable trigger circuit

8. 16-bit counter (10 MHz)

9.Output voltage 10V

10. Average service life - no less than 87600 hours.

4) Temperature sensor with a unified output signal Metran-280-1

Used as a mixture temperature meter.

Company: Metran

Rice. 7. temperature sensor

Characteristics:

1. Convertible temperature range: -50…200 °C

2. 4-20 mA/HART output signal

3. Digital transmission of information via the HART protocol

4. Remote control and diagnostics

5. Galvanic isolation of input from output

6. Increased protection against electromagnetic interference

7. Minimum measurement subrange: 25 °C

8. Electronic filter 50/60 Hz

9. Power: 18 - 42 VDC

10. Power: 1.0W

11. Calibration interval - 1 year

12. Average service life - no less than 43800 hours.

5) Rosemount 5300 Level Sensor

Used as a fill level meter in a mixer.

Company: Metran

Rice. 8. Level sensor

Characteristics:

1. Measured media: liquid and bulk

2. Measuring range: 0.1 to 50m

3. Output Signals: 4F20 mA with digital signal based on HART or Foundation™ Fieldbus protocol

4. Availability of explosion-proof version

5. Operating temperature: up to 150°C (302°F)

6.Standby current consumption: 21mA

7. Process pressure: from 0.1 to 34.5 MPa;

8. Relative humidity environment: up to 100%

9. Degree of protection from external influences: IP 66, IP67 according to GOST 14254

10. Calibration interval - 1 year

11. Average service life - 43800 hours.

6) Rosemount 2088 Pressure Transmitter

Used as a pressure gauge in the working tank.

Company: Metran

automatic functional technological margarine

Rice. 9.

Characteristics:

1. Upper measurement limits from 10.34 to 27579.2 kPa

2. Basic reduced measurement error ±0.075%; ±0.1%

3. Output signals 4D20 mA/HART, 1D5 V/HART, 0.8D3.2 V/HART

4. Reconfiguration of measurement ranges 20:1

5. Additionally: LCD indicator, brackets, valve blocks

6. Ambient temperature range from 40 to 85°C; measured medium from 40 to 121°С

7. Sensor response time no more than 300 ms

8. Instability of characteristics ±0.1% of Pmax for 1 year

11. Average service life - 61320 hours.

7) Omron-D8M weight sensor

Used as a product weight meter in a mixer.

Brand: Omron

Rice. 10.

Characteristics:

2. Digital output

3. Operating temperature range -10…+120°С

4. Upper limit of measurement: 60 MPa:

5. Rated force: 200N

6. Total reduced error, no more than: 5%

7. Maximum current consumption, no more than:

8. Bridge circuit input resistance, Ohm - 450±25.0

9. Bridge circuit output resistance, Ohm - 400±4.0

10. Calibration interval - 2 years

11. Average service life - 52560 hours.

8) Humidity sensor Omron-4000-04

Used as a moisture meter in the working tank.

Brand: Omron

Rice. eleven.

Characteristics:

1. Range of measured relative humidity: 0 - 100%

2. Output signal - voltage

3. Response time - 15 s

4. Rated output current - 0.05mA

5. Output voltage range: 0.8 - 3.9V

7. SIP housing 1.27 mm

8. Calibration interval - 2 years

9. Average service life - 43800 hours.

Used as an actuator for dosing components in the system.

Company: KZMEM

Rice. 12.

Characteristics:

1. Case type - pass-through, cast (brass)

2. Working pressure: 0 - 0.1MPa

3. Coupling connection

5. Power consumption - 0.15W

6. Number of operations - not less than 500,000

7. Response time - no more than 1 s

8. Average service life - 26280 hours.

Used as a device for pumping components in the system.

Firm: Grundfos

Rice. 13.

Characteristics:

1. Working volume from 0.12 to 0.34 cm 3 /rev

2. Working pressure up to 70 MPa

3. Rotation speed from 500 to 3600 rpm

Used as a device for mixing components in the system.

Firm: "Embodiment"

Rice. 14.

Characteristics:

1. Weight - no more than 215 kg

2. Working capacity of the tank - 156 l

3. Technical productivity - no more than 950 l/h

4. Installed power - no more than 3 kW

5. Frequency - 50 Hz

6. Average service life - 35040 hours.

12) Stainless steel tank

Used as a device for preparing the product.

Firm: Unical

Rice. 15.

Characteristics:

1. Tank volume - 300 l

2. Maximum working temperature- 120 C

3. Maximum operating pressure - 10 bar

4. Average service life - 26280 hours.

1. Hierarchical three-level structure of automated process control systems

Most often, distributed automated process control systems have a three-level structure. An example of a block diagram of a complex of technical means of such a system is shown in Figure 1.

At the top level with the participation of operational personnel, the tasks of process dispatching, optimization of modes, calculation of technical and economic indicators of production, visualization and archiving of the process, diagnostics and correction are solved software systems. The upper level of the automated process control system is implemented on the basis of servers, operator (work) and engineering stations.

On the Middle level- tasks of automatic control and regulation, starting and stopping equipment, logical command control, emergency shutdowns and protections. Average level implemented on the basis of PLC.

Lower (field) level The automated process control system ensures the collection of data on the parameters of the technological process and the condition of the equipment, and implements control actions. The main technical means of the lower level are sensors and actuators, distributed input/output stations, starters, limit switches, and frequency converters.

Fig.1

2. I/O level (field level)

Input signals from sensors and control actions on actuators can be supplied directly to the PLC (come from the PLC). However, if the TOU has a significant territorial extent, this will require long cable lines from each device to the PLC. This technical solution may not be rational for two reasons:

• high cost of cable products;
• increase in the level of electromagnetic interference with increasing line length.

In such a situation, it is more rational to use distributed peripheral stations located in close proximity to sensors and actuators. Such stations contain the necessary input and output modules, as well as interface modules for connecting to the PLC via a digital fieldbus (for example, using the Profibus DP, or Modbus RTU protocol). Digital transmission of all signals is carried out over one cable with high level noise immunity. So-called smart sensors and actuators (which include controllers and other units that provide signal conversion into digital form and implement data exchange via the field bus) can also be directly connected to the field bus.

A simplified I/O diagram using a distributed peripheral station is shown in Figure 2. The Profibus DP (Process field bus Distributed Periphery) field bus allows you to connect up to 125 devices, up to 32 per segment (PLCs, distributed peripheral stations, smart sensors and actuators). A distributed edge station consists of three main components:

• a base panel (Baseplate), on which I/O modules and interface modules are installed in special slots, or a special profile rail on which the modules are mounted;
• input/output modules (I/O Modules);
• Interface modules that provide data exchange with the PLC via a digital field bus.

Rice. 2

The number of slots for installing modules can be different (most often from 2 to 16). The leftmost slot is usually used to install an interface module. The power supply can be installed on the base panel or a separate (external) unit can be used. There are two buses running inside the base panel: one serves to supply power to the installed modules; the other is for information exchange between modules.

Figure 3 shows a photo of a Eurotherm model 2500 distributed input/output node. The base panel contains 8 input/output modules and a Profibus DP interface module, and the power supply is external. Figure 4 shows a photo of the Siemens ET 200M distributed peripheral station. The base panel contains 6 signal modules (input/output modules), 1 Profibus DP interface module (far left) and a power supply.

Fig.3

Fig.4

2.1 Signal modules (input/output modules)

I/O modules come in 4 types:

1) Analog input signal modules (AI, analogue input). They receive electrical signals of a unified range from sensors connected to its inputs, for example:

• 0-20 or 4-20 mA (current signal);
• 0-10 V or 0-5 V (potential signal);
• Thermocouple (TC) signals are measured in millivolts;
• signals from thermal resistance devices (RTD).

Let's say we have a pressure sensor with a measuring range of 0-6 bar and a current output of 4-20 mA. The sensor measures pressure P, which is currently 3 bar. Since the sensor linearly converts the measured pressure value into a current signal, the output of the sensor will be:

The input of the AI ​​signal module, configured for the same ranges (4-20 mA and 0-6 bar), accepts a 12 mA signal and does the reverse conversion:

Matching the range of the electrical signal between the module input and the output of the sensor connected to it is mandatory for correct operation of the system.

2) Discrete input signal modules (DI, discrete input). They receive a discrete electrical signal from the sensors, which can have only two values: either 0 or 24 V (in rare cases, 0 or 220 V). The DI module input can also respond to a closed/opened contact in the circuit connected to it. Contact-type sensors, manual control buttons, status signals from alarm systems, drives, positioning devices, etc. are usually connected to DI.

Let's say we have a pump. When it is not working, its status (output) contact is open. The corresponding digital input of the DI signal module is in state “0”. As soon as the pump is started, its status contact closes and 24 V voltage goes to the DI input terminals. The module, having received voltage at the discrete input, switches it to state “1”.

3) Discrete output signal modules (DO, discrete output). Depending on the internal logical state of the output (“1” or “0”), it sets the voltage at the terminals of the discrete output to 24 V or 0 V, respectively. There is an option when the module, depending on the logical state of the output, simply closes or opens the internal contact (relay type module). DO modules can control actuators, shut-off valves, light signal lights, turn on sound alarms, etc.

4) Analog output signal modules (AO, analogue output) are used to supply a current control signal to actuators with an analogue control signal. Let's say a control valve with a 4-20 mA control input needs to be opened 50%. In this case, current I out is supplied to the corresponding output AO, to which the valve input is connected:

Under the influence of an input current of 12 mA, the valve moves to 50% opening.

The range of the electrical signal between the output of the module and the input of the actuator connected to it is required. An input/output module is also characterized by channel capacity - the number of inputs/outputs, and, consequently, the number signal circuits, which can be connected to it. For example, the AI4 module is a four-channel analog input module. You can connect 4 sensors to it. DI16 is a discrete input module with sixteen channels. You can connect 16 status signals from technological units to it.

IN modern systems The arrangement of I/O modules on the base board is not strictly regulated, and they can be installed in any order. However, one or more slots are usually reserved for installation of a communication module. Sometimes it is possible to install two communication modules at once, operating in parallel. This is done to improve the fault tolerance of the I/O system.

One of the stringent requirements for modern I/O subsystems is the ability to hot-swap modules without turning off the power (hot swap function).

Communication modules provide data exchange between PLCs, distributed peripheral stations, smart sensors and actuators. The modules support one of the communication protocols:

• Profibus DP;
• Profibus PA;
• Modbus RTU;
• HART;
• CAN, etc.

Information exchange is usually carried out using a master-slave mechanism. Only the master device on the bus can initiate data exchange. Slave devices passively listen to all data flowing on the bus, and only if they receive a request from the master device do they send a response back. Each device on the bus has its own unique network address, which is necessary for unique identification. I/O nodes are typically slave devices, while controllers are master devices.

Figure 5 shows a digital fieldbus combining one controller (with monitor) and four I/O nodes. Each device connected to the bus has its own unique address. Let, for example, a PLC with address 1 want to read a pressure sensor. The sensor is connected to a distributed peripheral station with network address 5, to the AI ​​module located in slot 6, input channel 12. Then the PLC generates and sends the following request via the bus:

Rice. 5

Each node listens for all requests on the bus. Node 5 recognizes that the request is addressed to it, reads the sensor reading and generates a response in the form of the following message:

The controller, having received a response from the slave device, reads the data field from the sensor and performs the appropriate processing. Let, for example, after processing the data, the PLC generates a control signal to open the valve by 50%. The valve control input is connected to the second channel of the AO module located in slot 3 of node 7. The PLC generates a command with the following content:

Node 7, listening to the bus, encounters a command addressed to it. It writes the 50% setting to the register corresponding to slot 3, channel 2. At the same time, the AO module generates the required electrical signal at output 2. After which node 7 sends the controller confirmation of the successful execution of the command.

The controller receives a response from node 7 and considers that the command has been completed. This is just a simplified diagram of how the controller interacts with I/O nodes. In real automated process control systems, along with those discussed above, many diagnostic, control and service messages are used. Although the “request-response” (“command-confirmation”) principle itself, implemented in most field protocols, remains unchanged.

Let us recall once again that, along with the input/output circuit discussed above, the automated process control system can use input/output circuits through signal modules installed directly in the slots (or on the profile rail) of the PLC (without using distributed peripheral stations).

2.2 Processing of analog signals during input to the controller

To input an analog signal into the controller and its subsequent processing, it must be digitized, i.e. converted to digital code. The process of signal processing from an analog sensor to use in a controller is shown schematically in Figure 6.

Fig.6 Analog signal processing circuit when input to the controller

Signals from sensors are brought to a standardized level (4 – 20 mA, 0 – 10 V) by normalizing converters (NC) and go through an analog filtering stage. Analog filters eliminate high-frequency noise that can be caused, for example, by electromagnetic interference during signal transmission through a cable.

It should be noted that the signal must be filtered from high-frequency noise before digital processing in the controller. This is a prerequisite the right choice sampling period when inputting a signal. The fact is that for adequate restoration of the original analog signal from discrete data, the sampling frequency must be at least twice the highest frequency in the spectral decomposition of the input signal (the spectral composition can be obtained as a result of decomposing the signal into a Fourier series). At a lower sampling frequency, a false component (the so-called pseudo-frequency) will appear in the reconstructed signal, which cannot be detected and eliminated at the digital processing stage. The presence of high-frequency noise will require a very high sampling rate (sensor sampling rate), which will unnecessarily load the controller.

The filtered signals from the sensors are fed to an analog multiplexer, the main purpose of which is to sequentially connect signals from N sensors to a sample-storage device (SSD) and an analog-to-digital converter (ADC) for further processing. This scheme allows you to significantly reduce the total cost of the input system due to the use of only one UVH and ADC for all analog input channels. The UVH remembers the instantaneous value of the signal at the moment the sensor is connected and keeps it constant at its output during the conversion to the ADC.

In the controller, the entered digital signal is checked for physical plausibility and, if necessary, goes through a digital (software) filtering stage.

home » Useful » Block diagram of automated monitoring and control systems. Drawing up a functional diagram and description of the main functional units of the automated control system. Principal, functional and structural diagrams