home · Other · Technical means of automation. What is it and why is it needed? Automation of technological processes and production. Technology automation of production of higher professional education

Technical means of automation. What is it and why is it needed? Automation of technological processes and production. Technology automation of production of higher professional education

The classification of technical means of automation is not something too complicated and loaded. However, in general technological means automation have a fairly branched classification structure. Let's try to deal with it.

Modern automation tools are divided into two groups: switched and non-switched (programmed) technical automation tools:

1) Switched automation

Regulators

relay circuits

2) Programmed automation tools

ADSP processors

ADSP processors are an automation tool that is used for complex mathematical analysis of processes in the system. These processors have high-speed I/O modules that can transmit data at high frequency to the central processing unit, which, using complex mathematical tools, analyzes the operation of the system. An example is vibration diagnostic systems that use Fourier series for analysis, spectral analysis and a pulse counter. As a rule, such processors are implemented as a separate PCI card, which is mounted in the corresponding slot of the computer and uses the CPU for mathematical processing.

PLC (programmable logic controller)

PLCs are the most common automation tools. They have their own power supply, central processor, RAM, network card, I/O modules. Advantage - high reliability of the system, adaptation to industrial conditions. In addition, programs are used that run cyclically and have a so-called Watch Dog, which is used to prevent the program from freezing. Also, the program is executed sequentially and does not have parallel links and processing steps that could lead to negative consequences.

PKK (Programmable Computer Controllers)

PKK - a computer with input / output boards, network cards that are used to input / output information.

PACK

PAK ( programmed automated controllers) – PLC+PCC. They have a distributed network structure for data processing (several PLCs and PCCs).

· Specialized Controllers

Specialized controllers are not freely programmable automation tools, but use standard programs in which only some coefficients can be changed (PID controller parameters, actuator travel time, delays, etc.). Such controllers are focused on a previously known control system (ventilation, heating, hot water). At the beginning of the new millennium, these technical means of automation became widespread.

A feature of ADSP and PKK is the use of standard programming languages: C, C ++, Assembler, Pascal, - as they are created on the basis of a PC. This feature of automation is both an advantage and a disadvantage.

The advantage is that using standard programming languages, you can write more complex and flexible algorithm. The disadvantage is that to work with them, you need to create drivers and use a programming language that is more complex. The advantage of PLCs and PACs is the use of engineering programming languages ​​that are standardized by IEC 61131-3. These languages ​​are designed not for a programmer, but for an electrical engineer.

The principle of information transformation

Management principles are based on the principle of information transformation.

Converters are devices used to convert quantities of one physical nature to another and vice versa.

Sensors are devices that generate a discrete signal depending on the code of the technological process or the impact of information on them.

Information and ways to transform it

The information must have the following properties:

1. Information must be understandable in accordance with the accepted coding system or its presentation.

2. Information transmission channels must be noise-proof and prevent the penetration of false information.

3. Information should be convenient for its processing.

4. Information should be easy to store.

For the transmission of information, communication channels are used, which can be artificial, natural, mixed.

Rice. 3. Communication channels

We will talk more about communication channels a little later.

Technical means of automation (TSA) are designed to create systems that perform specified technological operations, in which a person is assigned, mainly, the functions of control and management.

According to the type of energy used, technical means of automation are classified into electrical, pneumatic, hydraulic And combined. Electronic means of automation are allocated to a separate group, since they, using electrical energy, are designed to perform special computing and measuring functions.

By functional purpose, technical means of automation can be subdivided in accordance with typical scheme automatic control systems for actuators, amplifying, corrective and measuring devices, converters, computing and interface devices.

Executive element - this is a device in an automatic regulation or control system that acts directly or through a matching device on a control element or system object.

Regulating element performs a change in the operation mode of the managed object.

Electrical actuator with mechanical output - electric motor- It is used as a final mechanical power amplifier. The effect exerted by an object or a mechanical load on the actuating element is equivalent to the action of internal, or natural, feedback. This approach is used in cases where a detailed structural analysis of the properties and dynamic features of the actuating elements is required, taking into account the effect of the load. The electrical actuator with mechanical output is an integral part of the automatic drive.

Electric drive - this is an electrical actuating device that converts the control signal into a mechanical action while simultaneously amplifying it in power due to an external energy source. The drive does not have a special link of the main feedback and is a combination of a power amplifier, an electric actuator, a mechanical transmission, a power source and auxiliary elements, united by certain functional connections. The output quantities of an electric drive are linear or angular speed, tractive force or torque, mechanical power etc. The electric drive must have an appropriate power margin necessary to act on the controlled object in the forced mode.

Electric servo is a servo drive that processes the input control signal with its power amplification. Elements of the electrical servomechanism are covered by special feedback elements and may have internal feedback due to the load.

mechanical transmission an electric drive or a servomechanism coordinates the internal mechanical resistance of the actuating element with a mechanical load - a regulatory body or a control object. Mechanical transmissions include various gearboxes, crank, lever mechanisms and other kinematic elements, including transmissions with hydraulic, pneumatic and magnetic bearings.

Electrical power supplies executive elements, devices and servomechanisms are divided into sources with almost infinite power, with the value of their internal resistance close to zero, and sources with limited power with an internal resistance value other than zero.

Pneumatic and hydraulic actuators are devices in which gas and liquid under a certain pressure are used as an energy carrier, respectively. These systems occupy a strong position among other automation tools due to their advantages, which, first of all, include reliability, resistance to mechanical and electromagnetic influences, a high ratio of the developed drive power to its own weight, and fire and explosion safety.

The main task of the actuator is to amplify the signal at its input to a power level sufficient to provide the required effect on the object in accordance with the goal of control.

An important factor when choosing an actuating element is to ensure the specified indicators of the quality of the system with the available energy resources and permissible overloads.

The characteristics of the actuating device must be determined from the analysis of the automated process. Such characteristics of actuators and servomechanisms are energy, static, dynamic characteristics, as well as technical, economic and operational characteristics.

A mandatory requirement for the actuator is to minimize the engine power while providing the required speeds and torques. This leads to minimization of energy costs. Very important factors when choosing an actuator or servo mechanism are weight restrictions, overall dimensions and reliability.

Amplifying and corrective devices are important components of automation systems. The common tasks solved by the corrective and amplifying devices of automation systems are the formation of the required static and frequency characteristics, the synthesis of feedback, matching with the load, ensuring high reliability and unification of devices.

Amplifying devices amplify the signal power to the level required to control the actuator.

Special requirements for the corrective elements of systems with variable parameters are the possibility and simplicity of restructuring the structure, program and parameters of the corrective elements. Amplifying devices must meet certain specifications by specific and maximum output power.

In terms of structure, the amplifying device is, as a rule, a multistage amplifier with complex feedbacks, which are introduced to improve its static, dynamic, and operational characteristics.

Amplifying devices used in automation systems can be divided into two groups:

1) electrical amplifiers with electrical power sources;

2) hydraulic and pneumatic boosters, using liquid or gas as the main energy carrier, respectively.

The power source or energy carrier determines the most significant features of amplifying automation devices: static and dynamic characteristics, specific and maximum power, reliability, operational and technical and economic indicators.

Electrical amplifiers include electronic vacuum, ion, semiconductor, dielectric, magnetic, magnetic-semiconductor, electromachine and electromechanical amplifiers.

Quantum amplifiers and generators constitute a special subgroup of devices used as amplifiers and converters of weak radio engineering and other signals.

Corrective devices form correction signals for the static and dynamic characteristics of the system.

Depending on the type of inclusion in the system, linear corrective devices are divided into three types: serial, parallel corrective elements and corrective feedback. The use of one or another type of corrective devices is determined by the convenience of technical implementation and operational requirements.

It is expedient to use corrective elements of the serial type if the signal, the value of which is functionally related to the error signal, is an unmodulated electrical signal. The synthesis of a sequential corrective device in the process of designing a control system is the simplest.

It is convenient to use corrective elements of the parallel type when forming a complex control law with the introduction of an integral and derivatives of the error signal.

Corrective feedbacks, covering amplifying or actuating devices, are most widely used due to the simplicity of technical implementation. In this case, a signal of a relatively high level is fed to the input of the feedback element, for example, from the output stage of an amplifier or motor. The use of corrective feedback makes it possible to reduce the influence of non-linearities of those devices of the system that are covered by them, therefore, in some cases, it is possible to improve the quality of the control process. Corrective feedback stabilizes the static coefficients of the covered devices in the presence of interference.

Automatic regulation and control systems use electrical, electromechanical, hydraulic and pneumatic corrective elements and devices. The simplest electrical corrective devices are implemented on passive quadripoles, which consist of resistors, capacitors and inductances. Complex electrical corrective devices also include separating and matching electronic elements.

In addition to passive quadripoles, electromechanical corrective devices include tachogenerators, impellers, differentiating and integrating gyroscopes. In some cases, an electromechanical corrective device can be implemented in the form of a bridge circuit, one of the arms of which includes an electric motor of the actuator.

Hydraulic and pneumatic corrective devices can consist of special hydraulic and pneumatic filters included in the feedback of the main elements of the system, or in the form of flexible feedback on pressure (pressure drop), flow rate of the working fluid, air.

Corrective elements with tunable parameters ensure the adaptability of systems. The implementation of such elements is carried out using relay and discrete devices, as well as computers. Such elements are usually referred to as logical corrective elements.

A computer operating in real time in a closed control loop has practically unlimited computational and logical capabilities. The main function of the control computer is the calculation of optimal controls and laws that optimize the behavior of the system in accordance with one or another quality criterion during its normal operation. The high speed of the control computer allows, along with the main function, to perform a number of auxiliary tasks, for example, with the implementation of a complex linear or nonlinear digital corrective filter.

In the absence of computers in systems, it is most expedient to use non-linear corrective devices as having the greatest functional and logical capabilities.

Control devices are a combination of actuators, amplifying and corrective devices, converters, as well as computing and interface units.

Information about the parameters of the control object and about possible external influences that affect it is supplied to the control device from the measuring device. Measuring devices in the general case, they consist of sensitive elements that perceive changes in parameters, according to which the process is regulated or controlled, as well as of additional converters, often performing the functions of signal amplification. Together with sensitive elements, these converters are designed to convert signals of one physical nature into another, corresponding to the type of energy used in the automatic regulation or control system.

In automation converting devices or converters call such elements that do not directly perform the functions of measuring controlled parameters, amplifying signals or correcting the properties of the system as a whole and do not have a direct impact on the regulatory body or controlled object. Converting devices in this sense are intermediate and perform auxiliary functions associated with the equivalent conversion of a quantity of one physical nature into a form more convenient for the formation of a regulatory action or for the purpose of coordinating devices that differ in the type of energy at the output of one and the input of another device.

Computing devices of automation means, as a rule, are built on the basis of microprocessor means.

Microprocessor- a software-controlled tool that carries out the process of processing digital information and its management, built on one or more integrated circuits.

The main technical parameters of microprocessors are bit depth, addressable memory capacity, versatility, the number of internal registers, the presence of microprogram control, the number of interrupt levels, the type of stack memory and the number of main registers, as well as the composition of the software. According to the word length, microprocessors are divided into microprocessors with a fixed word length and modular microprocessors with a variable word length.

Microprocessor means are structurally and functionally finished products of computer and control technology, built in the form or on the basis of microprocessor integrated circuits, which, from the point of view of testing, acceptance and delivery requirements, are considered as a whole and are used in the construction of more complex microprocessor means or microprocessor systems.

Structurally, microprocessor means are made in the form of a microcircuit, a single-board product, a monoblock or a standard complex, and products of the lower level of the constructive hierarchy can be used in products of a higher level.

Microprocessor systems - these are computing or control systems built on the basis of microprocessor tools that can be used autonomously or embedded in a managed object. Structurally, microprocessor systems are made in the form of a microcircuit, a single-board product, a monoblock of a complex, or several products of the indicated types, built into the equipment of a controlled object or made autonomously.

According to the scope of application, technical means of automation can be divided into technical means of automation of work on industrial productions and technical means of automating other work, the most important component of which is work in extreme conditions, where the presence of a person is life-threatening or impossible. In the latter case, automation is carried out on the basis of special stationary and mobile robots.

Technical means of automation of chemical production: Ref. ed. / V.S. Balakirev, L.A. Barsky, A.V. Bugrov and others - M .: Chemistry, 1991. -272 p.

Theme 2

1. Sensors

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

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

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

According to the type of output value to which the input value is converted, non-electric and electrical are distinguished: direct current sensors (EMF or voltage), AC amplitude sensors (EMF or voltage), AC frequency sensors (EMF or voltage), resistance sensors (active, inductive or capacitive), etc.

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

Electrical Quantities convenient to transmit over a distance, and the transmission is carried out with high speed;

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

They are accurately converted into a digital code and make it possible to achieve high accuracy, sensitivity and speed of measuring instruments.

According to the principle of operation, sensors can be divided into two classes: generator and parametric. A separate group is made up of radioactive sensors. Radioactive sensors are sensors that use such phenomena as changing parameters under the action of g and b rays; ionization and luminescence of certain substances under the influence of radioactive irradiation. Generator sensors carry out direct conversion of the input value into electrical signal. Parametric sensors convert the input value into a change in some electrical parameter (R, L or C) of the sensor.

According to the principle of operation, sensors can also be divided into ohmic, rheostatic, photoelectric (opto-electronic), inductive, capacitive, etc.

There are three classes of sensors:

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

Digital sensors generating a pulse train or a binary word;

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


Figure 1 - Classification of sensors for automation systems of mining machines


Requirements for sensors:


Unambiguous dependence of the output value on the input;

Stability of characteristics over time;

High sensitivity;

Small size and weight;

No feedback on controlled process and on the controlled parameter;

Work at various conditions operation;

Various options installation.

Parametric sensors

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

characteristic feature of these sensors is that they are used only when there is an external power supply.

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

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

Figure 1 - Schematic diagram of the reed sensor

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

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

The reed switches are available with NO and NC contacts, as well as changeover and polarized contacts. Some types of reed switches - KEM, MKS, MKA.

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

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

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

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

Figure 2 - Potentiometric sensor

For a linear potentiometer (see figure 2) with a length l the output voltage is given by:

,

where x is the movement of the brush; k=U p / l- gear ratio; U p - supply voltage.

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

The advantages of potentiometric sensors are their design simplicity, small size, and the ability to supply both direct and alternating current.

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

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

Figure 3 - Inductive sensor

The sensor circuit is powered from an alternating current source.

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

The sensor works as follows. Under the influence of the object, the armature, approaching the core, causes an increase in the flux linkage and, consequently, in the inductance of the coil. With clearance reduction d to the minimum value, the inductive reactance of the coil x L \u003d wL \u003d 2pfL increases to the maximum, reducing the load current RL, which is usually used as an electromagnetic relay. The latter switch circuits of control, protection, control, etc. with their contacts.

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

The disadvantages of inductive sensors are the non-linearity of the characteristic and a significant electromagnetic attractive force of attraction of the armature to the core. To reduce effort and continuously measure displacements, solenoid-type sensors are used or they are called differential.

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

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

According to the shape of the plates, flat, cylindrical and other types of variable capacitors are distinguished.

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

Generator sensors

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

Inductive sensors. IN induction sensors conversion of the input non-electric quantity into the induced emf. used to measure the speed of movement, linear or angular displacement. emf in such sensors is induced in coils or windings made of copper insulated wire and placed on magnetic cores made of electrical steel.

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

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

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

Е = cФn = сФω

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

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

Figure 5 - Scheme for controlling the speed of the conveyor belt synchronous

tachogenerator

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

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

scraper conveyor magnetic induction sensor

magnetoelastic sensors. The principle of operation of magnetoelastic sensors is based on the property of ferromagnetic materials to change the magnetic permeability m during their deformation. This property is called magnetoelasticity, which is characterized by magnetoelastic sensitivity

highest value S m \u003d 200 Gn / m2 is covered with permallay (iron-nickel alloy). Some varieties of permallay with an elongation of 0.1% increase the coefficient of magnetic permeability up to 20%. However, to obtain even such small elongations, a load of the order of 100–200 N/mm is required, which is very inconvenient and leads to the need to reduce the cross section of the ferromagnetic material and requires a power source with a frequency of the order of kilohertz.

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

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

The advantages of magnetoelastic sensors are simplicity and reliability.

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

Figure 7 - Magnetoelastic sensor

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

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

Figure 8 - Diagram of a thermocouple

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

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

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

Semiconductor thermistors are made in the form of small rods and discs with leads.

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

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

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

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

The bridge can be balanced or unbalanced.

A balanced bridge is used for the zero measurement method. In this case, the resistance R3 changes (for example, by a special automatic device) following the change in the resistance of the thermistor Rt in such a way that the potentials at points A and B are equal. The advantage of this method is high accuracy, and the disadvantage is the complexity of the measuring device, which is a tracking automatic system.

An unbalanced bridge generates a Uout signal proportional to the overheating of the object. By selecting the resistances of the resistors R1, R2, R3, the bridge is balanced at the initial temperature value, ensuring the fulfillment of the condition

Rt / R1= R3 / R2

When changing the value of the controlled temperature and, accordingly, the resistance Rt, the balance of the bridge will be disturbed. If you connect an mV device with a scale calibrated in degrees to its output, the arrow of the device will show the measured temperature.

Induction flow meter

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

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

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

Figure 9 - Structural diagram of the induction flowmeter

If we express the velocity v in terms of the volume flow Q, i.e.

Advantages of the induction flowmeter:

Possess insignificant inertia of indications;

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

Disadvantages of the flowmeter:

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

Ultrasonic flow meters

The principle of operation of ultrasonic flowmeters is that

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

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

Figure 10 - Structural diagram of the ultrasonic flow meter

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

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

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

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

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

k is a coefficient that takes into account the distribution of velocities in the flow.

Advantages of ultrasonic flowmeter:

a) high reliability and speed;

b) the ability to measure non-conductive liquids.

The disadvantage is the increased requirements for contamination of the controlled water flow.

2. Data communication devices

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

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

– power low-voltage and high-voltage Electricity of the net;

– infrared channels;

- radio channels.

The transmission of information over communication channels can be transmitted without information compression, i.e. one information signal (analogue or discrete) is transmitted over one channel, and with information compression - a plurality of information signals are transmitted over the communication channel. Compaction of information is used for remote transmission of information over a considerable distance (for example, from automation equipment located on a drift to a shearer or from a section of a mine to the surface to a dispatcher) and can be carried out using various types of signal coding.

Technical systems, which provide the transfer of information about the state of the object and control commands over a distance via communication channels can be remote control and measurement systems or telemechanical systems. In remote control and measurement systems, each signal uses its own line - a communication channel. How many signals, so many communication channels are required. Therefore, when remote control and measurement, the number of controlled objects, especially at large distances, is usually limited. In telemechanical systems for the transmission of many messages a large number objects use only one line, or one communication channel. Information is transmitted in an encoded form, and each object "knows" its code, so the number of controlled or managed objects is practically unlimited, only the code will be more complicated. Telemechanics systems are divided into discrete and analog. Discrete telecontrol systems are called telesignaling systems(TS), they provide the transfer of a finite number of object states (for example, "on", "off"). Analog telecontrol systems are called telemetry systems(TI), they provide the transmission of a continuous change in any parameters characterizing the state of the object (for example, a change in voltage, current, speed, etc.).

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

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

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

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

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

2. Executive devices

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

Figure 11 - Location of actuators in the block diagram of the local ACS

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

The actuator consists of the following basic elements:

executive engine (electric motor, piston, membrane);

clutch element (coupling, hinge);

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

power amplifier (electric, pneumatic, hydraulic, combined)

In a specific IM model, a number of elements (except for the executive engine) may be absent.

The main requirement for IM is: moving the RO with the least possible distortion of the laws of regulation formed by the PLC, i.e. IM must have sufficient speed and accuracy.

Main characteristics:

a) rated and maximum torque

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

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

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

d) dead zone.

Actuators are classified according to the following signs:

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

2) design(electric, hydraulic, pneumatic);

Electric - with drives electric motor and an electromagnet;

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

Pneumatic - with drives: piston, plunger, diaphragm, diaphragm, from a pneumatic motor.

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

electromagnetic;

electric motor.

Electromagnetic IMs are divided into:

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

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

Electric motor IMs are divided into:

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

multi-turn - for remote and local control pipe fittings(valves).

In automation systems of mining machines, electric hydraulic distributors, such as GSD and 1RP2, are widely used as actuators. Electric hydraulic distributor 1RP2 is designed to control the feed rate and cutting elements of the harvester as part of the URAN.1M automatic load regulators and the SAUK02.2M automation system. Electric hydraulic valve 1RP2 is a hydraulic spool valve with electromagnetic drive pull type.

The regulatory body (RO) is the final element of the ACS, which directly controls the OS. RO changes the flow of material, energy, the relative position of parts of apparatuses, machine tools or mechanisms in the direction of the normal course of the technological process.

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

RO provide:

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

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

General information about technological automation

Processes food production

Basic concepts and definitions of automation

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

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

Purpose of automation- increasing labor productivity, improving product quality, optimizing planning and management, eliminating a person from working in conditions hazardous to health.

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

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

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

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

The introduction of automation in production has made it possible to significantly increase labor productivity and reduce the proportion of workers employed in various areas of production. Before the introduction of automation tools, the replacement of physical labor took place through the mechanization of the main and auxiliary operations of the production process. Intellectual labor for a long time remained unmechanized. At present, the operations of intellectual labor are becoming the object of mechanization and automation.

Exist different kinds automation.

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

2. Automatic alarm is designed to notify about the limit or emergency values ​​of any physical parameters, about the place and nature of TP violations.

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

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

5. Automatic protection this is a set of technical means that ensure the termination of the controlled TP in the event of abnormal or emergency modes.

6. Automatic control includes a set of technical means and methods for managing the optimal course of TP.

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

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

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

Automatic control system(SAR) - set OU and an automatic regulator, interacting with each other, ensures the maintenance of the TP parameters at a given level or their change according to the required law, and also operates without human intervention. ATS is a type of ACS.

The definition of “automation object” includes a wide variety of technical objects (metallurgical furnaces, transport, various machines and others technical devices), as well as production processes that can be performed by one or a whole complex of technological units, installations or machines in their interaction with the control system. At this stage of human development, automation is actively being introduced into all areas human life, .

Continuous improvement and implementation of automation systems are absolutely interconnected processes. On the one hand, for the modernization of various industries, it is necessary to develop and implement mechanization and automation systems in already operating mechanisms, and on the other hand, when creating absolutely new technology it is necessary to provide ways of its effective automation.

According to their hierarchy, technical means of automation are classified into two classes:

  • Systems of automated (automatic) regulation of ACS and control of ACS;
  • Devices, elements and subsystems of ACS and ACS;

The common functional part of both systems is the object of regulation (control). Control object - controlled part of the system (machine or complex of machines), the established mode of operation of which must be supported by the control part of the system in accordance with the previously selected control task.

The control system (CS) is a dynamic closed complex, which consists of controlled objects and three subsystems: logic-computing, informational and executive. The generalized scheme is shown below:

An information subsystem is a set of technical means for receiving, presenting and transmitting information. The means whose purpose is to obtain and convert primary information about the internal and external factors of the operation of objects under control include measuring and sensitive elements, analyzers, sensors of primary information and other devices. This category also includes means for presenting and transmitting information in a form convenient for the control system - receivers, encoding / decoding devices, transmitters, communication channels, and so on.

Logic computing system - technical means, the task of which is the processing of information.

The main task of information processing tools is to develop solutions necessary to achieve the management objectives formulated in terms of reference in the manufacture of ACS. These solutions are usually implemented in the form of setting or control signals. The technical means of information processing include a variety of analog and digital computing tools, including microcontrollers.

Technical means, which are used to generate control signals and directly control the object, are called executive subsystem . The technical means of the executive subsystems mainly include electric drives, as well as lighting and temperature controllers, electromagnets hydraulic mechanisms and so on.

Control systems, in the course of which, including the stages of decision-making and development of control actions, there is no participation of the operator (the operator only observes production process) are called ACS automatic control systems .

Control systems in which computers (digital, analog or hybrid) participate in making decisions by the operator are called automated systems ACS control.