Applications - housing and communal services. Automation of the factory boiler plant
Automation of a boiler house based on an industrial programmable controller of the MELSEC FX series from Mitsubishi and the SCADA system Citect is a modern solution to the problem of integrated automation of boiler houses of various scale and complexity (hereinafter referred to as PTC - software and hardware complex). Communication between the operator's workstation of the boiler room and the PLC is carried out via Ethernet using the MS protocol (MELSEC Communication protocol). APCS of the boiler house provides a modern level of control of the boiler house equipment in accordance with the criteria of economic efficiency, improves the quality of regulation and guarantees economical fuel combustion.
The automated system implements full-scale control and monitoring functions for any boiler house, expands the capabilities of operating personnel, ensuring the stable operation of process equipment and increasing the service life of the units. The reliability of the automated system is ensured by the use of modern architectural and design solutions used in the design of the system, as well as the use of reliable elements, primarily controllers with high MTBF.
To organize the operation of two or three heating circuits in heating system they need to be connected to the boiler. This problem is solved in various ways, which are denoted by the technical term as "boiler room piping scheme". Heating circuits, depending on the method of obtaining the required temperature, are divided into direct and mixing. In the first case, the required water temperature is reached by the duration of the burner operation. In the second - the operation of the burner and the dampers of the actuators, which can be a mixer with an electric drive.
In direct heating circuits, it is quite easy to integrate the boiler and circuit radiator heating, while providing weather-dependent control. In the case when hot water supply (DHW) is additionally required, either a circuit with a 3-way valve or a circuit with two pumps is used. The first option with a 3-way motorized crane is the simplest solution.
Our company offers a solution that provides efficient control in automatic mode technological equipment boiler houses on the basis of software and hardware complexes of process control systems various companies, which, in addition to efficient operation, also guarantee high reliability, which makes it possible to implement the necessary algorithms adapted to the various requirements of the Customer.
It has been proven in practice that almost 75% of the operating time of boilers during heating period their productivity is in the range from 45% to 50%. That is, if we consider on average during the working season, boilers are used only by 35%. As a result, we have inefficient operation of the equipment during its operation. To increase the life of the boiler room equipment, it is necessary to implement everywhere the possibility of automated cascade control of 2-5 boilers (if available), periodically turning on / off the boilers and pumping units.
What can you do to keep your home warm and cozy? According to our climate heating season lasts from 3 to 5 months a year. Consider all the ways of heating houses, ranging from the most simple and well-known, and ending with the most exotic ways to maintain a comfortable temperature in cold weather.
All owners country houses the question arises: "How to heat your house on cold days?". Indeed, air conditioners are sold in your region and you can always purchase a model that also works for space heating. If you live in southern region and visit your country from time to time, then you are lucky and this issue is not so acute for you. In accordance with our climatic features, even if we do not live in an icy desert for half a year, then there is a heating season. And it lasts from 3 to 5 months a year.
The system is designed to automate the control and optimize the operation of a boiler unit with a capacity of 60 tons / hour, which runs on coke gas (main) and natural (auxiliary). The steam produced by the boiler unit is used for a number of technological and energy purposes. In total, the system contains 42 analog and 86 discrete signals. The automated workstation (AWS) of the operator is made on the basis of an Advantech industrial computer.
On the screens of the displays of the operator's workstation are displayed:
1. measured values of technological parameters, values of alarm settings, as well as the state of actuators;
2. color signaling of deviations of technological parameters from the prescribed values;
3. archival values of parameters and violations on them, in the form of graphs and a protocol of violations at various time intervals;
4. technical and economic indicators of values for 1 hour / shift / day.
Automation of the boiler room allows you to control the operating parameters of the Caldaie REX-300 boiler and the burner when operating on gaseous and liquid fuels, automatically control the operation of the boiler - start / stop / emergency stop of the boiler, on-off control of the heat output of the burner according to the temperature of the coolant at the outlet of the boiler, as well as to form and issue a signal "Boiler failure" to the alarm panel and the dispatcher's computer.
The automation system controls the water pressure at the outlet of the boiler, as well as the water pressure at the suction and pressure nozzles of the boiler pump. As stop valves are used Ball Valves and electric gate valves, which are controlled by the boiler control panel. The boiler room automation system allows you to control the main parameters of the boiler room.
Specialists of "SMART Systems" perform installation and commissioning automated systems management of boiler houses, as well as carry out Maintenance. Automation of liquid fuel boilers, as well as gas and other types of fuels, makes it possible to obtain significant savings in resources and make boiler operation safer.
Boiler room automation system provides:
- the ability to control boiler equipment in automatic mode;
- the ability to control the boiler in remote manual mode from an industrial controller;
- automatic regulation of thermal processes according to the temperature schedule depending on the outside air temperature;
- the ability to enter non-standard temperature chart and its adjustments during the operation of the boiler house.
The automated control system of the boiler house is designed to automatically control the boiler house with a capacity of 400 kW and maintain the necessary technological modes of operation. According to the design task, the engineers of our company developed an algorithm for the operation of the boiler room controller. To be able to control the consumption of various energy resources, all water / heat / gas / meters of the boiler room are connected to the controller.
All changes in the settings of the operating modes are stored in the non-volatile memory of the controller and the operation of the boiler room is automatically resumed when the power supply network of the boiler room is restored. The system allows you to alternate the roles of the main and 3 additional boilers after a specified time and indicate the time left before the change of roles of the boilers in hours.
Specialists of the SMART Systems enterprise together with the Customer's engineers developed and implemented a distributed process control system for a variable power gas boiler house based on Mitsubishi Electric equipment. The automatic process control system of a gas boiler house operates in two modes: automatic, which does not require the presence of operators in the boiler room, and semi-automatic mode, which in some situations requires the presence of operators.
The variable power gas boiler control cabinet is based on Mitsubishi Electric's FX3U controller and GOT-1020 operator panel. Communication with the general boiler controller of the system is carried out via the CC Link industrial network. It should be noted that the control cabinet for all network pumps of the gas boiler house is implemented using the FR-F740 frequency converter.
To organize the work of two or three heating circuits with different temperatures, it is necessary to use executive devices. The most common today are three- and four-way mixing taps (in other words, mixers). The principle of operation of mixers is that they regulate the temperature of the coolant through heat exchangers in each heating circuit, mixing water from the boiler with water from the return (that is, from the return line).
Therefore, the temperature of the heating medium in the flow circuit can vary from room temperature (minimum) to boiler water temperature (maximum), but never higher than this value. To automate this process, it is necessary to use a servo drive for a crane (special motor).
AT modern world such a phenomenon as the automation of boiler rooms is widespread. It is hard to imagine the construction of boiler houses without the introduction automatic systems. Almost all boilers include standard automation in their base.
Convenient tools that help in controlling the burner, in maintaining the set temperature and receiving notifications about the safety of the coolant. Boiler automation includes a large number of devices. Many companies offer a wide variety of boiler automation equipment. It remains only to select them technically correctly.
Boiler automation equipment
Ignition and flame control devices (for example, manufactured by MZTA OJSC: F34, FCH, FSP 1, FESP 2) - this is a tool that controls the level of flame in the boiler, ensures safe operation automatic boiler, by turning off the fuel supply when the torch disappears. This device guarantees protection of the boiler against a possible explosion.
Draft gauges, pressure gauges and draft pressure gauges are specialized sensors that measure draft in the boiler furnace. Thanks to these devices, the fuel supply to the boiler is regulated and the optimal mode of operation of the coolant is ensured. These devices also ensure the safety of the boiler.
To create local boiler room automation systems, graphical control panels are often used, which are very easy to use.
EC - control electrodes - a means that serves as a sensitive element in the boiler protection circuit and signaling of the boiler automation kit in case of extinction of the gas torch. Control electrodes in the automation system of boiler houses are widely used.
Integrated boiler room automation tools, such as boiler control cabinets, are optimal solutions for general boiler equipment and boiler automation. We recommend taking a closer look at the automatic control of boilers of the DKVR and DE types.
Effective reduction of heating costs thanks to automation of boiler rooms
The construction of new, modern, as well as the reconstruction of old boiler houses significantly reduces the cost of fuel and fuel and maintenance due to the introduction of automation systems. In addition to saving fuel and maintenance costs for boilers, upgrading boilers has many advantages. For example, an increase in the coefficient of performance (COP). Automation of boiler houses increases the efficiency of equipment parameters regulation. Modern modernization reduces the influence of the human factor on the efficiency of coolant control. Also, automation of boilers ensures prompt and timely detection of faults in the system.
The MasterSCADA software package is vertically integrated and object oriented. This is the most promising and convenient solution for the automation of boilers and boiler rooms. A large set of OPC servers provides communication with controllers that do not support vertical integration. Kepware is one of the world's leading manufacturers of OPC servers.
Various companies offer the implementation of complex work on the implementation of management systems for any objects of housing and communal services. This shouldn't be a problem.
"Automation of the factory boiler plant"
Introduction
Automation is the use of a set of tools that allow production processes to be carried out without the direct participation of a person, but under his control. Automation of production processes leads to an increase in output, a reduction in cost and an improvement in product quality, reduces the number of maintenance personnel, increases the reliability and durability of machines, saves materials, improves working conditions and safety. Automation frees a person from the need to directly control mechanisms. In an automated production process, the role of a person is reduced to setting up, adjusting, maintaining automation equipment and monitoring their operation. If automation facilitates the physical labor of a person, then automation aims to facilitate mental labor as well. The operation of automation equipment requires highly qualified technicians from the service personnel. In terms of automation, the heat power industry occupies one of the leading places among other industries. Thermal power plants are characterized by the continuity of the processes occurring in them. At the same time, the generation of heat and electricity at any time must correspond to the consumption (load). Almost all operations at thermal power plants are mechanized, and transient processes in them develop relatively quickly. This explains the high development of automation in thermal power engineering. Automation of parameters provides significant advantages: 1) reduces the number of working personnel, i. increase in the productivity of his work, 2) leads to a change in the nature of the work of the maintenance personnel, 3) increases the accuracy of maintaining the parameters of the generated steam, 4) increases the safety of work and the reliability of the equipment, 5) increases the efficiency of the steam generator. control, technological protection, thermal control, technological interlocks and alarms. Automatic control ensures the course of continuously occurring processes in the steam generator (water supply, combustion, steam overheating, etc.) regulate its mechanisms at a distance, from the remote control, where the control devices are concentrated. Thermal control over the operation of the steam generator and equipment is carried out using indicating and self-recording devices that operate automatically. The devices continuously monitor the processes occurring in the steam generator plant, or they are connected to the measurement object by service personnel or an information computer. Thermotechnical control devices are placed on panels, control panels, as convenient as possible for monitoring and maintenance. Technological interlocks perform a number of operations in a given sequence when starting and stopping the mechanisms of a steam generator plant, as well as in cases of technological protection operation. Interlocks exclude incorrect operations during maintenance of the steam generator set, ensure shutdown of the equipment in the required sequence in the event of an accident. occurrence of an emergency condition of the steam generator and its equipment. Sound and light alarms are used. The operation of boilers must ensure reliable and efficient generation of steam of the required parameters and safe working conditions for personnel. To fulfill these requirements, operation must be carried out in strict accordance with legal provisions, rules, norms and guidelines, in particular, in accordance with the "Rules for the Design and Safe Operation of Steam Boilers" of Gosgortekhnadzor, "Rules for the Technical Operation of Power Plants and Networks", "Rules for the Technical operation of heat-using installations and heat networks”, etc.
1. Technological part
1.1 Description of the technological process A steam boiler is a set of units designed to produce water vapor. This complex consists of a number of heat exchange devices interconnected and serving to transfer heat from the products of fuel combustion to water and steam. The initial carrier of energy, the presence of which is necessary for the formation of steam from water, is fuel. The main elements of the working process carried out in a boiler plant are: 1) the process of fuel combustion, 2) the process of heat exchange between the combustion products or the burning fuel itself with water, 3) the process of vaporization, consisting of heating water, its evaporation and heating the resulting steam. During operation, two interacting flows are formed in the boiler units: the flow of the working fluid and the flow of the heat carrier formed in the furnace. As a result of this interaction, steam of a given pressure and temperature. One of the main tasks that arise during the operation of the boiler unit is to ensure equality between the produced and consumed energy. In turn, the processes of vaporization and energy transfer in the boiler unit are uniquely related to the amount of substance in the flows of the working fluid and coolant. Fuel combustion is a continuous physical and chemical process. The chemical side of combustion is the process of oxidation of its combustible elements with oxygen. passing at a certain temperature and accompanied by the release of heat. The intensity of combustion, as well as the efficiency and stability of the fuel combustion process, depend on the method of supplying and distributing air between fuel particles. Conventionally, the process of fuel combustion is divided into three stages: ignition, combustion and afterburning. These stages basically proceed sequentially in time, partially overlap one another. Calculation of the combustion process usually comes down to determining the amount of air in m3 necessary for the combustion of a unit mass or volume of fuel, the quantity and composition of the heat balance and determining the combustion temperature. The value of heat transfer lies in heat transfer thermal energy released during the combustion of fuel, water, from which it is necessary to obtain steam, or steam, if it is necessary to increase its temperature above the saturation temperature. The process of heat transfer in the boiler goes through water-gas-tight heat-conducting walls, called the heating surface. Heating surfaces are made in the form of pipes. Inside the pipes there is a continuous circulation of water, and outside they are washed by hot flue gases or perceive thermal energy radiation. Thus, all types of heat transfer take place in the boiler unit: thermal conductivity, convection and radiation. Accordingly, the heating surface is divided into convective and radiation. The amount of heat transferred through a unit of heating area per unit of time is called the thermal stress of the heating surface. The voltage value is limited, firstly, by the properties of the material of the heating surface, and secondly, by the maximum possible intensity of heat transfer from the hot coolant to the surface, from the heating surface to the cold coolant. heating surface and the higher the purity of the surface. The formation of steam in boilers proceeds with a certain sequence. Already in the screen tubes, the formation of steam begins. This process takes place at high temperature and pressure. The phenomenon of evaporation lies in the fact that individual molecules of a liquid located near its surface and having high velocities, and therefore, greater kinetic energy than other molecules, overcoming the force effects of neighboring molecules, creating surface tension, fly out into the surrounding space. As the temperature increases, the rate of evaporation increases. The reverse process of vaporization is called condensation. The liquid formed during condensation is called condensate. It is used to cool metal surfaces in superheaters. The steam generated in the boiler unit is divided into saturated and superheated. Saturated steam, in turn, is divided into dry and wet. Since superheated steam is required at thermal power plants, a superheater is installed to superheat it, in this case a screen and conjunctive superheater, in which heat obtained from the combustion of fuel and exhaust gases is used to superheat the steam. The resulting superheated steam at a temperature of T=540 C and a pressure of P=100 atm. goes to technological needs. 1.2 Description of the structure of the object
steam boilers type DE with a steam capacity of 6.5 t / h, with an absolute pressure of 1.3 MPa (14 kgf / cm2) are designed to generate saturated or superheated steam used for technological needs industrial enterprises, for heat supply of heating systems and hot water supply. The mass of the boiler plant is 16.5 tons, the feed water temperature is 100 C, the steam temperature is 210 C. Gas or fuel oil is used as the fuel to be burned. Double-drum vertical water-tube boilers are made according to the design scheme "D", a characteristic feature of which is the lateral location of the convective part of the boiler relative to the combustion chamber. constituent parts boilers are the upper and lower drums 1, a convective beam and forming a combustion chamber 2, the left combustion screen (gas-tight partition), the right combustion screen, the screening pipes of the front wall of the furnace and the rear screen. From below, the air necessary for combustion of fuel is supplied to the furnace by means of blow fans 3. The combustion process takes place at high temperatures, therefore, the boiler screen tubes perceive a significant amount of heat by radiation. The products of fuel combustion, otherwise called gases, enter the boiler gas ducts, while the surface of the superheater 4 is heated, they wash the pipes of the economizer 6, in which the feed water is heated to a temperature close to 200 C entering the drums of the boiler 1. Next, the flue gases pass into the chimney 5 and enter the air heater 7. From it, the gases through chimney out into the atmosphere. Water is supplied to the boiler through pipeline 9, gas pipeline 10. Steam from the boiler drum, bypassing the superheater 4, enters the steam pipeline 11. One of the most important indicators of the design of the boiler unit is its circulating capacity. Uniform and intensive circulation of water and steam mixture contributes to the washing off of steam and gas bubbles released from the water from the wall, and also prevents the deposition of scale on the walls, which in turn ensures a low wall temperature (200–400 C), which is slightly higher than the saturation temperature and not yet dangerous for the strength of boiler steel. Steam boiler DE -10–14 G. belongs to boilers natural circulation.
1.3 Justification of the need for control, regulation and signaling of technological parameters The regulation of the supply of boiler units and the regulation of pressure in the boiler drum is mainly reduced to maintaining a material balance between the removal of steam and the supply of water. The parameter characterizing the balance is the water level in the boiler drum. The reliability of the boiler unit is largely determined by the quality of the level control. When the pressure rises, the decrease in the level below the permissible limits can lead to a violation of circulation in the screen pipes, resulting in an increase in the temperature of the walls of the heated pipes and their burnout. its failure. In this regard, very high requirements are imposed on the accuracy of maintaining a given level. The quality of feed regulation is also determined by the equality of the feed water supply. It is necessary to ensure uniform supply of water to the boiler, as frequent and deep changes in the feed water flow can cause significant temperature stresses in the economizer metal. Boiler drums with natural circulation have a significant storage capacity, which manifests itself in transient conditions. If in the stationary mode the position of the water level in the boiler drum is determined by the state of the material balance, then in transient modes the position of the level is affected by a large number of disturbances. The main ones are. change in feed water flow, change in boiler steam removal with a change in the load of the consumer, change in steam production with a change in the load of the furnace, change in the temperature of the feed water. Regulation of the gas-air ratio is necessary both physically and economically. It is known that one of the most important processes occurring in a boiler plant is the process of fuel combustion. The chemical side of fuel combustion is a reaction of oxidation of combustible elements by oxygen molecules. The oxygen in the atmosphere is used for combustion. Air is supplied to the furnace in a certain ratio with gas by means of a blower fan. The gas-air ratio is approximately 1.10. With a lack of air in the combustion chamber, incomplete combustion of the fuel occurs. Unburned gas will be released into the atmosphere, which is economically and environmentally unacceptable. With an excess of air in the combustion chamber, the furnace will cool down, although the gas will burn out completely, but in this case, the remaining air will form nitrogen dioxide, which is environmentally unacceptable, since this compound is harmful to humans and the environment. The automatic vacuum control system in the boiler furnace is designed to keep the furnace under pressurization, that is, to maintain a constant vacuum (approximately 4 mm of water column). In the absence of vacuum, the flame of the torch will be pressed, which will lead to burning of the burners and the lower part of the furnace. In this case, the flue gases will go into the shop premises, which makes it impossible for the maintenance personnel to work. Salts are dissolved in the feed water, the permissible amount of which is determined by the standards. During the process of steam formation, these salts remain in the boiler water and gradually accumulate. Some salts form sludge, a solid that crystallizes in the boiler water. The heavier part of the sludge accumulates in the lower parts of the drum and collectors. An increase in the concentration of salts in the boiler water above the permissible values can lead to their entrainment into the superheater. Therefore, salts accumulated in the boiler water are removed by continuous blowing, which in this case is not automatically controlled. The calculated value of blowdown of steam generators in the steady state is determined from the equations of the balance of impurities to water in the steam generator. Thus, the proportion of blowdown depends on the ratio of the concentration of impurities in the blowdown and feed water. The better the quality of the feed water and the higher the permissible concentration of impurities in the water, the lower the proportion of blowdown. And the concentration of impurities, in turn, depends on the proportion of additional water, which includes, in particular, the proportion of lost blowdown water. The alarm parameters and protections that act to shut down the boiler are physically necessary, since the operator or driver of the boiler is not able to keep track of all the parameters functioning boiler. As a result, an emergency may occur. For example, when water is let out of the drum, the water level in it drops, as a result of which the circulation may be disturbed and the pipes of the bottom screens may burn out. The protection that has worked without delay will prevent the failure of the steam generator. With a decrease in the load of the steam generator, the intensity of combustion in the furnace decreases. Combustion becomes unstable and may stop. In this regard, protection is provided for extinguishing the torch. The reliability of protection is largely determined by the number, switching scheme and reliability of the devices used in it. According to their action, the protections are divided into those acting to stop the steam generator; steam generator load reduction; performing local operations.
2. general characteristics control object and classification of variables
The steam generator is a heat technology device that converts water into steam. set parameters using the heat of combustion of the fuel.
The object of control is the process of converting water into steam, characterized by input and output parameters:
Input:
Y 1 -boiler water performance;
Y 2 -water temperature;
Y 3 - water level in the drum;
Y 4 -pressure in the gas line;
Y 5 - air consumption for combustion;
Y 6 - air temperature;
Y 7 -water pressure;
Y 8 - the flow of exhaust gases;
Y 9 - pressure in the drum.
Weekends:
X 1 - boiler performance for steam;
X 2 -temperature of exhaust gases;
X 3 -torch temperature;
X 4 - gas consumption.
3. Functional diagram of the system for stabilizing the rarefaction of gases in the boiler furnace
The PE sensor measures the pressure in the boiler furnace. The output signal of the pressure sensor PE is fed to the secondary device PR, which is installed on site. Further, the signal is transmitted to the PIC controller, which compares it with the signal of the setpoint H when these signals are equal to zero, there is no output signal from the controller. In case of discrepancy, the PIC controller generates a signal, which is amplified and converted in the controller electronics. Next, the signal is sent to the key SA1, designed to switch the control modes "automatic - semi-automatic". "The output signal from the SA1 switch is fed to the NS power amplifier." The amplified signal is fed to the M1 actuator, which consists of an electric motor and a gearbox located in the same housing. Actuator M1 changes the position of the gas valve, which leads to a change in gas flow. In this case, the steam pressure in the steam generator changes until the steam generator reaches the set pressure mode. Pushbutton switch SB1 is intended for the set switching on of the electric motor of the actuator M1 in manual control mode.
4. Selection of devices and automation equipment
Pressure difference measuring transducer Sapphire-22M-DV (model 2240):
– the largest deviation of the actual characteristic from the nominal static characteristic – ±γ=0.25%;
– limit of permissible basic error – ±γ=0.5%.
α=0.716 - initial flow coefficient of standard orifices depending on m
0.111744 kgf / cm 2 \u003d 11 kPaOverpressure sensor Sapphire - 22-DD (model 2434).
When measuring excess pressure, absolute pressure, vacuum pressure with Sapphire-22 sensors (DI, DA, DIV), the pressure of the working medium is supplied to the "+" chamber, while the "-" chamber communicates with the atmosphere. When measuring vacuum (DV), decreasing pressure moves the membrane in the opposite direction from excess pressure.
When measuring the pressure difference (DP), positive and negative pressures are fed into the "+" and "-" chambers, respectively.
The pressure (pressure difference) of the working medium acts on the membranes (the membranes are interconnected by a central rod, which is connected to the end of the strain gauge lever) and through the liquid acts on the strain gauge membrane.
In Metran-22 sensors of models 2151, 2161, 2171, 2351, 2051, 2061, the pressure of the working medium acts directly on the strain gauge membrane.
The sensitive element is a single-crystal sapphire plate with silicon film strain gauges (SOS structure) connected to the metal membrane of the strain gauge. The strain gauges are connected in a bridge circuit. Deformation of the measuring membrane (deformation of the strain gauge membrane) leads to a proportional change in the resistance of strain gauges and unbalance of the bridge circuit. The electrical signal from the output of the bridge circuit of the sensors with the AP enters the electronic unit, where it is converted into a unified current signal.
The microprocessor electronic transducer of sensors with MP, MP1 receives an analog signal from a pressure transducer and converts it into a digital code.
The microcontroller receives a digital signal, corrects and linearizes the characteristics of the pressure transducer, transmits the digital signal to a digital-to-analog converter, which converts it into an output current.
The non-volatile memory of the ADC is designed to store the coefficients for correcting the characteristics of the pressure transducer.
The control and parameter setting block is designed to change the sensor parameters.
The use of microprocessor electronics provided the possibility of self-diagnostics, control and adjustment of sensor parameters directly at the place of operation.
Control and adjustment of the sensor parameters are carried out using a three-button switch and an indicator device (LCD liquid crystal indicator).
Switch buttons 1 and 2 are used for:
– control of sensor parameters setting;
– zero setting;
– settings for units of measurement;
– settings of the output signal settling time (damping).
Button 3 is used for:
– setting the measurement range;
- setting the "shifted" initial value of the output signal;
– choice of direct or inverse characteristics;
- choosing a system of units of measurement;
– sensor calibration.
TRM12-PIC microprocessor-based programmable meter-regulator, together with the sensor, is designed to measure the input parameter and pulse control of the electric drive of shut-off and control and three-way valves according to the proportional-integral-derivative (PID) law. The device allows to ensure high accuracy of maintaining the value of the measured parameter for objects with a large inertia and with a small delay.
The device, equipped at the request of the customer with an expansion board PR-01, generates a standard current proportional to the measured value for the recording device, for example, a recorder, and also provides operation under the control of a computer with the registration of the measured value on it. The device is connected to the computer through the AC2 network adapter manufactured by the manufacturer of this device.
The device is designed to automate heating systems, hot water supply, as well as process control in the food and medical industries, agriculture and utilities.
Specifications
Supply voltage | 220V 50Hz | |
Supply voltage tolerance | -15…+10% | |
Power consumption | no more than 6 VA | |
Range of control when used on at the input of the device (resolution is indicated in brackets) ТСМ |
-50…+200 °С (0.1 °С) | |
Limit of permissible basic reduced error of measurement of the input parameter (excluding sensor error) | ±0.25 or ±0.5% depending on on the accuracy class of the device |
|
Maximum allowable load current |
electromagnetic relays | 8 A at voltage 220 V and cos f>0.4 |
transistor n-p-n keys | 0.2 A at +30 V | |
Control step duration | 4 sec | |
Number of steps s at which the duration of the control pulses remains unchanged | 1…99 | |
Controlled value display method | digital | |
Number of digits of the digital indicator | 4 | |
Communication interface with a computer via a network adapter * | RS-232 | |
The length of the communication line of the device with the network adapter * | no more than 1000 m | |
Recording current range at load 200…1000 Ohm* | 4…20 mA or 0…20 mA | |
Maximum permissible basic reduced error of the registration signal at a load of 400 Ohm relative to the measured value | no more than 0.5% | |
Permissible ambient air temperature | +5… +50 °С | |
Atmosphere pressure | 86…107 kPa | |
Relative humidity | 30…80% | |
Degree of protection of the case (panelboard / wall-mounted) | IP20/IP44 | |
Overall dimensions of the device (panelboard / wall-mounted) | 96x96x160 mm/105x115x65 mm | |
Weight of the device no more | 1.2 kg |
5. Construction and description of the generalized functional and structural diagrams of the automation system
Generalized functional diagram of the vacuum stabilization system of the dryer drum
The following designations are adopted on the diagram: PA - power amplifier; IM-executive mechanism; RU-regulating device; RO-regulatory body; OS – control object; DT temperature sensor.
RO, KD and DT form the object of regulation. BFZR, UM, IM blocks constitute the control device.
In accordance with the initial data for the design of the reactor plant, it must be a PI controller. The PI regulation law is formed by the BFZR block.
The following designations are accepted on the diagram: Z - setter; VFZR - block of formation of the law of regulation; RP - position regulator; PA - power amplifier; IM - executive mechanism; DP – position sensor; RU - control device; RO - regulatory body; OS - control object (dryer drum); DR - vacuum sensor; x is the controlled value; y is the control value; g - setting action; ε = g - x - deviation of the controlled value from the setting action.
RO, KD and DR form the object of regulation. Blocks BFZR, RP, UM, IM, DP constitute the control device.
The reactor plant, in accordance with the design assignment, must provide the PI control law. The shaper of the PI-law is the BFZR. To exclude the distortion of the regulation law, all subsequent RU blocks after the BFZR must be dynamically amplifying links.
This condition is satisfied for UM. The MI block in dynamic terms is an integrating link with a transfer function
where T IM is the time constant of the actuator.
To “transform” the IM from an integrating to an amplifying link and to exclude the distortions it introduces into the control law, the actuator, together with the PA, is covered by a negative feedback. Moreover, the IM shaft position sensor is included in the feedback circuit, and the proportional position controller is included in the direct branch. Structural diagram of IM covered by hard feedback is shown in fig. 3.
The sensor and the position controller are amplifying links with transfer functions W DP (p) = K DP and W RP (p) = K RP, respectively.
Since in practice, as a rule, the condition
> , (14)then the dynamic properties of the anti-parallel connection under consideration (see Fig. 5) are determined only by the amplifying feedback link, and the transfer function of the IM covered by the hard connection processing will be equal to
. (15)Rice. 3. Structural diagram of the actuator covered by hard negative feedback
To improve the fulfillment of condition (14), RP and PA are also covered by feedback.
The dynamic properties of the rarefaction sensor of the regulating body are characterized by an amplifying link, and the control object - by an aperiodic link with a delay (see the initial design data).
In view of the foregoing, the block diagram of the automation system that implements the Pi-law of regulation takes the form shown in fig. 4, which shows:
– transfer function (TF)amplifying link BFZR;
– PF of the BFZR integrating link; - Transmission functionposition regulator;
– PF of the power amplifier; (16) – PF of the actuator; – PF of the position sensor; – PF of the regulatory body; – PF of the control object; – PF of the vacuum sensor.Using the principles of transformation of block diagrams, we obtain the transfer function of the automation system in the following sequence.
1. BFZR transfer function
2. PF control device
or taking into account (15)
Rice. 4. Structural diagram of the vacuum stabilization system in the boiler furnace
3. Object transfer function
and taking into account (16)
. (17)
4. PF automatic control system
. (18)Relation (17) is the desired analytical expression for the transfer function of the automation system, the enlarged block diagram of which is shown in Fig. 5.
Rice. 5. Enlarged block diagram of the automation system
6. Analysis of the dynamic properties of the control object
The analysis of the dynamic properties of the OS is carried out according to the time and frequency characteristics.