基于PLC的锅炉温度控制系统 英文材料

最新问答

• 泡芙小工坊

  PLC BASED BOILER TEMPERATURE CONTROLLER

  Controlling appliances from our PC is quite interesting and convenient. In this project the simple circuit along with the software is used to interface the PC with the Electronic circuit. This project consists of three modules called PLC control panel, boiler sensor unit and display unit.

  The Gates(And, Or, Not etc) and the Input variables are set in the system. The corresponding signal is transmitted through parallel port and the PLC kit receives the signal.

  The High or Low Input are set in the PLC kit by using switches. The control operations are done in the Microcontroller using PLC(Ladder Logic) Programming.

  The output is derived in the PLC kit. By using the output one can control any machine or motor.

  Heat sensors are connected at the boiler. According to the heat sensed, the sensors send signal to the PLC kit. According to the variables set in the PLC kit, the kit sends signal to the display section. Thus the user can monitor the heat level of the boiler as well as he can control the boiler.

  This project uses Visual Basic as designing language and Assembly language as Microcontroller language. PIC16F73 is used as Microcontroller.

  Control of Boiler Operation using PLC – SCADA

  K. Gowri Shankar

  Abstract––This paper outlines the various stages of operation involved in the conversion of a manually operated boiler towards a fully automated boiler. Over the years the demand for high quality, greater efficiency and automated machines has increased in this globalised world. The initial phase of the paper focuses on passing the inputs to the boiler at a required temperature, so as to constantly maintain a particular temperature in the boiler. The Air preheater and Economizer helps in this process. And the paper mainly focuses on level, pressure and flow control at the various stages of the boiler plant. Thus the temperature in the boiler is constantly monitored and brought to a constant temperature as required by the power plant. The automation is further enhanced by constant monitoring using SCADA screen which is connected to the PLC by means of communication cable. By means of tag values set to various variable in SCADA the entire process is controlled as required. At the automated power plant, the boiler is controlled by Variable Frequency Drive (VFD) to put in action the required processes to be carried out at the boiler. Thus the entire cycle is carried out as a paper and at various stages each phase is detailed out. This paper has proved to be very efficient practically as the need for automation grows day by day.

  Index Terms––Automation, PLC – SCADA, Boiler.

  I. INTRODUCTION Over the years the demand for high quality, greater efficiency and automated machines has increased in the industrial sector of power plants. Power plants require continuous monitoring and inspection at frequent intervals. There are possibilities of errors at measuring and various stages involved with human workers and also the lack of few features of microcontrollers. Thus this paper takes a sincere attempt to explain the advantages the companies will face by implementing automation into them. The boiler control which is the most important part of any power plant, and its automation is the precise effort of this paper.

  In order to automate a power plant and minimize human intervention, there is a need to develop a SCADA (Supervisory Control and Data Acquisition) system that monitors the plant and helps reduce the errors caused by humans. While the SCADA is used to monitor the system, PLC (Programmable Logic Controller) is also used for the internal storage of instruction for the implementing function such as logic, sequencing, timing, counting and arithmetic to control through digital or analog input/ out put modules various types of machines processes. Systems are used to monitor and control a plant or equipment in industries such as telecommunications, water and waste control, energy, oil and gas refining and transportation.

  II. DRAWBACK OF CONVENTIONAL SYSTEM Conventional equipment systems are prone to errors due to the involvement of humans in the data collection and processing using complicated mathematical expressions. Thus what we require is a system that collects raw data, processes it and presents it in values which can be verified and compared with the standard values. In the coding process of this implementation with micro-controller, it requires a fast and efficient processing which on the other part depends on the length and sub-routines of the coding process. Thus it provides a real challenge with systems involving

  III. METHODS All the values can be filled up by the introduction of the automation technique into the power plants. The automation technique involving the automatic control of all the processes which includes the monitoring and inspection needs provides for a very efficient system. The automation process helps the company having the power plant to reduce the amount of errors that occur , reduction in the human resources, increased efficiency, and most importantly very cost effective.

  IV. CRITICAL CONTROL PARAMETERS IN BOILER A. Level Control Steam Drum level, De-aerator level and hot well level

  B. Pressure Control Force draft pressure, Induced draft pressure, Steam drum pressure, Deaerator pressure, Turbine inlet steam pressure, balanced draft pressure

  Proceedings of the International MultiConference of Engineers and Computer Scientists 2008 Vol II IMECS 2008, 19-21 March, 2008, Hong Kong

  ISBN: 978-988-17012-1-3 IMECS 2008

  C. Flow Control Air flow, Steam flow, Water flow

  D. Temperature Control Deaerator temperature, Steam drum temperature, Underbed boiler temperature, Turbine inlet steam temperature, Flue gas temperature.

  V. AUTOMATION Delegation of Human Control to technical Equipment aimed to wards achieving.

  Advantages Higher productivity, Superior quality of end product, Efficient usage of raw materials and energy, Improved safety in working condition.

  A. History of Control and Automation

  PLC ELECTRICAL CONTROL WITH LOGIC GATES WITH LOGIC GATES MANUAL CONTROL

  Manual Control In this, the Control and Automation are done by Manual Operations. Drawbacks: • Human Errors subsequently affect quality of end product. • Hard Wired Logic Control • In this, Contractor and relays together with timers and counters were used in achieving desired level of automation. • Bulky and complex wiring, Involves lot of rework to implement changes in control logic, the work can be started only when the takes is fully defined and this leads to longer project time.

  Electronics Control with Logic Gates In this, Contactor and Relays together with timers and counters were replaced with logic gates and electronic timers in the control circuits.

  Advantages • Reduced space requirements, energy saving, less maintenance and hence greater reliability. • The Major Drawbacks • Implementation of changes in the control logic as well as reducing the project lead- time was not possible.

  Programmable Logic Controller In this, instead of achieving desired control and automation through physical wiring of control devices, it is achieving through program say software.

  Advantages Reduced Space, Energy saving, Modular Replacement, Easy trouble shooting, Error diagnostics programmer, Economical, Greater life and reliability, The Compatibilities of PLC’S, Logic Control, PID control, Operator control, Signaling and listing, Coordination and communication.

  B. How PLC works Basics of a PLC function are continual scanning of a program. The scanning process involves three basic steps.

  Step 1: Testing input status First the PLC checks each of its input with intention to see which one has status on or off. In other words it checks whether a switch or a sensor etc., is activated or not. The information that the processor thus obtains through this step is stored in memory in order to be used in the following steps.

  Step 2: Programming execution Here a PLC executes a program instruction by instruction based on the program and based on the status of the input has obtained in the preceding step, and appropriate action is taken. The action might be activation of certain outputs and the results can be put off and stored in memory to be retrieved later in the following steps.

  Step 3: Checking and Correction of output status Finally, a PLC checks up output signals and adjust it has needed. Changes are performed based on the input status that had been read during the first step and based on the result of the program execution in step two – following execution of step three PLC returns a beginning of the cycle and continually repeats these steps . Scanning time = Time for performing step 1+ Time for performing step 2+ Time for performing step 3.

  VI. ALLEN BRADLEY PLC Programmable Logic Controller or PLC is an intelligent system of modules, which was introduced in the control, & instrumentation industry for replacing relay based logic [4]. Over a period of time, ter I/O handling capabilities and more programming elements have been added along with improvement in communication.

  Proceedings of the International MultiConference of Engineers and Computer Scientists 2008 Vol II IMECS 2008, 19-21 March, 2008, Hong Kong

  ISBN: 978-988-17012-1-3 IMECS 2008

  PLC Working At the beginning of each cycle the CPU brings in all the field input signals from the input signals from the module and store into internal memory as process of input signal. This internal memory of CPU is called as process input image (PII). User program (Application) will be available in CPU program memory. Once PII is read, CPU pointer moves in ladder program from left to right and from top to bottom. CPU takes status of input from PII and processes all the rungs in the user program. The result of user program scan is stored in the internal memory of CPU. This internal memory is called process output image or PIQ. At the end of the program run i.e., at the end of scanning cycle, the CPU transfers the signal states in the process image output to the output module and further to the field control.

  I/O driver (SCADA) picks up PII and PIQ and transfers the image to database and this image is called driver image. This driver image available in SCADA database is used for graphical view of process monitoring from operator station (OS) in the central control room.

  A. Features of Allen Bradley PLC Using Allen Bradley 1000PLC Micrologix 1000PLC has 20 digital outputs. The relationship with bit address to input and output devices is shown in the figure below.

  C. Connecting to the PLC • Open a SCADA application • Create a tag of type I/O discrete, select the type as discrete • Select read only if you don’t want to force values to PLC. Selecting read and write allows to the SCADA to read and force values to the PLC. • Type an access name. • The access name can visualized as a gateway for a group of resources. • Most of PLC drivers communicate with SCADA package using DDE, DDE requires three parameters namely name of the DDE server, topic name and item name. In case of reading a number of items from a particular PLC driver application name topic name are common, so this application name that is name of the DDE server and Topic name combine to form an access name. Access name is required to be defined only once then other items of driver can be accessed by using the Access name and item name. These details will be provided by the driver vendor or developer. • Click ok, the access name will be listed finally click done, then type the item name, click save to save the I/O tags. Go to run time to communicate with PLC.

  A. Flowchart The operation is summarized as flowchart as below

  CONCLUSION The most important aspect of any power plant is the boiler control. Several techniques can be implemented to control the boiler in power plant. The method that has to be used relies on varied objectives like superior quality, increased efficiency, high profit and other such points depending upon the purpose of the company that implies it. With the prime objective of catering to these necessities and the needs of the industrial sector, significance has been given here to automation. This paper presented here has kept in mind, the ceaseless changes that are relentlessly taking place in the contemporary scenario of the industrial segment. Emphasis has been given to the automation process that is now rapidly taking its place in all the power plants across the globe. The Paper has furnished itself to study the integral parts of the entire process involved, their implementation and the problems that may show up have also been given their due importance. The future work deals with the purification of water to the boiler and the air circulation for the boiler to burn the fuel using same automation technique.

  Introduction to Temperature Controllers
  How do Temperature Controllers work?
  

  To accurately control process temperature without extensive operator involvement, a temperature control system relies upon a controller, which accepts a temperature sensor such as a thermocouple or RTD as input. It compares the actual temperature to the desired control temperature, or setpoint, and provides an output to a control element. The controller is one part of the entire control system, and the whole system should be analyzed in selecting the proper controller. The following items should be considered when selecting a controller:

  1. Type of input sensor (thermocouple, RTD) and temperature range
  2. Type of output required (electromechanical relay, SSR, analog output)
  3. Control algorithm needed (on/off, proportional, PID)
  4. Number and type of outputs (heat, cool, alarm, limit)

  What Are the Different Types of Controllers, and How Do They Work?
  There are three basic types of controllers: on-off, proportional and PID. Depending upon the system to be controlled, the operator will be able to use one type or another to control the process.
  
  On/Off Control
  An on-off controller is the simplest form of temperature control device. The output from the device is either on or off, with no middle state. An on-off controller will switch the output only when the temperature crosses the setpoint. For heating control, the output is on when the temperature is below the setpoint, and off above setpoint. Since the temperature crosses the setpoint to change the output state, the process temperature will be cycling continually, going from below setpoint to above, and back below. In cases where this cycling occurs rapidly, and to prevent damage to contactors and valves, an on-off differential, or “hysteresis,” is added to the controller operations. This differential requires that the temperature exceed setpoint by a certain amount before the output will turn off or on again. On-off differential prevents the output from “chattering” or making fast, continual switches if the cycling above and below the setpoint occurs very rapidly. On-off control is usually used where a precise control is not necessary, in systems which cannot handle having the energy turned on and off frequently, where the mass of the system is so great that temperatures change extremely slowly, or for a temperature alarm. One special type of on-off control used for alarm is a limit controller. This controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.
  
  Proportional Control
  Proportional controls are designed to eliminate the cycling associated with on-off control. A proportional controller decreases the average power supplied to the heater as the temperature approaches setpoint. This has the effect of slowing down the heater so that it will not overshoot the setpoint, but will approach the setpoint and maintain a stable temperature. This proportioning action can be accomplished by turning the output on and off for short time intervals. This "time proportioning" varies the ratio of “on” time to "off" time to control the temperature. The proportioning action occurs within a “proportional band” around the setpoint temperature. Outside this band, the controller functions as an on-off unit, with the output either fully on (below the band) or fully off (above the band). However, within the band, the output is turned on and off in the ratio of the measurement difference from the setpoint. At the setpoint (the midpoint of the proportional band), the output on:off ratio is 1:1; that is, the on-time and off-time are equal. if the temperature is further from the setpoint, the on- and off-times vary in proportion to the temperature difference. If the temperature is below setpoint, the output will be on longer; if the temperature is too high, the output will be off longer.
  
  PID Control
  The third controller type provides proportional with integral and derivative control, or PID. This controller combines proportional control with two additional adjustments, which helps the unit automatically compensate for changes in the system. These adjustments, integral and derivative, are expressed in time-based units; they are also referred to by their reciprocals, RESET and RATE, respectively. The proportional, integral and derivative terms must be individually adjusted or “tuned” to a particular system using trial and error. It provides the most accurate and stable control of the three controller types, and is best used in systems which have a relatively small mass, those which react quickly to changes in the energy added to the process. It is recommended in systems where the load changes often and the controller is expected to compensate automatically due to frequent changes in setpoint, the amount of energy available, or the mass to be controlled.
  OMEGA offers a number of controllers that automatically tune themselves. These are known as autotune controllers.
  
  Standard Sizes
  Since temperature controllers are generally mounted inside an instrument panel, the panel must be cut to accommodate the temperature controller. In order to provide interchangeability ween temperature controllers, most temperature controllers are designed to standard DIN sizes. The most common DIN sizes are shown below.
  

  浏览 455赞 131时间 2023-06-17