Boiler Automation Using Programmable Logic Controller

Introduction

PLC applications are extensively used in industry to control and facilitate repetitive processes such as manufacturing cell management, fly-by-wire control, or nuclear plant shutdown systems. One of these applications is industrial automation which includes numerous automated processes. This again includes automation of boiler which demands determination of certain physical parameters (viz. pressure, temperature, etc.) & utilizing these parameters to make the boiler start-stop or function in any manner we want, but automatically, without involvement of any personal.

Project In Brief

OBJECTIVE: Designing of a PLC controlled boiler for production of steam.

PROJECT AT A GLANCE:

SOFTWARE AND COMPONENTS USED:

 KGL software (make LG)

 PLC module (make LG)

 Motor

 Water reserve

 Closed air tight container

 Level sensor(Digital)

 Temperature sensor with current output(Analog)

 Pressure sensor(Analog)

 Solenoid valve(Digital)

The most common parameters that have to be controlled in the boiler are temperature, pressure, water level. The controlling mechanism can be achieved by using microprocessor and microcontroller, PID controller or using PLC. Programmable logic control (PLC) provides an easy and sophisticated method to design automation in industry. It also provides easy trouble shooting method and flexibility to the industry.

Generally an industry has an emergency stop button to stop the whole process instantly if any error occurred during operation. The emergency stop buttons are normally closed type. To start the mechanism a start button (normally open type) switch is used which is connected after stop button. When start button is made ON the lower level sensor sense the water level below the lower level hence it start the motor to pump the water in to the boiler. The pump runs till the water reaches the higher level sensor. After that the pump stops running. The temperature sensor provides the temperature information to the PLC. If the temp. is less then the preset value the heater starts after 5 sec of motor OFF time. Temperature rises continuously and form water steam. The temp. should not rise beyond tolerance level of boiler hence the temp. should rise up to certain limit and the heater should stop at that moment. The temp. again decreases and if goes below preset value it start the heater. The above process continues. The steam produce in the boiler exert a pressure on the boiler which is picked up by the pressure sensor. If pressure reaches the preset value it make the valve open and steam with a definite pressure goes out through the pipe. The preset value of the pressure should be calculated carefully and it should not exceed maximum limit of boiler tolerance. This process result in decrease in water level and if falls below the lower level sensor the motor starts during which the heater stops and whole process repeats.

FLOW CHART:

YES

YES

NO

NO

DIFFERENT SECTIONS OF THE PROJECT: The project incorporates the requirement of a physical PLC trainer kit which is responsible for collection of data from field sensors (within the boiler), evaluate them & generate appropriate output for the boiler to operate in a specific desired procedure. Initially, we divided our project into four sections viz., power supply section, water supply section, boiler (including sensors) section, process controlling section.

Boiler Section: Boiling container, sensors (presssure,temperature & level sensors) & a heater assemble altogether to give rise to the boiler section.

Controlling Section: This section includes the PLC trainer kit which is responsible for data collection from field sensors, evaluation of collected data & generation of appropriate output signals for automatic actuation and termination of different peripherals incorporated in the overall system.

Water Supply Section: Water supply to the boiler is ensured by a water pump whose actuation & termination is controlled by the PLC trainer.

Power Supply Section: This takes care of the power requirements for the whole project. This mostly comprises of the circuits providing DC power for the field sensors and valves (solenoids).

APPLICATIONS: The main advantage of using PLCs is the drastic reduction in the requirement of electrical components in terms of number of switches, relays, wiring, etc.the applications of this project are solely the applications of a boiler i.e., production of steam and using it for numerous processes like rotating the generator fins and hence producing power for commercial or industrial purposes.

Stages Of Project Design:

We divided the overall construction of the project in two stages. These are described as follows:

STAGE 1:

This stage basically focuses on:

(i) Software design & simulation

(ii) Hardware design

(A).Power supply &

(b) .Sensing unit

 Level Sensing Unit

 Temperature sensing unit

Software Design & Simulation

The software design and simulation part of the whole project is done by using the software “KGL”. This software is used to design the ladder diagram of the overall project simulation in order to study it`s behaviour.The ladder design hence obtained is downloaded into the PLC CPU and thereby generating appropriate output signals required for the simulation.

Features of KGL for Windows

KGL for Windows is the Programming and Debugging Tool for LG Master-K Series.

KGL for Windows has abundant Features as below.

1) Program Compatible between LG Master-K Series.

A user can use the Program (*.PGM) created in LG Master-K Series for the Program created in other LG Master-K Series As well. The Program, Parameter or Variable/Comment created in KGL-DOS or GSIKGL can be also used in KGL for Windows.

2) PLC System Configuration by Project Structure

KGL for Windows manages the User-Defined Program as one Project including Parameter and Variable/Comment. Also a user can save a Program (*.PRG), Parameter (*.PMT), Variable (*.VAR) or Comment (*.CNT) respectively and the stored each File can be used for other Project files.

3) User Friendly Interface

Easy and useful interface for Creating, Editing and Monitoring.

4) Online Editing

A Real Time Editing is available in online mode. The Program edited in the online condition can be downloaded automatically without stopping PLC Hardware.

5) Monitoring the Information from PLC

A user can easily monitor PLC status such as Error Status, Network Information and System Status.

6) Debugging and Self-diagnosis (in New MASTER-K Series)

Trigger and Forced I/O Enable are available for the accurate Debugging

Creating a Program

Creating a Ladder Program

This chapter describes creating a program in Ladder Window using the Tool Bar.

#After selecting the Normally Open Contact icon in the Ladder Tool Bar, Move the cursor to the place to insert the

Contact

#Click the left button of the mouse or press Enter key, then the contact input dialog box appears.

#Type in the contact name (M0000) you want to insert and click OK button or press Enter key.

#Select the Output Coil icon in the Ladder Tool Bar and move the cursor to the next column of P000.

Click the mouse button or press Enter key.

#Type in the Output Coil (P040) and click OK button or press Enter key.

Create a Project

About a Project

#A Project is the highest level to communicate with PLC and KGL for Windows.

A Project consists of Program, Parameter and Variable/Comment of Device.

#KGL for Windows deals with User Defined Programs and includes all elements necessary for describing a Project.

#A Project consists of 3 Items (Program, Parameter and Variable/Comment) and Monitoring is activated when the Monitoring Window is opened. Each Item can be saved respectively for another Project.

#Saved Items (Program, Parameter and Variable/Comment) can be used for creating other Projects or to reuse for other Projects.

#A Project includes not only Program, Parameter and Variable/Comment, but also PLC type, used status of KGL and various information registered for monitoring. Thus, when you reopen the Project after saving a Project, the Window keeps the previous working condition.

#Only Program and Parameters can be downloaded to PLC.

#A Project is saved as *.PRJ File.

Create a Project

#To create a New Project file, Select File--New Project… ( ) from the Project pull-down Menu.

The New Project dialog box will appear as below.

#Open a Blank Project

#It creates a new Project.

#Create from Old Files

#To create a New Project using the already existed Item (Program or Parameters or Variable/Comment),

Select Item or items to be used by clicking the Find button in the dialog box.

#Click OK button after registering Items.

#Up to 3 items can be selected and non-selected items are set to default (Initial data).

#After selecting PLC Type and Programming Language, press the OK button. Then Project, Message and Program Windows will be opened.

#Create from DOS KGL file

#To create a New Project using Items (Program, Parameter and Variable/Comment) created in KGL for DOS,

Select PLC Type and Programming Language after selecting already created Items in KGL for DOS. Then, a New

Project will be opened.

#Create from KGL file

#To create a New Project from KGL file, Select already created files (*.PGM, *.CMT) from GSIKGL in the dialog box and select PLC Type and Programming Language.

Hot-Keys for Ladder Program Mode

Simulation part

End Of Software Design & Simulation

****** ******

Hardware Design

Chip Specifications:

1).LM35 (Precision Centigrade Temperature Sensors)

Description:

The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. The LM35 thus has an advantage over linear temperature sensors calibrated in °Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling.

Features:

  • Calibrated directly in ° Celsius (Centigrade)
  • Linear + 10.0 mV/°C scale factor
  • 0.5°C accuracy guarantee able (at +25°C)
  • Rated for full −55° to +150°C range
  • Suitable for remote applications
  • Low cost due to wafer-level trimming
  • Operates from 4 to 30 volts
  • Less than 60 μA current drain
  • Low self-heating, 0.08°C in still air
  • Nonlinearity only ±1⁄4°C typical
  • Low impedance output, 0.1 for 1 mA load

Absolute Maximum Ratings:

Supply Voltage +35V to −0.2V

Output Voltage +6V to −1.0V

Output Current 10 mA

Storage Temp. TO-220 Package −65°C to +150°C

Lead Temp. TO-92 and TO-220 Package, 260°C.

(Soldering, 10 seconds)

2).LM317 (3-Terminal Positive Adjustable Regulator)

Description:

This monolithic integrated circuit is an adjustable 3-terminal positive voltage regulator designed to supply more than 1.5A of load current with an output voltage adjustable over a 1.2V to 37V. It employs internal current limiting, thermal shut-down and safe area compensation.

Features:

  • Output Current In Excess of 1.5A
  • Output Adjustable Between 1.2V and 37V
  • Internal Thermal Overload Protection
  • Internal Short Circuit Current Limiting
  • Output Transistor Safe Operating Area Compensation

Absolute Maximum Ratings:

Input-Output Voltage Differential - 40 V.

Operating Junction Temperature - 0 ~ +125 °C

Range

Storage Temperature Range -65 ~ +125 °C.

Temperature Coefficient of ±0.02 % /°C

Output Voltage .

3).LM78XX (7805 & 7812)

Series Voltage Regulators

Description:

The LM78XX series of three terminal regulators is available with several fixed output voltages making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents.

Features

  • Output current in excess of 1A
  • Internal thermal overload protection
  • No external components required
  • Output transistor safe area protection
  • Internal short circuit current limit
  • Available in the aluminum TO-3 package

Voltage Range:

  • LM7805C 5V
  • LM7812C 12V
  • LM7815C 15V

Absolute Maximum Ratings:

Input Voltage (for VO = 5V to 18V) 35V.

(For VO = 24V)40V.

Thermal Resistance Junction-Cases (TO-220) 5 ｰC/W.

Thermal Resistance Junction-Air (TO-220) 65 ｰC/W.

Operating Temperature Range (KA78XX/A/R) 0 ~ +125 ｰC.

Storage Temperature Range - -65 ~ +150 ｰC.

4).HCF4093B:

QUAD 2 INPUT NAND SCHMITT TRIGGER

Description:

The HCF4093B is a monolithic integrated circuit fabricated in Metal Oxide Semiconductor technology available in DIP and SOP packages. The HCF4093B type consists of four Schmitt trigger circuits. Each circuit functions as a two input NAND gate with Schmitt trigger action on both inputs. The gate switches at different points for positive and negative going signals. The difference between the positive voltage (VP) and the negative voltage (VN) is defined as hysteresis voltage (VH).

Features:

  • SCHMITT TRIGGER ACTION ON EACH INPUT WITH NO EXTERNAL COMPONENTS
  • HYSTERESIS VOLTAGE TYPICALLY 0.9V at VDD = 5V AND 2.3V at VDD = 10V
  • NOISE IMMUNITY GREATER THAN 50%OF VDD (Typ.)
  • NO LIMIT ON INPUT RISE AND FALL TIMES
  • QUIESCENT CURRENT SPECIFIED UP TO 20V
  • STANDARDIZED SYMMETRICAL OUTPUT CHARACTERISTICS
  • 5V, 10V AND 15V PARAMETRIC RATINGS
  • INPUT LEAKAGE CURRENT II = 100nA (MAX) AT VDD = 18V TA = 25°C
  • 100% TESTED FOR QUIESCENT CURRENT.

ABSOLUTE MAXIMUM RATINGS:

Supply Voltage -0.5 to +22 V

DC Input Voltage -0.5 to VDD + 0.5 V

DC Input Current ± 10 mA

Power Dissipation per Package 200 mW

Power Dissipation per Output Transistor 100 mW

Operating Temperature -55 to +125 °C

Storage Temperature -65 to +150 °C

Power supply:

This comprises of 12V DC & 5V DC supply for the four sensors (2 level sensors, 1 temperature sensor & 1 pressure sensor) used in the boiler. The 230V AC supply is first stepped down to 12V AC using a step down transformer. The output of this transformer is then passed through a bridge rectifier to convert it to 12V DC output and hence to 5V. For the voltage consistency, IC 7812 & IC 7805 chips are used. The 12V DC and 5V hence obtained is utilized to activate all the four sensors.

Design Of Liquid Level Sensor

Most of the sensor placed inside the water cause electrolytic reaction between liquid and sensor causing loss of effectiveness. One solution to this problem is to ensure an AC potential rather than DC potential between the electrodes. The constant reversal of electrode polarity drastically inhibits the electrolytic process so that corrosion is considerable reduced and effectiveness doesn’t hampered.

In this liquid level sensor AC is generated by an oscillator by connecting a capacitor (C1) to the input of IC4093 (a NAND) gate and proving a feedback through the resistor (R1). This AC current is given to the capacitor (C4) to charge up through the AC coupled capacitors C2 and C3. Between C2 and C3 two sensor electrodes are placed so that when the liquid touches the electrode, a conducting path is being created by the liquid so that C4 can be charged. Two diodes D1 and D2 provide blockage to discharge capacitor C4. This high input of the charged capacitor C4 is given to the IC4093 whose output is used to drive the base of transistor BC557. A relay is connected to ground through BC557. As the transistor is driven by IC4093 which drive relay in and the 230 volt ac output of relay is used to drive the motor.

Circuit diagram of liquid level sensor

Design of temperature sensor

VOLTAGE REGULATOR CIRCUIT

A voltage regulator circuit provides a fixed value of voltage for particular values of circuit components. A 12 volt DC voltage circuit can be designed by connecting a 230:12 volt transformer, a bridge rectifier circuit and a capacitor, an IC7812.The transform gives 12 volt AC output which is rectified by bridge circuit, a capacitor is used to bypass the AC component and the IC7812 is used to provide constant 12 volt output which is use to drive other instruments.

Circuit diagram for voltage regulator circuit

Future work:

The 2nd stage of the project is to be done in the successive semester.

2nd stage of the project involves:

  1. Designing the pressure sensor circuit
  2. Interfacing of sensors with the plc trainer kit.
  3. Implementing the software program.
  4. Construction of boiler setup & incorporation of the sensor within the boiler.

reference

  1. LM 35 Precision Centigrade Temperature Sensors, National semiconductors, November – 2000.
  2. LM78XX Series Voltage Regulators, National semiconductors, May – 2000.
  3. User Manual for PLC Trainer Kit, LG Programmable logic controller KGL for windows [MASTER-K Series].

Project Guide: Project Group Members:

Ms. Limali Sahoo DHIRAJ KUMAR (348074013

GAURI SHANKAR KUMAR (348074030)

Md. ASRARUL HAQUE (348074017)

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