atul plc report

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“PROGRAMMABLE LOGIC CONTROLLER”

Seminar report submitted in partial fulfillment of the requirement for the award of the

degree of

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS & INSTRUMENTATION ENGINEERING

(UTTAR PRADESH TECHNICAL UNIVERSITY)

BY

ATUL KUMAR SRIVASTAVA

E.I. 6TH SEMETER

Roll No. 0821632008

Under the guidance of

MS. SWETA PANDEY

DEPARTMENT OF ELECTRONICS & INSTRUMENTATION ENGINEERING

IIMT COLLEGE OF ENGINEERING

GREATER NOIDA



Certificate

THIS IS TO CERTIFY THAT Mr.ATUL KUMAR SRIVASTAVA OF

B.TECH(3RDYEAR) ELECTRONICS AND INSTRUMENTATION ENGINEERING

DELIEVERED A SEMINAR AT “PROGRAMMABLE LOGIC CONTROL” is ON

11-03-2011. ACCORDING TO THE GAUTAM BUDDH TECHNICAL UNIVERSITY

CIRRICULUM HIS PERFORMANCE IN THE SEMINAR WAS EXCELLENT/VERY

GOOD /SATISFACTORY.

Ms.Swta Pandey Mrs.Taslima Ahmed

(SEMINAR GUIDE) (SEMINAR COORDINATOR)

Mr.UMESH KUMAR

(HEAD OF DEPARTMENT)



INDEX

Chapter No. Topics Page No.

1. Introduction 01

2. PLC Architecture 03

3. System Overview. 08

4. Hardware Configuration 10

5. Addresses 15

6. Software Description. 18

7. Syntax for Program 25

8. How to Use PLC. 26

9. Scope of Future Expansion. 28

10. Applications of PLC. 29

BIBLIOGRAPHY 32

APPENDIX A Automatic Mixing System. 33



Chapter 1



INTRODUCTION

Simplification of engineering and precise control of manufacturing

process can result in significant cost savings. The most cost-effective way, which

can pay big dividends in the long run, is flexible automation; a planned approachtowards integrated control systems. It requires a conscious effort on the part of

plant managers to identify areas where automation can result in better

deployment/utilization of human resources and savings in man-hours, down time.Automation need not be high ended and too sophisticated; it is the phased, step-

by-step effort to automate, employing control systems tailored to one’s specific

requirements that achieves the most attractive results. That is where Industrial

electronics has been a breakthrough in the field of automation and controltechniques.

ROLE OF ELECTRONICS IN AUTOMATION

A constant demand for better and more efficient manufacturing and process machinery has led to the requirement for higher quality and reliability in

control techniques. With the availability of intelligent, compact solid state

electronic devices, it has been possible to provide control systems that can reduce

maintenance, down time and improve productivity to a great extend. By installingefficient and user friendly industrial electronics systems for manufacturing

machinery or processors, one can obtain a precise, reliable and prolific means for

generating quality products.Considering the varied demand and increasing competition, one has to

provide for flexible manufacturing process. One of the latest techniques in solid

state controls that offers flexible and efficient operation to the user is

“PROGRAMMABLE CONTROLLERS”. The basic idea behind these

programmable controllers was to provide means to eliminate high cost associated

with inflexible, conventional relay controlled systems. Programmable controllersoffer a system with computer flexibility:

1. Suited to withstand the industrial environment

2. Has simplicity of operation

3. Maintenance by plant technicians and

4. Reduce machine down time and provide expandability for future.

DEFINATION OF PLC



A Programmable controller is a solid state user programmable control system

with functions to control logic, sequencing, timing, arithmetic data manipulation andcounting capabilities. It can be viewed as an industrial computer that has a central

processor unit, memory, input output interface and a programming device. The central

processing unit provides the intelligence of the controller. It accepts data, statusinformation from various sensing devices like limit switches, proximity switches,

executes the user control program store in the memory and gives appropriate output

commands to devices like solenoid valves, switches etc.Input output interface is the communication link between field devices and the

controllers; field devices are wired to the I/O interfaces. Through these interfaces the

processor can sense and measure physical quantities regarding a machine or process, such

as, proximity, position, motion, level, temperature, pressure, etc. Based on status sensed,the CPU issues command to output devices such as valves, motors, alarms, etc.

Programmer unit provides the man machine interface. It is used to enter the application

program, which often uses a simple user-friendly logic.

BENEFITS OF PROGRAMMABLE CONTROLLERS

1. Programmable controllers are made of solid state components and hence

provide high reliability.

2. They are flexible and changes in sequence of operation can easily be

incorporated due to programmability. They may be modular in nature and

thus expandability and easy installation is possible.

3. Use of PLC results in appreciable savings in Hardware and wiring cost.

4. They are compact and occupy less space.

5. Eliminate hardware items like Timers, counters and Auxiliary relays. The presence for timers and counters has easy accessibility.

6. PLC can control a variety of devices and eliminates the need for

customized controls.

7. It has total protections against obsolescence and has wide scope for upgradation.

Chapter 2



PLC ARCHITECTURE

PLCs contain three basic sections:

1. Central processing unit (CPU).

2. Memory: EPROM, RAM, and so on.

3. Input/output section for communication with peripherals (ADC, DAC).

A PLC is basically a black box with a number of inputs from, and a number of

outputs to, the outside world. It can make decisions, store data, do timing cycles, dosimple arithmetic, convert codes, and so on. The basic difference between this black

box and a hardware logic system using IC chips or a relay controlled system, is that

specific coded messages are stored in areas called program memory, which are

PROM or ROM and RAM chips. It is, however, much easier to change a programwhen a different process is required than to rewire the control system. For example,

it may take electricians a couple of weeks to require a pipe mill, whereas a programmer will spend only a fraction of this time to reprogram a PLC since no wires

will have to be changed. In addition, various recipes can be stored in memory and

accessed when required, making the program extremely flexible.The system operates through interaction with the processor and program memory.

When the power to the system is turned on, the processor reads the first instruction

stored in memory and acts on this instruction. When completed, it goes back to the

memory for the next instruction, and so on until task is complete. This operation iscalled the fetch-execute cycle. The processor communicates with the outside world

via input and output modules.

THE PARTS OF A PROGRAMMABLE CONTROLLER

Programmable logic controllers (PLC) can be considered to have three parts:

1. Input/output Section

The I/O section contains input modules and output modules. Functionally, the input

modules are equivalent to the signal converters (i.e. Analog to Digital or high power to

low power). All modern PLC input modules use optical devices to accomplishelectrically isolated coupling between the input circuit and the processor electronics.

Each input device is wired to a particular input terminal on the I/O section. Thus if the

switch is closed, 5v dc appears on input terminal, converts this dc voltage to a digital 1and sends it to the processor via programmable peripheral interface (PPI). Conversely, if

the switch is open, no dc voltage appears on input terminal. Input section will respond to

this condition by sending a digital 0 to the processor. The other input terminals behave

identically.



The Processor

The processor of a PLC holds and executes the user program. In order to carry out

this job, the processor must store the most up-to-date input and output conditions.

(a) Input image table:

The input conditions are stored in the input image table, which is a portion of the

processor’s memory. That is, every single input module in the I/O section has assignedto it a particular location within the input image table. That particular location is

dedicated solely to the task of keeping track of the latest condition of its input terminal.

As mentioned in earlier section, if the input terminal has 5v dc power fed to it by its input

device, the location within the input image table contains a binary 1(HI); if the inputterminal has no 5v dc power fed to it, the location contains a binary 0(LO).

The processor needs to know the latest input conditions because the user programinstructions are contingent upon those conditions. In other words, an individualinstruction may have one outcome if a particular input is HI and a different outcome if

that input is LO.

Output image table:

The output conditions are stored in the output image table, which is another portion of the processor’s memory. The output image table bears the same relation to the output

interface of the I/O section that while terminals are analog inputs. You can directly

connect any analog input to the processor via these terminals. Analog signal from these

terminals is first converted to digital value via programmable peripheral interface (PPI).The I/O section’s output modules are functionally the same as the output amplifiers.

They receive a low power digital signal from the processor and convert it into a high

power signal capable of driving an industrial load. A modern PLC output module isoptically isolated, and uses a triac, power transistor or relay as the series connected load

controlling device. Terminal 1 to 8 are these type of O/P terminals whereas terminal D/A

is Analog output terminal from processor. Each output device is wired to a particular output terminal on the I/O interface. Thus, for example, if output module 1 receives a

digital 1 by applying 5v dc to output terminal 1, thereby illuminating LED is

extinguished.Besides 5v dc (TTL devices), I/O module are also for interfacing to other industrial

levels, including 12v dc.

The input image table bears to the input modules. That is, every single output module

has assigned to it a particular memory location is dedicated solely to the task of keepingtrack of the latest condition of its output module.

Of course, the output situation differs from the input situation with regard to the direction

of information flow is from the output image table to the output modules, while in theinput situation the information flow is from the input modules to the input image table.



The locations within the input and output image tables are identified by addresses, which

refers to unique address of each terminal.

Central processing unit:

The subsection of the processor that actually performs the program execution will be called the central processing unit (CPU) with reference to input and output image table

CPU executes the user program and continuously updates the output image table.

The output image table has a dual nature; its first function is to receive immediateinformation from the CPU and pass if on to the output modules of the I/O section; but

secondly, it also must be capable of passing output information “backward” to the CPU,

when the user program instruction that the CPU is working on calls for an item of outputinformation. The input image table does not have its dual nature. Its single mission is to

acquire information from the input modules and pass that information “forward” to the

CPU when the instruction that the CPU is working on calls for an item of input

information.

User program memory:

A particular portion of the processor’s memory is used for storing the user program

instructions. We will use the name user program memory to refer to this processor subsection.

Before a PLC can begin controlling an industrial system, a human user must enter the

coded instructions that make up the user program. This procedure called programmingthe PLC.

As the user enters instructions, they are automatically stored at sequential locations

within the user program memory. This sequential placement of program instructions is

self-regulated by the PLC, with no discretion needed by the human user.The total number of instructions in the user program can range from a half dozen or

so, for controlling a simple machine, to several thousand, for controlling a complex

machine or process.After the programming procedure is complete, the human user manually switches the

PLC out to PROGRAM mode into RUN mode, which causes the CPU to start executing

the program from beginning to end repeatedly.

The complete scan cycle:

As long as the PLC is left in the RUN mode, the processor executes the user program

over and over again. Figure depicts the entire repetitive series of events. Beginning atthe top of the circle representing the scan cycle, the first operation is the input scan.During the input scan, the current status of every input module is stored in the input

image table, bringing it up to date.

Following the input scan, the processor enters its user program execution. Sometimescalled “program scan”. The program executes with reference to input and output image

tables and updates output image table.



Throughout the user program execution, the processor continuously keeps its output

image table up to date, as stated earlier. However, the output modules themselves are not

kept continuously up to date. Instead, the entire output image table is transferred to theoutput module during the output scan following the program execution.

(d) Data Memory:

A PLC is a computer, after all. Therefore, it can perform arithmetic, numeric

comparisons, counting, etc. Naturally the numbers and data can change from one scancycle to the next. Therefore the PLC must have a section of its memory set aside for

keeping track of variable data, or numbers, that are involved with the user program. This

section of memory we will call data memory.

When the CPU is executing an instruction for which a certain data value must beknown, that data value is brought in from data memory. When the CPU executes an

instruction that provides a numerical result, that result is put out into data memory. Thus,

CPU can read from or write to the data memory. Understand that this relationship is

different from the relationship between the CPU and the user program memory. Whenthe user program is executing, the CPU can only reads from the user program memory,

never write to it.

(e) Operating System of PLC:

The function of the operating system is to present the user with the equivalent of anextended machine or virtual machine that is easier to program than the underlying

hardware.

Due to this operating system, PLC is very easy to program. It can be programmedusing electrical schemes with familiar relay symbols so that a plant electrician can easily

access the PLC. Even though he does not know the assembly language or even if he may

not have any familiarity with computers and electronics, he will be able to program thePLC.

The function of PLC Operating system is:

1. Loads the user program from programming device to program memory.

2. To read status of input devices.

3. To execute user program.

4. To form and update input image table.

5. As per the status of output image table controls the output devices.

6. To provide user-friendly functions.

This O.S. makes supervision over entire system, so O.S. programs are said to

running in supervisory mode.



When the user completely enters his program in user memory, he transfers control

from PROGRAM mode to RUN mode. In RUN mode the control of the whole system is

transferred to operating system. Now operating system takes care of the whole systemsuch that the whole system becomes automatic and appears as magic to users.

Chapter 3



SYSTEM OVERVIEW

This low cost PLC system was designed to satisfy hunger of Automation of Indian Industry and also helps beginners as well as development engineers to get into

Automation field.

System consist of following main sections:

(1) The CPU:

The CPU uses the 89c51 microcontroller, which operates at 11.0592Mhz. It has

8k RAM, which can be used as data memory, 8k RAM that can be used as programmemory as well as data memory, 8k EEPROM that can be used as program memory.

(2) Input/output Section:

This part of system is on separate board connected to processor via cable. It allowsthe processor to communicate with the outside world. It is also called Data Acquisition

System (DAS).

This part of system provides 4 digital inputs consisting of 2 dc and 2 ac, 4 digital

outputs consisting of 2 dc and 2 ac each. It also provides 8 analog inputs with followingranges:

1. –5v to +5v (one channel).

2. 0v to 10v (one channel).

3. 4mA to 20mA (one channel).

4. 0v to 5v (five channel).

(3) Timer/Counter :

The system has 2 timers or 2 counters or 1 timer and 1 counter. The timer provides

maximum of 255sec delay and the counter provides maximum of 255 counts.

(4) Serial Communication:



The system uses RS-232 serial data standard. Chip ICL232 is used as communication

interface between RS-232 standard and TTL logic.

(5) Programming Device:

This system uses personal computer (PC) as programming device. The user can write

program in user friendly language. The programming devices (PC) converts this user

friendly language program into machine understandable language and transmit it to thePLC board via serial communication.

(6) Power Supply Unit:

This system provides +12v and -12v with maximum 2amps and +5v with maximum

of 1amps.



Chapter 4

HARDWARE CONFIGURATION

1. Microcontroller:

Here we are using 89c51 microcontroller, which has one full duplex serial data

receiver/transmitter, which is used for serial communication having interface with

ICL232 chip.

It has also two 16 bits timer/counter namely T0 and T1 which are used for timer andcounter applications. Timer T1 is used to set baud rate for serial communication in

program mode.

2. Memory:

The system consist of four types of memory:

a. 4k of EEPROM which is internal to 89c51 microcontroller. This memory is

used to store the operating system. It has address from 0000h to 0fffh. It canonly be accessed when the external access pin of controller is connected to

+5v. In our system this pin is permanently connected with +5v so external

program memory is accessed only when the address is beyond 0fffh.

b. 8k of RAM which is used as data memory. The CPU can read data from and

write data into this memory. This memory has address from 0000h to 1fffh.

c. 8k of RAM which is used as data memory as well as program memory. The

CPU can write program codes in and read program codes from this memory.

This memory has address from 2000h to 3fffh.

d. 8k of EEPROM, which is used as, program memory. The subroutines, which

are helpful in executing the main program, are stored here. This memory has

location from 4000h to 5fffh.

3. Programmable Peripheral Interface(PPI):

Here two 8255 are used as PPI. One is used to control the ADC and DAC, while

other is used for Input/output interface. The addresses for the 8255 used to control ADC

and DAC are:

Port A: 6000h



Port B: 6001h

Port C: 6002h

Control Word: 6003h

The addresses for the 8255 used for Input/output interfaces are:

Port A: 8000h

Port B: 8001h

Port C: 8002h

Control Word: 8003h

4. Analog to Digital Converter(ADC):

Here ADC0809 is used as an 8 bit ADC. 8255 whose addresses are 6xxxh is used togive control signals to this ADC. The port pins of 8255 are connected with the control

pins of ADC as shown below:

8255 Pins ADC Pins

PB0 ADD0 (A)

PB1 ADD1 (B)

PB2 ADD2 (C)

PB3 STC (Start of Conversion)

PB4 OE (Output Enable)

PC7 EOC (End of Conversion)

Note: Here PB4 is connected to OE pin of ADC through NOT Gate. So we have to give

negative pulse by pin PB4 to pin OE to give Output Enable.This ADC is used to convert the real world analog data into digital form.

5. Digital to Analog Converter (DAC):



Here the only control signal is “Start of Conversion”, which is connected with PC0 of

8255 having address 6xxxh. For converting the digital data to analog form first make

PC0 low and then put digital data on port0 of 89c51. Now make PC0 high.This particular part of the system is idle in our application, but it is kept for future

expansion.

6. Serial Communication:

Here in-built transmitter/receiver of 89c51 is used for serial communication in

conjunction with chip ICL232. Here the transmitter/receiver is of asynchronous type

(UART). So the data is communicated byte by byte. The UART is working in serial

communication mode 1. So the timer T1 is used to set the baud rate. The baud rate is setto 2400.

7. Switches and Indicators:

Switches:

a. Power ON/OFF switch.

b. Reset Switch.

c. Program/Run mode Switch.

Indicators:

a. Power ON/OFF LED(red)

b. Reset LED(red)

c. Program mode LED(orange)

d. Run mode LED(green)

e. Fault LED(red, green, orange, yellow)

8. Digital Input:



DC Input:

We have two digital DC inputs with following specifications:

1. 0v to 5v – LOW

2. 20v to 25v- HIGH

3. Optocoupler Isolation.

AC Input:

We have two digital AC inputs with following specifications:

1. 0v to 10v-LOW

2. 20v to 25v-HIGH

3. 47hz to 63hz frequency.


9. Digital Outputs:

DC outputs:

We here have two DC outputs with following specification:

1. 0v t0 3v-0v

2. 3.5v to 5v-24v

3. 0.5amp output current.


AC outputs:



We have two relays as AC outputs with following specification:

1. 0v to 3v- relay OFF

2. 3.5v to 5v- relay ON


4. Relay with12v, 4ohm.



Chapter 5

ADDRESSES

AC Output:

Output Address

Relay 1(Normally Open) 00

Relay 2(Normally Open) 01

Relay 1(Normally Close) 20

Relay 2(Normally Close) 21

DC Output:

Output Address

Out 1(Normally Open) 02

Out 2(Normally Open) 03

Out 1 (Normally Close) 22

Out 2 (Normally Close) 23

AC Input:

Input Address

In 1(Normally Open) 04


In 1(Normally Close) 24




DC Input:Input Address




In 2(Normally close) 27

Analog Input:

Input Address



In 3(Normally Open) 0a

In 4(Normally Open) 0b

In 5(Normally Open) 0c

In 6(Normally Open) 0d

In 7(Normally Open) 0e

In 8(Normally Open) 0f



In 3(Normally Close) 2a

In 4(Normally Close) 2b

In 5(Normally Close) 2c

In 6(Normally Close) 2d

In 7(Normally Close) 2e

In 8(Normally Close) 2f



Counter/Timer:

Counter/Timer Address

Counter 0/Timer 0 00(Normally OFF)

Counter 1/Timer 1 01(Normally OFF)

Counter 0/Timer 0 02

(Normally ON)

Counter 1/Timer 1 03

(Normally ON)

Note: The timer and counter has same address because at a time we can use only one of them i.e. either counter 0 with address 00 or timer o with address 00. Here normally OFF

means when timer/counter is running this remains low and when count of timer/counter

reaches it becomes high. Reverse is the case for normally ON.



OPERAND AREAS:

I Inputs

U Outputs

T Timer

C Counter

A AND Operation

O OR Operation

= Equals

E End of Program



STATEMENT LIST (STL) PROGRAMMING LANGUAGE:

In our system STL supports the following operations:

AND

OR

TIMER

COUNTER

AND Operation:

The AND operation scans to see if various conditions are satisfied simultaneously.

Circuit Diagram:

Output U 01 is “1” when all two inputs are “1”. The

Output is “0” if atleast one input is “0”.

I 04

I 05

U 01

Representation in Ladder Diagram: Representation in STL:

A I 04

A I 05I 04 I 05 U 01 = U 01



OR Operation:

The OR operation scans to see if one of two conditions has been satisfied.

Circuit Diagram:

Output U 01 is “1” when at-least one of the

I 04 I 05

Input is “1”. Output U 01 is “0” when all

inputs are “0” simultaneously.

U 01

Representation in STL:

O I 04

O I 05

= U 01

Representation in Ladder Diagram:


O I 04

I 04

I 05

U 01



O I 05

A

O I 06O I 07

= U 01

AND before OR Operation:

Output U 01 is “1” when at-least one AND condition has been satisfied. Output U 01 is“0” when neither of the two AND conditions has been satisfied.


A I 04A I 05

O

A I 06A I 07

= U 01

Circuit Diagram: Ladder Diagram:

I 04

I 05



Timer Operation:


A I 04

A I 05

= T 00 10

O I 05O T 00

= U 01

If both inputs I 04 and I 05 are “1” then only timer T 00 is activated. The count

10 after T 00 in third instruction specifies that the timer should continue till 10 seconds.

O T 00 specifies that the output U 01 is “1” only if I 05 is “1” or the count of timer hasreached 0. If we specify T 02 which is normally ON then the output U 01 is “1” if I 05 is

“1” or during timer is running.

This is for timer 0 if we use timer 1 then T 01 will remain “0” during the timer run and normally ON T 03 will remain “1” during timer run.

Counter Operation:


A I 04

A I 05

I 04 I 06

I 05 I 07

U 01 I 06I 07

U 01



= C 00 10

O I 06

O C 00= U 01

If both the inputs I 04 and I 05 are “1” then only counter 0 is activated. 10 in

third instruction represent the count of the counter. The output U 01 becomes “1” if input

I 06 is “1” or count of the counter becomes 0.Same applies for counter in normally ON and normally OFF mode as in case of

timer.

Chapter 7

SYNTAX FOR PROGRAM

1. Operand must be in upper case.

A I 04 right;



Ai 04 wrong;

2. Always leave only one space between operand.

A I 04right;

AI 04 wrong;

A I 04 wrong;

A I04 wrong;

A I 04 wrong;

AI04 wrong;

Clear out all the previously written instruction from the file before writing instruction for

another application.

Always specify hex number in lower case.

= T 00 0a right;

= T 00 0A wrong;

3. Specify the count of counter and delay of timer in hex.

= T 00 ff right;

= T 00 255 wrong;

4. Do not keep any line spacing between two instructions

.5. Always end your program with ‘E’.

Chapter 8

HOW TO USE PLC

Write program in STL language in file ‘PLC’ on PC using NORTON

EDITOR (Do not give any extension to the PLC file).



Switch on the PLC and confirm whether the power indicator LED ON or

not. If it is ON, switch the PLC in PROGRAM mode. Confirm that the REDLED indicating the PROGRAM mode is ON. Now PLC is ready for receiving

the control program written on PC.

Execute the program named “PLC” on PC in TC directory (i.e. TURBOC).

Wait till the message “PROGRAM IS TRANSMITTEDSUCCESSFULLY”.

Switch the PLC in RUN mode by changing the switch on RUN mode andthen press RESET switch. Confirm the GREEN LED indicating the RUN

mode is ON.

If one of the four FAULT LEDs is ON then check the reason and again

load whole of the program and repeat the above mentioned procedure.

TROUBLESHOOTING

If “POWER ON” LED (red) is OFF after switch ON the power, check the

FUSE. If blown then replace it.

If FAULT LED (red) is ON then “A” or “O” operand might have been

missing in start of instruction.

i.e. A I 04I 04

Correct it in the control program and again load the program.

If FAULT LED (green) is ON then “I” or “C” or “T” or “U” operand

might have been missing in instruction.

i.e. A I 05A 05

Correct it in the control program and again load the program.

If FAULT LED (saffron) is ON then “=” operand might be missing in

instruction.i.e. A I 05

A I 04

U 01

If FAULT LED (yellow) is ON then the TIMER/COUNTER is specified

other than ‘00’ or ‘01’.



i.e. A I 04

A I 05

= T 02 0a

Correct it and load the control program once mor

SOFTWARE ANALYSIS

The higher-level language program on PC side converts the control programwritten in STL language into specific hex codes and transmits these codes to the PLC.

The codes are stored in RAM location in PLC.

The lower-level language program, which is stored in EEPROM internal to the

controller, reads hex codes from memory location one by one. It compares the code read

from the memory location with the predefined hex code and executes the instruction with

accordance to it.

As soon as we put the PLC in RUN mod, it reads the status of all the I/P. It stores

the status in bit addressable memory location as ‘1’ or ‘0’ depends upon the status. Nowit runs the program and performs operation on the status bit directed as user program. It

stores the result in another bit addressable memory location which are corresponds to the

O/P. After this it updates all the O/P.

The Flow chart of the ASSEMBLY LANGUAGE program is given below:

Chapter 9

SCOPE FOR FUTURE EXPANSION

♦ At present in our system we have 4 digital inputs and 4 digital outputs

which are interfaced with CPU through port C of 8255 having address 8xxxh.



The port A and port B are not presently taken in use. By using these ports we can

expand digital inputs and outputs upto 8 digital inputs and outputs.

♦ Two memory slots of 8k each are not in present use. One of these slots

can be used for RAM and another one can be used for EEPROM. Using theseslots we can get more 8k of DATA memory using RAM and more 8k of

PROGRAM memory using EEPROM.

♦ Interfacing of DAC is provided on the PLC board, which can be used to

give an analog output.

♦ We can construct signal-conditioning circuit so we can directly connectthe transducers like PT100, thermocouple, LVDT etc.

♦ We can further construct PID controller module which can be switchedON or OFF by this PLC so we can control systems using continuous controller in

digital fashion.

♦ We can also design stepper motor controller, which can be interfaced with

PLC.

♦ Using chip 8279 we can provide keyboard and display facility on PLC board.

Chapter 10

APPLICATIONS OF PLC



In the present industrial world, a flexible system that can be controlled by user atsite is preferred. Systems, whose logic can be modified but still, used without disturbing

its connection to external world, is achieved by PLC. Utilizing the industrial sensors

such as limit switches, ON-OFF switches, timer contact, counter contact etc., PLCcontrols the total system. The drive to the solenoid valves, motors, indicators,

enunciators, etc are controlled by the PLCs.

The above said controlling elements (normally called as inputs of PLCs) and

controlled elements (called as outputs of PLCs) exist abundantly in any industry. Theseinputs, outputs, timers, counters, auxiliary contacts are integral parts of all industries. As

such, it is difficult to define where a PLC cannot be used.

Proper application of a PLC begins with conversion of information into convenient parameters to save money, time and effort and hence easy operation in plants and

laboratories.

The areas where PLC is used maximum are as follows:

1. The batch processes in chemical, cement, food and paper industries which

are sequential in nature, requiring time of event based decisions iscontrolled by PLCs.

2. In large process plants PLCs are being increasingly used for automaticstart up and shut down of critical equipment. A PLC ensures that

equipment cannot be started unless all the permissive conditions for safe

start have seen established. It also monitors the conditions necessary for safe running of the equipment and trips the equipment whenever any

abnormality in the system is detected.

3. The PLC can be programmed to function as an energy managementsystem for boiler control for maximum efficiency and safety.

4. In automation of blender reclaimers

5. In automation of bulk material handling system at ports.

6. In automation for a ship unloader.

7. Automation for wagon loaders.

8. For blast furnace charging controls in steel plants.

9. In automation of brick moulding press in refractories.

10. In automation for galvanizing unit.

11. For chemical plants process control automation.



12. In automation of a rock phosphate drying and grinding system.

13. Modernization of boiler and turbogenerator set.

14. Process visualization for mining application.

15. Criteria display system for power station.

16. As stored programmed automation unit for the operation of dieselgenerator sets.

17. In Dairy automation and food processing.

18. For a highly modernized pulp paper factory.

19. In automation system for the printing industry.

20. In automation of container transfer crane.

21. In automation of High-speed elevators.

22. In plastic moulding process.

23. In automation of machine tools and transfer lines.

24. In Mixing operations and automation of packaging plants.

25. In compressed air plants and gas handling plants.

26. In fuel oil processing plants and water classification plants.

27. To control the conveyor/classifying system.

Thus PLC is ideal for application where plant machine interlock requirements are

finalized at a later stage and need changes during engineering trial runs, commissioning

or normal use. It can be used extensively to replace conventional relay controls in power stations, refineries, cement, steel, fertilizer, petrochemical, chemical industries etc.

Applications can thus be extended from monitoring to supervision, control and

management.



FUTURE OF PLCs

The PLC offers a compromise between advance control techniques and present day

technology. It is extremely difficult to forecast the rate and form of progress of PLCs,

but there is strong evidence that development is both rapid and cumulative. Though aPLC is not designed to replace a computer, it is useful and cost effective for medium

sized control systems. With the capability of functioning as local controllers in

distributed control systems. PLCs will retain their application in large process plants.

A further development of PLCs leads to the development of programmable function

controller (PFC) is compatible to PCs and directly controls the desired functions.

In India every process industry is replacing relay control systems by PLCs and will go

for PFCs in near future. In the near future every flats and offices may possess PFCs to

control room temperature, as elevator controller, maintain water tank levels, as small

telephone exchange etc.

BIBLIOGRAPHY

(1) PROGRAMMABLE LOGIC CONTROLLERS, OPERATION, INTERFACINGAND PROGRAMMING.

JOB DEN OTTER.

(2) IBM PC AND CLONES

GOVINDRAJALU.



(3) MICROPROCESSORS AND INTERFACING PROGRAMMING AND

HARDWARE.

DOUGLAS HALL.

(4) THE 8051 MICROCONTROLLER ARCHITECTURE, PROGRAMMING AND

APPLICATIONS. KENNETH AYALA.

(5) MICROPROCESSOR ARCHITECTURE, PROGRAMMING ANDAPPLICATIONS.

RAMESH GAONKAR.

(6) MICROPROCESSORS AND MICROCOMPUTERS.

B. RAM.

(7) PROGRAMMING IN ANSI C.

E. BALAGURUSAMY.

(8) SIEMENS SIMATIC S5 PROGRAMMABLE CONTROLLER.

SYSTEM MANUAL.

(9) DIGITAL ELECTRONICS.

WIILIAM GOTHMAN.

(10) INTEGRATED CIRCUITS.

K R BOTKAR.

(11) DATA SHEETS FROM

NATIONAL SEMICONDUCTOR CORPORATION, INTEL, PHILLIPS,

FAIRCHILD SEMICONDUCTOR CORPORATION, MOTOROLA

CORPORATION.

(12) MAGAZINES – ELECTRONICS FOR YOU (EFY).

(13) OLD PROJECT REPORTS AND SEMINARS ON PLCS.

APPENDIX A

Automatic mixing system

Valve A Agitator



Float switch 1

Valve B

Float switch 2

Problem:

In figure when START button is pressed, solenoid valve A is energized and a

batch of liquid is entered in tank. Float switch 1 detects the upper limit of liquid of liquid

level and Float switch 2 detects the lower limit of liquid. As, tank begins to fill, Switch 2closes. When the tank is full, switch 1 shuts off the solenoid valve A and start agitator tomix the liquid. The Agitator mixes the liquid for 30 seconds and shuts off. When the

Agitator turn off, solenoid valve B is energized to drain the liquid. After the tank has

been emptied, float switch 2 opens and solenoid B shuts off.

The Addresses of I/P and O/P are given below.

DEVICE ADDRESS



NO NC

Stop Switch I 04 I 24

Start Switch I 05 I 25

Float Switch 1 I 06 I 26

Float Switch 2 I 07 I 27

Valve A U 00 U 20

Valve B U 01 U 21

Agitator Motor U 02 U 22

Control Relay U 03 U 23

The ladder diagram of this system is given below.



Program in STL language:

A I 04

A

O I 05

I 04 I 05

O 03

O 03

I 06 O 03 I 07

O 00

O 00

T 00

30

secI 06 O 03 O 01

EN

DN

DN I 06

O 02

I 07 DNO 01

O 01



O U 03

= U 03

A I 26A U 03

A

O I 27O U 00

= U 00

A I 06A U 03

A U 21

= T 00 1f

A T 02A I 06

= U 02

A I 07

AO T 00

O U 01= U 01

E

Explanation of Ladder Diagram:

In first rung the stop switch is connected in series with start switch to

activate the control relay. The stop switch is normally close type where as start switch is

normally open type. So when the start switch is pressed control relay is activated. Thestart switch is push to on type so normally on contact of control relay is used to latch.

In second rung the NC contact of float switch 1 and NO contact of control relay is

in series with valve A. When start switch is pressed and the liquid level is below floatswitch 1 the valve A is opened and it is closed when level touches the float switch 1.The

NC contact of float switch 2 is latched by the NO contact of valve A so valve A does not

opened as soon as the level falls below the float switch 1 level and remain close till the

tank is fully emptied.In third rung the normally open contact of float switch 1is connected in series

with timer so when liquid level reaches to float switch 1, the timer is started.

atul plc report

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