This chapter discusses PLC programming methods. It describes the ladder logic programming method which uses symbols like normally open contacts, normally closed contacts, and output coils to represent switches, relays, and control circuits. Ladder logic is a graphical programming language that resembles a ladder with power rails and rungs representing circuit logic. The chapter provides examples of simple ladder diagrams with two inputs and defines the basic symbols used in ladder logic programming. It also briefly mentions two other PLC programming methods: control system flowchart and statement list.

1. CHAPTER 1
INTRODUCTION
1.1 GENERAL
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 approach towards
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 control
techniques.
1.2 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 installing efficient 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 controllers offer a system with computer flexibility:
1.Suited to withstand the industrial environment
2.Has simplicity of operation
1

2. 3.Maintenance by plant technicians and
4.Reduce machine down time and provide expandability for future.
1.3 OBJECTIVES OF THE WORK
1. To study the plc.
2. To understand the lift management system using ladder diagram and various
limitations.
1.4 ORGANISATION OF THE THESIS
This thesis consists of five chapters including introduction as the first chapter.
In chapter 2 to understand the plc architecture.
In chapter 3 deals with plc programming.
Chapter 4 deals with hardware design.
Chapter 5 contain results and conclusion.
2

3. CHAPTER 2
2.1 INTRODUCTION
A Programmable controller is a solid state user programmable control system with
functions to control logic, sequencing, timing, arithmetic data manipulation and counting
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, status information 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.
2.2 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).
3

4. FIGURE 2.1 PLC ARCHITECTURE
FIGURE 2.2 PLC AS IN COMPUTER ARCHITECTURE
4

5. A PLC is basically a black box with a number of inputs from, and a number of
outputs is shown in Figure 2.2. It can make decisions, store data, do timing cycles, do simple
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 program when 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 is called the fetch-execute cycle. The processor
communicates with the outside world via input and output modules.
2.3 PROCESSOR MEMORY ORGANIZATION
The memory of a PLC is organized by types.The memory space can be divided into
two broad categories:
Program and Data Memory:
Advanced ladder logic functins allow controllers to perform calculatins, make
decisions and do other complex tasks. Timers and counters are examples of ladder logic
functions. They are more comples than basic inputs contacts and output coils and relay
heavily upon data stored in the memory of the PLC.
2.3.1 PROGRAM FILES:
5

6. FIGURE 2.3 PROGRAM FILES
The user program will account for most of the memory of a PLC system.Program files
contain the logic controlling machine operation.This logic consistes of instructions that are
programmed in a ladder logic format.
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 programming the
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.
2.3.2 DATA FILES:
FIGURE 2.4 DATA FILES
The data file protion of memory stores input and output status, processor
status, the status of various bits and numerical data. 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 scan cycle 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
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7. an instruction for which a certain data value must be known, 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. When the user program is executing, the CPU can only reads
from the user program memory, never write to it.
2.3.3 INPUT TABLE FILE OPERATION:
FIGURE 2.5 INPUT IMAGE TABLE
Processor continually reads current input status and updates input image table
file. 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 assigned to 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 input terminal 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 program instructions are contingent upon those conditions. In
other words, an individual instruction may have one outcome if a particular input is HI and a
different outcome if that input is LO.
7

8. 2.3.4 OUTPUT TABLE FILE OPERATION:
FIGURE 2.6 OUTPUT IMAGE TABLE
Processor continually activates or deactivates ouput status according to output
image table file status. 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 is optically 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 keeping track
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 the input situation the information flow is from the input
8

9. 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.
2.4 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.
2.5Central 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 immediate information 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 output information. 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.
2.6The 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 at the 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. Sometimes called “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 the output module during the output
scan following the program execution.
9

10. 2.7Operating System of PLC:
The function of the operating system is to present the user with the equivalent of an
extended 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 programmed using
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 the PLC. 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 PROGRASM 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
system such that the whole system becomes automatic and appears as magic to users.
2.8BENEFITS 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.
10

11. 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.Easy diagnostic facilities are provided as a part of the system. Diagnosis of the
external systems also becomes very simple. Thus easy service/maintenance.
8.Programming devices provide operator friendly interface with the machine. Being
an outcome of the latest art of electronics technology, Programmable controllers provide
higher level of performance with computers is possible. Useful management data can be
obtained and maintained.
9.It has total protections against obsolescence and has wide scope for upgradation.
2.9 CONCLUSION:
The basics operation of programmable logic controller and purpose of programmable
logic controller.And the benfit of plc .
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12. CHAPTER 3
PLC PROGRAMMING
3.1 INTRODUCTION
The basic need or purpose of writing a PLC program is the same for all PLCs.
However various PLC manufacturers follow their own programming method and give
different name for the method. The detailed programming method or procedures are available
in manufacturer‟s manuals. Mostly the task or what action or functions to be carried out are
first formulated as a circuit. Then functions are simply converted from the diagram into a
program in one of the method.
3.2 METHODS OF PLC
The methods used by popular siemens group a well known PLC in India fall under
three kinds
3.2.1 Logic ladder diagram method.
3.2.2 Control system flowchart method (CSF).
3.2.3 Statement list method (STL).
the basic symbols used in ladder diagram method. Normally opened Normally closed
FIGURE 3.1 NORMALLY OPEN CONTACT
FIGUER 3.2 NORMALLY CLOSED CONTACT
12

13. FIGURE 3.3 Output (or) Coil
FIGURE 3.4 INPUT AND OUTPUT COIL
3.2.1 Logic ladder diagram method:
In ladder diagram, the power source is representing by two vertical rail of ladder and
the various control circuit make up the rung. Normally open contacts of a switch or relay are
represented by two parallel vertical lines. Normally closed contacts are symbolized by
parallel vertical lines with a diagonal. Simple ladder diagrams with two inputs are drawn
below
3.2.1.1 Simple example Ladder diagram
Ladder diagrams are specialized schematics commonly used to document industrial
control logic systems. They are called "ladder" diagrams because they resemble a ladder, with
two vertical rails (supply power) and as many "rungs" (horizontal lines) as there are control
circuits to represent. If we wanted to draw a simple ladder diagram showing a lamp that is
controlled by a hand switch, it would look like this:
13

14. FIGURE 3.5 EXAMPLE FOR LADDER DIAGRAM
The "L1" and "L2" designations refer to the two poles of a 120 VAC supply, unless
otherwise noted. L1 is the "hot" conductor, and L2 is the grounded ("neutral") conductor.
These designations have nothing to do with inductors, just to make things confusing. The
actual transformer or generator supplying power to this circuit is omitted for simplicity
3.2.2 Control system flowchart method (CSF):
Control system flowchart method (CSF) is a graphical representation method. In this
the control task is marked using symbols defined by DIN40700 AND 40719 standard
numbers. The inputs are placed in the left side of the symbol and output is placed in the right
of symbol. For the control task we draw the control system flow chart and its equivalent
ladder diagram. Flow chart ladder diagram I:0/1AI01 O:4/1&AI02 = I:0/2O41 Here A, =, O
etc.., are the control statement. A represent AND operation, = represent result or assign
operation. The remaining parts are the operand which contains the identifier and parameters
or address.
3.2.3Statement list method (STL):
It uses mnemonic to formulate or represent the control task. Finally the program is
always stored in the statement list (MC5 machine language) in program memory of computer.
That is, the programmer automatically converts the program into STL from the Control
system flowchart method (CSF) or logic ladder before transferring it to computer. The task is
subdivided into individual control statements for execution by the PLC.A control statement is
the smallest indivisible unit of program. It acts as an instruction for the processor and
corresponds to the STL format.
3.3CONCLUSION:
This chapter consists of Logic diagram ladder method, control system flow chart
method(CSF) and statement list methods were used
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15. CHAPTER 4
HARDWARE DESIGN
4.1 INTRODUCTION:
The objective of the project is the design and implementation of a three-level elevator
system controlled by a Programmable Logic Controller (PLC). The design was limited to
three levels due to the limited number of inputs provided by the AB PLC available. Some
suggestions are given later as to how to extend the elevator system to more than three levels.
Moreover, the design was not based on a first-come first-served basis, since this approach
was not found to be practical. As a practical compromise between energy consumption and
speed of response, we decided to combine all requests going in one direction (up or down),
and then process them in sequential order. This was achieved in the following manner: if the
elevator is going up, all „up‟ requests are given higher priority than the „down‟ requests until
the elevator reaches the last destination upwards. Then the elevator goes down but now gives
priority to all „down‟ requests over the „up‟ ones. More details on this will given in the
section „Software design‟.
4.2 Hardware design:
15

16. The objective of the hardware design is to develop the interface circuit between the
PLC and the elevator system and the elevator control panel, with both external and internal
requests. These requests are produced by push buttons that send continuous signals to the
PLC when activated. Each push button is connected to an LED to identify the request placed.
In addition, the four floors are represented by three LEDs, one for each level. Furthermore, an
alarm switch is installed to produce a flashing signal whenever activated. This facility was
introduced to simulate the desire for a sudden stoppage of the elevator either for reasons of
safety or for requests for a repair job to be carried out on the elevator. In order to obtain the
desired setup, we needed to find a way to capture the pulse generated by a depressed push
button. We also needed to make sure that the PLC is recognizing these signals in order for it
to correctly perform the required action. As explained below, both issues were resolved by
using set/reset flip flops and relays respectively. The block diagram of the system‟s layout is
shown in Fig. 1, where both the interface between the PLC and the elevator system with the
control panel are drawn.
4.3Description of the interface circuit:
The hardware components used in the project are listed below: Ab 1400, SR flip flops and
buffers, respectively. Voltage supply. Push buttons, LEDs, resistors, relays, a switch, and
connecting wires. Since the number of required inputs and outputs, i.e. 12 and 8 respectively,
matches the maximum input/output capability of the PLC used, there is no need for any
multiplexing or demultiplexing operations. Thus all inputs and outputs used can be directly
controlled by the PLC. the push buttons were connected to the SR flip flops, since the PLC
needs continuous signals to process, and so do the lights that indicate the requests placed. The
flip flop holds the signal until the reset is activated. The reset of the flip flop is the level
position for levels L1 and L4. So when the elevator reaches one of these two levels and a
request is placed the output will reset the requested signal. However levels L2 and L3 are
reset by software. The reason for that is because L2 and L3 are intermediate levels. So when
the elevator is travelling upwards or downwards, it has to either flash at the level it passes to
show the current elevator position or service this level if its request has the appropriate
direction by setting its request. In this case, it will also reset all requests associated with the
serviced levels.
16

17. 17

18. 18

19. FIG 3.2 PLC based Lift management system
Ladder Diagram
19

20. Description of the control panel: The 12 inputs and 8 outputs used in this project are
listed and defined in Table 1. As shown in Fig. 3, the elevator system consists of three
sections: internal requests, external requests, and the elevator position. The internal requests
are represented by the push buttons inside the elevator which consists of three push buttons
(1–4) and a door open (DO) push button. A door close push button could not have been
included in the design because of the limited number of available inputs. The external
requests are represented by the six push buttons located outside the elevator and distributed
according to their corresponding floors. It consists of six push buttons distributed according
to the position of the level. The elevator position is displayed by the three LEDs, one for each
level, which are directly controlled by the PLC according to the location of the elevator.
4.4 APPLICATIONS OF PLC:
In the present industrial world, a flexible system that can be controlled by user at site
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., PLC controls 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. These
inputs, 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:
20

21. 1. The batch processes in chemical, cement, food and paper industries which are
sequential in nature, requiring time of event based decisions is controlled by
PLCs.
2. In large process plants PLCs are being increasingly used for automatic start 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 management system 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.
21

22. 15. Criteria display system for power station.
16. As stored programmed automation unit for the operation of diesel generator 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.
22

23. 4.5 CONCLUSION:
23

24. CHAPTER 5
RESULT AND CONCLUSION
5.1 RESULTS
Based on the user preferred floor request the lift car has been successfully
operated by using the programmable logic controller the program is very reluctant the
greater response time has been achieved from the controller.
5.2 CONCLUSION
Basically every lift car has been controlled by the microcontroller if that any
problem occurs it is difficult to find the problem, so we are using the plc controller in this
process we can easily find out the problem through Programmable Logic Controller.
Both in input and output the response time is greater than compared with other
digital controller since the durability, reliability and sustainability is higher.
24

25. REFERENCE:
(1) PROGRAMMABLE LOGIC CONTROLLERS, OPERATION, INTERFACING
AND 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 AND
APPLICATIONS. - 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.
25