PLC BASED AUTOMATED MONITORING AND CONTROL OF WATER SUPPLY IN A TANK
CHAPTER 1
INTRODUCTION
1.1 GENERAL DESCRIPTION:
Control engineering has evolved over time. In the past, humans were the main method for
controlling a system. More recently electricity has been used for control and early
electrical control was based on relays. These relays allow power to be switched on and
off without a mechanical switch. It is common to use relays to make simple logical
control decisions. The development of low cost computer has brought the most recent
revolution, the Programmable Logic Controller (PLC). The advent of the PLC began in
the 1970s, and has become the most common choice for manufacturing controls.
PLCs have been gaining popularity on the factory floor and will probably remain
predominant for some time to come. Most of this is because of the advantages they offer.
• Cost effective for controlling complex systems.
• Flexible and can be reapplied to control other systems quickly and easily.
• Computational abilities allow more sophisticated control.
• Trouble shooting aids make programming easier and reduce downtime.
• Reliable components make these likely to operate for years before failure.
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1.2 PROGRAMMABLE LOGIC CONTROLLERS:
A programmable logic controller (PLC) or programmable controller is a digital
computer used for automation of electromechanical processes, such as control of
machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in
many industries and machines. Unlike general-purpose computers, the PLC is designed
for multiple inputs and output arrangements, extended temperature ranges, immunity to
electrical noise, and resistance to vibration and impact. Programs to control machine
operation are typically stored in battery-backed-up or non-volatile memory. A PLC is an
example of a hard real time system since output results must be produced in response to
input conditions within a limited time, otherwise unintended operation will result.
Figure 1.1 Allen Bradley PLC Modules
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1.3 HISTORY:
The PLC was invented in response to the needs of the American automotive
manufacturing industry. Programmable logic controllers were initially adopted by the
automotive industry where software revision replaced the re-wiring of hard-wired control
panels when production models changed.
Before the PLC, control, sequencing, and safety interlock logic for manufacturing
automobiles was accomplished using hundreds or thousands of relays, cam timers,
and drum sequencers and dedicated closed-loop controllers. The process for updating
such facilities for the yearly model change-over was very time consuming and expensive,
as electricians needed to individually rewire each and every relay.
Digital computers, being general-purpose programmable devices, were soon applied to
control of industrial processes. Early computers required specialist programmers, and
stringent operating environmental control for temperature, cleanliness, and power quality.
Using a general-purpose computer for process control required protecting the computer
from the plant floor conditions. An industrial control computer would have several
attributes: it would tolerate the shop-floor environment, it would support discrete (bitform) input and output in an easily extensible manner, it would not require years of
training to use, and it would permit its operation to be monitored. The response time of
any computer system must be fast enough to be useful for control; the required speed
varying according to the nature of the process. In 1968 GM Hydramatic (the automatic
transmission division of General Motors) issued a request for proposal for an electronic
replacement for hard-wired relay systems. The winning proposal came from Bedford
Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was
Bedford Associates' eighty-fourth project, was the result. Bedford Associates started a
new company dedicated to developing, manufacturing, selling, and servicing this new
product: Modicon, which stood for Modular Digital Controller. One of the people who
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worked on that project was Dick Morley, who is considered to be the "father" of the
PLC.The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by
German Company AEG and then by French Schneider Electric, the current owner.
One of the very first 084 models built is now on display at Modicon's headquarters
in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit
was retired after nearly twenty years of uninterrupted service. Modicon used the 84
moniker at the end of its product range until the 984 made its appearance. The automotive
industry is still one of the largest users of PLCs.
1.4 DEVELOPMENT:
Early PLCs were designed to replace relay logic systems. These PLCs were programmed
in "ladder logic", which strongly resembles a schematic diagram of relay logic. This
program notation was chosen to reduce training demands for the existing technicians.
Other early PLCs used a form of instruction list programming, based on a stack-based
logic solver.
Modern PLCs can be programmed in a variety of ways, from ladder logic to more
traditional programming languages such as BASIC and C. Another method is State
Logic, a very high-level programming language designed to program PLCs based on state
transition diagrams.
Many early PLCs did not have accompanying programming terminals that were capable
of graphical representation of the logic, and so the logic was instead represented as a
series of logic expressions in some version of Boolean format, similar to Boolean
algebra. As programming terminals evolved, it became more common for ladder logic to
be used, for the aforementioned reasons and because it was a familiar format used for
electromechanical control panels. Newer formats such as State Logic and Function Block
(which is similar to the way logic is depicted when using digital integrated logic circuits)
exist, but they are still not as popular as ladder logic. A primary reason for this is that
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PLCs solve the logic in a predictable and repeating sequence, and ladder logic allows the
programmer (the person writing the logic) to see any issues with the timing of the logic
sequence more easily than would be possible in other formats.
1.5 FUNCTIONALITY:
The functionality of the PLC has evolved over the years to include sequential relay
control, motion control, process control, distributed control systems and networking. The
data handling, storage, processing power and communication capabilities of some
modern
PLCs
are
approximately
equivalent
to desktop
computers.
PLC-like
programming combined with remote I/O hardware, allow a general-purpose desktop
computer to overlap some PLCs in certain applications. Regarding the practicality of
these desktop computer based logic controllers, it is important to note that they have not
been generally accepted in heavy industry because the desktop computers run on less
stable operating systems than do PLCs, and because the desktop computer hardware is
typically not designed to the same levels of tolerance to temperature, humidity, vibration,
and longevity as the processors used in PLCs. In addition to the hardware limitations of
desktop based logic, operating systems such as Windows do not lend themselves to
deterministic logic execution, with the result that the logic may not always respond to
changes in logic state or input status with the extreme consistency in timing as is
expected from PLCs. Still, such desktop logic applications find use in less critical
situations, such as laboratory automation and use in small facilities where the application
is less demanding and critical, because they are generally much less expensive than
PLCs.
In more recent years, small products called PLRs (programmable logic relays), and also
by similar names, have become more common and accepted. These are very much like
PLCs, and are used in light industry where only a few points of I/O (i.e. a few signals
coming in from the real world and a few going out) are involved, and low cost is desired.
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These small devices are typically made in a common physical size and shape by several
manufacturers, and branded by the makers of larger PLCs to fill out their low end product
range. Popular names include PICO Controller, NANO PLC, and other names implying
very small controllers. Most of these have between 8 and 12 digital inputs, 4 and 8 digital
outputs, and up to 2 analog inputs. Size is usually about 4" wide, 3" high, and 3" deep.
Most such devices include a tiny postage stamp sized LCD screen for viewing simplified
ladder logic (only a very small portion of the program being visible at a given time) and
status of I/O points, and typically these screens are accompanied by a 4-way rocker pushbutton plus four more separate push-buttons, similar to the key buttons on a VCR remote
control, and used to navigate and edit the logic. Most have a small plug for connecting
via RS-232 or RS-485 to a personal computer so that programmers can use simple
Windows applications for programming instead of being forced to use the tiny LCD and
push-button set for this purpose. Unlike regular PLCs that are usually modular and
greatly expandable, the PLRs are usually not modular or expandable, but their price can
be two orders of magnitude less than a PLC and they still offer robust design and
deterministic execution of the logic.
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1.6 PLC COMPARED WITH OTHER CONTROL SYSTEMS
Figure 1.2 Allen-Bradley PLC installed in a control panel
PLCs are well adapted to a range of automation tasks. These are typically industrial
processes in manufacturing where the cost of developing and maintaining the automation
system is high relative to the total cost of the automation, and where changes to the
system would be expected during its operational life. PLCs contain input and output
devices compatible with industrial pilot devices and controls; little electrical design is
required, and the design problem centers on expressing the desired sequence of
operations. PLC applications are typically highly customized systems, so the cost of a
packaged PLC is low compared to the cost of a specific custom-built controller design.
On the other hand, in the case of mass-produced goods, customized control systems are
economical. This is due to the lower cost of the components, which can be optimally
chosen instead of a "generic" solution, and where the non-recurring engineering charges
are spread over thousands or millions of units.
For high volume or very simple fixed automation tasks, different techniques are used. For
example, a consumer dishwasher would be controlled by an electromechanical cam
timer costing only a few dollars in production quantities.
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A microcontroller-based design would be appropriate where hundreds or thousands of
units will be produced and so the development cost (design of power supplies,
input/output hardware and necessary testing and certification) can be spread over many
sales, and where the end-user would not need to alter the control. Automotive
applications are an example; millions of units are built each year, and very few end-users
alter the programming of these controllers. However, some specialty vehicles such as
transit buses economically use PLCs instead of custom-designed controls, because the
volumes are low and the development cost would be uneconomical.
Very complex process control, such as used in the chemical industry, may require
algorithms and performance beyond the capability of even high-performance PLCs. Very
high-speed or precision controls may also require customized solutions; for example,
aircraft flight
controls. Single-board computers using semi-customized or fully
proprietary hardware may be chosen for very demanding control applications where the
high development and maintenance cost can be supported. "Soft PLCs" running on
desktop-type computers can interface with industrial I/O hardware while executing
programs within a version of commercial operating systems adapted for process control
needs.
Programmable controllers are widely used in motion control, positioning control and
torque control. Some manufacturers produce motion control units to be integrated with
PLC so that G-code (involving a CNC machine) can be used to instruct machine
movements.
PLCs may include logic for single-variable feedback analog control loop, a "proportional,
integral, derivative" or "PID controller". A PID loop could be used to control the
temperature of a manufacturing process, for example. Historically PLCs were usually
configured with only a few analog control loops; where processes required hundreds or
thousands of loops, a distributed (DCS) would instead be used. As PLCs have become
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more powerful, the boundary between DCS and PLC applications has become less
distinct.
PLCs have similar functionality as Remote Terminal Units. An RTU, however, usually
does not support control algorithms or control loops. As hardware rapidly becomes more
powerful and cheaper, RTUs, PLCs and DCSs are increasingly beginning to overlap in
responsibilities, and many vendors sell RTUs with PLC-like features and vice versa. The
industry has standardized on the IEC 61131-3 functional block language for creating
programs to run on RTUs and PLCs, although nearly all vendors also offer proprietary
alternatives and associated development environments.
In recent years "Safety" PLCs have started to become popular, either as standalone
models (Pilz PNOZ Multi, Sick etc.) or as functionality and safety-rated hardware added
to existing controller architectures (Allen Bradley Guardlogix, Siemens F-series etc.).
These differ from conventional PLC types as being suitable for use in safety-critical
applications for which PLCs have traditionally been supplemented with hard-wired safety
relays. For example, a Safety PLC might be used to control access to a robot cell
with trapped-key access, or perhaps to manage the shutdown response to an emergency
stop on a conveyor production line. Such PLCs typically have a restricted regular
instruction set augmented with safety-specific instructions designed to interface with
emergency stops, light screens and so forth. The flexibility that such systems offer has
resulted in rapid growth of demand for these controllers.
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1.7 BENEFITS OF PROGRAMMABLE CONTROLLERS
Programmable controllers are made of solid state components and hence provide high
reliability.
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. Use of PLC results in appreciable savings in Hardware and
wiring cost. They are compact and occupy less space.
1) Eliminate hardware items like Timers, counters and Auxiliary relays.
The
presence for timers and counters has easy accessibility.
2) PLC can control a variety of devices and eliminates the need for customized
controls.
3) Easy diagnostic facilities are provided as a part of the system. Diagnosis of the
external systems also becomes very simple. Thus easy service/maintenance.
4) 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.
5) It has total protections against obsolescence and has wide scope for up gradation.
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1.8 SCADA:
SCADA is widely used in industry for Supervisory Control and Data Acquisition of
industrial processes; SCADA systems are now also penetrating the experimental physics
laboratories for the controls of ancillary systems such as cooling, ventilation, power
distribution, etc. More recently they were also applied for the controls of smaller size particle
detectors such as the L3 moon detector and the NA48 experiment, to name just two examples
at CERN.
SCADA systems have made substantial progress over the recent years in terms of
functionality, scalability, performance and openness such that they are an alternative to in
house development even for very demanding and complex control systems as those of
physics experiments.
Figure 1.3 Scada Network
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1.9 PROBLEM STATEMENT OF THE PROJECT:
In this project, an attempt has been made to fully automate the system of water supply
in a tank with an up gradation of providing remote access to the entire setup using the
software INTOUCH, Wonderware for Supervisory Control And Data Acquisition
(SCADA).
The system has been programmed for the operation of supplying water or any other
fluid from a source tank to the sink tank and for detecting the levels of the rising
liquid at different intervals.
Several safety measures and considerations have been taken to prevent the overfilling
of water.
Provisions have also been made to detect any fault in the supply of water to the tank
during the running process which is well adapted from the industrial scenario.
The continuous monitoring and control of the levels of liquid from a remote location
makes this project well applicable in the modern industries where the actual plant of
operation is quite far from the control room and the entire processing and
troubleshooting, if any is carried out from the control room.
The Allen Bradley (Micrologix 1000) Programmable Logic Controller is used here
for the operation.
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1.10 ORGANIZATION OF THE PROJECT
The remaining report is organized as follows.
Chapter 2 deals with brief over view of the components used in designing of the
hardware. Architecture of the programmable logic controllers and SCADA system is
discussed in detail.
Chapter 3 deals with the proposed path of solution of the problem statement along with
the block diagram and its description.
Chapter 4 concentrates the various hardware and software requirements of the project.
Chapter 5 presents the wiring or the complete circuit diagram along with the various
codes written onto the PLC for the operation.
Chapter 6, 7, 8 and 9 gives result after complete verification, advantages, applications
and limitations along with the concluding remarks and the future scope of the project
respectively.
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CHAPTER 2
PLC ARCHITECTURE
A programmable logic controller (PLC) is a special form of microprocessor-based
controller that uses programmable memory to store instructions and to implement
functions such as logic, sequencing, timing, counting, and arithmetic in order to control
machines and processes. It is designed to be operated by engineers with perhaps a limited
knowledge of computers and computing languages. They are not designed so that only
computer programmers can set up or change the programs. Thus, the designers of the
PLC have preprogrammed it so that the control program can be entered using a simple,
rather intuitive form of language. The term logic is used because programming is
primarily concerned with implementing logic and switching operations; for example, if A
or B occurs, switch on C; if A and B occurs, switch on D. Input devices (that is, sensors
such as switches) and output devices (motors, valves, etc.) in the system being controlled
are connected to the PLC. The operator then enters a sequence of instructions, a program,
into the memory of the PLC. The controller then monitors the inputs and outputs
according to this program and carries out the control rules for which it has been
programmed. PLCs have the great advantage that the same basic controller can be used
with a wide range of control systems. To modify a control system and the rules that are to
be used, all that is necessary is for an operator to key in a different set of instructions.
There is no need to rewire. The result is a flexible, cost-effective system that can be used
with control systems, which vary quite widely in their nature and complexity. PLCs are
similar to computers, but whereas computers are optimized for calculation and display
tasks, PLCs are optimized for control tasks and the industrial environment. Thus PLCs:
• Are rugged and designed to withstand vibrations, temperature, humidity, and noise.
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• Have interfacing for inputs and outputs already inside the controller.
• Are easily programmed and have an easily understood programming language that is
primarily concerned with logic and switching operations.
The first PLC was developed in 1969. PLCs are now widely used and extend from small,
self-contained units for use with perhaps 20 digital inputs/outputs to modular systems that
can be used for large numbers of inputs/outputs, handle digital or analog inputs/outputs,
and carry out proportional-integral-derivative control modes.
Figure 2.1 A Programmable Logic Controller
2.1 Hardware
Typically a PLC system has the basic functional components of processor unit, memory,
power supply unit, input/output interface section, communications interface, and the
programming device.
The processor unit or central processing unit (CPU) is the unit containing the
microprocessor. This unit interprets the input signals and carries out the control actions
according to the program stored in its memory, communicating the decisions as action
signals to the outputs.
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• The power supply unit is needed to convert the mains AC voltage to the low DC voltage
(5 V) necessary for the processor and the circuits in the input and output interface
modules.
• The programming device is used to enter the required program into the memory of the
processor. The program is developed in the device and then transferred to the memory
unit of the PLC.
• The memory unit is where the program containing the control actions to be exercised by
the microprocessor is stored and where the data is stored from the input for processing
and for the output.
Figure 2.2 The PLC System
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Figure 2.3 Signals
• The input and output sections are where the processor receives information from
external devices and communicates information to external devices. The inputs might
thus be from switches, as illustrated in with the automatic drill, or other sensors such as
photoelectric cells, as in the counter mechanism, temperature sensors, flow sensors, or the
like. The outputs might be to motor starter coils, solenoid valves, or similar things. Input
and output devices can be classified as giving signals that are discrete, digital or analog.
Devices giving discrete or digital signals are ones where the signals are either off or on.
Thus a switch is a device giving a discrete signal, either no voltage or a voltage. Digital
devices can be considered essentially as discrete devices that give a sequence of on/off
signals. Analog devices give signals of which the size is proportional to the size of the
variable being monitored. For example, a temperature sensor may give a voltage
proportional to the temperature.
• The communications interface is used to receive and transmit data on communication
networks from or to other remote PLCs. It is concerned with such actions as device
verification, data acquisition, synchronization between user applications, and connection
management.
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2.2 Internal Architecture
The basic internal architecture of a PLC is shown below. It consists of a central
processing unit (CPU) containing the system microprocessor, memory, and input/output
circuitry.
Figure 2.4 Basic Communication Model
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Figure 2.5 Architecture of a PLC
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The CPU controls and processes all the operations within the PLC. It is supplied with a
clock that has a frequency of typically between 1 and 8 MHz This frequency determines
the operating speed of the PLC and provides the timing and synchronization for all
elements in the system. The information within the PLC is carried by means of digital
signals. The internal paths along which digital signals flow are called buses. In the
physical sense, a bus is just a number of conductors along which electrical signals can
flow. It might be tracks on a printed circuit board or wires in a ribbon cable. The CPU
uses the data bus for sending data between the constituent elements, the address bus to
send the addresses of locations for accessing stored data, and the control bus for signals
relating to internal control actions. The system bus is used for communications between
the input/output ports and the input/output unit.
2.3 The CPU
The internal structure of the CPU depends on the microprocessor concerned. In general,
CPUs have the following:
• An arithmetic and logic unit (ALU) that is responsible for data manipulation and
carrying out arithmetic operations of addition and subtraction and logic operations of
AND, OR, NOT, and EXCLUSIVE-OR.
• Memory, termed registers, located within the microprocessor and used to store
information involved in program execution.
• A control unit that is used to control the timing of operations.
2.4 The Buses
The buses are the paths used for communication within the PLC. The information is
transmitted in binary form, that is, as a group of bits, with a bit being a binary digit of 1
or 0, indicating on/off states. The term word is used for the group of bits constituting
some information. Thus an 8-bit word might be the binary number 00100110. Each of the
bits is communicated simultaneously along its own parallel wire. The system has four
buses:
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• The data bus carries the data used in the processing done by the CPU. A microprocessor
termed as being 8-bit has an internal data bus that can handle 8-bit numbers. It can thus
perform operations between 8-bit numbers and deliver results as 8-bit values.
• The address bus is used to carry the addresses of memory locations. So that each word
can be located in memory, every memory location is given a unique address. Just like
houses in a town are each given a distinct address so that they can be located, so each
word location is given an address so that data stored at a particular location can be
accessed by the CPU, either to read data located there or put, that is, write, data there. It
is the address bus that carries the information indicating which address is to be accessed.
If the address bus consists of eight lines, the number of 8-bit words, and hence number of
distinct addresses, is 28 ¼ 256. With 16 address lines, 65,536 addresses are possible.
• The control bus carries the signals used by the CPU for control, such as to inform
memory devices whether they are to receive data from an input or output data and to
carry timing signals used to synchronize actions.
• The system bus is used for communications between the input/output ports and the
input/ output unit.
2.5 Memory
To operate the PLC system there is a need for it to access the data to be processed and
instructions, that is, the program, which informs it how the data is to be processed. Both
are stored in the PLC memory for access during processing. There are several memory
elements in a PLC system:
• System read-only-memory (ROM) gives permanent storage for the operating system
and fixed data used by the CPU.
• Random-access memory (RAM) is used for the user’s program.
• Random-access memory (RAM) is used for data. This is where information is stored on
the status of input and output devices and the values of timers and counters and other
internal devices. The data RAM is sometimes referred to as a data table or register table.
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Part of this memory, that is, a block of addresses, will be set aside for input and output
addresses and the states of those inputs and outputs. Part will be set aside for preset data
and part for storing counter values, timer values, and the like.
• Possibly, as a bolt-on extra module, erasable and programmable read-only-memory
(EPROM) is used to store programs permanently. The programs and data in RAM can be
changed by the user. All PLCs will have some amount of RAM to store programs that
have been developed by the user and program data. However, to prevent the loss of
programs when the power supply is switched off, a battery is used in the PLC to maintain
the RAM contents for a period of time. After a program has been developed in RAM it
may be loaded into an EPROM memory chip, often a bolt-on module to the PLC, and so
made permanent. In addition, there are temporary buffer stores for the input/output
channels. The storage capacity of a memory unit is determined by the number of binary
words that it can store. Thus, if a memory size is 256 words, it can store 256 _ 8 ¼ 2048
bits if 8-bit words are used and 256 _ 16 ¼ 4096 bits if 16-bit words are used. Memory
sizes are often specified in terms of the number of storage locations available, with 1K
representing the number 210, that is, 1024. Manufacturers supply memory chips with the
storage locations grouped in groups of 1, 4, and 8 bits. A 4K _ 1 memory has 4 _ 1 _
1024 bit locations. A 4K _ 8 memory has 4 _ 8 _ 1024 bit locations. The term byte is
used for a word of length 8 bits. Thus the 4K _ 8 memory can store 4096 bytes. With a
16-bit address bus we can have 216 different addresses, and so, with 8-bit words stored at
each address, we can have 216 _ 8 storage locations and so use a memory of size 216 _
8/210 ¼ 64K _ 8, which might be in the form of four 16K _ 8-bit memory chips.
2.6 Input/output Unit
The input/output unit provides the interface between the system and the outside world,
allowing for connections to be made through input/output channels to input devices such
as sensors and output devices such as motors and solenoids. It is also through the
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input/output unit that programs are entered from a program panel. Every input/output
point has a unique address that can be used by the CPU. It is like a row of houses along a
road; number 10 might be the “house” used for an input from a particular sensor, whereas
number 45 might be the “house” used for the output to a particular motor.
The input/output channels provide isolation and signal conditioning functions so that
sensors and actuators can often be directly connected to them without the need for other
circuitry.
Figure 2.6 An Optoisolator
Electrical isolation from the external world is usually by means of optoisolators (the term
optocoupler is also often used). The figure shows the principle of an optoisolators. When
a digital pulse passes through the light-emitting diode, a pulse of infrared radiation is
produced. This pulse is detected by the phototransistor and gives rise to a voltage in that
circuit. The gap between the light-emitting diode and the phototransistor gives electrical
isolation, but the arrangement still allows for a digital pulse in one circuit to give rise to a
digital pulse in another circuit. Outputs are specified as being of relay type, transistor
type, or triac type:
• With the relay type, the signal from the PLC output is used to operate a relay and is able
to switch currents of the order of a few amperes in an external circuit. The relay not only
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allows small currents to switch much larger currents but also isolates the PLC from the
external circuit. Relays are, however, relatively slow to operate. Relay outputs are
suitable for AC and DC switching. They can withstand high surge currents and voltage
transients.
• The transistor type of output uses a transistor to switch current through the external
circuit. This gives a considerably faster switching action. It is, however, strictly for DC
switching and is destroyed by over current and high reverse voltage. For protection,
either a fuse or built-in electronic protection is used. Optoisolators are used to provide
isolation.
• Triac outputs, with optoisolators for isolation, can be used to control external loads that
are connected to the AC power supply. It is strictly for AC operation and is very easily
destroyed by over current. Fuses are virtually always included to protect such outputs.
2.7 Sourcing and Sinking
The terms sourcing and sinking are used to describe the way in which DC devices are
connected to a PLC. With sourcing, using the conventional current flow direction as from
positive to negative, an input device receives current from the input module, that is, the
input module is the source of the current. With sinking, using the conventional current
flow direction, an input device supplies current to the input module, that is, the input
module is the sink for the current. If the current flows from the output module to an
output load, the output module is referred to as sourcing. If the current flows to the output
module from an output load, the output module is referred to as sinking.
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Figure 2.7 Inputs/Outputs Sourcing & Sinking
It is important know the type of input or output concerned so that it can be correctly
connected to the PLC. Thus, sensors with sourcing outputs should be connected to
sinking PLC inputs and sensors with sinking outputs should be connected to sourcing
PLC inputs. The interface with the PLC will not function and damage may occur if this
guideline is not followed.
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2.8 PLC Connections
When a process is controlled by a PLC it uses inputs from sensors to make decisions and
update outputs to drive actuators. The process is a real process that will change over time.
Actuators will drive the system to new states (or modes of operation). This means that the
controller is limited by the sensors available, if an input is not available, the controller
will have no way to detect a condition.
Figure 2.8 The Separation of Controller & Process
The control loop is a continuous cycle of the PLC reading inputs, solving the ladder
logic, and then changing the outputs. Like any computer this does not happen instantly.
When power is turned on initially the PLC does a quick sanity check to ensure that the
hardware is working properly. If there is a problem the PLC will halt and indicate there is
an error. For example, if the PLC backup battery is low and power was lost, the memory
will be corrupt and this will result in a fault. If the PLC passes the sanity check it will
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then scan (read) all the inputs. After the inputs values are stored in memory the ladder
logic will be scanned (solved) using the stored values – not the current values. This is
done to prevent logic problems when inputs change during the ladder logic scan. When
the ladder logic scan is complete the outputs will be scanned (the output values will be
changed). After this the system goes back to do a sanity check, and the loop continues
indefinitely. Unlike normal computers, the entire program will be run every scan. Typical
times for each of the stages is in the order of milliseconds.
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2.9 Ladder Logic Inputs
PLC inputs are easily represented in ladder logic. The three types of inputs are shown.
The first two are normally open and normally closed inputs, discussed previously. The
IIT (Immediate Input) function allows inputs to be read after the input scan, while the
ladder logic is being scanned. This allows ladder logic to examine input values more
often than once every cycle.
Figure 2.9 Symbols
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2.10 Ladder Logic Outputs
In ladder logic there are multiple types of outputs, but these are not consistently available
on all PLCs. Some of the outputs will be externally connected to devices outside the
PLC, but it is also possible to use internal memory locations in the PLC. The first is a
normal output, when energized the output will turn on, and energize an output. The circle
with a diagonal line through is a normally on output. When energized the output will turn
off. This type of output is not available on all PLC types. When initially energized the
OSR (One Shot Relay) instruction will turn on for one scan, but then be off for all scans
after, until it is turned off. The L (latch) and U (unlatch) instructions can be used to lock
outputs on. When an L output is energized the output will turn on indefinitely, even when
the output coil is deenergized. The output can only be turned off using a U output. The
last instruction is the IOT (Immediate Output) that will allow outputs to be updated
without having to wait for the ladder logic scan to be completed.
Figure 2.10 Output Symbols
Note: Outputs are also commonly shown using parentheses - ( ) - instead of the circle.
This is because many of the programming systems are text based and circles cannot be
drawn.
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2.11 SCADA
SCADA is an acronym for Supervisory Control and Data Acquisition. SCADA 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. These systems encompass the transfer of data between a SCADA central
host computer and a number of Remote Terminal Units (RTUs) and/or Programmable
Logic Controllers (PLCs), and the central host and the operator terminals. A SCADA
system gathers information (such as where a leak on a pipeline has occurred), transfers
the information back to a central site, then alerts the home station that a leak has
occurred, carrying out necessary analysis and control, such as determining if the leak is
critical, and displaying the information in a logical and organized fashion. These systems
can be relatively simple, such as one that monitors environmental conditions of a small
office building, or very complex, such as a system that monitors all the activity in a
nuclear power plant or the activity of a municipal water system. Traditionally, SCADA
systems have made use of the Public Switched Network (PSN) for monitoring purposes.
Today many systems are monitored using the infrastructure of the corporate Local Area
Network (LAN)/Wide Area Network (WAN). Wireless technologies are now being
widely deployed for purposes of monitoring.
SCADA systems consist of:
• One or more field data interface devices, usually RTUs, or PLCs, which interface to
field sensing devices and local control switchboxes and valve actuators
• A communications system used to transfer data between field data interface devices and
control units and the computers in the SCADA central host. The system can be radio,
telephone, cable, satellite, etc., or any combination of these.
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• A central host computer server or servers (sometimes called a SCADA Center, master
station, or Master Terminal Unit (MTU)
• A collection of standard and/or custom software [sometimes called Human Machine
Interface (HMI) software or Man Machine Interface (MMI) software] systems used to
provide the SCADA central host and operator terminal application, support the
communications system, and monitor and control remotely located field data interface
devices
Figure 2.11 Scada Networking
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2.11.1 Types of SCADA:
1. D+R+N (Development +Run + Networking)
2. R+N (Run +Networking)
3. Factory focus
2.11.2 Features of SCADA:
1. Dynamic process Graphic
2. Alarm summery
3. Alarm history
4. Real time trend
5. Historical time trend
6. Security (Application Security)
7. Data base connectivity
8. Device connectivity
9. Scripts
10. Recipe management
2.11.3 Manufacture of SCADA:
Modicon (Telemecanique) Visual look
Allen Bradley: RS View
Siemens: win cc
Gefanc:
KPIT: ASTRA
Intelution: Aspic
Wonderware: In touch
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2.11.4 Architecture
Hardware Architecture:
One distinguishes two basic layers in a SCADA system: the "client layer" which caters
for the man machine interaction and the "data server layer" which handles most of the
process data control activities. The data servers communicate with devices in the field
through process controllers. Process controllers, e.g. PLCs, are connected to the data
servers either directly or via networks or field buses that are proprietary (e.g. Siemens
H1), or non-proprietary (e.g. Profibus). Data servers are connected to each other and to
client stations via an Ethernet LAN. The data servers and client stations are NT platforms
but for many products the client stations may also be W95 machines.
Figure 2.12 Typical Hardware Architecture
Software Architecture:
The products are multi-tasking and are based upon a real-time database (RTDB) located
in one or more servers. Servers are responsible for data acquisition and handling (e.g.
polling controllers, alarm checking, calculations, logging and archiving) on a set of
parameters, typically those they are connected to. However, it is possible to have
dedicated servers for particular tasks, e.g. historian, data logger, alarm handler.
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2.11.5 Communications
Internal Communication:
Server-client and server-server communication is in general on a publish-subscribe and
event-driven basis and uses a TCP/IP protocol, i.e., a client application subscribes to a
parameter which is owned by a particular server application and only changes to that
parameter are then communicated to the client application.
Access to Devices:
The data servers poll the controllers at a user defined polling rate. The polling rate may
be different for different parameters. The controllers pass the requested parameters to the
data servers. Time stamping of the process parameters is typically performed in the
controllers and this time-stamp is taken over by the data server. If the controller and
communication protocol used support unsolicited data transfer then the products will
support this too. The products provide communication drivers for most of the common
PLCs and widely used field-buses, e.g., Modbus. Of the three field buses that are
recommended at CERN, both Profibus and Worldfip are supported but CANbus often
not. Some of the drivers are based on third party products (e.g., Applicom cards) and
therefore have additional cost associated with them. A single data server can support
multiple communications protocols: it can generally support as many such protocols as it
has slots for interface cards. The effort required to develop new drivers is typically in the
range of 2-6 weeks depending on the complexity and similarity with existing drivers, and
a driver development toolkit is provided for this.
Interfacing:
Application Interfaces / Openness:
The provision of OPC client functionality for SCADA to access devices in an open and
standard manner is developing. There still seems to be a lack of devices/controllers,
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which provide OPC server software, but this improves rapidly as most of the producers of
controllers are actively involved in the development of this standard. The products also
provide:
• An Open Data Base Connectivity (ODBC) interface to the data in the archive/logs, but
not to the configuration database,
• An ASCII import/export facility for configuration data,
• A library of APIs supporting C, C++, and Visual Basic (VB) to access data in the
RTDB logs and archive. The API often does not provide access to the product's internal
features such as alarm handling, reporting, trending, etc. The PC products provide
support for the Microsoft standards such as Dynamic Data Exchange (DDE) which
allows e.g. to visualize data dynamically in an EXCEL spreadsheet, Dynamic Link
Library (DLL) and Object Linking and Embedding (OLE).
Database:
The configuration data are stored in a database that is logically centralized but physically
distributed and that is generally of a proprietary format.
System (RDBMS) at a slower rate either directly or via an ODBC interface.
Scalability:
Scalability is understood as the possibility to extend the SCADA based control system by
adding more process variables, more specialized servers (e.g. for alarm handling) or more
clients. The products achieve scalability by having multiple data servers connected to
multiple controllers. Each data server has its own configuration database and RTDB and
is responsible for the handling of a sub-set of the process variables (acquisition, alarm
handling, archiving).
Redundancy:
The products often have built in software redundancy at a server level, which is normally
transparent to the user. Many of the products also provide more complete redundancy
solutions if required.
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2.11.6 SCADA SUBSYSTEMS:
A SCADA system usually consists of the following subsystems:
 A human–machine interface or HMI which presents process data to a human
operator who monitors and controls the process.
 A supervisory (computer) system for gathering data on the process and sending
commands to the process.
 Remote terminal units (RTUs) connecting to sensors in the process, converting
sensor signals to digital data and sending digital data to the supervisory system.
 Programmable logic controller (PLCs) used as field devices because they are
more economical, versatile, flexible, and configurable.
 Communication infrastructure connecting the supervisory system to the remote
terminal units.
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Figure 2.13 Components of SCADA
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2.11.7 Potential benefits of SCADA
The benefits one can expect from adopting a SCADA system for the control of
experimental physics facilities can be summarized as follows:

A rich functionality and extensive development facilities. The amount of effort
invested in SCADA product amounts to 50 to 100 p-years!

The amount of specific development that needs to be performed by the end-user is
limited, especially with suitable engineering.

Reliability and robustness. These systems are used for mission critical industrial
processes where reliability and performance are paramount. In addition, specific
development is performed within a well-established framework that enhances
reliability and robustness.

Technical support and maintenance by the vendor.
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CHAPTER 3
OBJECTIVE & METHODOLOGY
3.1 PROJECT OBJECTIVE:
The PLC program simulates a process tank being filled with a fluid. The tank will start
filling (via a valve) whenever the start process button is enabled and the tank is below
50% full. It will shut off when the tank is 100% full. In case the level sensor is out of
calibration or not working properly, there is a high-level safety limit to prevent the tank
from overfilling. If the high limit is met at a preset value of 102% full process will shut
down and a strobe light will turn on. Indicator lights are activated when the tank level
reaches 50%, 75% and 100% full as shown in the diagram of the tank in Figure 1. There
is a slight dead band to prevent flickering lights when tank levels vary slightly due to
filling or splashing.
If the tank for some reason does not fill up to a minimum level of 50% within 5 minutes
after the valve energizes, an alarm will notify an operator. The operator will be able to
silence the alarm for 5 minutes by pressing a silence button. After five minutes the alarm
will trigger notifying the operator once again. The operator will be able to silence the
alarm two times. If the silence button is pressed a third time, the alarm will remain on
and an energized strobe light will notify anyone within the site of the tank. The silence
button will be tamper proof by utilizing a one-shot rising instruction to prevent an
operator from holding the button in. If the tank remains under 50% full, the only way to
de-energize the alarm and strobe is to stop the process.
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3.2 CONTROLLING WATER LEVEL:
Sustainability of available water resource in many reason of the word is now a dominant
issue. This problem is quietly related to poor water allocation, inefficient use, and lack of
adequate and integrated water management. Water is commonly used for agriculture,
industry, and domestic consumption. Therefore, efficient use and water monitoring are
potential constraint for home or office water management system. Last few decades
several monitoring system integrated with water level detection have become accepted.
Measuring water level is an essential task for government and residence perspective. In
this way, it would be possible to track the actual implementation of such initiatives with
integration of various controlling activities. Therefore, water controlling system
implementation makes potential significance in home applications. The existing
automated method of level detection is described and that can be used to make a device
on/off. Moreover, the common method of level control for home appliance is simply to
start the feed pump at a low level and allow it to run until a higher water level is reached
in the water tank. This is not properly supported for adequate controlling system. Besides
this, liquid level control systems are widely used for monitoring of liquid levels,
reservoirs, silos, and dams etc. Usually, this kind of systems provides visual multi level
as well as continuous level indication. Audio visual alarms at desired levels and
automatic control of pumps based on user’s requirements can be included in this
management system. Proper monitoring is needed to ensure water sustainability is
actually being reached, with disbursement linked to sensing and automation.
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3.3. BLOCK DIAGRAM AND DESCRIPTION:
Figure 3.1 Block Diagram of the Project
Basic concepts:
The technique of water level monitoring and controlling system concentrated with some
basic parts which are softly aggregated together in our proposed method. Basic
descriptions of some parts are described below
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Water Level Indicator
For water level indication unit we can use some LED light which will work for water
level indication. By touching different water levels through water level sensor, LED
should be indicated as on/off (i.e. on: yes sensor senses water).
Water Level Sensor
To make special water level sensor we would like to introduce some convenient materials
such as Iron rod, nozzles, resistance, rubber etc. A connecting rod made by iron and steel
which should be connected with ground and we need at least four nozzles which should
be connected with +5v via a 1kΩ resistance. When the sensor touches water, nozzles and
connecting rod get electric connection using water conductivity.
Design and implementation:
For this project we have used Micrologix 1000 Allen Bradley PLC and the whole system
consists of the following parts:
1. Source and sink tanks
2. Float proximity sensors
3. NPN NO capacitive type sensor(CUT OFF Sensor)
4. SMPS
5. Silence alarm(12 V DC)
6. Pump
7. Relays
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3.4 Sensor unit
3.4.1 Float sensors
Level sensors detect the level of substances that flow, including liquids, slurries, granular
materials, and powders. Fluids and fluidized solids flow to become essentially level in
their containers (or other physical boundaries) because of gravity whereas most bulk
solids pile at an angle of repose to a peak. The substance to be measured can be inside a
container or can be in its natural form (e.g., a river or a lake). The level measurement can
be either continuous or point values. Continuous level sensors measure level within a
specified range and determine the exact amount of substance in a certain place, while
point-level sensors only indicate whether the substance is above or below the sensing
point. Generally the latter detect levels that are excessively high or low.
There are many physical and application variables that affect the selection of the optimal
level monitoring method for industrial and commercial processes. The selection criteria
include the physical: phase (liquid, solid or slurry), temperature, pressure or vacuum,
chemistry, dielectric constant of medium, density (specific gravity) of medium, agitation
(action), acoustical or electrical noise, vibration, mechanical shock, tank or bin size and
shape. Also important are the application constraints: price, accuracy, appearance,
response rate, ease of calibration or programming, physical size and mounting of the
instrument, monitoring or control of continuous or discrete (point) levels.
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Figure 3.2 Float Sensor
a) Magnetic and mechanical float
The principle behind magnetic, mechanical, cable, and other float level sensors involves
the opening or closing of a mechanical switch, either through direct contact with the
switch, or magnetic operation of a reed. With magnetically actuated float sensors,
switching occurs when a permanent magnet sealed inside a float rises or falls to the
actuation level. With a mechanically actuated float, switching occurs as a result of the
movement of a float against a miniature (micro) switch. For both magnetic and
mechanical float level sensors, chemical compatibility, temperature, specific gravity
(density), buoyancy, and viscosity affect the selection of the stem and the float. For
example, larger floats may be used with liquids with specific gravities as low as 0.5 while
still maintaining buoyancy. The choice of float material is also influenced by
temperature-induced changes in specific gravity and viscosity – changes that directly
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affect buoyancy. Float-type sensors can be designed so that a shield protects the float
itself from turbulence and wave motion. Float sensors operate well in a wide variety of
liquids, including corrosives. When used for organic solvents, however, one will need to
verify that these liquids are chemically compatible with the materials used to construct
the sensor. Float-style sensors should not be used with high viscosity (thick) liquids,
sludge or liquids that adhere to the stem or floats, or materials that contain contaminants
such as metal chips; other sensing technologies are better suited for these applications.
A special application of float type sensors is the determination of interface level in oilwater separation systems. Two floats can be used with each float sized to match the
specific gravity of the oil on one hand, and the water on the other. Another special
application of a stem type float switch is the installation of temperature or pressure
sensors to create a multi-parameter sensor. Magnetic float switches are popular for
simplicity, dependability and low cost.
b) Pneumatic
Pneumatic level sensors are used where hazardous conditions exist, where there is no
electric power or its use is restricted, and in applications involving heavy sludge or slurry.
As the compression of a column of air against a diaphragm is used to actuate a switch, no
process liquid contacts the sensor's moving parts. These sensors are suitable for use with
highly viscous liquids such as grease, as well as water-based and corrosive liquids. This
has the additional benefit of being a relatively low cost technique for point level
monitoring.
c) Conductive
Conductive level sensors are ideal for the point level detection of a wide range of
conductive liquids such as water, and is especially well suited for highly corrosive liquids
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such as caustic soda, hydrochloric acid, nitric acid, ferric chloride, and similar liquids.
For those conductive liquids that are corrosive, the sensor’s electrodes need to be
constructed from titanium, Hastelloy B or C, or 316 stainless steel and insulated with
spacers, separators or holders of ceramic, polyethylene and Teflon-based materials.
Depending on their design, multiple electrodes of differing lengths can be used with one
holder. Since corrosive liquids become more aggressive as temperature and pressure
increase, these extreme conditions need to be considered when specifying these sensors.
Conductive level sensors use a low-voltage, current-limited power source applied across
separate electrodes. The power supply is matched to the conductivity of the liquid, with
higher voltage versions designed to operate in less conductive (higher resistance)
mediums. The power source frequently incorporates some aspect of control, such as highlow or alternating pump control. A conductive liquid contacting both the longest probe
(common) and a shorter probe (return) completes a conductive circuit. Conductive
sensors are extremely safe because they use low voltages and currents. Since the current
and voltage used is inherently small, for personal safety reasons, the technique is also
capable of being made “Intrinsically Safe” to meet international standards for hazardous
locations. Conductive probes have the additional benefit of being solid-state devices and
are very simple to install and use. In some liquids and applications, maintenance can be
an issue. The probe must continue to be conductive. If buildup insulates the probe from
the medium, it will stop working properly. A simple inspection of the probe will require
an ohmmeter connected across the suspect probe and the ground reference.
Typically, in most water and wastewater wells, the well itself with its ladders, pumps and
other metal installations, provides a ground return. However, in chemical tanks, and other
non-grounded wells, the installer must supply a ground return, typically an earth rod.
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3.4.2CUT OFF Sensor
a) NPN NO Capacitive Proximity sensor
Capacitance level sensors excel in sensing the presence of a wide variety of solids,
aqueous and organic liquids, and slurries. The technique is frequently referred to as RF
for the radio frequency signals applied to the capacitance circuit. The sensors can be
designed to sense material with dielectric constants as low as 1.1 (coke and fly ash) and
as high as 88 (water) or more. Sludges and slurries such as dehydrated cake and sewage
slurry (dielectric constant approx. 50) and liquid chemicals such as quicklime (dielectric
constant approx. 90) can also be sensed. Dual-probe capacitance level sensors can also be
used to sense the interface between two immiscible liquids with substantially different
dielectric constants, providing a solid state alternative to the aforementioned magnetic
float switch for the “oil-water interface” application.
Since capacitance level sensors are electronic devices, phase modulation and the use of
higher frequencies makes the sensor suitable for applications in which dielectric
constants are similar. The sensor contains no moving parts, is rugged, simple to use, and
easy to clean, and can be designed for high temperature and pressure applications. A
danger exists from build-up and discharge of a high-voltage static charge that results
from the rubbing and movement of low dielectric materials, but this danger can be
eliminated with proper design and grounding.
Appropriate choice of probe materials reduces or eliminates problems caused by abrasion
and corrosion. Point level sensing of adhesives and high-viscosity materials such as oil
and grease can result in the build-up of material on the probe; however, this can be
minimized by using a self-tuning sensor. For liquids prone to foaming and applications
prone to splashing or turbulence, capacitance level sensors can be designed with
splashguards or stilling wells, among other devices.
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A significant limitation for capacitance probes is in tall bins used for storing bulk solids.
The requirement for a conductive probe that extends to the bottom of the measured range
is problematic. Long conductive cable probes (20 to 50 meters long), suspended into the
bin or silo, are subject to tremendous mechanical tension due to the weight of the bulk
powder in the silo and the friction applied to the cable. Such installations will frequently
result in a cable breakage.
Figure 3.3 Cut off Sensor
3.5 Control unit
The basic operation of control unit is the controlling water pump by PLC which is
defined by particular program. Water pump is connected with an output pin of PLC via a
relay circuit . In the relay circuit, one relay is used for sending positive signal in one
direction to the fourth port of the PLC and the other relay circuit is to pump the motor
with ac signal.
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CHAPTER 4
REQUIREMENS
4.1 HARDWARE REQUIREMENTS:

PLC MICROLOGIX 1000 (ALLEN BRADLEY)

SWITCHED MODE POWER SUPPLY (SMPS) 24V

SOURCE TANK

SINK TANK

SUBMERSSIBLE PUMP

LEVEL SENSORS

CUT OFF SENSOR

INDICATORS

SILENCE ALARM

PUSH BUTTONS

RELAYS

EXIT VALVE

CONNECTING WIRES
4.1.1 MICROLOGIX 1000 SPECIFICATIONS:
 Memory Size: 1 K EEPROM
 Power supply voltage: 20.4-26.4 V DC
 Power Supply Max. Inrush Current: 30A for 8 ms
 Operating Temp.: Horizontal mounting: 0°C to +55°C (+32°F to +131°F) for
horizontal mounting
 Storage Temp.: –40°C to +85°C (–40°F to +185°F)
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 Operating Humidity: 5 to 95% non-condensing
 Timers/Counters, Max.: 40 timers; 32 counters (fixed)
 I/O Scan Time, Typical: 0.21 ms
4.1.2 SUBMERSSIBLE PUMP:
This is used to pump the water from the source tank to the sink tank using a connecting
pipe.
The specifications are: CHAMPION PUMP
MODEL NO: SP1250
MAXIMUM HEIGHT: 1.5m
FLOW: 1100 lit/hr
4.1.3 LEVEL SENSORS:
Figure 4.1 Two-wire horizontally mountable level switch
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SPECIFICATIONS

Accuracy: ±5 mm in water

Repeatability: ±2 mm in water

Reed Type: dry contact, SPST

Thread NPT: 1/2"

Length, Overall: 114 mm (4.5")

Float Diameter: 18 mm (0.70")

Max. Temperature: -40 to 107 Degrees C (-40 to 225 Degrees F)

Cable: 60 cm (2'), 2 wire 22 gauge

Max. Pressure Rating: 100 psi

Min. Sp. Gravity Liquid: 0.55

Max. Switching Current: 20 VA @ 120 Vac (CE: 30 Vrms and 42.2 Vpeak or
60 Vdc)

Signal Output: Dry switch closure, selectable NO or NC states

Orientation: Horizontal
Side mount level switches are designed for use in small tanks and vessels. Engineered
plastic versions offer broad compatibility in water, oils and chemicals. Stainless steel or
zinc bodies are ideal for use in rugged environments. The all-stainless steel versions are
generally recognized as safe with FDA for food contact regulations.
Because of their horizontal attitude side-mounted units use a different actuation method
from other float level products. The basic principle, however, is the same: as a direct
result of rising or falling liquid, a magnetic field is moved into the proximity of a reed
switch, causing actuation.
Depending on the mounting position, the float on these switches can either rise or lower
with the liquid level. By rotating the switch 180°, the switch operation can be Normally
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Open or Normally Closed. Arrows on exterior of mounting indicate N.O. when pointing
up.
Figure 4.2 Operation of the sensor
When the switch is mounted so that the float lowers with the liquid level, the switch is
N.O.
When the switch is mounted so that the float rises with the liquid level, the switch is N.C.
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4.1.4 CUT OFF SENSOR:
The cutoff sensor used here for preventing the wastage of water due to overfilling is the
3-wire NPN NO CAPACITIVE PROXIMIY SENSOR.
Figure 4.3 NPN NO Proximity Switch
Three-Wire Proximity Switch: An AC or DC proximity sensor with three leads, two of
which supply power and the third that switches the load.
NPN means the sensor switches the load to the negative terminal. The load should be
connected between the sensor output and positive terminal.
Specifications:
Table 4.1 Specifications of Cutoff Sensor
Product Name
Model
Type
Theory
Output Type
Maximum load
EI DEPARTMENT, SRMGPC, LUCKNOW
Proximity Switch
LJC30A3-H-Z/BX
DC 3 Wire Type (Brown, Blue, Black)
Capacitive Sensor
NPN NO(Normal Open)
300 mA
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Detecting Distance
Supply Voltage
100 to 200 mm
DC 10-30V
Control Output
300mA
Operating Temperature
Size
Cable Length
External Material
Net Weight
Color
-25°C to +55°C
7.5 x 4cm/2.9" x 1.57"(L*Max. W)
120cm/47"
Plastic, Metal
140g
Silver tone
Principles of Operation for Capacitive Proximity Sensors
Capacitive proximity sensors are designed to operate by generating an electrostatic field
and detecting changes in this field caused when a target approaches the sensing face. The
sensor’s internal workings consist of a capacitive probe, an oscillator, a signal rectifier, a
filter circuit and an output circuit.
In the absence of a target, the oscillator is inactive. As a target approaches, it raises the
capacitance of the probe system. When the capacitance reaches a specified threshold, the
oscillator is activated which triggers the output circuit to change between “on” and “off.”
The capacitance of the probe system is determined by the target’s size, dielectric constant
and distance from the probe. The larger the size and dielectric constant of a target, the
more it increases capacitance. The shorter the distance between target and probe, the
more the target increases capacitance.
4.1.5 PUSHBUTTONS:
The most common switch is the pushbutton. It is also the one that needs the least
description because it is widely used in automotive and electronic equipment
applications. There are two types of pushbutton, the momentary and maintained. The
momentary pushbutton switch is activated when the button is pressed, and deactivated
when the button is released. The deactivation is done using an internal spring. The
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maintained pushbutton activates when pressed, but remains activated when it is released.
Then to deactivate it, it must be pressed a second time. For this reason, this type of switch
is sometimes called a push-push switch. The on/off switches on most desktop computers
and laboratory oscilloscopes are maintained pushbuttons.
The contacts on switches can be of two types. These are normally open (N/O) and
normally closed (N/C). Whenever a switch is in its deactivated position, the N/O contacts
will be open
(Non-conducting) and the N/C contacts will be closed (conducting). There is no internal
electrical connection between different contact pairs on the same switch. Most industrial
switches can have extra contacts “piggy backed” on the switch, so as many contacts as
needed of either type can be added by the designer. Note that it is the symbol for the
momentary pushbutton with a “see-saw” mechanism added to hold in the switch actuator
until it is pressed a second time. As with the momentary switch, the maintained switch
can have as many contacts of either type as desired.
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Pushbutton Switch Actuators
The actuator of a pushbutton is the part that is depressed to activate the switch. These
actuators come is several different styles as shown in each with a specific purpose.
Figure 4.4 Push buttons
4.1.6 RELAYS:
A relay is an electrically operated switch. Many relays use an electromagnet to operate a
switching mechanism mechanically, but other operating principles are also used. Relays
are used where it is necessary to control a circuit by a low-power signal (with complete
electrical isolation between control and controlled circuits), or where several circuits
must be controlled by one signal. The first relays were used in long distance telegraph
circuits, repeating the signal coming in from one circuit and re-transmitting it to another.
Relays were used extensively in telephone exchanges and early computers to perform
logical operations.
A type of relay that can handle the high power required to directly control an electric
motor or other loads is called a contactor. Solid-state relays control power circuits with
no moving parts, instead using a semiconductor device to perform switching. Relays with
calibrated operating characteristics and sometimes multiple operating coils are used to
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protect electrical circuits from overload or faults; in modern electric power systems these
functions are performed by digital instruments still called "protective relays".
Figure 4.5 8 pin relay connections
Figure 4.6 Relay module and socket
It is an electromagnetic device composed of a frame (or core) with an electromagnet coil
and contacts (some movable and some fixed). The movable contacts (and conductor that
connects them) are mounted via an insulator to a plunger which moves within a bobbin.
A coil of copper wire is wound on the bobbin to create an electromagnet. A spring holds
the plunger up and away from the electromagnet. When the electromagnet is energized by
passing an electric current through the coil, the magnetic field pulls the plunger into the
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core, which pulls the movable contacts downward. Two fixed pairs of contacts are
mounted to the relay frame on electrical insulators so that when the movable contacts are
not being pulled toward the core (the coil is de-energized) they physically touch the upper
fixed pair of contacts and, when being pulled toward the coil, touches the lower pair of
fixed contacts. There can be several sets of contacts mounted to the relay frame. The
contacts energize and de-energize as a result of applying power to the relay coil. When
the coil is de-energized, the movable contacts are connected to the upper fixed contact
pair. These fixed contacts are referred to as the normally closed contacts because they are
bridged together by the movable contacts and conductor whenever the relay is in its
"power off" state. Likewise, the movable contacts are not connected to the lower fixed
contact pair when the relay coil is de-energized. These fixed contacts are referred to as
the normally open contacts. Contacts are named with the relay in the de-energized state.
Normally open contacts are said to be off when the coil is de-energized and on when the
coil is energized. Normally closed contacts are on when the coil is de-energized and off
when the coil is energized. Those that are familiar with digital logic tend to think of N/O
contacts as non-inverting contacts, and N/C contacts as inverting contacts.
4.1.7 INDICATORS:
The 50% level, 75%level and the 100% level of water in the sink tank is indicated using
the LED (LIGHT EMMITING DIODE) indicators in the hardware.
As and when the level is reached the corresponding indicator lights glow up.
They basically indicate the level sensor status.
4.1.8 SILENCE ALARM:
This is a fault indicator alarm operating on 12V dc supply. It is connected with a 500
ohms resistance in series with the output port 4 of the programmable logic controller.
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The main reason for incorporating this alarm is to indicate any fault in the supply of the
water to the sink tank from the source tank. The alarm starts beeping when the liquid
level does not reach a prescribed level within a specified time limit indicating the fault at
the place of installation.
It can be silenced for 2 times using the SILENCE pushbutton and the fault can be
detected. On pressing the pushbutton for the third time the pump will turn off and the
entire process will stop. This guarantees a safety check at the place of operation.
4.1.9 EXIT VALVE:
This valve is used to simply empty he sink tank. It can be operated using the EXIT
pushbutton simply.
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4.2 SOFTWARE REQUIREMENTS:
We have used RSLogix and RSLinx softwares for the operation of the PLC and the
software INTOUCH, Wonderware has been used to monitor the process using SCADA
for providing remote access.
The RSLogix 500 software package is designed to enable users to monitor and modify
the activity of PLC processor in windows environment using a computer that is offline or
online with a PLC processor.
A computer running RSLogix software communicates with a PLC processor using
RSLinx Classic software. RSLinx Classic provides Allen-Bradley programmable
controller access to a wide variety of Rockwell Software and Allen-Bradley applications.
INTOUCH software (Wonderware, Singapore) for SCADA (SUPERVISORY
CONTROL AND DATA ACQUISITION SYSTEM) is also used to provide remote
access to the entire setup
4.2.1 INTOUCH SOFTWARE:
InTouch is world’s leading supervisory control and data acquisition software.
The
InTouch software package consists of Tags (Memory + I/O). The package is available in
64, 256, 1000 and 64,000 Tags with the two options
1. Development + Runtime + Network (DRN)
2. Runtime + network (RN).
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Table 4.2 Version Information about InTouch
S.N.
1
Version
OS
License
5.6b
Win95
Hardware lock & installable floppy.
Run setup.exe program from floppy.
2
6.0
Win NT
Same as above
3
7.0
Win NT
Hardware lock & installable floppy.
Win95/98
Copy wwsuite.lic file from floppy to license
subdirectory of the intouch.(file size 2 kb)
New features in InTouch 7.0
Application Explorer
WindowMaker's Application Explorer is a hierarchical graphical view of your
application. It shows you what items you have configured in your application and
provides you easy access to those items. It also provides you with quick access to many
of WindowMaker's most commonly used commands and functions.
Applications Run on Windows NT Operating System or Windows 95
The applications you create on the Windows 95 or the Windows NT operating systems
are interchangeable. They can run on either operating system without requiring
conversion.
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Tagname Cross Referencing
The Tagname Cross Referencing utility allows you to determine both your tagname and
SuperTag usage and, in which window or QuickScript that a specific tagname is used.
For convenience, the Tagname Cross Reference utility can remain open in WindowMaker
while you perform other tasks. It also allows you to view any QuickScript or
QuickFunction where a tagname is found.
ActiveX Container
InTouch is an ActiveX container. It allows you to install any third-party ActiveX control
and use it in any application window. For easy access to your installed ActiveX controls,
you can add them to your WindowMaker Wizards/ActiveX Toolbar. By using ActiveX
controls, you can handle control events, control methods, and control properties all from
InTouch QuickScripts. You can also associate the ActiveX control properties directly to
InTouch tagnames.
Instrument Failure Monitoring
Beginning with Version 7.0, InTouch supports three tagname dot fields (.RawValue,
.MinRaw and .MaxRaw) that you can use in InTouch QuickScripts to monitor instrument
values to determine out-of-range, out-of-calibration or, failure.
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Application Development In InTouch Involves
1. Creating new application
2. Creating windows / MIMIC page
3. Tag definition
4. Drawing objects
5. Animation properties
6. Writing scripts
7. Real-time Trends
8. Historical Trends
9. Alarms and Events
4.2.2 RS LINX CLASSIC SOFTWARE:
RSLinx Classic™ is the most widely installed communication server in automation
today. RSLinx Classic provides plant-floor device connectivity for a wide variety of
Rockwell Software applications such as RSLogix™ 5/500/5000 and RSView32. RSLinx
Classic also provides open interfaces for third-party HMI, data collection and analysis
packages, as well as custom client-applications. RSLinx Classic supports multiple
software applications simultaneously, communicating to a variety of devices on many
different Rockwell Automation Industrial networks.
RSLinx Classic is available in packages with features to meet the demand for a variety of
cost and functionality requirements. In addition, RSLinx Classic benefits include:
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
Routing

Graphical Interface

Integrated Configuration and Monitoring Tools

Remote OPC

Diagnostic Tools

Open Interfaces

Data Collection Modes

Feature Comparison Chart
4.2.3 RSLOGIX 500 SOFTWARE:
The RSLogix™ family of IEC-1131-compliant ladder logic programming packages helps
to maximize performance, save project development time, and improve productivity. This
family of products has been developed to operate on Microsoft® Windows® operating
systems. Supporting the Allen-Bradley SLC™ 500 and MicroLogix™ families of
processors, RSLogix™ 500 was the first PLC® programming software to offer
unbeatable productivity with an industry-leading user interface.
These RSLogix products share:

Flexible, easy-to-use editors

Common look-and-feel

Diagnostics and troubleshooting tools

Powerful, time-saving features and functionality
RSLogix programming packages are compatible with programs created with Rockwell
Software’s DOS-based programming packages for the SLC 500 and MicroLogix families
of processors, making program maintenance across hardware platforms convenient and
easy.
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RSLogix programming packages are compatible with programs created with Rockwell
Software's DOS-based programming packages for the SLC 500 and MicroLogix families
of processors, making program maintenance across hardware platforms convenient and
easy. In addition, RSLogix 500 benefits include:

Ladder

Cross-Reference Information

Drag-and-Drop Editing

Diagnostics

Dependable Communications

Database Editing

Reporting

Compatibility

Interoperability
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CHAPTER 5
IMPLEMENTATION
5.1 LADDER LOGIC:
Early PLCs were designed to replace relay logic systems. These PLCs were programmed
in "ladder logic", which strongly resembles a schematic diagram of relay logic. This
program notation was chosen to reduce training demands for the existing technicians.
Other early PLCs used a form of instruction list programming, based on a stack-based
logic solver.
Modern PLCs can be programmed in a variety of ways, from ladder logic to more
traditional programming languages such as BASIC and C. Another method is State
Logic, a very high-level programming language designed to program PLCs based on state
transition diagrams
Ladder logic is a method of drawing electrical logic schematics. It is now a graphical
language very popular for programming Programmable Logic Controllers (PLCs). It was
originally invented to describe logic made from relays. The name is based on the
observation that programs in this language resemble ladders, with two vertical "rails" and
a series of horizontal "rungs" between them.
A program in ladder logic, also called a ladder diagram, is similar to a schematic for a set
of relay circuits. An argument that aided the initial adoption of ladder logic was that a
wide variety of engineers and technicians would be able to understand and use it without
much additional training, because of the resemblance to familiar hardware systems. (This
argument has become less relevant given that most ladder logic programmers have a
software background in more conventional programming languages, and in practice
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implementations of ladder logic have characteristics — such as sequential execution and
support for control flow features — that make the analogy to hardware somewhat
imprecise.)
Ladder logic is widely used to program PLCs, where sequential control of a process or
manufacturing operation is required. Ladder logic is useful for simple but critical control
systems, or for reworking old hardwired relay circuits. As programmable logic
controllers became more sophisticated it has also been used in very complex automation
systems.
Ladder logic can be thought of as a rule-based language, rather than a procedural
language. A "rung" in the ladder represents a rule. When implemented with relays and
other electromechanical devices, the various rules "execute" simultaneously and
immediately. When implemented in a programmable logic controller, the rules are
typically executed sequentially by software, in a loop. By executing the loop fast enough,
typically many times per second, the effect of simultaneous and immediate execution is
obtained. In this way it is similar to other rule-based languages, like spreadsheets or SQL.
However, proper use of programmable controllers requires understanding the limitations
of the execution order of rungs.
EXAMPLE OF SIMPLE LADDER LOGIC PROGRAM:
The language itself can be seen as a set of connections between logical checkers
(contacts) and actuators (coils). If a path can be traced between the left side of the rung
and the output, through asserted (true or "closed") contacts, the rung is true and the
output coil storage bit is asserted (1) or true. If no path can be traced, then the output is
false (0) and the "coil" by analogy to electro-mechanical relays is considered "deenergized". The analogy between logical propositions and relay contact status is due
to Claude Shannon.
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Ladder logic has contacts that make or break circuits to control coils. Each coil or contact
corresponds to the status of a single bit in the programmable controller's memory. Unlike
electromechanical relays, a ladder program can refer any number of times to the status of
a single bit, equivalent to a relay with an indefinitely large number of contacts.
So-called "contacts" may refer to physical ("hard") inputs to the programmable controller
from physical devices such as pushbuttons and limit switches via an integrated or
external input module, or may represent the status of internal storage bits which may be
generated elsewhere in the program.
Each rung of ladder language typically has one coil at the far right. Some manufacturers
may allow more than one output coil on a rung.

—( )— A regular coil, energized whenever its rung is closed.

—(\)— A "not" coil, energized whenever its rung is open.

—[ ]— A regular contact, closed whenever its corresponding coil or an input
which controls it is energized.

—[\]— A "not" contact, open whenever its corresponding coil or an input which
controls it is energized.
The "coil" (output of a rung) may represent a physical output which operates some device
connected to the programmable controller, or may represent an internal storage bit for use
elsewhere in the program.
Here is an example of what one rung in a ladder logic program might look like. In real
world applications, there may be hundreds or thousands of rungs.
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For example:
1. ----[ ]---------|--[ ]--|------( )
X
| Y |
|
S
|
|--[ ]--|
Z
The above realizes the function: S = X AND ( Y OR Z )
Typically, complex ladder logic is 'read' left to right and top to bottom. As each of the
lines (or rungs) are evaluated the output coil of a rung may feed into the next stage of the
ladder as an input. In a complex system there will be many "rungs" on a ladder, which are
numbered in order of evaluation.
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5.2 CIRCUIT DIAGRAM:
Figure 5.1 PLC Wiring
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5.3 PROGRAMMING:
Figure 5.2 Programming Window 1 (Code Lines 0000-0003)
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Figure 5.3 Programming Window 2 (Code Lines 0004-0007)
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Figure 5.4 Programming Window 3 (Code Lines 0008-0011)
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5.4SCADA REPRESENTATION
Figure 5.5 Scada Diagram
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CHAPTER 6
RESULTS AND DISCUSSION
Figure 6.1 Hardware Circuit Board
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Figure 6.2 Hardware Setup
The hardware shown above in the picture has been tested and verified and is completely
fulfilling its objective of creation.
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CHAPTER 7
ADVANTAGES, APPLICATIONS & LIMITATIONS
7.1 ADVANTAGES:
In industries that exist right now, the presence of PLC is necessary especially to replace
the wiring or cabling systems that previously were used in controlling a system. By using
the PLC will get many benefits which are as follows:
1. Flexible
In the past, each different electronic device was controlled by a different controller.
Suppose ten machines require ten controllers, but now with only one tenth PLC machine
can be run with each program.
2. Changes and error correction system easier
If one system will be modified or corrected, the change is only done on the programs
contained in computers, in a relatively short time, after that it downloaded to the PLC. If
not using a PLC, for example relays the amendments made by altering the wiring cables.
This course takes a long time.
3. Number of contacts many
Number of contacts held by the PLC on each coil is more than the contacts held by a
relay.
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4. Cheaper
PLC is capable of simplifying a lot of cabling compared to a relay. So the price of a PLC
is cheaper than some full relay capable of doing the wiring for the same amount with a
PLC. PLC includes relays, timers, counters, sequencers, and other functions.
5. Operating speed
PLC operation speed is faster than the relay. Speed PLC scan time is determined by its in
units of milliseconds.
6. Resistant character test
Solid state devices are more resistant than the relay and test mechanical or electrical
timers. PLC is a solid state device that is more resistant test.
7. Simplifies the control system components
The PLC also has counters, relays and other components, so it does not require
components such as additional. Use of relays requires counters, timers or other
components as additional equipment.
8. Documentation
Printout of the PLC can be directly obtained and do not need to see the blueprint of his
circuit. Unlike the printout relay circuit cannot be obtained.
9. Security
Changing the PLC cannot be done unless the PLC is not locked and programmed. So
there is no unauthorized person can change the PLC program for a PLC is locked.
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10. Can make changes by reprogramming
Since the PLC can be programmed quickly reset the production process that mixes can be
completed. For example part B will be executed but sections of A is still in the process,
the process in section B can be re-programmed in seconds.
11. Addition of faster circuits
Users can add a circuit controller at any time quickly, without requiring great effort and
cost as in conventional controllers.
Besides the above mentioned advantages of a PLC, the advantages of the project under
consideration are:
1. Well adapted to a range of automation tasks.
2. In industries where water supply tanks are to be monitored continuously to prevent he
wastage due to overfilling.
3. Can be used in chemical factories to store and manage the level of various hazardous
and expensive solutions.
4. Remotely accessible setup is operational over a wide range of systems.
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7.2 APPLICATIONS:
PLCs are well-adapted to a certain range of automation tasks. These are typically
industrial processes in manufacturing where the cost of developing and maintaining the
automation system is high relative to the total cost of the automation, and where changes
to the system would be expected during its operational life. PLCs contain input and
output devices compatible with industrial pilot devices and controls; little electrical
design is required, and the design problem centers on expressing the desired sequence of
operations in ladder logic (or function chart) notation. PLC applications are typically
highly customized systems so the cost of a packaged PLC is low compared to the cost of
a specific custom-built controller design. For high volume or very simple fixed
automation tasks, different techniques are used.
The given project has a wide application in industries where water supply tanks are to be
continuously monitored to prevent any wastage of water. The same arrangement can also
be used in any other chemical factories to store and manage the level of various other
hazardous and expensive solutions and liquids used in their manufacturing process. A
onetime investment in almost all areas of usage can prevent a lot of wastage of water and
that too by remote access using SCADA along with PLC. It also ensures a completely
safe working environment in the factories and is capable of notifying the person in charge
by the level alarms set up in the system.
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7.3 LIMITATIONS:

Cost of PLC is high.

The project is applicable for industrial purposes only.

The technology is still new so changing the old control system using relay ladder
or to a PLC computer concept is difficult for some areas of operation.
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CHAPTER 8
CONCLUSIONS
Water is one of the most important basic needs for all living beings. But unfortunately a
huge amount of water is being wasted by uncontrolled use. Some other automated water
level monitoring system is also offered so far but most of the method has some shortness
in practice. We tried to overcome these problems and implemented an efficient
automated water level monitoring and controlling system. Our intension of this research
work was to establish a flexible, economical and easy configurable system which can
solve our water losing problem. We have successfully experiment the system in lab and
therefore proposed a PLC based water level monitoring and controlling network which
flexibility would offer us to control this system from any place via a remote computer
with different type of devices. This could have a substantial benefit from this research
work for efficient management of water.
The main difference from other computers is that PLC’s are armored for severe condition
(dust, moisture, heat, cold, etc) and has the facility for extensive input/output (I/O)
arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches,
analog process variables (such as temperature and pressure), and the positions of complex
positioning systems. Some even use machine vision. On the actuator side, PLCs operate
electric motors, pneumatic or hydraulic cylinders, magnetic relays or solenoids, or analog
outputs. The input/output arrangements may be built into a simple PLC, or the PLC
mahave external I/O modules attached to a computer network that plugs into the PLC.
Many of the earliest PLCs expressed all decision making logic in simple ladder logic
which appeared similar to electrical schematic diagrams. The electricians were quite able
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to trace out circuit problems with schematic diagrams using ladder logic. This program
notation was chosen to reduce training demands for the existing technicians. Other early
PLCs used a form of instruction list programming, based on a stack-based logic solver.
The functionality of the PLC has evolved over the years to include sequential relay
control, motion control, process control, distributed control systems and networking. The
data handling, storage, processing power and communication capabilities of some
modern PLCs are SCADA systems have made substantial progress over the recent years
in terms of functionality, scalability, performance and openness such that they are an
alternative to in house development even for very demanding and complex control
systems as those of physics experiments.
The combined usage of PLC for several control applications along with SCADA which
allows remote access of industrial units have found wide applications in almost all areas
of engineering.
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CHAPTER 9
FUTURE SCOPE OF THE PROJECT
A variety of market trends are driving companies toward the next generation of industrial
automation and manufacturing solutions. Technological advancements in process
monitoring, control and industrial automation over the past decades have contributed
greatly to improve the productivity of virtually all manufacturing industries throughout
the world. Many Inc's have developed advanced, easy-to-use machining process
simulation and measurement software which is used by a number of companies around
the world.
In case of the concerned project, it has a wide application in all areas of automation
industries. Also the scope of his project lies in chemical, petrochemical, pharmaceuticals,
etc. companies which makes it more industry oriented.
Usage of SCADA for remote operation of the setup has wide scope for converting all
similar automation plants remotely accessible via a computer. The greatly increasing
trend of control room operations in industries is all because of SCADA, i.e. Supervisory
Control and Data Acquisition.
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