Download Industrial Automation System

International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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PLC Based Industrial Automation System
1
Gavali Amit Bhimrao, 2Patil Mahadev S.
Department of Electronics and Telecommunication
Rajarambapu Institute of Technology Rajaramnagar, Islampur, Sangli, India
Email: [email protected], [email protected]
Abstract - This paper describes how the present
automation system comes in to existence through its
various stages. In the past, automation is done through
relays and contactor logics. Since the human intervention is
more, the scope of errors was also more. But with the
advent of microprocessors & microcontrollers several new
tools as PLCs (Programmable Logic controllers) come in to
use. These have reduced human intervention. This in turn
has increased accuracy, precision and efficiency.
II. Programming logic controllers (PLC)
I (a) RELAY SYSTEM:
The relay, which operates much like a solenoid, is an
electromagnetic device that consists of a coil with a soft
iron core and electric contacts mounted on, but insulated
from, the moving armature or plunger. The relay allows
one circuit to control another.
Keywords — Automation, PLC, PLC based Control Panel
I. INTRODUCTION
Automation, a Greek word means self dedicated.
Automation is the key to modernization and has been
conceptually understood as a way to increase efficiently
and to improve productivity. The process of having
machine follow a predetermined sequence of operation
with little or no human labor, using special equipment
and devices that perform and control manufacturing
processes is known as automation. The goals of
automation are Integration of various aspects of
manufacturing operations to reduce labor cost. The
fundamental constituents of any automated process are
(1) a power source, (2) a feedback control mechanism,
and (3) a programmable command as shown in figure 1.
Figure 1: Fundamental constituents automated process
Aautomation tools:
Figure 2: Relay mechanism
Relay Operation: When current is supplied to the coil, the
resulting magnetic field pulls the armature and the
contacts toward the coil. The relay is in energized
position when the armature is fully seated. Contacts that
were open are now closed. These contacts are referred to
as the normally open (NO) contacts. Contacts that were
closed are now open. These contacts are called the
normally closed (NC) contacts. Therefore, the terms
“normally open” and “normally closed” refer to the
condition of the contacts when the relay coil is deenergized. A relay may have one or both types of
contacts and may also have multiple sets of contacts for
controlling several circuits at once. When the coil circuit
is opened, current cannot flow in the coil, the magnetic
field collapses, and the relay de-energizes. A spring
attached to the armature returns the contacts to their
normal positions.
I. Relays and contactor logic
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Relays comes in different configurations are SPST
(Single Pole Single Throw) is the simplest only two
contacts, SPDT (Single Pole Double Throw) has three
contacts. The contacts are usually labled common,
normally open & normally closed. The normally closed
contact will be connected to the common contact when
no power is applied to the coil. The normally open
contact will be open (i.e. not connected) when no power
is applied to the coil. When the coil is energized the
common is connected to the normally open contact and
the normally closed contact is left floating. The double
pole version are the same as the single pole version
except there are two switches that open and close
together. Select a relay with contact that can handle the
voltage and current requirements of the load. Keep in
mind that some loads (such as motor) draw more current
when first turned on than they do not at steady state.
Relay Application: The relay can be used to open and
close high-voltage or high-current circuits with relatively
little voltage and current in the coil circuit. The
controlling circuit is electrically isolated from the
controlled circuit. In other words, current from the
controlling circuit does not flow in the controlled circuit.
The link between the two circuits is strictly magnetic.
The relay is also useful for remote be located at one point
and other circuit components located some distance
away. Because the controlling circuit is usually operated
by a low-current power source, relatively small gage
wires can be used to connect the remote switch device.
Relay Ratings: The electrical contacts are rated for the
voltage and current that they can safely switch. The relay
is also rated for the voltage and current required to
properly energize the coil. If a time delay is desired, thus
value must also be specified. The value of these ratings
will depend on how the relay is used in the system.
Disadvantages of Relay System: The maintenance cost
of the relay system is quite high, as the frequent
maintenance is required in it. A driver circuit is required
along with larger relays. Very high human intervention
is required in this system. They do not allow manual
adjustment of the relay state when the control power is
off. These are only use for ON/OFF control.
Intermediate controlling is not possible by the relays.
They increased electrical noise when conducting.
contact system is the current carrying part of the
contactor. This includes Power Contacts, Auxiliary
Contacts, and Contact Springs. The electromagnet
system provides the driving force to close the contacts.
The enclosure system is a frame housing the contact and
the electromagnet. Enclosures are made of insulating
materials like Bakelite, Nylon 6, and thermosetting
plastics to protect and insulate the contacts and to
provide some measure of protection against personnel
touching the contacts. Open-frame contactors may have
a further enclosure to protect against dust, oil, explosion
hazards and weather. The major disadvantage of relays
and controller logic is that it does not have any
redundant system it means that if system fails then, it
does not have any controlling system to continue its
controlling and monitoring process. So if system fails
then we have to rectify the control system so that
controlling & monitoring could be restarted.
II PROGRAMMING LOGIC CONTROLLER:
A digitally operating electronic apparatus which uses a
programmable memory for the internal storage of
instructions by implementing specific functions such as
logic sequencing, timing, counting, and arithmetic to
control, through digital or analog input/output modules.
A Programmable Logic Controller or Programmable
Controller is a digital computer used for automation of
electromechanical processes, such as control of
machinery on factory assembly. 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.
I (b) CONTACTOR LOGIC:
A contactor is an electrically controlled switch (relay)
used for switching a power circuit. A contactor is
activated by a control input which is a lower voltage /
current than that which the contactor is switching.
Contactors come in many forms with varying capacities
and features. Unlike a circuit breaker a contractor is not
intended to interrupt a short circuit current.
Basic Features of Contactor Logic are as follows: A
contactor is composed of three different systems. The
Figure 3: Block diagram of PLC
PLC has 4 main units: 1) Programmable Memory- The
instruction for logical control sequence is stored here. 2)
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Data Memory- The status of the switches interlocks, past
values of data and other working data is stored here. 3)
O/P Devices- These are hardware or software drives for
industrial process actuators, such as solenoid, switches,
motor and valves. 4) I/P Devices- These are hardware or
software driver for industrial process sensors such as
switch status sensors, proximity detectors interlock
setting.
Working principal of PLC: Inputs Modules: Inputs come
from sensors that physically translate into electrical
signals. The simplest form of inputs are digital. In
smaller PLCs the inputs are normally built in and are
specified when purchasing the PLC. For larger PLCs the
inputs are purchased as modules, or cards, with 8, 16,
32, 64, 96 inputs of the same type on each card.
Scanning Principle of PLC: The PLC program is
executed as part of a repetitive process referred to as a
scan. A PLC scan starts with the CPU reading the status
of inputs. The application program is executed using the
status of the inputs. Once the program is completed, the
CPU performs internal diagnostics and communication
tasks. The scan cycle ends by updating the outputs, then
starts over. The cycle time depends on the size of the
program, the number of I/Os, and the amount of
communication required.
Figure 6: Scan cycle of PLC
Figure 4: Example of input card
Outputs Modules: Output modules rarely supply any
power, but instead act as switches. External power
supplies are connected to the output card and the card
will switch the power on or off for each output. A
common choice when purchasing output cards is relay
transistors or triacs. Relays are the most flexible output
devices. They are capable of switching both AC and DC
outputs. But, they are slower, cost more, and they will
wear out after millions of cycles. The most important
consideration when selecting relays, or relay outputs on
a PLC, is the rated current and voltage
A PLC resolves the logic of a ladder diagram (program)
rung by rung, from the top to the bottom. Usually, all the
outputs are updated based on the status of the internal
registers. Then the input states are checked and the
corresponding input registers are updated. This process
is run in a endless cycle. The time it takes to finish one
cycle is called the scan time. In some controllers the idle
state is eliminated. In this case, the scan time varies
depends on the program length.Scan cycle depends upon
number of I/Os. More I/Os more scan time. Application
decides the scan time of a PLC. Scan time in normal
applications is 1 ms to 2 ms & in bigger applications 100
ms to 200 ms
Advantages of using PLC’s are as follows: 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.
II.
Figure 5: Example of output card
SWITCHED MODE POWER
SUPPLY
A switched-mode power supply is an electronic power
supply that incorporates a switching regulator to convert
electrical power efficiently. Like other power supplies,
an SMPS transfers power from a source, like mains
power, to a load, such as a personal computer, while
converting voltage and current characteristics. An SMPS
is usually employed to efficiently provide a regulated
output voltage, typically at a level different from the
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input voltage. (Figure7. Shows DELTA SMPS supply
230 VDC, 5A)
IV.
RELAY BOARD
Figure 7: Switched Mode Power Supply
III.
MINIATURE CIRCUIT BREAKER
A circuit breaker is an automatically operated electrical
switch designed to protect an electrical circuit from
damage caused by overload or short circuit. Its basic
function is to detect a fault condition and interrupt
current flow. Unlike a fuse, which operates once and
then must be replaced, a circuit breaker can be reset
(either manually or automatically) to resume normal
operation. Circuit breakers are made in varying sizes,
from small devices that protect an individual household
appliance.(Figure.8 shows SEIMENS MCB 2P C4A, 1P
C2A)
Figure 9: Relay board
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.
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 contractor. 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 protect electrical circuits from
overload or faults; in modern electric power systems
these functions are performed by digital instruments still
called "protective relays". (Figure. 9 shows CONNECT
WELL 8 channel, 5A, coil-24VDC)
V. SOFTWARE FOR PLC
Figure 8: Miniature Circuit Breaker
All circuit breakers have common features in their
operation, although details vary substantially depending
on the voltage class, current rating and type of the circuit
breaker. The circuit breaker must detect a fault
condition, in low-voltage circuit breakers this is usually
done within the breaker enclosure. Circuit breakers for
large currents or high voltages are usually arranged with
pilot devices to sense a fault current and to operate the
trip opening mechanism. Once a fault is detected,
contacts within the circuit breaker must open to interrupt
the circuit, some mechanically-stored energy ( such as
springs) contained within the breaker is used to separate
the contacts, although some of the energy required may
be obtained from the fault current itself. Small circuit
breakers may be manually operated.
CoDeSys V2.3: CoDeSys is a complete development
environment for Nexgenie messung PLC. CoDeSys
stands for Controlled Development System. CoDeSys
puts a simple approach to the powerful IEC language at
the disposal of the PLC programmer. Use of the editors
and debugging functions is based upon the proven
development program environments of advanced
programming languages. POU (Program Organization
Unit) Functions, function blocks, and programs are
POUs which can be supplemented by actions. Each POU
consists of a declaration part and a body. The body is
written in one of the IEC programming languages which
include IL, ST, SFC, FBD, LD or CFC. CoDeSys
supports all IEC standard POUs. POU can call up other
POUs. However, recursions are not allowed. Function A
function is a POU, which yields exactly one data
element (which can consist of several elements, such as
fields or structures) when it is processed, and whose call
in textual language can occur as an operator in
expressions.
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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Input devices are various switches, sensors and such.
Output devices are solenoids, motors, relays as well as
instruments for sound and light signalization.
Third, we wrote ladder diagram for a program by
sequence of operations that was determined in the first
step. Finally, program uploaded into the PLC controller
memory. When finished with programming, checkup is
done for any existing errors in a program code (using
functions for diagnostics) and, if possible, an entire
operation is simulated. Before this system is started, we
need to check once again whether all input and output
instruments are connected to correct inputs or outputs.
By bringing supply in, system starts working.
Figure 10: Example of Ladder diagram
VI.
ELECTRICAL CONTROL PANEL
In an automated system, a PLC controller is usually the
central part of a process control system. With the
execution of a program stored in program memory, PLC
continuously monitors status of the system through
signals from input devices. Based on the logic
implemented in the program, PLC determines which
actions need to be executed with output instruments.
Most disadvantages of a classic control panel are too
much work required in connecting wire, Difficulty with
changes or replacements, Difficulty in finding errors;
requiring skillful work force, When a problem occurs,
hold-up time is indefinite, usually long.
Figure 11: Example of conventional control panel
(Contactor logic control panel)
Advantages of control panel that is based on a PLC
controller can be presented in few basic points:
Compared to conventional process control system,
number of wires needed for connections is reduced.
Consumption is greatly reduced because a PLC
consumes less than a bunch of relays. Diagnostic
functions of a PLC controller allow for fast and easy
error detection. Change in operating sequence or
application of a PLC controller to a different operating
process can easily be accomplished by replacing a
program through a console or using a PC software (not
requiring changes in wiring, unless addition of some
input or output device is required). It is cheaper
compared to a conventional system, especially in cases
where a large number of I/O instruments are needed and
when operational functions are complex Reliability of a
PLC is greater than that of an electro-mechanical relay
or a timer (shown in figure 12)
Material which is required for making PLC based
control panel for PLC based fully automatic hydraulic
press machine shown in figure 12. Specifications of PLC
used are: Nexgenie NG16DL, Input power: 24VDC,
2.4W. Expansions: 4 maximum, Program software: IEC
61131-3 compatible programming software CoDeSys,
Programming languages: Ladder language, Expansions
modules (NE08IX): Nexgenie PLC expansion 8 i/p,
24VDC, Seimens MCB 2P C4A, MCB 1P C2A, MCB
2P C16A, Seimens 9A Contactor, Delta SMPS supply
230AC, output 24VDC 5A, Connect Well 8 ch. coil24VDC, connecting strips, 16 pin, 10 pin 16A malefemale socket.
Systematic approach in designing a process control
system: First, we need to select an instrument or a
system that we wish to control. Function of a process
control system is constantly watched by input devices
(sensors) that give signals to a PLC controller. In
response to this, PLC controller sends a signal to
external output devices (operative instruments) that
actually control how system functions in an assigned
manner.
Secondly, we need to specified all input and output
instruments that will be connected to a PLC controller.
Figure 12: PLC based electrical control panel
We are designed PLC operated fully automatic hydraulic
press machine. For that sequence of operation is when
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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start Push Button is pressed the motor starts running.
There are two modes of operation Auto and Manual
mode
Start
Motor start/ running push
button
Auto Mode: For Auto Mode you need press cycle start
push button, initially both the valves will be in off state,
when cycle start push button is pressed the solenoid
valve 1 is made ON as soon as the valve turns ON the
hydraulic ram moves forward to do its job now when the
ram comes in contact with down sensor the valve 1 turns
off and automatically Solenoid valve 2 turns ON hence
making the Ram to move backwards to its home
position, valve 2 turns off when the Ram comes in
contact with Up sensor. (Flow chart shown in figure 14)
Manual (Setup) Mode: For the machine to run in Manual
(setup) mode you need to press separate push buttons for
two different operations. Firstly press the main ram
forward push button the valve 1 turns ON, ram moves
forward when the ram gets comes in contact with down
sensor the valve 1 turns OFF, now release the main ram
forward push button & press main ram return push
button now the valve 2 turns ON hence making the ram
move backwards to its home position, valve 2 turns off
when the Ram comes in contact with Up sensor. Motor
acts as universal element the modes of operation should
only operate when the motor is running. The master stop
push button is used to stop the motor at any instance of
operation. The emergency main ram return is used to
ON the Solenoid Valve 2 (i.e. main ram to move
backwards) at any Instance of operation. Note:
emergency main ram return works only for Auto Mode.
(Flow chart shown in figure 15)
Motor running
Is temp >= tempSET
NO
YES
Motor stop
SETUP MODE
NO
Is solenoid
valve 1
activated?
YES
NO
Is M.S
activated?
YES
RAM forward
movement
Motor stop
NO
Is down sensor
detected metal?
YES
Stop RAM
forward movement
NO
Is solenoid
valve 2
activated?
YES
NO
Is M.S
activated?
RAM backward
movement
YES
Motor stop
NO
Is up sensor
detected
metal?
YES
Figure 13: PLC operated fully automatic hydraulic press
machine
Figure 13 shows example of PLC based industrial
automation system (i.e. PLC based fully automatic
hydraulic press machine) suitable for different types of
heavy duty works in different commercial and industrial
applications. This press machine can be used for cutting,
punching, compression, modeling etc and can be used
on the assembly lines of automotive industries. It also
can be used in plastic industries for pressing application.
Stop RAM
backward
movement
Stop
Figure 15: Flow chart for Setup (Manual) Mode
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International Journal of Electrical, Electronics and Computer Systems (IJEECS)
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VII.
CONCLUSION
Start
A PLCs is specifically made to fit in industrial
environment, where it is exposed to hostile condition
such as heat ,dust, humidity, unreliable power
,mechanical shocks and vibration. PLCs have both
hardware and software features that make them
attractive as controllers of wide range of industrial
equipments. A PLC can work in the harsh and
extreme conditions of the industry where other
systems such as a Micro-Controller cannot.
Programming is a lot easier as compared to other
embedded system which makes the job easy for the
technicians. PLC’s allow end user to configure and
control the application which is more useful in
industries.
Select AUTO MODE
A
STATUS
1. Cycle start
2. Emg. main ram
return
3. Master stop
1
3
Solenoid valve 1 active
Stop motor
2
B
C
Return to home position
Stop
RAM forward
movement
REFERENCES
[1] Xiaoli Wang, Yu Wa, “Control System Design
for 100KN Double Column Universal hydraulic
machine”, Journal and applied Information
Technology, vol. 48(1), 10th Feb 2013
YES
NO
B
Is down sensor
detected metal?
Stop RAM
forward
movement
1.E.M.R.R.
2.M.S
3.N.B.P
1
2
Solenoid valve
2 active
C
[2] LV Yuan-jun, “The control of paperboard
pressing machine”, Fifth IEEE International
Conference
on
Intelligent
Computation
Technology and Automation, 2012
3
B
Return to home
position
C
RAM backward
movement
NO
A
Is up sensor
detected metal?
YES
Stop RAM backward
movement
Stop motor
[3] M. Sumaila, A. Okonigbon, “Design and
Manufacture of a 30-ton hydraulic press”, AU
J.T. vol.14,No.3, pp 196-200, Jan 2011
[4] Liping Guo, “Design projects in a programmable
logic controller (PLC) course in electrical
engineering technology” The technology
interface journal vol.10 No.1, Fall 2009
[5] Sanjiv Kumar, Devendra Kumar, “Industrial
Automation System”, XXXII National System
Conference, December 17-19,2008
[6] George K. Adam, “Design and Control of a
Mechatronic Hydraulic Press System”, IEEE
International Conference on Mechtronics, 2004
A
Figure 14: Flow chart for Auto Mode
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