plc
TRANSCRIPT
PLC : Introduction
A programmable logic controller, which is the usually called a PLC or programmable
controllers is solid- state, digital, industrial computer. Upon first glance, a programmable
controller may seen to be no more than black box with wires bringing signals in and other wires
sending signals out. It might also appear there some magic being done inside that somehow
decides when field devices should be turned on. In actuality, there is no magic. PLC is a
computer and someone had to tell it what to do. The PLC knows what to do through a program
that was developed and then entered into its memory. The PLC is a computer, however
without a set of instructions telling it what to do, it nothing more than a box full of
electronic components. Without instructions, the black box that we call a PLC can do nothing.
The user program is the list of instructions that tells the PLC what to do.
1.1 What is a PLC?
The PLC can be classified as a solid state member of the computer family. A programmable
controller is an industrial computer in which control devices such a limit switches, push buttons
proximity or photoelectric sensors. Float switches or pressure switches to name a few, provide
incoming control signals into the unit. An incoming control signals is called an input.
Inputs interact with instructions specified in the under ladder program which tells the PLC how
to react to the incoming signals. The user program also directs the PLC on how to control field
device like motor starters, pilot lights, and solenoids. A signal going out of the PLC to control a
field device is called an output. Figure 1 gives an overview of the interaction between the system
inputs, PLC and its ladder program, and the pilot light output.
A formal definition of a PLC comes from the National Electrical Manufacturers Association
( NMEA) : A programmable controller is a digitally operated electronic system designed
for use in an industrial environment, which uses a programmable memory for the internal
storage of use-orientation instructions for implementing specific functions such as logic,
sequencing, timing, counting, and arithmetic to control, though digital or analog inputs and
outputs, various types of machines or processor.
1.2 Features
The PLC is the hardened industrial computer. A PLC is made so that it can survive in the
manufacturing environment. Notebook and desktop personal computers are not designed for
continuous use in the manufacturing environment. When a computer needs to reside in the harsh
manufacturing environment, an industrially hardened computer that is designed to withstand
stress is the correct choice. Industrial computers are designed to withstand the dirt, shock,
vibration, high temperatures and wash downs found in the factory environment by incorporating
the following features:-
1. PLC is small, easy to install units. A PLC is easy to install because all inputs and outputs
connections are connected to terminals strips in a central location.
2. Air filters on intake fans.
3. Fans with ball bearing.
4. National electrical manufacturers Association (NMEA) 12,4 and 4X enclosure rating.
5. Shock mounted hard drives.
6. 0 to 55 degree centigrade compared to 0 to 40 degree centigrade operating environment.
7. Industrial computers are modular, which results in faster and easier repair.
8. Industrial computers do not need to be placed in a fan- cooled or air- conditioned
enclosure with a viewing window.
9. Easier troubleshooting.
10. Total Response time = Input response + Programme execution time + output response
time.
1.3 History of PLC
Early machines were controlled by mechanical means using cams gears, levers and other basic
mechanical devices. As the complexity grew, so did the need for a more sophisticated control
system. These elements were wired as required to provide the control logic necessary for the
particular type of machine operation. Relay and switch logic was cumbersome and time
consuming to modify. Wiring had to be removed and replaced to provide for the new control
scheme.
This modification was difficult and time consuming to design and install and any small “bug” in
the design could be a major problem to correct since it also required rewiring of the system. A
new means to modify control circuitry was needed. The Development and testing ground for this
new means was U.S auto Industry. The time period was the late 1960s and early 1970s and the
result was the PLC. Automotive plants were confronted with a change of manufacturing
techniques every time a model changed and, in some cases, for changes on the same model if
improvements had to be made during the model year. The PLC provided an easy way to
reprogram the wiring rather than actually rewiring the control system.
The PLC that was developed during this time was not very easy to program. The language was
cumbersome to write, requiring highly trained programmers. These early devices were merely
relay replacements and could do very little else. Older PLCs were capable of only handling
discrete inputs and outputs (i.e. ON-OFF type signals). While today’s systems can accept and
generate analog voltages and currents as well as wide range of voltage levels and pulsed
signals. Unlike their personal computer cousin, they can typically withstand the vibration, shock,
elevated temperature, and electrical noise to which manufacturing equipment is exposed.
As more manufactures become involved in PLC production and developments, and PLC
capabilities expand, the programming language is also expanding. Also, manufacturers tend to
develop their own versions of ladder logic language.
Comparison
PLC MICROPROCESSOR MICROCONTROLLLER
1. A plc is a type of 1. A microprocessor is the 1. A microcontroller is a special
computer designed
specifically for industrial
applications.
Central Processing Unit
(CPU) of a computer.
purpose computer system, usually
programmed to perform a single
task.
1. All PLCs contain
microprocessors.
2. Not all microprocessors
are used in PLCs.
2. Microcontrollers have
microprocessors as a part of their
system hardware.
2. A PLC can be stated as a
complete computer in
itself with a
microprocessor.
3. A microprocessor is only
one component of an
electronic device and
requires additional
circuits, memories etc.
before it can function.
3.A microcontroller is a small task-
specific computer. They contain
microprocessors on-board to
handle logic and instruction
processing but they still must have
all the essential elements of any
computer system.
4. A PLC can be
programmed or re-
programmed to control
different types of
devices using Ladder Logic
et c.
5. A general computer or
microprocessor system
can be tasked with a wide
variety of jobs.
4. Usually a microcontroller is
a programmed for a specific
task and left alone to do it
without further human input.
6. Applications include
automation and process
based industries etc.
7. Applications include
computers, telephone
industry home appliances
such as microwave.
5.Applications include
monitoring water level in a
tank etc.
Hardware Components:
There are two fundamental uses of switches. First, switches are used for operator to send
instructions to the control circuit. Second, switches may be installed on the moving parts of a
machine to provide automatic feedback to the control system.
Push Button: The most common switch is the push button.
It is also the one that needs the least description because it is widely used in an automotive.
The momentary push button switch is activated when the button is pressed and deactivated
when the button is released. The deactivation is done using an internal spring.
The maintained push buttons switch activates when press, but remains activated when it is
released. 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 contacts on switches can be of two types: There 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 ) shows the
schematic symbols for (a) a normally open push buttons and (b) a normally closed ( push-
Buttons. 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.
Selector Switches: A selector switch is also known as a rotary switch. An automobile ignition
switch and an oscilloscope’s vertical gain and horizontal time base switches are examples of
selector switches. Selector switches use the same symbol as a momentary pushbutton, except
a lever is added to the top of the actuator as shown. The switch is open when the selector is
turned to the left and closed when turned to the right. The switch has two sets of contacts. The
top contacts are closed when the switch selector is turned to the left position and open when the
selector is turned to right. The bottom set of contacts works exactly opposite. There is no
electrical connection between the top and bottom pairs of contacts. For the switch, the control
panel would be labeled with the STOP position to the left and the RUN position to the right.
Metal Detector Switch: It is another hardware component that works same as that of push-button
being sensitive to metal. It gets turned on when it gets into contact with metal and gets turned
off when the metal contact is removed.
MANUFACTURE AND CLASSIFICATION
Manufacturer PLC Memory I/D Count Communications
options
General Electric VersaMax Nano 2 K 6 input
4 Output
Serial
Siemens Simatic S7- 200,
CPU 221
4 K Program 2 K
data
6 input
4 Output
Optional RS 485
Mitsubishi FXO 1.6K Up to 16
inputs
Up to 14
outputs
Serial, Profibus-
DP,CC- Link
Network
Rockwell MicroLogix 1 K Up to 20
inputs
Up to 12
outputs
Serial, Data
Highway 485,
DeviceNet
General Electric VersaMax
Micro
9 K Up to 84 Serial, RS-485
Omran CPMNM1A 3 K 100 Host link, NT
Link, 1:1 Link
Mitsubishi FX2N Super
Micro
Up to 16 K Up to 256 Serial and RS-
422/485 Profibus-
DP and CC- Link.
Omran CQMI 13 k Up to 256 Device, Net.
CompoBus/ S;
Host Link, NT
Link,, 1:1 Link
Siemens Simatic S7-300 6 to 512 K Upto 512
discrete or
128
analog
Point-to – point
links, AS-
Interface,
profibus- DP,
Profibus- FMS,
Industrial
Ethernet
Rockwell SLC 500 Up to 64 K Up to
4096
inputs and
outputs
Serial DH- 485,
DH+, Device Net,
Control Net,
Ethernet.
Omran Cvmi Up to 62 K Up to
2048
Ethernet, Sysmac-
net, Sysmatic-
Link controller
Link, Device,
Nete, Host Llink,
NT Link.
Mitsubishi AnN Series Up to 320 K Up to
2048
Modbusm
Profibus- DP,
Ethernet
Rockwell ControlLogix 750- Kthru 8 M
bytes
Up to
128.000
Serial DH- 485,
DH+, Device Net,
Control Net,
Ethernet
Plc Manufacturing Companies
Modicon from France
Allen Bradely USA
Siemens Germany
ABB USA
OMRON Japan
Mistubushi South Korea.
GE Fanuc South Korea
LG Japan
Phillip U.K
Yokogava Japan
3.2 Types of PLC
1. Compact type (Number of input are fined). e.g. Zelio, Twido.
2. Modular type or rack type ( Number of input increase or decrease according to
requirement).e.g. Allen bradley
3.2.1 Zelio PLC
Manufacturer : Schneider Electrical
Software : Zelio soft 2
Twido PLC
Manufacturer : Schnieder
Software : Twido soft
Comm Protocol : Modbus urial
Connector : 8 Pin Mini Din
Comm port : RS 485
Plc Series : TWDLCAA 24DRF
PROGRAMMING A PROGRAMMABLE CONTROLLER
The PLC can do nothing without someone developing a program and loading this user program
into the CPU’s memory. Once the CPU has the program in memory and has been put into run
mode, it can look at inputs and a result of solving the user program ladder logic instructions it
can control the outputs and their associated field devices.
There are multiple ways to program a PLC.
1. One of the oldest methods of programming a PLC is by pressing buttons on a handheld
programming terminal to enter a user program a PLC.
2. The most popular method of PLC programming is using a personal desktop computer
and either a DOS or Windows operating system to run the manufacturers software for the
specific PLC. Illustrates the choice of an SLC 500 handheld terminal or a personal
computer for programming. Allen Bradley SLC 500 programming options. Either a
handheld programmer or a personal computer can be used to program the PLC. (Used
with permission of Rockwell Automation).
3. PLC programming can be accomplished using a notebook personal computer running
PLC programming software and a Personal computer Memory Card International
Association ( PCMCIA) interface card, or in some cases, a direct connection between the
personal computer serial port and the PLC CPU.
4. Using the industrial computer and the PLC manufacturer’s program software.
5. Using third- party “open software” and running a personal computer as the PLCs CPU.
4.1 Programming Devices
A program device is needed to enter, modify and troubleshooting the PLC program, or to check
the condition of the processor. Once the program has been entered and the PLC is running, the
programming device may be disconnected. Three types of programmers are generally used
1. Hand held ( smaller, cheaper portable but limited display capability and few
functions)
2. Dedicated desktop user- friendly, designed or industrial use, portable but costly,
limited PLCs can be programmed, limited documentation and limited
graphics capability.
3. Personal computer with software available for all major brands of PLCs, the PC
today is the most common programming device. It can store program on floppy
disc/hand disc. If for some reason the program is lost the restoration of the
program is simple.
On line programming changing programs while the processor and driven equipments running,
must be done by persons with a complete understanding of circuit operation and the process or
driven equipment.
Off line programming the programming is being developed off line (without being connected to
the process or driven equipment). Since few program are ever created without mistakes, it is the
most common and safest method of programming. After testing and verifying the program
offline, the PLC can be put in the ON LINE mode for final verification and operation.
4.2 Programming Languages of PLC
IEC 1131-3 is the international standard for programmable controller programming languages.
The following is a list of programming languages specified by this standard:
1. Ladder diagram (LD)
2. Sequential Function Charts (SFC)
3. Function Block Diagram (FBD)
4. Structured Text (ST)
5. Instruction List (IL)
One of the primary benefits of the standard is that it allows multiple languages to be used within
the same programmable controller. This allows the program developer to select the language best
suited to each particular task.
Ladder Logic
Ladder logic is the main programming method used for PLC's. As mentioned before, ladder logic
has been developed to mimic relay logic. The decision to use the relay logic diagrams was a
strategic one. By selecting ladder logic as the main programming method, the amount of
retraining needed for engineers and trades people was greatly reduced.
The first PLC was programmed with a technique that was based on relay logic wiring
schematics. This eliminated the need to teach the electricians, technicians and engineers how to
program - so this programming method has stuck and it is the most common technique for
programming in today's PLC.
Mnemonic Instruction
There are other methods to program PLCs. One of the earliest techniques involved mnemonic
instructions. These instructions can be derived directly from the ladder logic diagrams and
entered into the PLC through a simple programming terminal.
Sequential Function Charts (SFC)
SFC have been developed to accommodate the programming of more advanced systems. These
are similar to flowcharts, but much more powerful. This method is much different from
flowcharts because it does not have to follow a single path through the flowchart.
Structured Text (ST)
Programming has been developed as a more modern programming language. It is quite similar to
languages such as BASIC and Pascal.
Structured Text (ST) is a high level textual language that is a Pascal like language. It is very
flexible and intuitive for writing control algorithms.
Function Block Diagram (FBD)
FBD is another graphical programming language. The main concept is the data flow that start
from inputs and passes in block(s) and generate the output.
4.3 Rung
1. A rung of ladder diagram code can contain both input and output instructions.
a) Input instructions perform a comparison or test and set the rung state based on the
outcome.
b) Normally left justified on the rung.
2. Output instructions examine the rung state and execute some operation or function.
a) In some cases output instructions can set the rung state.
b) Normally right justified on the rung.
Fig 4.1 Rung
4.4 Logics for Basic Gates
Table III Logics Symbols
LOGIC SYMBOLS
logic element AND OR NOT NAND NOR
Logic
Element
Function
Output If All
Of the Control
Inputs On
Output if any
one of the
control input is
on
Output if
single control
input signal
is off
Output if all
control input
signals are on
Output if any
of the control
inputs are on
MIS-STD 80
6B Logic
Symbol
Electric Relay
Logic Symbol
Electrical
Switch Logic
Symbol
4.5 Timer and Counter
One of the major enhancements to the original programmable controller was to add timing and
counting abilities. Early PLCs had optional timing circuit cards that the user could slide into the
CPU to add timer or counter functionality to the PLC. Timing cards had physical solid- state
timing chips installed on slide- in timer boards. Today’s PLC uses modern microprocessor
technology and have timers and counters included in the instructions set.
4.5.1 Timer
A timer consists of the following parts: timer address, preset value, time base and
accumulated value. There are bits associated with the current state of the timer called status
bits. The timer address is a timer unique identifier in PLC memory. A timer instruction is one
element. A timer element is made up of three 16- bits words:-
1. Word zero contains the three states bit, EN, TT and DN (status bits will be covered as we
introduce each timer instruction).
2. Word one is for the present value.
3. Word two is for the accumulated value.
4.5.1.1 The ON Delay Timer Instruction
Uses the on- delay timer instruction program a time delay before an instruction becomes true.
Timer Addressing
Timer addressing is as follows: T (Timer file number): (Timer element number). The timer
address T4:0 is addressing timer file 4, timer element 0.
4.5.1.2 OFF- Delay Timer Instruction
Uses the off-delay timer instructions if you want to program a time delay to being after rung
inputs go false. As an example, an external cooling fan on a motor is to run all the time the motor
is running and for 100 seconds after the motor is returned off. This involves a 100- second off-
delay timers. The 100- second timing cycle begins when the motor is turned off. Figure
illustrates an off- delay timer, which Allen Bradley calls a timer off delay and its associated
ladder rungs.
TIMER INSTRUCTIONS
Instructions Use this instruction to Functional description
On- Delay Program a time delay to
before instruction
become true
When you want an action to begin a specified
time after the input become true.
Off- Delay Program a time delay to
begin after rung inputs to
false.
If an external cooling fan on a motor is to run all
the time the motor is running and for five minutes
after the motor is turned off, you have a five
minute off- delay timer. The five- minute timing
cycle begins when the motor is turned off.
Retentive Retain accumulated value Use a retentive timer to track the running time of
through power losses,
processor mode change.
Or rung state going from
true to false
a motor for maintenance purposes. Each time the
motor is turned off, the timer will remember the
elapsed time. Next time the motor is turned on,
the time will increase from that point. When you
want to reset this timer, use a reset instruction.
Reset Reset the accumulated
value of a timer or
counter
Typically used to reset a retentive timer’s
accumulated value to zero.
4.5.2 Counter
Every PLC has counter instructions Although most PLC counter work the same the instructions
symbols used and method of programming will change for different manufactures. The typical
counter counts from 0 to a predetermined values, called the ‘preset” value. The counter which
counts from 0 to a desired value is called count-up or up-counter and the counter which counts
down is called a desired value to 0 is called down- counter or count- down counter. A counter
instruction is one element. A counter element is made up of three 16- bits words. Thus the
counter instructions contain three parts.
4.5.2.1 The Count-Up Instruction
Use the count-up instruction if you want to counter to increment one decimal value each time it
registers a rung transition from false to true.
4.5.2.2 The Count Down Instruction
Use this instruction if you want to count down over the range of + 32, 767 to – 32,768. Each time
the instruction sees a false-to-true transition, the accumulated value will be decremented by one
count.
COUNTER INSTRUCTIONS
Instructions Use this instruction to Functional Description
Count up Count from zero up to a
desired value
Counting the number of parts produced during a
specific work shift, or in the current batch. Also,
counting the number of rejects from this batch.
Count down Count down from a desired
value to zero
An operator interface display shows the operator the
number of parts remaining to be made for a lot of 100
parts ordered.
SCOPE OF PLC
A PLC (Programmable Logic Controller) is one of the main devices used in industry to
implement: monitoring, logic, control, or other events/functions impossible (or to complicated)
to be done mechanically. With respect to embedded systems, a PLC is in fact an embedded
system running a program to provide the various functions PLCs typically provide.
5.1 Advantages of PLC
1. Flexibility: One single Programmable Logic Controller can easily run many machines.
2. Correcting Errors: In old days, with wired relay-type panels, any program alterations
required time for rewiring of panels and devices. With PLC control any change in circuit
design or sequence is as simple as retyping the logic. Correcting errors in PLC is
extremely short and cost effective.
3. Space Efficient: Today's Programmable Logic Control memory is getting bigger and
bigger this means that we can generate more and more contacts, coils, timers, sequencers,
counters and so on. We can have thousands of contact timers and counters in a single
PLC. Imagine what it would be like to have so many things in one panel.
4. Low Cost: Prices of Programmable Logic Controlers vary from few hundreds to few thousands. This is nothing compared to the prices of the contact and coils and timers that you would pay to match the same things. Add to that the installation cost, the shipping cost and so on.
5. Testing: A Programmable Logic Control program can be tested and evaluated in a lab.
The program can be tested, validated and corrected saving very valuable time.
6. Visual observation: When running a PLC program a visual operation can be seen on the
screen. Hence troubleshooting a circuit is really quick, easy and simpler.
7. 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
8. Cheaper: PLC is capable of simplifying a lot of cabling compared to a relay. So the price
of a PLC at a price cheaper than some fruit relay capable of doing the wiring for the same
amount with a PLC. PLC includes relays, timers, counters, sequencers, and other
functions.
9. Operating speed: PLC operation speed is faster than the relay. Speed PLC scan time is
determined by its in units of milliseconds.
10. 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.
11. Simplifies the control system components: The PLC also have 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.
12. 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.
13. 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.
14. 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.
15. Addition of faster circuits: Users can add a circuit controller at any time quickly,
without requiring great effort and cost as in conventional controllers.
5.2 Disadvantages of the PLC
1. The drivers of Hilo in the area of weighbridge queue have to keep their idling of engines and
their pressure up of brake in light option anticipation.
2. It is not likely for the system to distinguish between burnt and unburnt cane. It means that
the favoring old system of one tandem or the burnt cane has must be discarded
3. There's too much work required in connecting wires.
4. There's difficulty with changes or replacements.
5. It’s always difficult to find errors; and require skillful work force.
6. When a problem occurs, hold-up time is indefinite, usually long.
7. 5.3 Limitations of PLC
The system now has some limitations even though these could be reduced by program changes
or method changes the allocation of light sequence:
1. The hauliers with interconnects have a advantage of payload over standard trailers as the
light ratio options in the sequence is presently based on loads number only, and is not
weighted based on the payload differences.
2. If there is haulier with a small tonnage would occurrence huge delays if allocated a detailed
light.
3. It should a vehicle progress to the wrong system tandem is ignorant of this and another load
is not called even though it is requisite. This trouble could be programmed out with a routine
of time delay.
5.4 Trouble Shooting
Careful start up procedures is necessary to prevent the damage to the driven equipment and PLC
or more important injury to personal. Prior to binging a system start up procedure, it is important
to check and verify that the system has been installed according to the manufacturers
specifications and that the installation, meets local, state and national codes. Special attention be
given to system grounding.
Before applying power to the controller following is to be ensured
1. Verifying that incoming power matches the jumper selected voltage setting of the power
supply.
2. Verify that a hardwired safety circuit or other emergency stop device has been installed and
is in open position.
3. Check all power and communication cables to ensure that connector pins are straight and not
bent or pulled out.
4. Connect all cables making sure that connectors are fully inserted into their sockets secure
connectors as applicable.
5. Ensure that modules are securely held in the I/O rack.
SCADA: SCADA stands for Supervisory Control and Data Acquisition. As the name
indicates, it is not a full control system, but rather focuses on the supervisory level. As such, it is
a purely software package that is positioned on top of hardware to which it is interfaced, in
general via Programmable Logic Controllers (PLCs), or other commercial hardware modules.
SCADA systems are used not only in industrial processes: e.g. steel making, power generation
(conventional and nuclear) and distribution, chemistry, but also in some experimental facilities
such as nuclear fusion.
SCADA runs on a PC and is generally connected to various PLCs and other peripheral devices.
It enables you to generate applications for the most demanding requirements of plant engineers,
operators, managers tailored precisely to the needs of each plant. SCADA constantly gathers a
data from the plant in real-time, stores and processes it in the database, evaluates and
generates alarms. Displays information to plant operators to plant operators, supervisors and
managers and can issued instructions to PLCs on the plant floor. SCADA systems used to run on
DOS, VMS and UNIX; in recent years all SCADA vendors have moved to NT and some also to
Linux.
Features of SCADA
1. Dynamic Process graphic mimics developed in SCADA software should resemble the
process mimic. SCADA should have good library of symbols so that you can develop
the mimic as per requirements. Once the operator sees the screen he should know what
is going on in the plant.
2. Real time and Historical Trend: The trends play very important role in the process
operation. If our batch fails or the plant trips, we simply go to historical trend data and do
the analysis. We can have better look of the parameters through the trends. Ex: we
commission a SCADA system for Acid Regeneration plant where the plant has to be
operated on 850- deg temperature. If the operator operates the plant at 900 deg you can
imagine how much additional LPG he is putting into the reactor. Again what will happen
to the bricks of the reactor? So the production manager’s first job will be to go through
the trends how the operators are operating the plant. Even when the plant trips there are
more than 25 probable reasons for the same but you go through the history trends, it’s
very easy to identify the problems.
3. Alarms have a very vertical role in automation. Generally we have alarm states for each
inputs/outputs like your temperature should not cross 80 deg or lever should be less than
60. So if the parameter goes in Alarm state then operator should be intimated with the
alarm. Most of the SCADA software support our types of alarms like LOLO, LO, HI and
HIHI. Dead band the value of dead band defines the range after which a high low alarm
condition returns to normal.
4. Alarms are most important of plant control applications because the operator must know
instantly when something goes wrong. It is often equally important to have a record of
alarm and whether an alarm was acknowledged. An alarm occurs when something goes
wrong. It can signal that a device or process has ceased operating within acceptable,
predefined limits or it can indicate breakdown, wear or process malfunction.
5. Recipe Management is an additional feature. Some SCADA software support it, some
do not. Most of the plants are manufacturing multi products. When you have different
product to manufacture, you just have to load the recipe of the particular product.
6. Security is one facility people generally look for. You can allocate certain facilities or
features to the operator, process people, engineering department and maintenance
department for example operators should only operate system, he should not be able
change the application. The engineers should have access to changing the application
developed.
7. Device connectivity we will find there are hundreds of automation software manufacturer
like Modicon, Siemens, Allen Bradley, Yokogawa, ABB. Everybody has their own way
to communication or we can say they have their own communication protocol. SCADA
software should have connectivity to the different h/w used in automation. It should not
happen that for Modicon I am buying one software and for Seimens another on. The
software like Aspic or Wonderware has connectivity to almost all hardware used in
automation.
Evolution
SCADA vendors release one major version and one to two additional minor versions once per
year. These products evolve thus very rapidly so as to take advantage of new market
opportunities, to meet new requirements of their customers and to take advantage of new
technologies.
Most of the SCADA products that were evaluated decompose the process in "atomic"
parameters to which a Tag-name is associated. This is impractical in the case of very large
processes when very large sets of Tags need to be configured. As the industrial applications are
increasing in size, new SCADA versions are now being designed to handle devices and even
entire systems as full entities (classes) that encapsulate all their specific attributes and
functionality. In addition, they will also support multi-team development.
As far as new technologies are concerned, the SCADA products are now adopting:
1. Web technology, ActiveX, Java, etc.
2. OPC as a means for communicating internally between the client and server modules. It
should thus be possible to connect OPC compliant third party modules to that SCADA
product.
Architecture :
7.4.1 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.
7.4.2 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.
Manufacturers of SCADA
Modicon (Telemecanique) Visual look
Allen Bradly : RS View
Siemens : win cc
KPIT : ASTRA
Intelution : Aspic
Wonderware : Intouch
Usefulness of SCADA
7.6.1 Production department
1. Real time production status: manufacturing status is updated in real time in direct
communication to operator and control device.
2. Production schedules: production schedules can be viewed and updated directly.
3. Production information management: production specific information is distributed to all.
7.6.2 Quality department
1. Date integrity and quality control is improved by using a common interface.
2. It is an open platform for statistical analysis.
3. Consolidation of manufacturing & Lab data.
7.6.3 Maintenance department
1. Improved troubleshooting and de- bugging: direct connection to wide variety of the
devices, displays troubleshooting reduced diagnostic/ debugging time.
2. Plant can be viewed remotely. Notification can include pagers, e-mails, and phones.
3. C0-ordinationi between maintenance and management reduces unscheduled downtime
7.6.4 Enterprise department
1. Corporate information and real time production data can be gathered and viewe3d from
anywhere within your operations.
2. User specific information ensures better informed decision
3. Data exchange with standard database and Enterprise systems provides integrated
information solutions.
7.6.5 Engineering department
Integrated Automation solutions reduce design and configuration time
1. Common configuration platform offers flexibility for constant configuration in all areas.
2. Capable of connecting to wide variety of systems. Reduces start up time and system
training with industry proved open interfaces.
7.6.6 Manufacturing department
1. Unscheduled down time is reduced due swift alarm detection and event driven
information.
2. Makes operations easier and more repeatable with its real time functionality.
3. Secured real time operation is maintained with windows.
Application of SCADA
7.7.1 Configuration
The development of the applications is typically done in two stages. First the process
parameters and associated information (e.g. relating to alarm conditions) are defined through
some sort of parameter definition template and then the graphics, including trending and
alarm displays are developed, and linked where appropriate to the process parameters.
7.7.2 Development Tools
The following development tools are provided as standard:
1. A graphics editor, with standard drawing facilities including freehand, lines, squares
circles, etc. It is possible to import pictures in many formats as well as using predefined
symbols including e.g. trending charts, etc. A library of generic symbols is provided that
can be linked dynamically to variables and animated as they change. It is also possible to
create links between views so as to ease navigation at run-time.
2. A data base configuration tool (usually through parameter templates). It is in general
possible to export data in ASCII files so as to be edited through an ASCII editor or Excel.
3. A scripting language
4. An Application Program Interface (API) supporting C, C++, VB.
7.7.3 Bottling of Soft Drinks
The bottling of soft-drink in a plant is done by using SCADA software. The plant used for this
bottling is highly automated and hence SCADA software finds application here. The process
makes use of the conveyer belt, on which the bottles move for filling. The motion of the
conveyer belt is so programmed such that the conveyer belt stops the bottle below the nozzle for
only that much time that is required for the bottle to get filled. After that the conveyer belt is
moved further and second bottle is undergone the same process.
The other part of this plant which is programmed is the tank containing the drink. This tank is
also programmed in a way that the liquid will come out in that much amount only which is
required to fill the bottle and this tank is in synchronization with the conveyer belt such that the
liquid will come out only when the bottle is exactly below the nozzle of the tank.
As the bottles are filled, they are carried by the same conveyer belt to the placing racks.
Automation: ''Automation'' or industrial automation or numerical control is the use of control
systems such as computers to control industry industrial machinery and industrial process
processes, reducing the need for human intervention. In the scope of industrialization,
automation is a step beyond mechanization. Whereas ''mechanization'' provided human operators
with machinery to assist them with the ''physical'' requirements of work, ''automation'' greatly
reduces the need for human ''sensory'' and ''mental'' requirements as well. Processes and systems
can also be automated.
Automation plays an increasingly important role in the global economy and in daily experience.
Engineers strive to combine automated devices with mathematical and organizational tools to
create complex systems for a rapidly expanding range of applications and human activities.
Many roles for humans in industrial processes presently lie beyond the scope of automation.
Human-level pattern recognition, language recognition, and language production ability are well
beyond the capabilities of modern mechanical and computer systems. Tasks requiring subjective
assessment or synthesis of complex sensory data, such as scents and sounds, as well as high-level
tasks such as strategic planning, currently require human expertise. In imany cases, the use of
humans is more cost-effective than mechanical approaches even where automation of industrial
tasks is possible.
Specialised hardened computers, referred to as programmable logic controllers (PLCs), are
frequently used to synchronize the flow of inputs from (physical) sensors and events with the
flow of outputs to actuators and events. This leads to precisely controlled actions that permit a
tight control of almost any industrial process.
Automation Tools: Different types of automation tools exist:
1. ANN - Artificial neural network
2. DCS - Distributed Control System
3. HMI - Human Machine Interface
4. SCADA - Supervisory Control and Data Acquisition
5. PLC - Programmable Logic Controller
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