Introduction For Programmable logic controller(PLC)
What is PLC?
Programmable Logic Controllers is a kind of computer control system that continuously monitors the state of the input and output and makes logic-based decisions for automated processes or machines. Basically, the PLC provides a simple solution for modifying the operation of a control system. Using this type of control system almost any production line, process or machine function can be greatly enhanced.
History of PLC :
In the late 1960s PLC was introduced by inventor Richard Morley to provide the same functions as relay logic systems. And also the first PLC is model 084 invited by Richard Morley. At the time relay system supposed to fails and create delays. That time technicians had to troubleshoot the whole wall of relays to fix the problem. Basically, this kind of control device was in importance to the needs of the American automation manufacturing industry, where software edition replaced the re-wiring of hard-wired relay-based control panels when outcome models changed. To replace relay logic systems, early PLCs were designed and these PLCs were designed for programmed in ladder logic. To reduce training demands for the existing technicians, this program modulator was chosen. Modern days PLCs can be programmed in several types of ways, as like as from the relay-derived ladder logic to programming languages. To program PLC based on state transition diagrams a very high programming language was designed, and this method is State Logic.
Description of PLC :
In the automobile manufacturing
industry PLC was for the first time developed to give flexible, simple, easily
programmable controllers to replace timers and sequencers, hard-wired relays.
After that time they have been highly adapted to PLC for automation control in
harsh environments. PLC performs the more complex task in a simple and easiest
way, takes much less space and is more customizable than mechanical technologies.
To operate continuously without maintenance they are very well known and they
had a great impact on digitizing a great many industries, particularly
production.
Even though PLCs were great
progress than relays, there were still restrictions. Mainly, they were planned
for specific applications in the automotive industry.
Types of PLC:
There are different types of PLC.
And you need to choose a PLC depends on the input and output.
Compact PLC: In a compact PLC input and output capabilities are
decided by the manufacturer, not by the user. The compact PLC can not able to
expand the module as it has a fixed number of inputs, output module and
external input, and output card.
Modular PLC: A modular PLC is built with a variety of components
that are corked into a common rack or bus with expandable input, output
capabilities. Modular PLC contains central processing unit (CPU), power supply,
and the input-output modules that are connected together in the same rack,
which are from the same manufacturer or different manufacturers.
This PLC is divided into
different sizes with computing capabilities, input-output capabilities,
variable power supply, etc.
Small-sized PLC: This is a kind of PLC which is designed in such a
way that, it can be installed next to the controlled equipment. The counters,
timers, hard wired-relays, etc are replaced by this type of PLC.
Medium-sized PLC: This kind of PLC is mostly used in industries. Medium-sized
PLC allows many plugs in modules that are mounted on the backplane of the
system. In this PLC provide additional input-output cards, so you can add a
hundred or more input-output module. Adding these input-output cards-
communication module facilities provided by this PLC.
Large-sized PLC: Larger-sized PLC basically used in such a complex
process control function. These PLC’s capacity is much higher than the medium-sized
PLC’s in terms of input-output points, programming language, memory, a
communication module, etc.
Renowned Types of PLC in the world of technology
Siemens PLC
Siemens Programmable Logic
Controllers are a perfect PLC system. Siemens PLC is a German-based company.
Siemens brought a variety of PLC product line in the SIMATIC S7 family. Some
are S7-200, S7-300 and S7-400. Among all of them Siemens’s series, Siemens S7
is the most powerful and useful solution for industrial automation sectors.
They also include a programming environment for Siemens programming logic
controllers (PLC). By using this software, users get unique and powerful
programming tools including benefits: single project integration of multiple
automation devices, a structured architecture, and creation of re-useable
logic.
Siemens Programmable Logic
Controllers are basically two types: Compact type and Modular type. In a
compact type, Siemens PLCs input and output number always have been fixed. On
the other hand, modular type Siemens PLCs input and output number can be as per
selection.
Mitsubishi PLC
Mitsubishi proposals
comprehensive computerization the solution that can create a fully unified
control platform extending from the touchscreen all the way to the device
inaccessible I/O module. Integration among PLC, HMI, Robot, Motion Controller,
VFD, Servo and enterprise network is made probably with their straightforward
programming suites.
The system unifies all of the
Mitsubishi Electric Automation disciplines into a one-of-a-kind modular
Programmable Automation controller. The IQ platform is only proficient in
mixing individual Sequence, Motion, CNC, and Robot control onto a single
back-plane rack. There are many types of Mitsubishi PLC.
Delta PLC
The Delta is a Chinese based
company. It offers industrial automation solutions and automation products with
high performance and reliability, including industrial control and automation,
power supply improvement, human-machine interfaces (HMI), sensors, meters,
motor control systems, etc. The Delta Programmable Logic Controllers provides stable,
high-speed and highly reliable applications for industrial automation systems.
PLC Hardware:
CPU, Memory, Input/Output, Power The supply unite and the programming device are the hardware components of PLC.
CPU: To avoid errors, the CPU always keeps checking the PLC
controller. They perform several kinds of functions as like as computer
interfaces, arithmetic operations, logic operations and many more. In a PLC,
CPU process and store program data.
Memory: CPU is used the fixed data. For the operating system,
Systems (ROM) store the data permanently. Information on the status of input
and output devices, and the values of timers, counters and other internal
devices are stored by RAM.
Input/Output: The main objectives of Input and Output, connect the
PLC to the rest of the machine. Input/Output module can be either digital or analog.
In Input, the device might include switches, sensors, and meters. On the other
side output device might include drives, valves, lights, and relay
Power Supply: The certain Programmable Logic Controller has an isolated power supply. But maximum PLC works at 220 V AC or 24 V DC.
Programming Device: Into the memory of the processor, the device is
used to feed the program. First, the program is fed to the programming device,
and later the program is transmitted to the PLCs memory
System Buses: There are 4 system
buses. These are-
- Data buses: The objective of this data bus is, to transfer data
among different elements by using the CPU.
- Control buses: Transferred signal to the related activities which
are controlled internally.
- Address buses: Address buses send the location address to access
the data.
- System buses: The application of this system bus is helping the Input/Output
port and Input/Output unit so that they can communicate with each other.
How Does a PLC Operate?
In the operations of all PLCs, there are four basic steps.
Input scan, Program scan, Output scan, and Housekeeping. And all these steps
are repeating step by step indefinite times.
Input Scan: The
state of the input, which is connected externally is scanned. Switches,
Pushbuttons, proximity sensors, limit switches, and pressure switches are included
by these inputs. Mainly they are not relays, they are transformers.
Program Scan: To
carry out the function appropriately, the program scan executes the program
logic.
Output Scan: Energize
or de-energize all output devices. Because the input source has control over
the output port. This relay can triac, transistors depending on the PLC.
Housekeeping: Communication
includes programming terminals and internal symptoms by this step.
Applications of PLC:
The easiest proper application is a conveyor system. The
conveyor system requires some functions. These are the following:
A programmable logic controller is always used to run and
stop the motors which motors are in conveyor belts. Three segmented conveyor belts
in a conveyor system, each segment is run by a motor. A proximity switch is
positioned at the end of the segments to detect the position of a plate. Every
time the first conveyor system is needed to turn on. The objectives of the
proximity switches, which is locating in the first segment detect the plate
turn on the second segment system. When the proximity switch detects the plate
at the second conveyor, the third conveyor segment is turned on. The second
conveyor is stopped after 20 seconds, as the plate comes out of the detection
range. The third conveyor segment is
stopped after 20 seconds if the proximity switches fail to detect the plate.
Why Should I Use a PLC?
PLC can perform several kinds of
tasks, as relay-switching tasks, as well as count, calculate and compare
analog process values.
By using PLC there is no need for
re-wiring every time for each new logical configuration. Ideally PLC eliminates
the need for rewiring and also adding surplus hardware for each new logical
configuration.
This type of controller raises
the functionality of controls and does not take up physical space.
Since PLCs are divisional, they
can be sophisticated and resembled. So you can take the best combination of
input and output devices for your required operations.
The flexibility of PLC’s makes it
simple to control logic at any time.
Costing of PLCs is very much
effective for controlling complex systems.
For any kind of problem, PLC can
provide a simple solution.
Advantages of PLCs:
Using PLCs over relay systems there are 6 major advantages
as follows:
- Flexibility
- Low cost
- Space efficiency
- Testing
The comfort of the solving problem
Flexibility: It is very much possible to easily run many machines
by a single PLC.
Low Cost: By using PLC saves the shipping cost and installation
cost. And the price of this device is very low. The price of this device varies
from a few hundred to a few hundred.
Space Efficiency: In a PLC system fewer components are required than
the usual hardware systems. The PLC can perform several functions like
counters, sequencers, functions of timers and control relays, so those hardware
devices are not required.
Testing: Prior to performance in the field, a PLC program can be
tested, evaluated and validated in a lab.
The Comfort of Solving Problems: Before
PLCs, that time required a lot of time to rewiring of devices and panels. But
with PLC devices changing any circuit design, the function of timers,
sequences, the function of timers is as simple as retyping logic
Disadvantages of PLC:
- It is an exhausting job when you need to replacing or
bringing any changes to it.
- There need much effort to connect the wires.
- To find its errors, need a skillful workforce.