PLC - Programming Logic controllers | Technical definition

 Programmable logic controller (PLC) is an electronic device that operates on a digital signal. Programmable logic controllers are operated with the help of computer. It performs the function of interfacing between machine and human. With this help, any machine is automatically controlled and various types of operations are performed. Various types of automation and machine operations are controlled by PLC. With this help, various types of instructions are stored in the memory and they are used when the respective operation is performed.

PLCs

PLC is a computer commonly used to control industrial operations. All its functions are similar to those of computers, which are complete with hardware and software. The PLC performs central processing unit, memory, input-output port, timer and counter, analog-to-digital converter, digital-to-analog converter, serial port, interrupt logic, oscillator etc. Thus various types of integrated circuits are used in PLC which operate various functions related to it. Programmable logic controller is a composite form of solid state digital logic element designed to provide logical decision making and output. PLC is used to operate and control the equipment and machinery of manufacturing units. Currently it is mainly used in remote control, telephone bills, printing machines, automatic power regulators, automatic and semiotic machines, microwave ovens, automobiles and devices related to measurement devices. Thus by using PLC the size of any work area can be reduced and its work time can be reduced and the product can be extended. The use of programmable logic controllers is also known by name. The order of the product is used to control, which is used for sequential controllers.

For example, a car manufacturing company first prepares its structure to manufacture a car. After this, its parts are made and all are added with the help of one processing and its body is prepared Is and a certain color is given.  Thus, this process is completed in many steps, which is called automatic manufacturing.  PLC is mainly used in this.

Technical Definition – 

PLC is a technical device as defined by the National Electrical Manufacturer Association (NEMA, USA). "Programmable logic controller is a digitally operated electronics system that is used to perform various types of functions in an industrial environment. It performs specific functions such as logic sequencing, timing, counting, economical operations, etc. It uses key inputs for a variety of machines and their processes through analog inputs and outputs that are stored in memory. "

Need of PLC –

Programmable logic controller devices are mostly used in the industrial sector for automatic event based control, interlocking and sequencing operations. It is necessary for thermal power stations, steel industry, cement industry, pharmaceutical industry, petrochemical industry, fertilizer industry, etc.

Function of PLC – 

Control Relay 

• Relays are used in large industries for start or stop operation of electrical power devices, such as heaters, pumps, blowers, etc. The relay is activated and deactivated by the PLC.

Timing Functions

• It displays like a PLC timer and provides time delay.  PLC uses programmable timers which are easily set by the timer parameter to the users in a short time.  After a specific time interval, PLC timers operate the devices of the fixed processes and perform the timer operation. 

Analog Control 

• The PLC can receive and generate analog signals.  This function receives signals through various analog devices such as temperature, pressure, flow, level transducers, etc.  With this help, analog output devices such as control valves, shunt motors, etc. are controlled by the PLC. 

Counting Function 

• PLC behaves like a counter and can also count the finished products of the industries.  Bottles, drums bags and vehicles etc. can be counted through PLC.  Defected products can also be counted by this.  PLC uses a programmable counter which the user uses in a variety of counting programs.  In this way, objects are sensed by the sensor and its output signals are transferred to the counter 

Miscellaneous Function 

• Logical operations like AND, OR, NOT, XOR etc. are performed on the process data by PLC and addition, operations like addition, subtraction, division, multiplication etc. are performed. Comparison, sequencer, data transfer operations are also performed by PLC in this type of function.

Advantages of PLC–

Flexibility – 

• Earlier, each electronic component required separate controllers to operate. Thus 15 controllers were used to run 15 machines but now 15 machines can be operated with a single controller 

Vishal Operation

• With the help of PLC, an operation can be seen directly on the CRT and monitor screen. Thus, if a fault occurs during an operation, the process can be stopped there itself. 

Speed of Operations

• PLC programming has high speed.  In this, the operation cannot be operated immediately by relay.  The PLC performs the operation in no time, whose operational time is a few milliseconds. 

Ladder or Boolean Programming 

• Ladder or Boolean programming is performed in ladder mode by an electrician or technician. In this way, this programming is done by a ladder or boolean programmer 

Faster Response Time 

• PLC is designed for a real-time application with high speed. Programmable controllers operate in real time. In this way, the PLC operates an operation only on command, thereby increasing the speed of any process.

Minimum Maintenance 

• PLC operated devices require less maintenance.

Easier to Troubleshoot 

• PLC has resident diagnostics and override functions that allow the user to easily trace and correct software and hardware problems, so that the user can solve the problem easily 

Pilot Running 

• The PLC program and circuit is pre-tested which is run in an office or lab. Some changes are made according to the output in its program and circuit

Lower Cost 

• Various devices available in PLC such as relay, timer, counter and sequencer can be obtained at very low cost

Documentation 

• In the PLC documentation, the printout of a circuit is obtained in no time and is easily made useful. PLC booklets are used in this

Communications Capability 

• The PLC performs and interacts with a variety of functions, such as supervisory control, data gathering, device parameters, downloading and uploading, etc., to perform various types of operations

Security

• Changes to the PLC program cannot be made until it is properly unlocked. In this way, the PLC's data can be prevented from being stolen 

PLC losses –

1. Newar Technology – It is difficult to change the relay and ladder of PLC when new technology comes.  In this way, when the new technology comes, the entire system and software has to be changed, which the electrician and technician have to learn the course related to the new technology 
2. Environmental Consideration – The use of PLC generates high heat which damages other electronic devices and the industrial environment 
3. Unemployment– By using PLC, a process is completed very quickly and by a small number of people, leading to unemployment 
4. Fail -Safe Operation – In relay operation the stop button electrically disconnects the circuit.  If power outages occur, the system stops.  Additionally, it does not restart once the relay system is powered on, for which a fixed PLC program is used 
5. Requirements of Modules – PLC requires modules to interface with various input and output devices that are not readily available 
6. Difficulty of Design – The PLC is manufactured for relay ladder logic.  It does not receive signals to interface with some advanced devices
7.  Difficulty of Training – The PLC is manufactured for relay ladder logic.  It does not receive signals to interface with some advanced devices

Types of PLC and Specifications

➡️Types of PLC and Specifications

➡️Block diagram of PLC

➡️Operation of PLC and Respons time

➡️ Structure of PLC