Industrial Tranining
Introduction
PLC stands for Programmable Logic Controller. It is simply a special computer device which is used for industrial control systems. PLC consists of a microprocessor which is programmed using the computer language. The program is written on a computer and is downloaded to the PLC via cable. These loaded programs are stored in non – volatile memory of the PLC. During the transition of relay control panels to PLC, the hard wired relay logic was exchanged for the program fed by the user. A visual programming language known as the Ladder Logic was created to program the PLC.
Basic Components of PLC
Some basic components of PLC are as following:-
1) CPU (Central Processing Units
2) Memory
3) Input/output
4) Power Supply Unit
5) Programming Device
Function of Various Components
1. CPU
CPU stands for Central Processing Units. The main function is checking the PLC controller to avoid errors. They perform functions including logic operations, arithmetic operations, computer interface and many more.
2 Memory Unit
The System (ROM) stores the data permanently for the operating system. RAM stores the information of the status of input and output devices, and the values of timers, counters and other internal devices.
3. Input/output
Input keeps a track on field devices which includes sensors, switches. Output has a control over the other devices which includes motors, pumps, lights and solenoids. The I/O ports are based on Reduced Instruction Set Computer (RISC).
4. Power Supply Unit
Certain PLCs have an isolated power supply. But, most of the PLCs work at 220VAC or 24VDC.
5 Programming Devices
This device is used to feed the program into the memory of the processor. The program is first fed to the programming device and later it is transmitted to the PLC’s memory.
How PLCs Work
A programmable logic controller is a specialized computer used to control machines and processes. It therefore shares common terms with typical PCs like central processing unit, memory, software and communications. Unlike a personal computer though the PLC is designed to survive in a rugged industrial atmosphere and to be very flexible in how it interfaces with inputs and outputs to the real world.
Size of PLC
- The power supply and rack
- The central processing unit
- The input/output (I/O) section
- Now, let’s start off by removing all our modules which leaves us with a naked PLC with only the power supply and the rack.
Operation system
Example of PLC used in Daily Life
Ladder Logic
When we press the button the bulb is glow.
A few examples of Programmable Logic Controller programming applications that has been successfully completed and is in use today.
- Manufacturing Industry
- Lead acid battery plant, complete manufacturing system
- Extruder factory, silo feeding control system - Travel Industry
- Escalator operation, monitored safety control system
- Lift operation, monitored safety control system - Aerospace
- Water tank quenching system - Printing Industry
- Offset web press print register control system
- Multistage screen washing system - Food Industry
- Filling machine control system
- Main factory feed water pump duty changeover system
ADVANTAGES OF PROGRAMMABLE CONTROLLER
1. Very fast
2. Easy to change logic i.e. flexibility
3. Reliable due to absence of moving parts
4. Low power consumption
5. Easy maintenance due to modular assembly
6. Facilities in fault finding and diagnostic
7. Capable of handling of very complicated logic operations
8. Good documentation facilities
9. Easy to couple with the process computers
10. Analog signal handling and close loop control programming
11. Counter, timer and comparator can be programmed
12. Ease operator interface due to colourographic and advisory system introduction