Programmable logic controller
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A PLC is a digitally operated electronic device that uses programmable memory to implement specific functions. It has several advantages including flexibility, easy error correction, cost effectiveness, and reliable operation. The PLC processor and memory are located in the CPU. The CPU contains fixed and alterable memory. The control unit manages input/output scanning and logic processing based on the user-written program. PLCs are commonly used in industrial manufacturing applications for process control.
Programmable logic controller
- 1. Compiled by - Shruti Bhatanagar Dasgupta
- 2. A PLC is a digitally operational electronic equipment which uses programmable memory of internal storage of instructions to implement a specific function.
- 3. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Flexibility: can run many types of machines at the same time with their own distinct programs. Easy implementation of changed and correction of errors. Large no. of contact coils available for programming. Its cost effective. It has pilot running feature enabling the pre-run and evaluation of a program in the office or lab. Its speed of operation can be determined through its scan time. The programming method is through ladder logic using Boolean logic. It is more reliable and easy to maintain as compared to solid-state components Ease of documentation of PLC Circuit. Fail safe operation.
- 4. INPUTS Multiple Wires C R C O E OUTPUTS D E TO OUTPUTS R O D TO INPUTS Connection s to I/P Contacts Connectio ns to O/P Coils, Alar ms,etc CPU PROGRAMME R MONITOR PRINTE R RECORDE R
- 5. Data processing and Process Control Computer Keyboard Light-Pen Mouse Data Processing Computer System Heat Sensor Plotter Motor Motion Sensor Sound Sensor Video Display Terminal Printer Process Control Computer System Solenoid Heater
- 6. The PLC Processor and Memory are always in the same unit called the CPU. The CPU fixed memory contains the program set by the manufacturer System program is set into special IC Chip called Read Only Memory (ROM), which cant be altered or erased. The memory space that can be erased or programmed by the user is stored in the CPR Random Access Memory (RAM).
- 7. Operational Section of PLC CPU Fixed Memory - Logic - Edit - Monitor - ROM Power Supply Alterable Memory - Diagram - Numerics - I/O Status - RAM Processor - Logic - Clock, et c. I/P Peripherals Battery Backup O/P Peripherals
- 8. ROM with fixed operating system Control Unit ALU Control Section Registe rs Analysi s Peripherals - Keyboard s - Tape - Print - Disk I/P INPUT SCAN BLOCK Logic Scan Program (Where User Writes for Process Cntrl) OUTPUT SCAN BLOCK O/P Interfaces with other CPUs etc.
- 9. The processor is programmable, and since it can perform many logic and arithmetic functions its also known as the Microprocessor. Its classified as per bit size and clock speed S.No. Bit Size (bit) Clock Speed (M Hz) 1 8085 8 1 2 8086 16 4.77 3 80186 16 8 4 80286 16 12.5 5 80386 32 33 6 Microprocessor 80486 32 50 The bit size determines the no. of bits of data the microprocessor can manipulate and clock speed determines the speed of execution of the instruction.
- 10. The ROM with fixed operating system program interfaces to the control section. It manages the operation of the PLC. The control Section, contains a Control unit with storage registers. The Control Section determines which operating sections are to be functional, in what order and for how long. The I/P Scan block, scans the I/Ps and places the I/p statuses in the Ram Memory, when required to do so. After analysis the Logic Scan updates the O/P Scan Block to the Appropriate state and changes the O/P respectively. The O/P Scan Block then scans the O/P and updates their statuses in the RAM.
- 11. Used in typical industrial processes in manufacturing where the cost of developing and maintaining the automation system is high relative to the total cost of the automation, and where changes to the system would be expected during its operational life. Used in Automotive applications. Used in very complex process control, such as used in the chemical industry, may require algorithms and performance beyond the capability of even high-performance PLCs. Also used in very high-speed or precision controls may also require customized solutions; for example, aircraft flight controls. Programmable controllers are widely used in motion control, positioning control and torque control. Some manufacturers produce motion control units to be integrated with PLC. PLC with feedback is also used in temperature control units also.