Unit 4-PROGRAMMABLE LOGIC INTERFACE-ME6702– MECHATRONICS
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This document provides an overview of programmable logic controllers (PLCs). It describes the basic structure of a PLC including input/output modules, a central processing unit, memory, and a programming unit. The document outlines how PLCs are used for automation in industrial processes as a replacement for hardwired relay controls. It also discusses PLC programming using ladder logic and provides examples of logic functions, timers, counters, and data handling capabilities of PLCs. Selection factors for choosing a suitable PLC are presented.
Unit 4-PROGRAMMABLE LOGIC INTERFACE-ME6702– MECHATRONICS
- 1. UNIT 4 PROGRAMMABLE LOGIC CONTROLLER
- 2. UNIT IV PROGRAMMABLE LOGIC CONTROLLER • Introduction – Basic structure – Input and output processing – Programming – Mnemonics – Timers, counters and internal relays – Data handling – Selection of PLC.
- 3. Content • Introduction • Basic structure • Input and output processing • Programming • Mnemonics • Timers, counters and internal relays • Data handling • Selection of PLC
- 4. PROGRAMMABLE LOGIC CONTROLLER • A Programmable Logic Controller(PLC) is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides or light fixtures.
- 5. Applications • Automated manufacturing process equipment and machinery • Packaging and filling equipment • Chemical mixing • Conveyor systems and distillation etc.,
- 6. Features and specification • They are rugged and designed to withstand vibration, temperature, humidity and noise • The interfacing for inputs and outputs is inside the controller. • They are easily programmed and have an easily understood programming language. • Programming is primarily concerned with logic and switching operation.
- 8. Hardwired motor circuit with PLC
- 10. • PLC is designed as a replacement for the hardwired relay and timer logic, where PLC provides ease and flexibility of control based on programming and executive logical instruction. • The internal functions such as timers, counter and shift registers making sophisticated control possible using even the smallest PLC.
- 11. • PLC capable of performing function such as – counting, – logistics, – numerical application, – comparing and processing of signals. • A PLC is divided in to 4 parts. They are – Input/output module (I/O) – Central processing Unit (CPU) – Memory – Programming unit
- 12. i) Input/output module (I/O) • It is used to transfer the data between external devices and CPU • It is incorporated into PLC in two ways I. Fixed I/O – it is a small unit that comes in one piece with processor i.e., the I/O terminals cannot be changed in fixed I/O II. Modular I/O – it is packed together i.e., there are several compartment of I/O module are plugged together.
- 13. Central processing Unit (CPU) • It is consisting of a microprocessor which interrupts the input signal and carries out the control actions according to the program stored in the memory, communicating the decision as an action signal to the output. • It scan the total information package stored in the memory and input and output devices continuously. • During the scan the CPU executes instruction based on input data, sends appropriate output responses to the output devices, updates data acquisition systems and indicate condition changes
- 14. • Scan time for larger unit depends on the size of the memory and configuration of the system • Power supply unit is needed to convert the AC voltage to the low DC voltage necessary for the processor and to supply power to other circuit in the input and output interface module.
- 15. Memory Unit • The memory in PLC stores the digital control logic, the process program and the necessary instruction to operate the system. • The memory used in PLC are • Non-volatile memory • Volatile memory • According to purpose of usage • RAM –volatile memory • ROM- permanent storage
- 16. Programming unit • It is used to enter the required program into the memory of the processor • There are normally 3 approaches followed by the program – Use of hand held programmer – Terminal with video display unit – PC with appropriate software
- 17. Architecture
- 18. • Buses – Data buses – it is used for communicating data b/n elements – Address buses-it is used to read the address of locations for accessing stored data – Control buses- it is used for internal control action carried by the CPU – System buses- it is used for communication b/n Input/output ports and input/output units
- 19. • Memory – RAM – ROM • PROM • EPROM • Electrically EPROM
- 20. Optoisolator • Electrical connection from the external world is usually by means of optoisolator • When a digital pulses passes through the LED, a pulse of Infrared radiation is produced. • This pulses is detected by the phototransistor and gives rise to a voltage in that circuit.
- 21. Optoisolator
- 22. Input channel with optoisolator
- 23. • Common input voltage is 5V and 24V • Output voltage is 24V and 240V • Output are often specified as being of – Relay type – Transistor type – Triac type
- 24. Relay type of output The relay type output is used for both ac and dc switching Relay are slow to operate
- 25. Transistor type output The transistor type output is used for dc switching This give faster switching action
- 26. Triac type of output The triac type output is used for switching AC voltages
- 27. Programming • The programming of PLC is based on the ladder diagram. • Ladder diagram involve writing a program in a similar maner to drawing a switching circuit.
- 31. Switch controlling Solenoid e.g., solenoid valve open to allow water to enter a vessel Ladder Diagram for Switch Control
- 33. Logic functions An AND System An OR System
- 36. Cylinder Sequencing A+, B+, A- and B-
- 37. List of Mnemonics used for the Mitsubishi f Series PLC
- 38. Mnemonics for Logic system
- 39. Mnemonics for Logic system
- 40. Timer
- 41. Delay ON Timers: • The term delay is used to indicate that this timer burns on, after waiting for a fixed time delay period. • When there is an input, the timer is energized and starts timing, after some pre-set value, the timer contacts are closed to output. • TON is used to denote ON-delay
- 42. Delay OFF Timers: • OFF delay timers are maintained as ON for a fixed time of delay period before turning off. • TOF is used to denote OFF-delay.
- 43. Timer circuit programmed to cause an output to go ON for 0.5s, then OFF for 0.5s, then OFF for 0.5s and so on ON-OFF cycle timer
- 44. Internal relay
- 45. COUNTERS • Counters are used to count a specified number of contact operatio Types of Counters: • Up Counters • Down Counters ns
- 46. Up Counters • Up counters count up from the zero to pre – set value • The events are added until the pre – set value is reached • When the counter reaches the set value, its contacts change state
- 47. Down Counters • Down counters count down from the pre – set value to zero • The events are subtracted until the pre – set value is reached • When the counter reaches the Zero value, its contacts change state
- 48. Counter
- 50. JUMP Instruction
- 51. Data handling • Data movement • Data comparison • Arithmetic operation • Code conversion
- 52. Data Movement Moving data from one memory location to another
- 54. Arithmetic operation • AND • OR • NOT • EX-OR • NAND
- 55. Code Conversions • All the internal operations in the CPU of a PLC are carried out through binary numbers. • Most PLCs provide BCD-to-binary and binary- to-BCD conversion for use. • When a decimal (input) signal is given, BCD conversion is used.
- 56. • Similarly, when a decimal output is required, Decimal conversion is used. • The data at the source address is in BCD and converted to binary and placed at the destination address.
- 57. Controlling the speed of motor
- 58. Selection of PLC • System definition • Choosing the I/O hardware • I/O timing consideration • Analog I/O module –resolution, voltage level • Conversion speed • Analog closed control • Communication • Counter, encoders and positioning • Selecting suppliers