1. Programmable Logic Controller (PLC)

2. Contents Control Process What is PLC? General Architecture of PLC
PLC Operating Cycle
PLC Hardware Type
PLC Architecture Evolution
Programming of PLC
Basic PLC Advantages
Applications

3. Control Process
Physical Quantity is sensed in the form of small current/voltage e.g. Temperature, Pressure, Flow, Level etc (Sensor)
This Electrical Signal is amplified to a certain level (Amplifier)
Then amplified analogue output is converted into digital form. (Analogue to Digital Converter i.e. A/D)
This digital output is fed to the controller of the system to control the various physical quantities with the help of different devices. (PLC, Microcontroller, DSP etc…)

4. Block Diagram Physical Quantity Amplifier A/D Controller Devices
Amplified Analogue output
Physical Quantity
(Temperature, Pressure etc..)
Amplifier
A/D
Digital
Analogue output in mA/mV
Controller
(PLC, Microcontroller etc…)
Control signals Digital /Analogue
Devices
(Motors etc…)

6. http://www. ac-nancy-metz

7. What is PLC?
A digitally operating electronic apparatus which uses a programmable memory for internal storage of instructions
Implement specific functions, such as logic, sequencing, timing, counting and arithmetic
Control various types of machines or process through digital or analogue input/output.

8. Traditional concept of PLC
PLC performs relay equivalent functions
PLC performs ON/OFF control
Designed for industrial environment

9. General Architecture of PLC

10. Input of PLC Types of Voltages: DC: 12V, 24V, 48V AC: 120V/220V
Input Devices:
Pushbuttons
Sensors
Relay Contacts etc…
*Input of a PLC can be Digital as well as Analogue

11. PLC input is the load in the circuit, sensing if voltage is present.
Contd…
PLC input is the load in the circuit, sensing if voltage is present.

12. Output of PLC Types of Voltages: Output Devices: DC: 12V, 24V, 48V
AC: 120V/220V
Output Devices:
Relays (24V DC/AC, 120V/220V AC)
Transistors MOSFET (24V DC)
Valves
Solenoids
Light
Fan etc….
*Output of a PLC can be Digital as well as Analogue

13. PLC output is a switch, controlling the current flow to the load.
Contd…
PLC output is a switch, controlling the current flow to the load.

14. PLC Operating Cycle

15. PLC Signal Flow
Output

16. PLC Hardware Type
A most basic PLC system is a self contained PLC which has two terminal blocks, one for the Input and other for the Output, called “Micros”.
Typically they provide front panel LED status indication of I/O and processor status.

17. 2. Modular Chassis Based PLC
The vast majority of PLC’s installed today are modular chassis based PLC consisting of:

18. 3. Modular Chassis-less PLC Systems
The advanced PLC’s are chassis-less
These are modular PLC systems.
These systems also have:
-Processor Power supply
-I/O modules Communication card
These components mount directly on a panel to allow easy insertion and removal.

19. General PLC Blocks Personal Computer 220V, 50/60Hz RS 232 Power Supply
CPU
Communicat-ion Module
Analogue Input
Analogue Output
Digital Input
Digital Output
AC to DC conversion (12V or 48V)

20. Contd…

21. Contd…
48V DC

22. Contd…
48V DC

23. Contd…

24. Contd…
Bus system is

25. PLC Architecture Evolution

26. PLC Architecture Evolution

27. PLC Architecture Evolution

28. PLC Architecture Evolution

29. PLC Architecture Evolution

30. PLC Architecture Evolution

31. PLC Application Considerations
Number of I/O: 10, 16, 20, 32, 156 etc…
Memory:
-Types: Flash or Battery Backed
- Size: 1k, 6k, 12k, 16k, 64k etc…
Functions Required:
- Instruction Set: Messaging, PWM etc..
- Arithmetic
- Communications: Ethernet, Profibus etc…
Report Generation

32. Programming of PLC
The purpose of a PLC program is to control the state of outputs based on the current condition of the inputs.
Types of programming :
Ladder Logic (Analogous to Relay Technology)
Function Block (FB’s based on AND-OR logic)
Visual Basic (VB based on C language)
*DOS based programming (Old Technology)

33. 1. Ladder Logic
Most popular and most commonly used PLC language is known as “Ladder Logic” .
Ladder Logic purposely resembles relay logic.
In order to control a process we try to design the logical continuity from input to output of program.

34. Ladder Logic Concepts
Line
Neutral

35. Ladder Logic Concepts

36. Ladder Logic Concepts

37. Read and Write Instruction
Read Instruction
Write Instruction

38. Some Important Instructions
Latching/Unlatching Instruction:
Latch
Retain the output energized until reset
Unlatch

39. Retentive timer-on delay(RTO)
Timer Instructions
Timer ON Delay(TON)
Timer OFF Delay(TOF)
Retentive timer-on delay(RTO)

40. Counter Instructions
Counter Up (CTU)
Counter Down (CTD)

41. Comparison Instructions
Equal (EQU)
Not Equal (NEQ)
Less Than (LES)
Less Than or Equal (LEQ)
Greater Than (GRT)
Greater Than or Equal (GEQ)
Some other instructions are Sequencer Instruction, Shift Register Instruction
etc…

42. Function Block Based on pre-defined blocks of various functions A B
AND

43. Basic PLC Advantages Ease of Programming Ease of Maintenance
Designed for Industrial Environment
Suitable for Extreme Environmental Conditions
Quick Installation
Adaptable to Change

44. Applications