PLC_Introduction to programming updated.pptx

PLC and Design

1. 21EE1930 PLC Programming

2. Higher Productivity Why Automation? Superior quality of end product Efficient usage of energy and raw materials Improved safety in working condition etc… Greatly man power is reduced

3. Evolution of PLC PLC Control Electronics Control Hard – Wired Control (or) Relay Logic Control Manual Control Pneumatic Control

4. History of PLC During the late 1960s, General Motors (USA) was interested in the computer application to replace the hardwire systems. Bedford Associates ( Modicon ) and Allen Bradley responded to General Motors. The name given was “Programmable Controllers” or PC. Programmable Logic Controller or PLC was a registered trademark of the Allen Bradley. Later, PC was used for “Personal Computer” and to avoid confusion PLC for “Programmable Controller” and PC for a personal computer.

5. Definition: A programmable logic controller (PLC) is a specialized computer used to control machines and process. Programmable Logic Controller It uses a programmable memory to store instructions and execute specific functions that include On/Off control, timing, counting, sequencing , arithmetic , and data handling. The very first PLC was developed by modicon in later 1965.

6. What is a PLC? Inputs Outputs The Basic Block A PROGRAMMABLE LOGIC CONTROLLER is a solid state control system that continuously monitors the status of devices connected as inputs. Based upon a user written program, stored in memory, it controls the status of devices connected as outputs. CPU

7. What is Control? “ CONTROL is the process in a system in which one or several input variables influence other variables. “ C O N T R O L S Y S T E M P L A N T INFORMATION COMMANDS ACTUATORS SENSORS A Simple View of a Control System

8. How Does a PLC Work? Power Supply Program Memory Processor Input modules Output modules 24 VDC GND Sensors Actuators / Annunciators The sensors are connected to the INPUT MODULES The processor in the CPU MODULE executes the program and scans the individual input for presence or absence of voltage Depending on the state of the inputs, the processor directs the OUTPUT MODULES to switch voltages The ACTUATORS or ANNUNCIATORS are switched “ON” or “OFF” according to the voltage states

9. PLC Signal Flow Programming Terminal O:0/7 O:0/7 O:1/5 Output Devices Output Modules Processor Memory Input Module Input Devices Ladder Program O:0/7 O:1/5 I:0/6 I:1/4 O:1/5 I:0/6 I:1/4 I:0/6 I:1/4 Data Input Image Table Output Image Table

10. Advantages of a PLC Control System Eliminates much of the hard wiring that was associated with conventional relay control circuits. The program takes the place of much of the external wiring that would be required for control of a process.

11. Advantages of a PLC Control System Increased Reliability: Once a program has been written and tested it can be downloaded to other PLCs. Since all the logic is contained in the PLC’s memory, there is no chance of making a logic wiring error.

12. Advantages of a PLC Control System More Flexibility: Original equipment manufacturers (OEMs) can provide system updates for a process by simply sending out a new program. It is easier to create and change a program in a PLC than to wire and rewire a circuit. End-users can modify the program in the field.

13. Advantages of a PLC Control System Lower Costs: Originally PLCs were designed to replace relay control logic. The cost savings using PLCs have been so significant that relay control is becoming obsolete, except for power applications. Generally, if an application requires more than about 6 control relays, it will usually be less expensive to install a PLC.

14. Advantages of a PLC Control System Communications Capability: A PLC can communicate with other controllers or computer equipment . They can be networked to perform such functions as: supervisory control, data gathering, monitoring devices and process parameters, and downloading and uploading of programs.

15. Advantages of a PLC Control System Faster Response Time: PLCs operate in real-time which means that an event taking place in the field will result in an operation or output taking place. Machines that process thousands of items per second and objects that spend only a fraction of a second in front of a sensor require the PLC’s quick response capability.

16. Advantages of a PLC Control System Easier To Troubleshoot: PLCs have resident diagnostic and override functions that allows users to easily trace and correct software and hardware problems. The control program can be watched in real-time as it executes to find and fix problems

17. Architecture of PLC System

18. ARCHITECTURE OF PLC

19. What are Inputs? Switches and Pushbuttons Sensing Devices Limit Switches Photoelectric Sensors Proximity Sensors Condition Sensors Pressure Switches Level Switches Temperature Switches Vacuum Switches Float Switches Encoders

20. What are Outputs? Valves Motor Starters Solenoids Actuators Control Relays Horns & Alarms Stack Lights Fans Counter Pumps Printers

21. I/O Configurations Fixed I/O Is typical of small PLCs Comes in one package, with no separate removable units. The processor and I/O are packaged together. Lower in cost – but lacks flexibility.

22. I/O Configurations Modular I/O Is divided by compartments into which separate modules can be plugged. This feature greatly increases your options and the unit’s flexibility. You can choose from all the modules available and mix them in any way you desire.

23. I/O Configurations Modular I/O When a module slides into the rack, it makes an electrical connection with a series of contacts - called the backplane. The backplane is located at the rear of the rack.

24. Power Supply Supplies DC power to other modules that plug into the rack. In large PLC systems, this power supply does not normally supply power to the field devices. In small and micro PLC systems, the power supply is also used to power field devices.

25. Processor (CPU) Processor Module Is the “brain” of the PLC. Consists of a microprocessor for implementing the logic, and controlling the communications among the modules. Designed so the desired circuit can be entered in relay ladder logic form. The processor accepts input data from various sensing devices, executes the stored user program, and sends appropriate output commands to control devices.

26. I/O Section Consists of input modules and output modules.

27. I/O Section Input Module Forms the interface by which input field devices are connected to the controller. The terms “field” and “real world”are used to distinguish actual external devices that exist and must be physically wired into the system.

28. I/O Section Output Module Forms the interface by which output field devices are connected to the controller. PLCs employ an optical isolator which uses light to electrically isolate the internal components from the input and output terminals.

29. Programming Device PC with appropriate software A personal computer (PC) is the most commonly used programming device. The personal computer communicates with the PLC processor via a serial or parallel data communications link . If the programming unit is not in use, it may be unplugged and removed. Removing the programming unit will not affect the operation of the user program . The computer monitor is used to display the logic on the screen . The software allows users to create, edit, document, store and troubleshoot programs .

30. Programming Device Hand-held programming devices are sometimes used to program small PLCs. They are compact, inexpensive, and easy to use, but are not able to display as much logic on screen as a computer monitor. Hand-held units are often used on the factory floor for troubleshooting , modifying programs, and transferring programs to multiple machines . Hand-held unit with display

31. PLC Operating Cycle - Program Scan During each operating cycle, the processor reads all inputs, takes these values, and energizes or de-energizes the outputs according to the user program. This process is known as a scan . I/O scan – records status data of input devices. Energizes output devices that have their associated status bits set to ON (1) Program scan – instructions are executed sequentially Because the inputs can change at any time, the PLC must carry on this process continuously.

32. Scan Process Read inputs Adjusts outputs Run program The scan is a a continuous and sequential process

33. Scan Patterns Horizontal Scanning Order The processor examines input and output instructions from the first command, top left in the program, horizontally, rung by rung. End of ladder In addition to the program itself, the scan time is also dependent on the clock frequency of the processor!

34. Scan Patterns Vertical Scanning Order The processor examines input and output instructions from the first command, vertically, column by column and page by page. Pages are executed in sequence. End of ladder Misunderstanding the way the PLC scans can cause programming bugs!

35. Ladder diagram language is the most commonly used PLC language and is designed to mimic hardwired relay logic. Hardwired relay control circuit Equivalent ladder diagram program

36. Functional block diagram programming uses instructions that are programmed as blocks wired together to accomplish certain functions.

37. Sequential function chart programming language is similar to a flowchart of your process. The program is split into steps with multiple operations happening in parallel branches .

38. Structured text is a high level language primarily used to implement more complex procedures. Ladder diagram Equivalent structured text program . (High level languages)

39. Instruction list programming language consists of a series of instructions that refer to the basic AND, OR , and NOT logic gate functions. Hardwired relay control circuit Equivalent instruction list program

40. OR GATE

41. AND GATE

42. NOT GATE

43. NAND GATE

44. NOR GATE

45. Ex-OR GATE

46. For instance, if we want to energize a load based on the inverse, or NOT, of a normally-open contact, we could do this : CR1

47. BASIC INSTRUCTION SET Relay Logic Instructions

48. The timer will be ON when a start input signal is received and when a preset timing is reached, the signal state of the output changes from 0 to 1 On Delay Timer Diagram

49. The Toff timer will keep the output energized for a preset time after the rung signal has gone false Off Delay Timing Diagram