-basic concept and history-of-plc-ppt.pptx

Training about basic concept of programable logic controller

1. BASICS OF PLC P r epa r e d B y : JAY BHAVSAR

2. Contents History Introduction Difference between PLC and DCS and PC Data flow overview Major components PLC scan cycle PLC communication PLC Programming language Ladder logic Advantage and disadvantage Application

3. History of PLC Devloped to replace relays in late 1960’s. In 1970’s PLC become most common choice for manufacturing controls Plc was first design and developed by modicon as a relay replacer for general motors

4. INTRODUCTION What is PLC? PLC is a continuously monitor the status of devices connected as inputs. Based upon a user written program ,stored in memory it control the status of devices connected as output A programmable logic controller (PLC) is an industrially computer-based unit that performs discrete or continuous control functions in a variety of processing plant and factory environments.

5. What is PLC? It is capable of storing instructions to implement control functions such as sequencing, timing, counting, arithmetic, data manipulation and communication. The I/O interfaces provide the connection between the PLC and the information providers (inputs like pushbuttons, sensors,…) and the controllable devices (outputs like pumps,valves , relays, lamps,…).

6. What is PLC?

7. Components of automation Sensor: Produce the input value for the controller as feedback. For example, RTD, strain gauge. Controller: Controls the process by sending the particular value according to the set value and feedback coming from the sensor. Difference between them called feedback. According to the behavior of error, control strategies is being decided. Controllers can be Digital controllers, PLCs etc. Actuators : Component which is acting on the response of the controller. And as a result process value will be effected.

8. comparison between PLC and PC

9. Difference between PLC and DCS

10. PLC is usually used for controlling medium or large scale application Whereas DCS is used for controlling entire plant

11. Difference between PLC and DCS

12. Difference between PLC and DCS

13. Leading Brands Of PLC AMERICAN 1. Allen Bradley 2. Modicon 3. Texas Instruments 4. General Electric 5. Westinghouse 6. Cutter Hammer 7. Square D EUROPEAN 1. Siemens 2 K & M 3. Festo

14. Selecting a PLC Criteria • Number of logical inputs and outputs. • Memory • Number of special I/O modules • Scan Time • Communications • Software

15. PLC Size 1. SMALL it covers units with up to 128 I/O’s and memories up to 2 Kbytes. MEDIUM It have up to 2048 I/O’s and memories up to 32 Kbytes. LARGE the most sophisticated units of the PLC family. They have up to 8192 I/O’s and memories up to 750 Kbytes. can control individual production processes or entire plant.

16. PLC SCAN CYCLE PHASE 1 Read Inputs Scan PHASE 2 Program Execution PHASE 3 Diagnostics/ Comm PHASE 4 Output Scan

17. Cycle time depends on the size of the programs, no. of I/O’s and and amount of communication requried PHASE 1 – Input Status scan A PLC scan cycle begins with the CPU reading the status of its inputs. PHASE 2– Logic Solve/Program Execution The application program is executed using the status of the inputs

18. PHASE 3– Logic Solve/Program Execution Once the program is executed, the CPU performs diagnostics and communication tasks PHASE 4 - Output Status Scan An output status scan is then performed, whereby the stored output values are sent to actuators and other field output devices. The cycle ends by updating the outputs.

19. As soon as Phase 4 are completed, the entire cycle begins again with Phase 1 input scan. The time it takes to implement a scan cycle is called SCAN TIME . The scan time composed of the program scan time , which is the time required for solving the control program, and the I/O update time , or time required to read inputs and update outputs. The program scan time generally depends on the amount of memory taken by the control program and type of instructions used in the program. The time to make a single scan can vary from 1 ms to 100 ms.

20. DATA FLOW OVERVIEW

21. DATA FLOW OVERVIEW

22. DATA FLOW OVERVIEW

23. PLC SCAN PROCESS

24. PROGRAMING DEVICE HAND-HELD UNIT WIH DISPLAY Hand held units are often used on the factory floor for troubleshooting, modifying programs, and transferring program to multiple machines It is not able to display long programming so its not widely used in industy

25. PROGRAMING DEVICE PC WITH APPROPRIATE SOFTWARE The software allows users to create ,edit and store program The plc is communicate with PC via a serial or parallel data communication

26. Major components of PLC From SENSORS Pushbuttons, contacts, limit switches, etc. I M N O P D U U T L E PROCESSOR O M U O T D P U U L T E To OUTPUT Solenoids, contactors, alarms etc. PROGRAMMING DEVICE POWER SUPPLY

27. Major components of PLC 1. Power supply : The power supply converted line voltage commonly 120 or 240 volts AC AC Voltage converted into commonly 24v To power on the PLC and its components 2. I/O MODULES : Provides signal conversion and isolation between the internal logic- level signals inside the PLC and the field’s high level signal.

28. I/O Module The I/O interface section of a PLC connects it to external field devices. The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices. Input modules converts signals from discrete or analog input devices to logic levels acceptable to PLC’s processor. Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices.

29. INPUT MODULE These module act as interface between real time status of process variable and the CPU Analog input module : typically input to these module is 4-20mA, 0-10v Example - level Tx , RTD , thermocouple Digital input module : input to these modules is 24V DC 115V AC 230VAC switch , pushbuttons relays

30. PLC INPUTS OUTPUTS MOTOR LAMP CONTACTOR PUSHBUTTONS

31. OUTPUT MODULE These module act as a link between the CPU and the output devices Analog output module : typically output to these module is 4-20mA, 0-10v Ex – control valves, speed, vibration Digital output module : output to these modules is 24V DC 115V AC 230VAC Ex – solenoid valve, actuator, lamp, on off control

32. PLC SCAN PROCESS RAIL RUNG

33. PLC SCAN PROCESS

34. PLC SCAN PROCESS

35. PLC Communications Serial Communications PLC communications facilities normally provides serial transmission of information. RS 232 Used in short-distance computer communications, with the majority of computer hardware and peripherals. Has a maximum effective distance of approx. 30 m.

36. PLC Communications Local Area Network (LAN) Local Area Network provides a physical link between all devices plus providing overall data exchange management or protocol, ensuring that each device can “talk” to other machines and understand data received from them. LANs provide the common, high-speed data communications bus which interconnects any or all devices within the local area. LANs are commonly used in business applications to allow several users to share costly software packages and peripheral equipment such as printers and hard disk storage.

37. RS 422 / RS 485 Used for longer-distance links, often between several PCs in a distributed system. RS 485 can have a maximum distance of about 1000 meters.

38. PLC PROGRAMMING LANGUAGE

39. Ladder diagram (LD) Sequential Function Charts (SFC) Function Block Diagram (FBD) Structured Text (ST) Instruction List (IL)

40. IEC 1131-3 is the international standard for programmable controller programming languages. The following is a list of programming languages specified by this standard: 5 types of programming language used in PLC 1. Ladder diagram (LD) 2.Sequential Function Charts (SFC) 3.Function Block Diagram (FBD) 4.Structured Text (ST) 5.Instruction List (IL) One of the primary benefits of the standard is that it allows multiple languages to be used within the same programmable controller. This allows the program developer to select the language best suited to each particular task.

41. Ladder Logic Ladder logic is the main programming method used for PLC's. As mentioned before, ladder logic has been developed to relay logic XIC - Examine if Closed XIO - Examine if Open OTE - Output Energize OTL - Output Latch

42. XIC Examine if Closed

43. XIC Examine if OPEN

44. OTE Output Energize Definition Turns a bit on or off Use OTE instruction in your ladder logic to turn on a bit when rung condition is evaluated as true EXAMPLE Light Motor run signal Internal bits

45. Output Energize

46. TIMER TON - Timer On Delay TOF - Timer Off Dealy RTO - Retentive Timer

47. TON Timer On Delay Symbol Definition Count time base intervals when the instruction is true. The Timer On Delay instruction begins to count time base intervals when rung conditions become true. As long as rung conditions remain true, the timer adjust its accumulated value (ACC) each evaluation until it reaches the preset value (PRE). The accumulated value is reset when rung conditions go false, regardless of whether the timer has timed out.

48. TOF Timer Off Delay DEFINATION: Counts time base intervals when the instruction is false. The Timer Off Delay instruction begins to count time base intervals when the rung makes a true to false transition. As long as rung conditions remain false, the timer increments its accumulated value (ACC each scans until it reaches the preset value (PRE). The accumulated value is reset when rung conditions go true regardless of whether the timer has timed out.

49. RTO Retentive Timer DEFINATION: Counts time base intervals when the instruction is true and retains the accumulated value when the instruction goes false or when power cycle occurs. The Retentive Timer instruction is a retentive instruction that begins to count time base intervals when rung conditions become true.

50. The Retentive Timer instruction retains its accumulated value when any of the following occurs: Rung conditions become false. Changing Processor mode from run /Test / program mode. The processor loses power while battery back up is still maintained.and a fault occurs. RTO Retentive Timer

51. COUNTERS

52. COUNTERS CTU - Count Up CTD - Count Down RES - Reset

53. CTU Count UP Increments the accumulated value at each false to true transition and retains the accumulated value when the instruction goes false or when power cycle occurs. The CTU is an instruction that counts false to true transition. When this transition happens the accumulated value is incremented by one count. A CTU accumulation is reset by the RES instruction. If the accumulation value is over the maximum range then the overflow (OV) bit will be true.

54. RES Reset Resets the accumulated value and status bit of a timer or counter. Use a RES instruction to reset timers or counters. When the RES instruction is enabled, it resets the Timer On Delay, Retentive Timer, and Counter Up, Counter Down instruction having the same address as the RES instruction.

55. VARIOUS SYMBOL USED IN LADDER LOGIC

56. Coils 60 Coils represent relays that are energized when power flows to them. When a coil is energized it causes a corresponding output to turn on by changing the state of the status bit controlling the output to 1. That same output status bit maybe used to control normally open or normally closed contact anywhere in the program.

57. BOXES Boxes represent various instructions or functions that are Executed when power flows to the box. Some of these Functions are timers, counters and math operations.

58. Function Block Diagram Function Block diagram (FBD) is used for PLC programs described in terms of graphical blocks. Functional blocks can have standard functions, such as those of the  logic gates or counter or timers  or have functions defined by the user, e.g. a block to obtain an average value of inputs.

59. Statement List In statement-list programming approach, an instruction set similar to assembly language for a microprocessor is used. Statement lists, available on few brands of PLCs, are  the most flexible form of programming for the experienced user  but are by no means as easy to follow as ladder diagrams or logic symbols.

60. DIGITAL OPERATION

61. Different Logic Gates Circuit Diagrams a logic gate is an idealized or physical device implementing a Boolean function; that is, it performs a logical operation on one or more logical inputs, and produces a single logical output Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In modern practice, most gates are made from field-effect transistors (FETs), particularly MOSFETs (metal–oxide–semiconductor field-effect transistors)

62. Combinational Logic Combinational Logic Circuits are made up from basic logic NAND, NOR or NOT gates that are “combined” or connected together to produce more complicated switching circuits. These logic gates are the building blocks of Combinational Logic Circuits.

63. AND OPERATION Each rung or network on a ladder program represents a logic operation. In the rung above, both inputs A and B must be true (1) in order for the output C to be true (1). Rung A B C

64. OR OPERATION In the rung above, it can be seen that either input A or B is be true (1), or both are true, then the output C is true (1). Rung A B C

65. NOT OPERATION In the rung above, it can be seen that if input A is be true (1), then the output C is true (0) or when A is (0), output C is 1. Rung A C

66. Programing example

67. ADVANTAGE Very High Accuracy Low Power Consumption (Energy Saving) Small in Size (Required Lased space) Easily programmable Easy Maintenance

68. Disadvantages High Skilled Engineering Required for that high skilled person required Difficulty with changes or replacements Some high Initial Cost.

69. 74 Areas of Application Manufacturing / Machining Food / Beverage Metals Power Mining Petrochemical / Chemical 74

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