Module-4 PLC for Automation and control.pptx
- 1. Module 4 : Walchand College of Engineering, Sangli.
- 2. What is Automation? “The technique of making an apparatus, a process, or a system operate automatically.” “The creation and application of technology to monitor and control the production and delivery of products and services.”
- 3. Automation Power electronics Closed Loop Controller Sensors and Actors Switchgear, Contactors and Relays Pneumatic and Hydraulic Electronic Controls and Microcontroller Motors Programmable Logic Controller
- 4. Electromechanical Relays: The relay is an electromechanical switch used as a protecting device and also as a controlling device for various circuits, equipment and electrical networks in a power system. The electromechanical relay can be defined as an electrically operated switch that completes or interrupts a circuit by physical movement of electrical contacts.
- 5. Relay Logic
- 8. History and Origin of PLC Developed to replace relays in the late 1960s PLC began in the 1970s, and has become the most common choice for manufacturing controls. The PLC was invented in response to the needs of the American automotive manufacturing industry(primarily General motors) Costs dropped and became popular by 1980s Now used in many industrial designs
- 9. Definition of PLC A PLC is a special form of microprocessor- based controller that uses programmable memory to store instructions and to implement functions such as logic, sequencing, timing,counting and arithmetic in order to control machines and processes.
- 10. PLCs are similar to computers, but whereas computers are optimized for calculation and display tasks, PLCs are optimized for control tasks in the industrial environment.
- 12. Input devices 1. Switches and Pushbuttons 2. Sensing Devices • Limit Switches • Photoelectric Sensors • Proximity Sensors 3. Condition Sensors • Pressure Switches • Level Switches • Temperature Switches • Vacuum Switches • Float Switches 4. Encoders
- 13. Output Devices • Valves • Motor Starters • Solenoids • Actuators • Horns and Alarms • Stack lights • Control Relays • Counter/Totalizer • Pumps • Printers • Fans
- 14. 14 Leading Brands Of PLC AMERICAN 1. Allen Bradley 2. Gould Modicon 3. Texas Instruments 4. General Electric 5. Westinghouse 6. Cutter Hammer 7. Square D EUROPEAN 1. Siemens 2. Klockner & Mouller 3. Festo 4. Telemechanique
- 15. 15 Leading Brands Of PLC JAPANESE 1. Toshiba 2. Omron 3. Fanuc 4. Mitsubishi
- 16. Sr. No. Advantage Description 1 Flexibility Universal Controller Can replace various independent/ standalone controller. Provide Multiple programming abilities. 2 Implementing changes and correcting errors Relay type systems require complete rewiring In PLC, rewiring is not necessary. Only ladder logic is changed. 3 Large quantities of contacts In relay the number of contacts for each coil are limited In PLC, the contacts for a coil are dependent on program. 4 Lower cost More functions in smaller and less expensive packages 5 Pilot running (Simulation Capability) Relay systems have to be tested on factory floor PLC program can be pre-run and evaluated in lab PLC Advantages
- 17. 6 Visual observation Fault detection and Error handling is easy in PLC systems Error messages can be easily be displayed on CRT screen 7 Speed of operation Number of bits of processor Operating frequency (Scan time) 8 Ladder or Boolean programming method PLC programmer who works in Digital or Boolean control system can also perform PLC programming. 9 Reliability and maintainability Solid state devices(semiconductors)-very reliable More reliable than relays which have mechanical wear and tear 10 Simplicity of ordering control system components Counter, Relays,Timers etc. in single PLC
- 18. 11 Documentation Printout of ladder logic can be printed easily No wire tracing is needed for verification 12 Ease of changes by reprogramming Ability to program and reprogram, loading and down loading 13 Security Software lock on a program (Password) Relay systems tend to undergo undocumented changes 14 Capable of task not possible with relays before as indicated by the following: Calculation, information exchange, text and graphic display, data processing, networking
- 19. PLC Disadvantages Sr. No. Disadvantage Description 1 Newer technology Change from ladder and relay to PLC concept 2 Fixed program applications PLC systems may be costlier for single function applications Not economical where multiple programming capabilities are not required 3 Environmental considerations Not adapted for very high temperature, high humidity level, high vibration, etc. 4 Fail-safe operation Relay systems provide direct electrical isolation on pressing stop button PLCs have to be additionally programmed for fail safe operations 5 Fixed-circuit operation In the circuits where alterations are hardly required, PLCs turn out to be ineffective
- 20. 20 Areas of Application Manufacturing / Machining Food / Beverage Metals Power System Mining Petrochemical / Chemical
- 21. Areas of PLC Applications • Annunciators • Injection Molding • Auto Insertion • Assembly • Bagging • Motor Winding • Baking • Oil Fields • Blending • Painting • Boring • Palletizers • Brewing • Pipelines • Calendaring • Polishing • Casting • Reactors • Chemical Drilling • Robots • Color Mixing • Rolling • Compressors • Security Systems • Conveyors • Stretch Wrap • Cranes • Slitting • Crushing • Sorting • Cutting • Stackers • Digesters • Stitching • Drilling • Stack Precipitators • Electronic Testing • Threading • Elevators • Tire Building • Engine Test Stands • Traffic Control • Extrusion • Textile Machine • Forging • Turbines • Generators • Turning • Gluing • Weaving • Grinding • Web Handling • Heat Treating • Welding • Manufacturing/ Machining • Food / Beverage • Metals • Power • Mining • Petrochemical/ Chemical
- 22. Selecting a PLC Criteria • Electrical requirements • Number of logical inputs and outputs. • Memory • Operator interface(Types of I/Os) • Speed of operation. • Communication requirements • Software • Physical environments
- 23. Examples of PLC Programming Software: 1. Allen-Bradley – Rockwell Software RSLogix500 2. Modicon - Modsoft 3. Omron - Syswin 4. GE-Fanuc Series 6 – LogicMaster6 5. Square D- PowerLogic 6. Texas Instruments – Simatic 7. Telemecanique – Modicon TSX Micro
- 25. Hardware or Parts of PLC
- 26. The processor unit or central processing unit (CPU) is the unit containing the microprocessor. This unit interprets the input signals and carries out the control actions according to the program stored in its memory, communicating the decisions as action signals to the outputs. The power supply unit is needed to convert the mains AC voltage to the low DC voltage (5 V) necessary for the processor and the circuits in the input and output interface modules.
- 27. The programming device is used to enter the required program into the memory of the processor. The program is developed in the device and then transferred to the memory unit of the PLC. The memory unit is where the program containing the control actions to be exercised by the microprocessor is stored and where the data is stored from the input for processing and for the output.
- 28. The input and output sections are where the processor receives information from external devices and communicates information to external devices. The communications interface is used to receive and transmit data on communication networks from or to other remote PLCs
- 29. PLC Input Module: Input module senses the presence or absence of an input signal at each of its input terminal.The input signal tells what switch, sensor, or other signal is on or off in the process being controlled. It converts the input signal for high, or on, to a DC level usable by the modules electronic circuit. For a low or off input signal, no signal is converted indicating off. Input module carries out electronic isolation by electronically isolating the input module output from its input. Finally, output logic produces output signal, to be sensed by PLC CPU.
- 31. A typical input module has 4,6,8,12,16 or 32 terminals, plus common and safety ground terminals. All terminals in a given module have identical circuits. The first block receives input signal from switch, sensor and so on. For AC voltage input, DC converter consists of rectifiers and means to step down the voltage to usable level, usually with zener diode. For DC input voltage DC to DC converters are used.
- 32. The optoisolator protects CPU from input surges or circuit malfunctions. Each module is assigned with coded series of numbers by its SIP switch settings.The on off status is checked on each sweep of input scan. Finally, output logic produces output signal, to be sensed by PLC CPU
- 34. A DC signal from CPU is converted through each module section to a usable output voltage, either AC or DC. A typical output module has 4,6,8,12,16 or 32 terminals or sections. The signal then passes through isolation stage. Isolation is necessary so that any erratic voltage from output device does not get back into the CPU and cause damage. The isolator output is transmitted to switching circuitry or output relay.AC switching is accomplished by triac.The output of a module section may be through a relay or ac or dc output. All terminals of a single module have the same output system.
- 35. 35 PLC Operation Basic Function of a Typical PLC Read all field input devices via the input interfaces, execute the user program stored in application memory, then, based on whatever control scheme has been programmed by the user, turn the field output devices on or off, or perform whatever control is necessary for the process application. This process of sequentially reading the inputs, executing the program in memory, and updating the outputs is known as scanning.
- 36. 36 While the PLC is running, the scanning process includes the following four phases, which are repeated continuously as individual cycles of operation: PHASE 2 Program Execution PHASE 3 Diagnostics PHASE 4 Output Scan PHASE 1 Read Inputs Scan
- 37. 37 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.
- 38. PLC Ladder Programming Conventions in drawing a ladder diagram- The vertical lines of the diagram represent the power rails between which circuits are connected.The power flow is taken to be from the left-hand vertical across a rung. Each rung on the ladder defines one operation in the control process. A ladder diagram is read from left to right and from top to bottom. When the PLC is in its run mode, it goes through the entire ladder program to the end, the end rung of the program being clearly denoted, and then promptly resumes at the start. This procedure of going through all the rungs of the program is termed a cycle
- 41. The end rung might be indicated by a block with the word END or RET, for return, since the program promptly returns to its beginning.The scan time depends on the number of rungs in the program, taking about 1 ms per 1000 bytes of program and so typically ranging from about 10 ms up to 50 ms. Each rung must start with an input or inputs and must end with at least one output. Electrical devices are shown in their normal condition. Thus a switch that is normally open until some object closes it is shown as open on the ladder diagram.A switch that is normally closed is shown closed.
- 42. A particular device can appear in more than one rung of a ladder. For example, we might have a relay that switches on one or more devices. The same letters and/or numbers are used to label the device in each situation. The inputs and outputs are all identified by their addresses; the notation used depends on the PLC manufacturer. This is the address of the input or output in the memory of the PLC.
- 45. AND Gate
- 46. OR Gate
- 47. NOT Gate
- 48. NAND Gate
- 49. NOR Gate
- 50. Exclusive OR (XOR) Gate
- 51. Latching There are often situations in which it is necessary to hold an output energized, even when the input ceases. A simple example of such a situation is a motor that is started by pressing a push-button switch.Though the switch contacts do not remain closed, the motor is required to continue running until a stop push-button switch is pressed. The term latch circuit is used for the circuit that carries out such an operation. It is a self-maintaining circuit, that after being energized, maintains the state until another input is received.
- 54. PLCTimers All PLC’s have timer instructions.Timers are output instructions that are internal to the programmable logic controller.Timers provide timed control of the devices that they activate or de-activate.The basic functions of timer are: Timers are used to delay an action. Timers are used to run an operation for a predetermined period of time. Timers are also used to record the total accumulated time of continuous or intermediate events. The types of Timers are : 1. On-Delay timer (TON) 2. Off-Delay timer (TOF) 3. Pulse timer (TP)
- 55. On-DelayTimer
- 56. On-DelayTimer The TON instruction is used to turn an output on or off after the timer has been on for preset time interval.The TON instruction begins to count time base intervals when the rung makes a FALSE-to-TRUE transition. As long as rung conditions remain true, the timer adjusts 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.
- 57. Allen Bradley Timer Instruction Timer :-T4:X T = Identifies this as a timer file. 4 = Represents the default timer file 4. X = This is timer in file 4. Viz.T4:0,T4:1 likewise. Time Base :- The time base indicates the increments by which the timer moves to the preset value, such as 0.001 s, 0.01 s, 0.1 s or 1 s. Accumulator (ACC) Bit :- The accumulated value specifies the number of milliseconds/seconds that have elapsed since the TON instruction was enabled. Preset (PRE) Bit : - The preset value specifies the value which the accumulated value must reach before the instruction sets the DN bit.
- 58. The instruction mainly includes three status bits namely EN,TT, DN. Enable (EN) Bit :- The enable bit indicates the TON instruction is enabled Timer-Timing (TT) Bit :- The timing bit indicates that a timing operation is in process and it remains on until the accumulator reaches the preset value. Done (DN) Bit :- The done bit changes state whenever the accumulated value reaches the preset value.
- 59. PLC Counters A counter is a simple device intended to do one simple thing-count. Every PLC has counter instructions. Using counters sometimes be little challenging because many manufacturers seem to use them different way. In other words, the instruction symbol used and method of programming will change for different manufacturers.
- 61. Working of a counter A counter instruction is always an output instruction. The counter instruction counts each time the input logic changes the rung state from false to true. This input logic can be signal from an external device, for e.g. limit switch or sensor, or a signal from internal logic. Every time the counter instruction sees a false-to-true rung transition, a count-up counters accumulated value is incremented by one.The working of down-counter is little different. Each time when count-down counter sees a false-to-true rung transition, its accumulated value is decremented by one, so the accumulated value must be chosen as the starting point of the count.
- 62. Counter addressing In Allen-bradley counter, the default counter file is file 5. The counter data is stored in counter file. To address the counter as a unit the addressing format used is C5:4 C= C identifies this as a counter file and counter 4 in counter file 5.
- 63. UP-Counter (counting from 0 to 50)
- 64. The preset value (PRE) is the count value that the counter must accumulate before the counter output is 1. The accumulated value (ACC) is the accumulated number of 0 to 1 transitions of the counter rung. The count-up (CU) enable bit is 1 when the input logic makes the up counter rung 1 and 0 when the rung is 0. The count-down (CD) enable bit is 1 when the input logic makes the down- counter rung 1 and 0 when the rung is 0. The done (DN) bit is 1 for both counters when the ACC value is equal to or greater than the PRE value and 0 when it is less. Reset (RES) returns counter accumulator values to zero. As long as RES is 1, ACC and all output bits are held at 0.When RES is 0, the counter is able to start counting.
- 65. DOWN-Counter, (counting from 50 to 0)