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PLC Basics Presentation.ppt thank you for all
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- 2. PLC Presentation Contents Introduction Whatis a PLC Why Use PLCs? Advantages Industrial and PLC control system PLC Types Choosing PLC Hardware PLC Applications Programming PLC’s Advantages of PLCs Questions
- 3. GM Criteria forPLCs - 1968 Easy to program Easy to maintain Highly reliable in an industrial environment Expandable Cost competitive Compact Communicate Accept 120 VAC input signals Operate 120 VAC devices
- 4. What is aPLC? Nema Definition circa 1978 The PLC, also known as programmable controller is defined by the National Electrical Manufacturers Association (NEMA) in 1978 as: "a digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequencing, timing, counting and arithmetic, to control through digital or analog input/output, various types of machines or process".
- 5. Traditional PLC Concept PLCperforms relay equivalent functions PLC performs ON/OFF control Ladder diagram programming Designed for industrial environment
- 6. Industrial Control systems •In a traditional industrial control system, all control devices are wired directly • .
- 7. In a PLCSystem: • The PLC replaces the wiring between the devices. Thus, instead of being wired directly to each other, all equipment is wired to the PLC. 1. The control program inside the PLC provides the “wiring” connection between the devices. 2. The control program is the computer program stored in the PLC’s memory that tells the PLC what’s supposed to be going on in the system. 3. The use of a PLC to provide the wiring connections between system devices may be called soft wiring This soft wiring feature is useful.
- 8. Why Use PLC? Traditionalsystem • control function is modified by physically changing the wiring between the devices • This is costly and time consuming endeavor PLC system • Soft wiring • control function is modified by just changing the control program inside the PLC • These changes are easy and cheap
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- 10. |/| CR3 CR3 M1 PB1 LS1SOL2 PB2 LS1 LS3 LS4 I/8 I/4 I/6 O/0 O/1 | | | | ( ) I/5 I/7 B/0 | | | | ( ) | | |/| B/0 ( ) Relay Logic vs. PLC & Ladder Logic | | I/9 Programmable Logic Controller Inputs Outputs C R
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- 12. Basic PLC Advantages •Ease of programming • Ease of maintenance • Designed for industrial environment • Quick installation • Adaptable to change
- 13. Other Advantages ofPLC In addition programming flexibility, PLC System offers: • High reliability • Reduced costs • Expandability • Computing capabilities • Small space requirements • Ability to withstand harsh operating conditions
- 14. Advantages over Relays •All the capabilities of the earlier systems • Dramatic performance increase over the relay logic systems • Greater reliability • Little maintenance due to no moving parts • No special programming skills required by maintenance personnel • Physical size of the PLC system is much smaller than the conventional relay based logic • And most importantly much lower cost Source: C.Maynard@curtin.edu.au
- 15. Advantages over SBC’s(single board computers) • SBC’s have high design costs – Contract or Staff with overhead and maintenance issues associated with each • SBC’s are Repair / Service nightmare for customers – Depending on markets served supplier must develop/support services • SBC’s requires high level of technical expertise by technicians – Specialized circuit boards require specialized equipment and technical staff • SBC’s not stocked through local distributors – Suppliers sell the controller imbedded, replacement parts are not readily available even in emergency situations • SBC’s typically do not meet worldwide standards – Certifications cost money, typically a single controller does not warrant the investment. Volumes are not high enough and re-certification on each revision is unrealistic • SBC’s typically a “Domestic” product – Because of these issues many manufacturers limit themselves to a single market.
- 16. Advantages over Computerbased Software • Maintenance personnel already experienced in PLC troubleshooting and servicing relay latter logic programming, not PC software • Better power failure response • Cost advantages for simple machine control • Higher reliability that minimizes the expense of shutdown, troubleshooting, repair, & startup • Industrially hardened packaging • Long availability and support for product models without the rapid obsolescence of PCs.
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- 18. Inside a PLC CR Isolation Barrier Isolation Barrier MEMORY programdata High Voltage High Voltage Low Voltage AC Power Supply 85-264 VAC, 50/60Hz O u t p u t C i r c u i t s External DC Power Supply or Communications I n p u t C i r c u i t s Central Processor
- 19. Terminal Block 1 2 3 4 5 6 7 8 9 Input Devices L1 L1 L2 10 COM P L C Isolation Barrier Input Wiring:PLC input is the load in the circuit, sensing if voltage is present
- 20. Input Devices • Pushbuttons •Selector Switches • Limit Switches • Level Switches • Photoelectric Sensors • Proximity Sensors • Motor Starter Contacts • Relay Contacts • Thumbwheel Switches • 120/230 VAC • 24 VDC – Sourcing – Sinking
- 21. OUT 1 Output Devices L2 L2 L1 OUT1 OUT 2 OUT 2 OUT 3 OUT 3 OUT 4 OUT 4 OUT 5 OUT 5 OUT 6 OUT 6 CR L1 P L C Terminal Block Isolation Barrier Output Wiring: PLC output is the switch, controlling current flow to load
- 22. Output Devices • Valves •Motor Starters • Solenoids • Control Relays • Alarms • Lights • Fans • Horns • Relays – 120 VAC/VDC – 240 VAC – 24 VAC/VDC • Triac – 120/230 VAC • Transistor MOSFET – 24 VDC
- 23. Input Scan Program Scan OutputScan Housekeeping START Each ladder rung is scanned using the data in the Input file. The resulting status (Logic being solved) is written to the Output file (“Output Image”). The status of external inputs (terminal block voltage) is written to the Input image (“Input file”). The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF. Internal checks on memory, speed and operation. Service any communication requests, etc. PLC Operating Cycle
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- 25. Most Basic ofPLC Systems In the most basic of PLC systems, a self contained (shoe box) PLC has 2 terminal blocks, one for Inputs and one for Outputs Today, most PLC’s in this category are know as Micros. Typically they provide front panel LED status indication of I/O and Processor states Programmable Controller Inputs Outputs C R
- 26. Modular Chassis BasedPLC’s The vast majority of PLC’s installed today are modular chassis based systems consisting of: 1. Processor Module (CPU) 2. Input & Output Modules 3. Chassis 4. Power Supply
- 27. Modular Chassis-less PLCSystems Also available from many vendors are “Chassis less” but still Modular PLC systems. These systems still require a Processor, I/O Modules, and Power Supply, but in place of a chassis these components mount directly onto a panel, din rail, and many use a tongue and grove system to allow easy insertion and removal
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- 29. PLC Application Considerations •Inputs/Outputs – Type, • AC, DC, sourcing, sinking, etc. – Number of • 10, 16, 20, 32, 156 • Memory – Type • Flash or Battery backed – Size • 1k, 6k, 12k, 16k, 64k • Functions required – Instruction set • Messaging • PID • PTO, PWM – Arithmetic – Communications • DeviceNet, Ethernet • Remote I/O, DH+ – Report generation
- 30. SOURCING vs. SINKING +VDC SOURCINGPushbutton (PNP) SINKING Pushbutton (NPN) DC Power Supply + - DC COM DC Power Supply + -
- 31. SOURCING vs. SINKINGDC Inputs DC Power Supply Field Device DC Input Module + - DC COM IN1 DC Input Module Field Device DC Power Supply + - +VDC IN1 SOURCING (PNP) SINKING (NPN)
- 32. Rules • Field deviceson the positive side (+VDC) of the field power supply are sourcing field devices. • Field devices on the negative side (DC COM) of the field power supply are sinking field devices. • Sourcing field devices must be connected to sinking I/O cards and vice versa. • Sinking field devices must be connected to sourcing I/O cards and vice versa. RULES
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- 34. Programming PLC’s The purposeof a PLC Program is to control the state of PLC outputs based on the current condition of PLC Inputs Different PLC’s support different languages, but the most popular PLC language is know as “Ladder Logic”. PLC Ladder Logic purposely resembles Relay Logic
- 35. START STOP output START STOP output EQUIVALENT DIAGRAMS Normally OpenContact Normally Closed Contact Motor Control Ladder Diagram
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- 37. relay coil relay contacts relay core normally open contact normally closed contact relaycoil Control Relay 1) Control relays are the basic component of ladder diagram logic (control relay logic) 2) Control relays are simulated by PLCs
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- 41. Motor Control LadderDiagram relay coil control circuit voltage relay coil motor power circuit control circuit relay contacts relay core relay not activated motor not activated CR1 START STOP
- 42. Motor Control LadderDiagram relay coil relay coil motor power circuit relay contacts relay core relay activated motor activated CR1 START STOP relay core "pushed" "activated"
- 43. Motor Control LadderDiagram relay coil relay coil motor power circuit control circuit relay contacts relay core relay not activated motor not activated CR1 START STOP "released"
- 44. Motor Control LadderDiagram relay coil relay coil motor power circuit control circuit relay contacts relay core relay not activated motor not activated CR1 START STOP CR1
- 45. Motor Control LadderDiagram relay coil relay coil motor power circuit relay contacts relay core relay activated motor activated CR1 START STOP relay core "pushed" "activated" CR1
- 46. Motor Control LadderDiagram relay coil relay coil motor power circuit relay contacts relay core relay activated motor activated CR1 START STOP relay core "released" "activated" “held” CR1
- 47. Motor Control LadderDiagram relay coil relay coil motor power circuit control circuit relay contacts relay core relay not activated motor not activated CR1 START STOP CR1 “pushed”
- 48. Motor Control LadderDiagram relay coil relay coil motor power circuit control circuit relay contacts relay core relay not activated motor not activated CR1 START STOP CR1 “released”
- 49. output CR1 START STOP CR1 PLC LadderDiagram condition area of a rung
- 50. In a PLCall internal states, inputs and outputs are assigned to bits. B3 B3 B3 B3 1 2 3 4 B3 4
- 51. I:0 I:0 B3 12 4 B3 4 O:1 7 SLOT 0 TERMINAL 1 INPUT ? All external inputs and outputs are assigned to modules.
- 52. Ladder Logic Concepts || |/| Read / Conditional Instructions Write / Control Instructions | | |/| | | |/| | | | | |/| ( ) | | ( ) ( ) ( ) ( ) | | Start (Rung #1) End (Rung #5)
- 53. Ladder Logic Concepts Read/ Conditional Instructions Write / Control Instructions No Logical Continuity |/| | | T F F |/| |/| ( ) ( ) T T T Logical Continuity
- 54. Logical AND Construction IFinput 4 AND input 5 have power THEN energize output 0 | | I/4 | | I/5 ( ) O/0 Logical Continuity T T T On
- 55. Logical OR Construction IFinput 4 OR input 5 have power THEN energize output 0 | | I/4 | | I/5 ( ) O/0 Logical Continuity F T On | | I/4 | | I/5 ( ) O/0 Logical Continuity T F On
- 56. Complex Construction |/| I/11 | | I/5 |/| I/7 |/| I/1 || I/3 | | I/2 | | I/4 |/| I/0 | | I/1 | | I/1 |/| I/8 | | I/9 ( ) O/0 | | I/10
- 57. Read Instructions Unused I/ 2 I / 1 I / 0 COM I / 3 I / 6 I / 5 COM I / 4 I / 7 I / 9 I / 8 Supply Voltage Unused LS 1 False True Examine OFF -|/|- XIO False The instruction is: The input bit is Logic 0 Logic 1 True Examine ON -| |- XIC If the input device is Open (0) Closed (1)
- 58. Write Instruction Rung State Output Bit Output Terminal De-energized TRUE FALSE ON OFF OTE Output Energize -()- | | |/| ( ) T T T ENERGIZED GND L 1 O / 0 VAC VDC L 2 / N VAC VDC VAC VDC O / 2 VAC VDC O / 1 O / 3 O / 5 O / 4 VAC VDC Supply Voltage
- 59. Putting it Together || ( ) I/8 O/0 GND L 1 O / 0 VAC VDC L 2 / N VAC VDC VAC VDC O / 2 VAC VDC O / 1 O / 3 O / 5 O / 4 VAC VDC Supply Voltage Unused I / 2 I / 1 I / 0 COM I / 3 I / 6 I / 5 COM I / 4 I / 7 I / 9 I / 8 Supply Voltage Unused PB1
- 60. Addressing Example L1 L2 PB1LS1 PS2 SOL6 DEVICE PB1 LS1 PS2 SOL6 | | ( ) | | | | I/5 I/6 O/0 I/7 HHP I/5 I/6 I/7 O/0 Logix I:0/5 I:0/6 I:0/7 O:0/0 ADDRESS
- 61. INPUT Address Assignment: PB1-I/4 PB2- I/5 LS1- I/6 LS2- I/7 LS3- I/8 LS4- I/9 OUTPUT Address Assignment: SOL2- O/0 M1- O/1 |/| CR3 CR3 M1 PB1 LS1 SOL2 PB2 LS1 LS3 LS4 I/8 I/4 I/6 O/0 O/1 | | | | ( ) I/5 I/7 B/0 | | | | ( ) | | |/| B/0 ( ) Relay Logic to Ladder Logic | | I/9
- 62. Advanced Instructions • SEQUENCERS •SHIFT REGISTERS • DATA HANDLING • HIGH SPEED COUNTER • SUBROUTINES
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- 64. Installed and RunningSystems in RI - Conveyors - Curtain rods - Deodorants - Donuts - Duplex Receptacles - Fibers - Filters - Forged Parts - Glass - Goggles - Grinding and Polishing - Heat Treating Metal Products - Jails - Lenses - Nails - Natural Gas - Paper - Pharmaceuticals - Plastics - Plating - Plating Machines - Power Generation - Power Supplies - Product Assembly Machines - Rubber products - Seafood Processing - Soda - Staples - Warehouse Automation - Waste Water Systems - Drinking Water Systems - Water Heaters - Web Handling (paper/plastic) - Wire / Cable
- 65. Solenoid 1 Solenoid 2 Sensor1 Sensor 2 Inlet valve Typical PLC Application
- 66. Motor Solenoid 1 Solenoid2 Solenoid 3 Sensor 1 Sensor 2 Ingredient A Ingredient B Typical PLC Application
- 67. Motor Solenoid 1 Solenoid2 Solenoid 3 Sensor 1 Sensor 2 Ingredient A Ingredient B Operation of Mixer (Sequence of Control) • Solenoid 1 – On = Sol 3 is off, and Motor is off, and Sensor 2 is off, and Auto Switch is on – Off = Sol 3 is on, or Motor is on, or Sensor 2 is on • Solenoid 2 – On = Sol 3 is off, and Motor is off, and Sensor 2 is on – Off = Sol 3 is on, or Motor is on, or Sensor 1 is on • Motor – On = Sensor 1 is on, and Solenoid 2 is off, and Solenoid 1 is off – Off = Solenoid 3 on • Solenoid 3 – On = Sol 1 is off, and Sol 2 is off, and Motor has run for 30 sec. – Off = Solenoid 3 has been on for 60 sec.
- 73. Storage Area withCounter and Comparator The following figure shows a system with two conveyor belts and a temporary storage area in between them. Conveyor belt 1 delivers packages to the storage area. A photoelectric barrier at the end of conveyor belt 1 near the storage area determines how many packages are delivered to the storage area. Conveyor belt 2 transports packages from the temporary storage area to a loading dock where trucks take the packages away for delivery to customers. A photoelectric barrier at the end of conveyor belt 2 near the storage area determines how many packages leave the storage area to go to the loading dock. A display panel with five lamps indicates the fill level of the temporary storage area.
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- 77. 1. What arethe possible causes if the Robot arm failed to grasp the product form conveyer A? 2. What are the possible causes if the Robot arm is unable to release the product into conveyer B?
Editor's Notes
- #6 Let us say that a push button is supposed to control the operation of a motor. In a traditional control system, the push button would be wired directly to the motor. In a PLC system, however, both the push button and the motor would be wired to the PLC instead. Then, the PLCs control program would complete the electrical circuit between the two, allowing the button to control the motor
- #8 If you want a device in a PLC system to behave differently or to control a different process element, all you have to do is change the control program. In a traditional system, making this type of change would involve physically changing the wiring between the devices, a costly and time-consuming endeavor.
- #10 Again, the similarities are virtually identical. The primary enhancement is that if changes are needed, or if other logic or conditions need to be added, it’s as simple as a few keystrokes on the computer.
- #11 Again, the similarities are virtually identical. The primary enhancement is that if changes are needed, or if other logic or conditions need to be added, it’s as simple as a few keystrokes on the computer.
- #19 This is an illustration of how inputs are connected to the PLC. Power (L1) is connected to one side of the input device. The “switched” side of the input device is then wired to the PLC inputs. To complete the electrical path, L2 (electrical common) is wired to the PLC input common. This provides the electrical path for current flow, when the switch is closed (continuity) the PLC will detect the input device is on.
- #20 Field input devices provide an electrical signal based on a condition ON, OFF etc.. The design of the inputs determines the type of electrical signal that can be used. Different applications, and regions may use different voltages. Larger rack mount PLC’s typically support a wider range of input voltages TTL (5Vdc), 12Vdc, 24Vdc/VAC, 48Vdc, 72Vdc, 120Vac, 220Vac etc...
- #21 This is an illustration of how isolated outputs are connected to the PLC. Not all Micro PLC’s have isolated outputs, isolated outputs remove any chance that an output device with unique requirements could affect any of the other output devices. Power is connected to: On isolated outputs to one side or terminal of the output terminal pair. On “common” outputs to the Common terminal associated with a specific group of outputs. The “switched” side of the output terminal is then wired to the field load. First 2 output are always a isolated relay
- #22 Field output devices are controlled by electricity being switched by the PLC. ON, OFF etc.. PLC’s “Switch” electricity, they do not “supply” electricity The design of the outputs determines the type of electrical “Load” that can be used. Different applications may require specialized output designs. Voltage/Current issues include Higher current - relays Longer life cycle - solid state (Triacs for AC, MOSFET for DC) Triacs 120Vac applications 1/2 amp maximum load MOSFET 24Vdc applications 1 amp maximum load Isolation issues can be crucial for an application. Typically the more isolation provided between output points the better. (The more individual commons the better) This provides customers greater flexibility in wiring and controlling different loads with the same PLC.
- #23 The job description of the PLC when it is the RUN mode
- #61 Again, the similarities are virtually identical. The primary enhancement is that if changes are needed, or if other logic or conditions need to be added, it’s as simple as a few keystrokes on the computer.
- #65 Here we have a typical example of an application that a PLC would be ideal for: Digital (on/off) controls Highly repetitive
- #66 Here we have a typical example of an application that a PLC would be ideal for: Digital (on/off) controls Highly repetitive
- #67 The first item a user must understand/appreciate is what is the “sequence” of control. This is typically done on a piece of paper by someone who understands and appreciates what needs to occur. Do not “hook up” the PLC and attempt to “write” the program without first determining the application on paper. This is a fairly typical process. The way the notes are written on the side of an illustration is a common practice. This makes it easy to visualize and understand. It will also help when the program is debugged.