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BEE2931 BEE2931 -- Basic PLC Basic PLC Based Model : OMRON CQM1HBased Model : OMRON CQM1H-- CPU51CPU51
1 Jon Stenerson “Industrial Automation and Process Control”,Upper Saddle River, NJ: Prentice Hall,2003
2 John R Hackworth & Frederick D Hackworth,Jr “Programmable Logic Controller:Programming Method and Application”,Upper Saddle River,NJ:Prentice Hall,2004
3 OMRON “Sysmac CQM1H Series Operation Manual”,Revised August 2005
4 F k D P t ll “P bl L i C t ll ” 3 d Editi M4 Frank D. Petruzella, “Programmable Logic Controllers”, 3rd Edition, Mc-Graw Hill, 2005.
5 Omron, “Programming Manual”, Revised December 2003, Omron Corporation, 2003.
1.1 What is Control System1.1 What is Control System
In general, a control system is a collection of electronics devices and equipments to of electronics devices and equipments to ensure the stability ,accuracy and smooth transition of a process or a manufacturing activity.
1.2 What is a Programmable 1.2 What is a Programmable ControllerController
In an automated system, the PLC is commonly regarded as the heart of the commonly regarded as the heart of the control system.The PLC may used to control a simple and repetitive task.Or a few of them may be interconnected together with other controller or host together with other controller or host computer through a sort of communication network, in order to integrate the control in a complex process.
1.2 What is a Programmable 1.2 What is a Programmable ControllerControllerPLC (Programmable Logic Controller)
A PLC works by looking at its inputs and depending on their state, and the user entered program, turns on/off outputs.
A PLC can be thought of as: Industrial Computers with
i ll d i d p
specially designed architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices (input / output connections to the real world).
1.3 PLC Development1.3 PLC DevelopmentEarly control systems consisted of huge control boards consisting of hundreds to thousands of electromechanical relaysthousands of electromechanical relays.
The schematic was commonly called “Ladder Schematic”
The Ladder displayed all switches, sensors, motors, valves, relays etc in the system.
Problems: Long commissioning time, Mechanical Reliance, Any system logic design change required the power to the control board to be isolated stopping production.
1.3 PLC Development1.3 PLC DevelopmentGeneral Motors was among the first to recognize a need to replace the systems “wired control board”
Goal – Eliminate the high cost associated with inflexible, relay controlled systems.
New Controller Specifications:◦ Solid State System◦ Computer Flexibility
O ( ) ◦ Operate in Industrial Environment (vibrations, heat, dust etc.) ◦ Capability of being reprogrammed◦ Easily programmed and maintained by electricians and
1.3 PLC Development1.3 PLC DevelopmentIn 1969 Gould Modicon developed the first PLC.
St th P d ith L dd L i f ti Strength – Programmed with Ladder Logic, function block, statement list
Initially called Programmable Controllers PC’s Now - PLC’s, Programmable Logic Controllers
PLC’s have evolved from simple on/off control to being PLC s have evolved from simple on/off control to being able to communicate with other control systems, provide production reports, schedule production, diagnose machine and process faults.
Wire Logic Vs PLCWire Logic Vs PLCITEM WIRED LOGIC PLC
Controlled Device (Hardware)
Specific Purpose General Purpose ( )Control Scale Small and Medium Medium and large
Change or addition to specification
Difficult Easy
Delivery period Several Days Almost immediate
Maintenance (by makers and users)
Difficult Easy and users)Reliability Depends on design and
manufacture Very High
Economic Efficiency Advantage on small scale operation
Advantage on small medium and large scale operation
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Advantageous of using PLC Advantageous of using PLC Shorter project implementation timeEasier modification without cost penaltyp yProject cost can be accurately calculatedShorter training time requiredDesign easily changed using softwareA wide range control applicationEasy maintenanceHigh reliabilityStandardization of Controller Hardware
What PLC Can Do?What PLC Can Do?CONTROL TYPE FUNCTIONS
Sequences Control •Conventional Relay Control Logic Replacer /P.C.B Card Controller Replacerp•Timers/Counters•Auto/Semi-auto/Manual Control of machine and Processes
Sophisticated Control / Regulatory Control
•Arithmetic Operation•Information handling•Analog Control (Temperature, Pressure)•P I D (Proportional-Integral-Derivation)P.I.D (Proportional Integral Derivation)•Servo Motor and Stepper Motor
Supervisory Control •Process Monitoring and Alarm•Fault Diagnostic and Monitoring•Interfacing with Computer -Printer/ASCII •Factory Automation•Local Area Network / Wide Area Network
PLC operationPLC operation1. CHECK INPUT STATUS◦ First the PLC takes a look at each input to determine
if it is on or off. In other words, is the sensor if it is on or off. In other words, is the sensor connected to the first input on? How about the second input? How about the third... It records this data into its memory to be us
2. EXECUTE PROGRAM◦ Next the PLC executes your program one instruction
at a time. Maybe your program said that if the first input was on then it should turn on the first output input was on then it should turn on the first output. Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step.
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PLC operationPLC operation3. UPDATE OUTPUT STATUS◦ Finally the PLC updates the status of the outputs. It updates
the outputs based on which inputs were on during the first the outputs based on which inputs were on during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true.
Check i/p Status Execute Program Update o/p Status
2.0 PLC HARDWARE 2.0 PLC HARDWARE DESIGNDESIGN
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PLC ConfigurationPLC Configuration
Rack Mini
Shoe Box
Micro
PLC ConfigurationPLC ConfigurationThe configuration of PLC refers to the packaging of the components.
Typical configurations are listed below from largest to smallest.◦ Rack Type : A rack can often be as large as 18” by 30” by 10”
◦ Mini: These are similar in function to PLC racks, but about the half size. Dedicated Backplanes can be used to support the cards OR DIN rail mountable with incorporated I/O bus in module.
◦ Shoebox: A compact, all-in-one unit that has limited expansion biliti L t d t k th id l f ll capabilities. Lower cost and compactness make these ideal for small
applications. DIN rail mountable.
◦ Micro: These units can be as small as a deck of cards. They tend to have fixed quantities of I/O and limited abilities, but costs will be lowest. DIN rail mountable.
The Central Processing Unit (CPU) Module is the brain of the
SelfCheck
ExecuteC d
ScanInputs
UpdateO t t
PLC.Primary role to read inputs, execute the control program, update outputs.The CPU consists of the arithmetic logic unit (ALU), timing/control circuitry,
CodeOutputsaccumulator, scratch pad memory, program counter, address stack and instruction register.A PLC works by continually scanning a program
PLC ProgramSCAN
MemoryMemoryThe memory includes pre-programmed ROM memory containing the PLC’s operating system, driver programs and application programs and the RAM memory.
PLC manufacturer offer various types of retentive memory to save user-programs and data while power is removed, so that the PLC can resume execution of the user-written control program as soon as power is restoredrestored.
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Memory cont’dMemory cont’dMany PLCs also offer removable memory modules, which are plugged into the CPU module.
Memory can be classified into two basic categories: volatile and non-volatile.
- Volatile memory is that which loses state (the stored information) when power is removed.
- Nonvolatile memory, on the other hand, maintains the information in memory even if the power is interrupted.
Memory cont’dMemory cont’dSome types of memory used in a PLC include:
Compact Flash – Can store complete program information, read & write text files
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I/O ModulesI/O Modules
Input and output (I/O) modules connect the PLC to sensors and connect the PLC to sensors and actuators.
Provide isolation for the low-voltage, low-current signals that the PLC uses internally from the higher-power electrical circuits required by
d most sensors and actuators.
Wide range of I/O modules available including: digital (logical) I/O modules and analog(continuous) I/O modules.
Inputs ModulesInputs ModulesInputs come from sensors that translate physical or chemical phenomena into electrical signals.
The simplest form of inputs are digital/discrete in
AC/DC.
In smaller PLCs the inputs are normally built in and are
specified when purchasing the PLC.
F l PLC h i h d d l For larger PLCs the inputs are purchased as modules, or cards, with 8,16, 32, 64, 96 inputs of the same type on each card.
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Inputs ModulesInputs Modules
The list below shows typical ranges for input voltagesranges for input voltages.
◦ 5 Vdc
◦ 12 Vdc
◦ 24 Vdc
◦ 48 Vdc
◦ 12 Vac
◦ 24 Vac
◦ 120 Vac
◦ 240 Vac
Outputs ModulesOutputs ModulesOutput modules rarely supply any power, but instead act as switches.
External power supplies are connected to the output card and the card will switch the power on or off for each output.
A common choice when purchasing output cards is relays, transistors or triacs.
Relay are the most flexible output devices. They are capable of switching both AC and DC outputs. But, they are slower, cost more, and they will wear out after millions of cycles.
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RelaysRelaysThe most important consideration when selecting grelays, or relay outputs on a PLC, is the rated current and voltage.
For transistor outputs or higher density output cards relay terminal blocks are available. terminal blocks are available. ◦ Advantage of individual standard
replaceable relays
Output ModulesOutput Modules
Typical output voltages are listed belowlisted below.
◦ 5 Vdc
◦ 12 Vdc
◦ 24 Vdc
◦48 Vdc
◦24 Vac
◦120 Vac
◦240 Vac
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Analogue Inputs/OutputsAnalogue Inputs/OutputsAnalogue input cards convert continuous signals via a A/D converter into discrete values for the PLC
Analogue output cards convert digital values in then PLC to continuous signals via a D/A converter.
Resolution can be important in choosing an applicable card
Example, for a temperature input of 0 to 100 degrees C◦ For 8 bit resolution the value in the PLC is 0 to 255
◦ For 12 bit resolution the value in the PLC is 0 to 4095◦ For 12 bit resolution the value in the PLC is 0 to 4095
◦ For 12.5 bit resolution the value in the PLC is 0 to 6000
◦ For 13 bit resolution the value in the PLC is 0 to 8192
◦ For 16 bit resolution the value in the PLC is 0 to 32768
CPU and Expansion I/O Block◦ CPU: Up to 5 units (exclude I/O Control unit)◦ CPU: Up to 5 units (exclude I/O Control unit)◦ Expansion: Up to 11 units (exclude I/O Interface
Typically flows from left to right. • Divided into sections called rungs, • Each i/os instruction is assigned an address Each i/os instruction is assigned an address
indicating the location in the PLC memory where the state of that instruction is stored.
If the execution condition remains ON long enough for TIM to time down to
ONON
long enough for TIM to time down to zero, the Completion Flag for the TC number used will turn ON and will remain ON until TIM is reset (execution condition goes OFF).
CNT is used to count down from SV when the execution condition on the count pulse -CP, goes execution condition on the count pulse CP, goes from OFF to ON.The present value (PV) will be decremented by one whenever CNT is executed with an ON execution condition for CP and the execution condition was OFF for the last execution
The Completion Flag for a counter is turned ON when the PV reaches zero and will
ONON
ON when the PV reaches zero and will remain ON until the counter is reset.CNT is reset with a reset input, R.When R goes from OFF to ON, the PV is reset to SV.
Increments Wd, without affecting Carry (CY)Carry (CY).For INC(38) and DEC(39) the source and result words are the same. That is, the contents of the source word is overwritten with the instruction result.