2 Agenda History PLC Overview Hardware Inputs/Outputs Operation Programming SoftwareCommunicationWhat you need to know when specifying a PLCGlossary
3 History of the PLCFirst Programmable Logic Controllers were designed and developed by Modicon as a relay replacer for GM and Landis.These controllers eliminated the need for rewiring and adding additional hardware for each new configuration of logic.The new system drastically increased the functionality of the controls while reducing the cabinet space that housed the logic.The first PLC, model 084, was invented by Dick Morley in 1969.The first commercial successful PLC, the 184, was introduced in 1973 which was designed by Michael Greenberg.
4 Inputs Outputs What is a PLC? The Basic Block CPU 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.
5 What is a PLC with Distributed I/O? Getting ComplexCPUInputsOutputsRemote
6 Getting Really Complex What is a PLC with Distributed Control?Getting Really ComplexCPUCPUOutputsInputsRemote
7 Inside a PLC Central Processor Unit (CPU) MEMORY Circuits Circuits CommunicationsPortCircuitsCircuitsCentralProcessorUnit(CPU)InputOutputCRHighVoltageHighVoltageMEMORYprogramdataIsolationBarrierIsolationBarrierPrimary components of virtually all PLC’s, no matter what size are:Input CircuitryOutput CircuitryCentral ProcessorMemoryCommunications Port(s)Power SupplyPLC’s are industrially hardened devices capable of operating in extreme environmentsWide Temp extremes 0-60º CHigh humidityHigh Vibration“Dirty” Electrical PowerHigh “Noise” (electrical) environmentsLow VoltageorAC Power SupplyDC Power Supply
8 Inside a PLCThe CPU contains an “Executive” program that tells the PLC how to:Execute the control InstructionsUser’s ProgramCommunicate with other devicesOther PLCs, Programming devices, I/O devices, etc.Perform Housekeeping activitiesDiagnostics, etcThis program is stored in “nonvolatile” memoryMeaning that the program will not be lost if power is removed
9 What are Inputs? Switches and Pushbuttons Sensing Devices Limit SwitchesPhotoelectric SensorsProximity SensorsCondition SensorsPressure SwitchesLevel SwitchesTemperature SwitchesVacuum SwitchesFloat SwitchesEncoders
10 What are Outputs? Valves Motor Starters Solenoids Actuators Control RelaysHorns & AlarmsStack LightsFansCounter/TotalizerPumpsPrinters
11 PLC Operating Cycle Four Steps in the PLC Operations Input Scan Scan the state of the InputsProgram ScanProcesses the program logicOutput ScanEnergize/de-energize the outputsHousekeepingThis step includes communications, Internal Diagnostics, etc.The steps are continually repeated - processed in a loopSTARTInputScanProgramHousekeepingOutput
12 Programming the PLC Types of Programming Software Languages Ladder Logic (LL)IEC FormatFunction Block Diagram (FBD)Structured Text (ST)Instruction List (IL)Ladder Diagram (LD)Sequential Function Chart (SFC) - also known as “Grafcet”
20 Communication Basics Protocols Communication Relationships A set of rules for data exchange (format and timing of data) in a communications systemStack / profile = selected set of protocols for a communication applicationCommunication RelationshipsMaster / Slave - request / response & response onlyPeer-to-Peer - client / server, publisher / subscriberCommunication ArchitecturesStar (point-to-point)Bus, Ring, LAN (multidrop)
21 Communication Protocols EthernetModbus PlusModbusS908LonWorksInterbusProfi-busDeviceNetUni-TelwayCAN-OpenASiSeriplexFIPIO/FIPwayRIOHARTDIOControlNetASCIIProtocols are similar to languages -Devices must support the same protocol to understand each other
22 What you need to know when specifying a PLC Quantity, Type and Location of I/ONumber of Inputs and output pointsAC or DC voltageAnalog or DiscreteConcentrated or spread out (distributed)Communication RequirementsProtocol/Network usedDevices to communicate with (HMI, other PLCs, etc)Speed of ApplicationResponse time required (throughput) of the systemHow fast does the process change
23 What you need to know when specifying a PLC Control Architecture PhilosophyCentralized Control, Distributed Control or combinationRedundancy - CPUs, Power Supplies, etcProgramming SoftwareIEC vs. 984Installed base / what is currently being usedUser LogicSize and complexity of ProgramFeedback control usedetc.
24 Alphabet SoupHMI / MMI Human Machine Interface / Man Machine InterfaceI/O Input(s) and/or Output(s)LSB / MSB Least Significant Bit / Most Significant BitMODICON MOdular DIgital CONtollerPID Proportional Integral Derivative (feedback control)RF Radio FrequencyRTU Remote Terminal UnitSCADA Supervisory Control And Data AcquisitionTCP/IP Transmission Control Protocol / Internet Protocol