Presentation on theme: "Programmable Logic Controllers PLC’s"— Presentation transcript:
1 Programmable Logic Controllers PLC’s An Overview, Use in HVAC and Web TechnologiesBy Sleepy Wombat
2 Overview What is a PLC ? History Overview of Technology PLC Configuration and SelectionProgramming PLC’sPLC’s in HVACWeb Technologies
3 What is a PLC ? PLC (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 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).
4 History 1/4Early control systems consisted of huge control boards consisting of hundreds to thousands of electromechanical relays.An Engineer would design the system logic.Electricians would receive a schematic outline of logic then implement the logic with 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.
5 History 2/4General Motors was among the first to recognise a need to replace the systems “wired control board”Hydramatic Division of GM specified the design criteria for the programmable controller in 1968.Goal – Eliminate the high cost associated with inflexible, relay controlled systems.
6 History 3/4 New Controller Specifications: Solid State System Computer FlexibilityOperate in Industrial Environment (vibrations, heat, dust etc.)Capability of being reprogrammedEasily programmed and maintained by electricians and technicians.
7 History 4/4 In 1969 Gould Modicon developed the first PLC. Strength – Programmed with Ladder LogicInitially called Programmable Controllers PC’sNow - PLC’s, Programmable Logic ControllersPLC’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.
9 Basic PLC Schema CPU Power Supply Memory Input Blocks Output Blocks CommunicationsExpansion Connections
10 CPU ModuleThe Central Processing Unit (CPU) Module is the brain of the PLC.Primary role to read inputs, execute the control program, update outputs.The CPU consists of the arithmetic logic unit (ALU), timing/control circuitry, accumulator, scratch pad memory, program counter, address stack and instruction register.A PLC works by continually scanning a programPLC ProgramSCAN1
11 MemoryThe 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 restored.1
12 Memory 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.
13 Memory cont’d Some types of memory used in a PLC include: ROM (Read-Only Memory)RAM (Random Access Memory)PROM (Programmable Read-Only Memory)EPROM (Erasable Programmable Read-Only Memory)EEPROM (Electronically Erasable Programmable Read-Only Memory)FLASH MemoryCompact Flash – Can store complete program information, read & write text files
14 I/O ModulesInput and output (I/O) modules 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 most sensors and actuators.Wide range of I/O modules available including: digital (logical) I/O modules and analog (continuous) I/O modules.1
15 Inputs 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.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.1
16 Inputs Modules The list below shows typical ranges for input voltages. 5 Vdc12 Vdc24 Vdc48 Vdc12 Vac24 Vac120 Vac240 Vac1
18 Outputs 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.1
19 RelaysThe most important consideration when selecting relays, 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.Advantage of individual standard replaceable relays1
20 Outputs Typical output voltages are listed below, 5 Vdc 12 Vdc 24 Vdc 24 Vac120 Vac240 VacWARNING: Always check rated voltages and currents for PLCs and never exceed.1
23 Analogue Inputs/Outputs Analogue input cards convert continuous signals via a A/D converter into discrete values for the PLCAnalogue output cards convert digital values in then PLC to continuous signals via a D/A converter.Resolution can be important in choosing an applicable cardExample, for a temperature input of 0 to 100 degrees CFor 8 bit resolution the value in the PLC is 0 to 255For 12 bit resolution the value in the PLC is 0 to 4095For 12.5 bit resolution the value in the PLC is 0 to 6000For 13 bit resolution the value in the PLC is 0 to 8192For 16 bit resolution the value in the PLC is 0 to 32768
24 Special Modules RF ID Voice Gas Flow Calculation Weigh Cell Hydraulic ServoASCIIFuzzy LogicTemperature SensorTemperature ControlHeat/Cool ControlField Bus CardsDeviceNet, Profibus etcLonworks, BACNetFast Response (Interrupt)PIDLoop ControllerBASIC CardsRS232 Comm’sModbus ASCII/RTUEthernet Comm’sHigh Speed CountersPosition Control CardsPer to Per Comm’sController LinkDH+Modbus Plus
25 Available Instructions SequenceInputOutputControlLogicTimer and CountersComparisonRange ComparisonData MovementData ShiftStep / Step NextSerial CommunicationsText String ProcessingFile ManipulationIncrement/DecrementConversionASCIINumber SystemsMathFloating Point MathStatisticsScalingPIDPID with Auto tuneClock / DateBlock ProcessingIF,THEN,ELSE,LOOPTable ProcessingLIFO, FIFO
26 NetworksASIDevicenetInterbus-SProfibusInterbusFieldbusEthernet I/PSmart Distributed System (SDS)SeriplexCANopenLonworksBACNetGateways enable communications between different network topologies
28 The Configuration of PLC The 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 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.1
29 Sizing of PLC Micro PLCs: I/O up to 32 points Small PLC: I/O up to 128 pointsMedium PLC: I/O up to 1024 pointsLarge PLC: I/O up to 4096 pointsVery Large: I/O up to 8192 points1
30 Selecting a PLC Criteria Number of logical inputs and outputs Memory Number of special I/O modulesExpansion CapabilitiesScan TimeCommunicationSoftwareSupportDollars1
38 PLC Standardization Open Controller IEC 61131Based on IEC 1131 (1992) standard, developed to be a common and open framework for PLC architecture.IEC OverviewIEC Requirements & Test ProceduresIEC Data Types & ProgrammingIEC User GuidelinesIEC CommunicationsIEC Fuzzy ControlIEC Guidelines for the application and implementation of programming languages
39 IEC 61131-3 IL (Instruction List) – mnemonic programming LD (Ladder Diagram) – Relay logicST (Structured Text) – A BASIC like programming languageFDB (Functional Block Diagram) – Graphical dataflow programming languageSFC (Sequential Flow Chart) – Graphical method for structured programs
40 IEC 61131-3 Examples Ladder Instruction List Structured Text Function BlockSequential Flow Chart
42 PLC’s in HVAC controlDespite the versatility of today’s PLC’s, many controls professionals are skeptical of applying PLC’s to new applications such as HVAC control.Reasons included :Lack of knowledge of these systemsRequirement for programmingLack of initial capability of technologyPremium first up cost
43 AdvantagesPLC’s remain a predominate piece of equipment on the factory floor and will probably remain so for some time to come.The advantages they offer are:Cost effective for controlling complex systemsFlexible and can be reapplied to control other systems quickly and easilyComputational abilities allow more sophisticated controlTrouble shooting aids make programming easier and reduce downtimeReliable components (high MTBF) ensure operation for years
44 Advantages continued…. Variety of I/O interfacesSmall sizeGrowing with technology, faster scan times, capability etcQuick I/O disconnects that aids in field servicingModularity in hardware architectureModularity in software design (programmer dependant)Software Timers/Counter, RelaysClean failure modeOn-line programmingSelf inspecting for operation code during executionAvailability of programmers/trouble shooters/integratorsAvailability of replacement parts
45 BenefitsThe benefits achieved with programmable controllers will grow with the individual using them:“The more you learn about PLC’s, the more you will be able to solve other control problems.”
46 Examples Southgate – Melbourne Millennium Dome – London Woolworths – BritainST Microelectronics – FranceEinstein III Building - Munich
48 Web Enabled Automation...? Is it just more Internet hype or is there some benefit behind the idea.Is it possible to connect all of these systems by their PLC’s to the Internet ?Is it practical ?Is it profitable ?
49 Short Answers……Internet access can provide compelling competitive advantages linking customers, suppliers, subcontractors, front line management.Improve fault reporting and response timeEnhance flexibilityOptimise process controlProven affordable technologies are readily available to connect any PLC, Process Controller or I/O to the Internet and Intranet.Process to Internet access has the potential to become a standard utility.
50 What is Web EnablingWeb enabling gives real time access to data and control, virtually anytime, anywhere.It uses communication with any manufactures PLC or I/O to send information via the Internet to anywhere in the world.Web enabled automation drives real-time accessibility “Vertically Down” to the control device level.
51 What can we do with it ?Check real time process data without waiting for end of shift reportsTrack equipment run time and initiate maintenance requestsAutomatically notify a technician via or GSM phone etc of faults and allow rectificationCollect process data on a server PC and analyse with statistics and control (SPC)Use HTML help files including graphicsMonitor and control remote operations reducing field staffing and unnecessary travel
52 What pieces and parts are required ? InterfaceWeb ServerData ServiceBrowser
53 InterfaceAn interface to the equipment to be monitored and controlled via the web (network) connectionEthernet LineModem / Phone lineISDNWireless Modem (eg b Ethernet)Type of connection is typically determined by the thin server and the existing network infrastructure – or lack thereof
54 Web ServerWeb Server (or “thin server” data service) to enable the remote browser to view the desired displays and web pages.Typical installation requires a connection to an existing PLC or proprietary controller.Most PLC’s support at least a serial connection using the vendor supplied protocol to communicate.Use an Open network controller (interface)Some PLC’s have Web Servers built into their Ethernet Units.
55 Data ServiceA data service or interface to handle exchanging data between the local equipment/ process (server) and the remote system (client)A common “language”, protocol is required..XML (Extended Markup Language)Benefit of XML is its independence from senders and receivers hardware, OS, and application.
56 Browser InterfaceUse the thin servers assigned IP address to access the remote system.Simple browsing requires standard browser interface found on a desktop computer, PDA, WAP, or “Thin Client”For application information sharing (SPC, Enterprise Software), if the thin server and remote application software support a common interface such as OPC, setting up the data exchange can be accomplished in a couple of minutes
57 New term … OPC OLE for Process Control Object Linking and Embedding One of industries most popular standardsMaintained by OPC foundationOPC standard is non proprietary technical specification based on Microsoft's OLE/DCOM technology.
61 Web Servers Computer Based Displays SCADA – Supervisory Control and Data AcquisitionCitect, Wonderware, Fix, Iconics, GeniusEthernet, Serial, OPC (OLE for Process Control), Dedicated Computer Boards for Propriety BusesDedicated Packages for BMSCitect SCADA FacilitiesEmbedded Web ServersOpen Network Controller Interface – GatewayEmbedded Web Servers in PLC’s Ethernet cardsNew Dedicated HMI Screens – some have embedded Web ServersExample of Web Technology visit