2This Talk Brief overview of Profibus family Profibus DP - Where it came from, how it worksProfibus GSD FilesProfibus Slave OperationEurotherm GSD File editorFuture
3Profibus Family Profibus DP Profibus PA Profibus FMS Fast transfer of time critical I/O dataMachine building/Automation ~ 10mS scan time‘DPV1’ adds ‘Acyclic’ messages and high level data type definitionsProfibus PADPV1 Messaging + Device Profiles + Intrinsic SafetySlower Physical Medium (31.25 kbit/s) with loop powerProcess ApplicationsProfibus FMS‘Full’ Messaging (I/O + non time critical)Higher level Communications (PLC <-> PLC)
4‘Traditional’ PLC Control System Internal ‘Backplane’Transfers Input and Output databetween CPU and Modules priorto PLC scan cycleData from modules ‘appears’in I/O registers in the CPU.Processed by applicationPoint to Point wiring to Plant - Essentially 1 wire per signal
5PLC Control With DP Internal backplane replaced by external High Speed RS485 cableconnected to Scanner Module.I/O data from devices is transferredcyclically - ‘appears’ in PLC registersto be processed by application.Modules replaced by ‘Devices’ -I/O or special function
6Cyclic I/O Data Transfer Slave Input Data (To PLC)PLC RegistersTemperatureWorking SetpointLoop Output PowerAlarm Status wordSlave Output Data (From PLC)Target SetpointManual OutputApplication usesdata from inputregisters andsets values inoutput registersScanner transfers I/OData from/to PLC onceeach scan cycle for eachslave ~ 10mS cycle
7General Benefits of using Fieldbuses Wiring Cost reduction ( % of total)Easier maintenance, and flexibility to add new devices when and where neededUse ‘best of breed’, specialised, devices easily at all points in the application - reduces load on PLCDevices located close to point of application and closely coupled to itFeedback from smart devices reduces planned maintenance and allows quality improvement via SPC etc.Not limited to modules produced by vendor of PLC (or PC3000!)
8DP is popular with users... Easily understandable - no need to read the spec!Easily applicable - devices interwork without problemsTransparent to PLC programmersVery little ongoing network maintenanceSupported by a very wide range of device and PLC vendorsDP systems are now being constructed on a very routine basis without problems - not an R&D exercise.
9DP is popular with vendors Based on a range of Siemens ASICs - easy hardware implementation for slave devicesPre-Canned modules available (Siemens, Hilscher, SST etc) to add DP to products without significant hardware developmentEasy to support - ASICs ensure third party devices work in a consistent and predictable mannerResult is a healthy proliferation of different kinds of I/O and specialised devices
10Why Eurotherm chose Profibus DP DP is currently the best choice for networking PLCs with I/O and other devices. Fast, simple, and available.DeviceNet is too limited in bandwidth for larger applications, and third party support not as comprehensive.Foundation Fieldbus not widely adopted.Profibus DP now adopted within Eurotherm as our main Fieldbus platform.
11Profibus - Weaknesses.Limited ‘acyclic’ capacity. Not good for SCADA or large scale file transfers.Not really plug and play (like DeviceNet)No pre-defined Function Block library (like FF)
12Eurotherm’s Profibus Range SCADA - PC CardsWonderware, Wizcon, InterlutionT940PC3000/PC300T800subselect.meOK2900eCPUHeatTempInner TempMain AirMain FanAux AirAux FanRunCoolRaiseLowerResetHoldServoFridgeLight 1LoadLight 2LoopRelay 4DI/DO 82000F PIDControllersThyristorPowerControllersT630 ProcessControllerAC/DCDrivesChartRecorders2500Multi-loop
13GSD1 FilesDefine third party devices to Profibus DP network configuration tools.Include timing information, supported baud rates, links to bitmap images, etc.Include details of I/O Mapping and ‘Parameterisation’Contents downloaded to Slave devices on network startupIn Eurotherm products, define the set of device variables transferred over Profibus. Set up using our ‘GSD File Editor’1Gerätestammdaten
15DP Slave Operation Units first ‘parameterised’ by Master Sends up to 244 bytes of Vendor Specific DataData comes from GSD fileIn Eurotherm devices, defines content of I/O messagesUnits then ‘Configured’ by MasterUp to 244 bytes Type and Size data defining I/OSlave enters ‘Data Exchange’Exits back to parameterisation on timeout“Diagnostic” requests made on status change or fatal error“Diagnostics”Not well understood (even by Siemens!)Flagged during I/O exchangeProvide indication of Fatal Device Fault orProvide indication of Status (e.g. sensor fail)
16Profibus DP “Slave State Machine” “Config Data”from GSD File“User Parametisation Data ”from GSD File
17Why Use a GSD Editor?Profibus designed for simple bulk I/O devices (e.g. 16 words I + 0)Our products are much more complex ( parameters).Impossible to choose a universal subset for I/O, and wasteful of bandwidth to transfer unnecessary variables.Best approach to allow I/O mapping selection by users on a per application basis
18ProblemsGSD file provides user data. Obvious place to define I/O transfer, and values from file may be changed by user using network configuration toolHowever data type definitions are also in the GSD file, and closely coupled to I/O definition.Data type definitions are not usually changeable using the network configuration toolSolution Chosen - Create a GSD Editor tool to define I/O transfer in users’s terms, and manage type definitions automatically...
19Eurotherm GSD File Editor Creates Custom ‘GSD’ file for use by network configurators
20Why Use the GSD File editor Very easy to use - drag and drop interfaceAllows optimum use of network ‘bandwidth’ - only transfer the variables you needPermits very flexible use of devices - no need for a ‘lowest common denominator’ mappingAvoids manual editing of GSD file employed by other vendors - error prone and complicatedBuild up a library of GSD files for different applicationsUse the PLC to ‘wire’ between device variables for complex control strategies‘Web’ button for latest hints and tips on-line
21Demand Data Cyclic Data interchange is great, but… Relentlessly overwrites values set via the front panel of the instrument (though this can be overcome with sequence logic)Allows access to a limited number of device variables‘Demand Data’ provided to solve this problemUses 4 words in the input and output areasAllows read or write access to all device variables ‘on demand’Uses a simple ‘mailbox’ system, easily programmable using a PLC sequence programSwitched on or off by the GSD File EditorSupported by specialised PC3000 Function BlocksDPV1 provides “proper” acyclic messaging (currently 2500 E-Suite only)
22Future Profibus group pushing ProfiNet (Profibus on Ethernet) Various other developments (Plug and Play, ProfiSafe, Expansion of Profibus PA).May be better long term bets for higher level Ethernet protocols (e.g. FF)
23ConclusionProfibus DP allows easy interconnection of Eurotherm and third party devicesGood for small scale “Machine Building” networksLess good as a SCADA networkGSD file editor and ‘Demand Data’ allow great flexibility of operation with Eurotherm slaves.