Tim Linnell (Eurotherm Ltd) Profibus Tim Linnell (Eurotherm Ltd)

This Talk Brief overview of Profibus family Profibus DP - Where it came from, how it works Profibus GSD Files Profibus Slave Operation Eurotherm GSD File editor Future

Profibus Family Profibus DP Profibus PA Profibus FMS Fast transfer of time critical I/O data Machine building/Automation ~ 10mS scan time ‘DPV1’ adds ‘Acyclic’ messages and high level data type definitions Profibus PA DPV1 Messaging + Device Profiles + Intrinsic Safety Slower Physical Medium (31.25 kbit/s) with loop power Process Applications Profibus FMS ‘Full’ Messaging (I/O + non time critical) Higher level Communications (PLC <-> PLC)

‘Traditional’ PLC Control System Internal ‘Backplane’ Transfers Input and Output data between CPU and Modules prior to PLC scan cycle Data from modules ‘appears’ in I/O registers in the CPU. Processed by application Point to Point wiring to Plant - Essentially 1 wire per signal

PLC Control With DP Internal backplane replaced by external High Speed RS485 cable connected to Scanner Module. I/O data from devices is transferred cyclically - ‘appears’ in PLC registers to be processed by application. Modules replaced by ‘Devices’ - I/O or special function

Cyclic I/O Data Transfer Slave Input Data (To PLC) PLC Registers Temperature Working Setpoint Loop Output Power Alarm Status word Slave Output Data (From PLC) Target Setpoint Manual Output Application uses data from input registers and sets values in output registers Scanner transfers I/O Data from/to PLC once each scan cycle for each slave ~ 10mS cycle

General Benefits of using Fieldbuses Wiring Cost reduction (35 - 40% of total) Easier maintenance, and flexibility to add new devices when and where needed Use ‘best of breed’, specialised, devices easily at all points in the application - reduces load on PLC Devices located close to point of application and closely coupled to it Feedback from smart devices reduces planned maintenance and allows quality improvement via SPC etc. Not limited to modules produced by vendor of PLC (or PC3000!)

DP is popular with users... Easily understandable - no need to read the spec! Easily applicable - devices interwork without problems Transparent to PLC programmers Very little ongoing network maintenance Supported by a very wide range of device and PLC vendors DP systems are now being constructed on a very routine basis without problems - not an R&D exercise.

DP is popular with vendors Based on a range of Siemens ASICs - easy hardware implementation for slave devices Pre-Canned modules available (Siemens, Hilscher, SST etc) to add DP to products without significant hardware development Easy to support - ASICs ensure third party devices work in a consistent and predictable manner Result is a healthy proliferation of different kinds of I/O and specialised devices

Why 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.

Profibus - 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)

Eurotherm’s Profibus Range SCADA - PC Cards Wonderware, Wizcon, Interlution T940 PC3000/PC300 T800 subselect.me OK 2900 e ° CPU Heat Temp Inner Temp Main Air Main Fan Aux Air Aux Fan Run Cool Raise Lower Reset Hold Servo Fridge Light 1 Load Light 2 Loop Relay 4 DI/DO 8 2000F PID Controllers Thyristor Power Controllers T630 Process Controller AC/DC Drives Chart Recorders 2500 Multi-loop

GSD1 Files Define 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 startup In Eurotherm products, define the set of device variables transferred over Profibus. Set up using our ‘GSD File Editor’ 1Gerätestammdaten

DP Network Configuration GSD GSD GSD

DP Slave Operation Units first ‘parameterised’ by Master Sends up to 244 bytes of Vendor Specific Data Data comes from GSD file In Eurotherm devices, defines content of I/O messages Units then ‘Configured’ by Master Up to 244 bytes Type and Size data defining I/O Slave 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 exchange Provide indication of Fatal Device Fault or Provide indication of Status (e.g. sensor fail)

Profibus DP “Slave State Machine” “Config Data”from GSD File “User Parametisation Data ”from GSD File

Why Use a GSD Editor? Profibus designed for simple bulk I/O devices (e.g. 16 words I + 0) Our products are much more complex (500-3000 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

Problems GSD file provides user data. Obvious place to define I/O transfer, and values from file may be changed by user using network configuration tool However 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 tool Solution Chosen - Create a GSD Editor tool to define I/O transfer in users’s terms, and manage type definitions automatically...

Eurotherm GSD File Editor Creates Custom ‘GSD’ file for use by network configurators

Why Use the GSD File editor Very easy to use - drag and drop interface Allows optimum use of network ‘bandwidth’ - only transfer the variables you need Permits very flexible use of devices - no need for a ‘lowest common denominator’ mapping Avoids manual editing of GSD file employed by other vendors - error prone and complicated Build up a library of GSD files for different applications Use the PLC to ‘wire’ between device variables for complex control strategies ‘Web’ button for latest hints and tips on-line

Demand 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 problem Uses 4 words in the input and output areas Allows read or write access to all device variables ‘on demand’ Uses a simple ‘mailbox’ system, easily programmable using a PLC sequence program Switched on or off by the GSD File Editor Supported by specialised PC3000 Function Blocks DPV1 provides “proper” acyclic messaging (currently 2500 E-Suite only)

Future 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)

Conclusion Profibus DP allows easy interconnection of Eurotherm and third party devices Good for small scale “Machine Building” networks Less good as a SCADA network GSD file editor and ‘Demand Data’ allow great flexibility of operation with Eurotherm slaves.