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EUROTHERM CONTROLS

ProfibusProfibus

Tim Linnell (Eurotherm Ltd)

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EUROTHERM CONTROLS

This TalkThis 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

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Profibus FamilyProfibus Family

Profibus DP – 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)

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‘‘Traditional’ PLC Control SystemTraditional’ 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

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PLC Control With DPPLC Control With DP

Internal backplane replaced byexternal High Speed RS485 cable connected to Scanner Module.

I/O data from devices is transferred cyclically - ‘appears’ in PLC registersto be processed by application.

Modules replaced by ‘Devices’ -I/O or special function

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Cyclic I/O Data TransferCyclic I/O Data Transfer

Slave Input Data (To PLC)

Slave Output Data (From PLC)

Temperature

Working Setpoint

Loop Output Power

Alarm Status word

PLC Registers

Target Setpoint

Manual Output

Scanner transfers I/OData from/to PLC once each scan cycle for eachslave ~ 10mS cycle

Application uses data from inputregisters and sets values in output registers

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General Benefits of using FieldbusesGeneral 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!)

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DP is popular with users...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.

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DP is popular with vendorsDP 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

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Why Eurotherm chose Profibus DPWhy 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.

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Profibus - Weaknesses.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)

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Eurotherm’s Profibus RangeEurotherm’s Profibus Range

T940

SCADA - PC CardsSCADA - PC CardsWonderware, Wizcon, Interlution

subselect.me

OK OK OK OK OKOK OK OK OK OK

2000F PIDControllers

T630 ProcessController

ThyristorPower Controllers

ChartRecorders

AC/DCDrives

2900 °

CPU

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Loop Loop Relay 4 DI/DO 8

2500 Multi-loop

PC3000/PC300 T800

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GSDGSD11 Files 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

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DP Network ConfigurationDP Network Configuration

GSD

GSD

GSD

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DP Slave OperationDP 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

– Data comes from GSD file 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)

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Profibus DP “Slave State Machine”Profibus DP “Slave State Machine”

“Config Data”from GSD File

“User Parametisation Data ”from GSD File

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Why Use a GSD Editor?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

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ProblemsProblems

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...

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Eurotherm GSD File EditorEurotherm GSD File Editor

Creates Custom ‘GSD’ file for use by network configurators

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Why Use the GSD File editorWhy 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

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Demand DataDemand 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)

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FutureFuture

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)

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ConclusionConclusion

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.