Transcript Profibus DP

Profibus
Tim Linnell (Eurotherm Ltd)
EUROTHERM
CONTROLS
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This Talk
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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 Family
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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
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Profibus PA
– DPV1 Messaging + Device Profiles + Intrinsic Safety
– Slower Physical Medium (31.25 kbit/s) with loop power
– Process Applications
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Profibus FMS
– ‘Full’ Messaging (I/O + non time critical)
– Higher level Communications (PLC <-> PLC)
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‘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
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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
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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
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Scanner transfers I/O
Data from/to PLC once
each scan cycle for each
slave ~ 10mS cycle
Application uses
data from input
registers and
sets values in
output registers
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General Benefits of using Fieldbuses
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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...
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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 vendors
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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 DP
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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.
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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 Range
T940
PC3000/PC300
T800
SCADA - PC Cards
Wonderware, Wizcon,
Interlution
subselect.me
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e2900
2000F PID
Controllers
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T630 Process Thyristor
Power
Controller
Controllers
AC/DC
Drives
Chart
Recorders
Main Air
Aux Air
DI/DO 8
Run Reset
Hold Servo
FridgeLight 1
Load Light
2
Raise
Lower
Main Fan
Aux Fan
Relay 4
Loop
Heat
Loop
Temp
CPU
Cool
Inner Temp
OK OK OK OK OK
OK OK OK OK OK
2500
Multi-loop
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GSD1 Files
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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’
1
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Gerätestammdaten
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DP Network Configuration
GSD
GSD
GSD
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DP Slave Operation
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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
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Units then ‘Configured’ by Master
– Up to 244 bytes Type and Size data defining I/O
– Data comes from GSD file
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Slave enters ‘Data Exchange’
– Exits back to parameterisation on timeout
– “Diagnostic” requests made on status change or fatal error
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“Diagnostics”
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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”
“Config Data”from GSD File
“User Parametisation Data
”from GSD File
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Ref: P
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Why Use a GSD Editor?
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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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Problems
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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 Editor
Creates Custom ‘GSD’ file for use by network configurators
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Why Use the GSD File editor
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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 Data
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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
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‘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
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DPV1 provides “proper” acyclic messaging (currently 2500 ESuite only)
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Future
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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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Ref: P
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Conclusion
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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.
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