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© 2007 Fieldbus Foundation
The Foundation Fieldbus Physical Layer …… and how to diagnose it
24th of August, 2007,Hotel Intercontinental - The Grand,
Andheri (East), Mumbai INDIA
Andreas AgostinIndustrial Network Sales SpecialistMTL Pte Ltd Singapore
Fieldbus FoundationFieldbus Foundation – India Marketing Committee
2© 2007 Fieldbus Foundation
Introduction
The Fieldbus ‘Physical Layer’ and its elementsWhy are Physical Layer diagnostics needed?Typical problems
during start-up and commissioningduring operation
Which parameters should be measured?Ad-hoc and on-line maintenance tools
Turn data into information Use Information for Predictive and Preventative Maintenance
3© 2007 Fieldbus Foundation
OSI Model
TRANSPORT LAYER
SESSION LAYER
PRESENTATION LAYER
APPLICATION LAYER
PHYSICAL LAYER
DATA LINK LAYER
NETWORK LAYER
H1 @ 31.25 kbit/s
H1 DLL
Fieldbus Message SpecFieldbus Data Access
Sublayer
1
2
3
4
5
6
7
H1 PHYSICAL LAYER
H1STACK
USERLAYER
H1 FOUNDATION Fieldbus Model
USERLAYER
What is the Fieldbus Physical Layer?
Physical layer represents the actual data transmission
4© 2007 Fieldbus Foundation
Physical layer elements – Gen. Purpose
Wiringcomponents
HostComputer
H1 Interface
Device 1 Device 3 Device 2
T
Wiring Block& Terminator
(non-IS) Spurs(non-IS) Trunk
FFPST
FF Power Supply& Conditioner&Terminator
24VDC
Cable
Power supply / Conditioner
This concept is typically applied to:• Any kind of instrument in the safe (non hazardous) area• Ex nA instruments in Zone 2• Ex d instruments in Zone 1
5© 2007 Fieldbus Foundation
Physical layer elements – High Energy
HostComputer
H1 Interface(non-IS) Trunk
FFPST
FF Power Supply& Conditioner&Terminator
24VDC
Power supply / Conditioner
Cable
This concept is typically applied to:• Ex nL instruments in Zone 2• Ex i instruments in Zone 1 or 0
Fieldbus barrier
Device 1 Device 3 Device 2
Fieldbus barrier& Terminator
IntrinsicallySafe Spurs
TFieldbus
barrier
6© 2007 Fieldbus Foundation
Physical layer elements – FISCO/FNICO
HostComputer
H1 Interface
24VDC
Wiringcomponents
Device 1 Device 3 Device 2
T
IS Wiring Block& Terminator
IntrinsicallySafe Spurs
This concept is typically applied to:• Ex nL/FNICO instruments in Zone 2• Ex i/FISCO instruments in Zone 1 or 0
Intrinsic safeFF Power Supply
& Conditioner&Terminator
FISCO/FNICO Power supply
Intrinsically Safe Trunk
TFFPS
T
7© 2007 Fieldbus Foundation
Physical layer diagnostics
Which parameters? … voltage, …?What about efficient commissioning?How can I troubleshoot properly?Can I do a health check-up
from time to timeor constantly on-line?
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Why physical layer diagnostics?
Need to maximize plant availabilityIdentify problems before the process is affectedReduce troubleshooting time
Not covered by instrument diagnosticsInstrument diagnosis permits early diagnosis of sensor and actuator faultsPhysical layer diagnosis covers the health of the interconnecting networkFFPS
T
A failure could result in loss of revenue, production and/or damage to plant
9© 2007 Fieldbus Foundation
Physical layer experience
“Fieldbus physical layer has proved very reliable with no problems since installation. We used good quality cabling and a quality contractor for the installation.”
Plant Engineer, European Chemical Plant
“The power supplies and wiring components have not made any problems since they were installed and put into operation. The high reliability provides solid foundation for the successful applications of the Fieldbus.”
Head of AutomationChinese Integrated Polymer Plant
10© 2007 Fieldbus Foundation
Physical layer experience
“Most common problem on fieldbus segments is wrong grounding of cable screen..”
Fieldbus Support Specialist, Major Automation Contractor
“Problems observed included electrical noise from welding on site, capacitance imbalance of field device and wiring component deforming signal when noise on bus.”
Instrument EngineerEuropean Chemical Plant
11© 2007 Fieldbus Foundation
Physical layer experience“Visited site with problems of lots of noiseon fieldbus and were using 3 terminators as way of reducing noise. Checked screen grounding which was connected to control system ground bar, but ground bar had not been connected to earth. This was connected to earth, noise eliminated and segments now operate with 2 terminators”
Fieldbus Support Specialist, Physical Layer Supplier
“Communication errors were experienced on site. Visited site and identified problems of loose connections. Correctly tightening screw terminals with a torque screwdriver resolved the communication issues.”
Fieldbus Support Specialist, Physical Layer Supplier
12© 2007 Fieldbus Foundation
Theoretical approach
Fieldbus specification defines all FF parameters with limits.If the network operates within the specified limits, it should work properly.
13© 2007 Fieldbus Foundation
Theoretical approach
Problem with that:Impossible to measure all parameters in a system environmentIndividual components can meet individual criteria, but problems can arise due to interactionIf you know a parameter is off-limit, what to do next?Never fix a running system
14© 2007 Fieldbus Foundation
Practical approach
Proper commissioningFix all problems as far as possibleEstablish a baseline (take a snapshot)
Which are the relevant parameters that can eventually lead to a failure?
Measure themMonitor themIf they worsen, fix it before it fails
15© 2007 Fieldbus Foundation
Faults at start-up/commissioning
Wiring errorsWrong connections Device does not appear on DCSOpen/short circuits Diagnostic tool will tell youIntermittent connections Device log on DCS, tool infoReversed polarity Diagnostic tool will tell you
Too many or too few terminators Signal amplitudeFaulty components Communication retransmissions
Power supply or fieldbus barrier Insufficient voltage / LF noiseFieldbus instrument Retransmissions / FF noise
Inadequate grounding Retransmissions / HF noiseMultiple grounds in fieldNo clear grounding strategy
16© 2007 Fieldbus Foundation
Faults in operation
Environmental damageWater ingressCorrosionVibrationTemperature Variations
Manually inflicted damageInsufficient MaintenanceSurge damage
LightningOn-site welding
Electrical noiseFaulty or improperly grounded electrical apparatus
Component failurePhysical layer component or fieldbus device
Compare measurements to baseline.Observe differences.Are differences related to a particular device only, or to the whole segment?Combine the various measurements from diagnostic tool to draw conclusion.
17© 2007 Fieldbus Foundation
Prevention
Installation ToolsTorque screwdriverFerrulesWire strippersDigital Multimeter
18© 2007 Fieldbus Foundation
Prevention
MonitoringEstablish baselineduring commissioningOn-line
Tools:Portable fieldbus diagnostictest equipmentPlug-on fieldbus diagnosticmonitoring
19© 2007 Fieldbus Foundation
Portable diagnostic tools
PDIPortable
Diagnostic Instrument
Device 1 Device 3 Device 2
T
Wiring Block& Terminator
(non-IS) Spurs
FFPST
FF Power Supply& Conditioner&Terminator
24VDC
HostComputer
H1 Interface
Connect at respective location to obtain accurate measurement.
20© 2007 Fieldbus Foundation
Portable diagnostic tools
PDIPortable
Diagnostic Instrument
FFPST
FF Power Supply& Conditioner&Terminator
24VDC
HostComputer
H1 Interface
Fieldbus barrier
Device 1 Device 3 Device 2
Fieldbus barrier& Terminator
IntrinsicallySafe Spurs
TFieldbus
barrier
To measure at fieldbus barrier, PDI needs to be Ex i approved.Important since the galvanic isolation of fieldbus barrier impacts on measurement.
21© 2007 Fieldbus Foundation
Portable diagnostic tools
Hand-heldDiagnostic Module
wiring components
Fieldbus powersupply system
Junction box
Use plug on Power supplies and wiring components
Use clips on instruments and open cable ends
22© 2007 Fieldbus Foundation
Typical measured parameters
Shield shortEasy to measure and understandFurther measurements can identify location
Signal levelMinimum level is specified by Fieldbus specificationLow or high levels on all devices suggests incorrect bus terminationIf only one device, suggests problem on single spur
DC voltageIndicates correct function of power supply/conditionerInstrument supposed to operate from 9V onwards
NoiseMaximum level is specified by Fieldbus specificationTri-band measurement helps identify source
RetransmissionsGood measurement of physical layer healthRe-tries can obscure faulty device or network
23© 2007 Fieldbus Foundation
Portable diagnostic tools
Establish baseline during commissioning1. Connect fieldbus tester to network
(between rack room and field devices)2. Store measurements3. Upload to PC4. Record data as Excel spreadsheet
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Portable diagnostic tools– turn data into information
Repeat this process from time to time1. Use Excel to create trend charts2. Identify long-term degradation
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Good diagnostic information
Easy to measureDoesn’t require extreme skill or long time
Easy to understandUseless if operators don’t know what it means
Gives definite indication of a problemUse thresholds and limits to indicate problems
Eliminates possible causesProvide short list, or ideally exact source
ActionableLeads to next step in troubleshooting process
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Good diagnostic information (?)
OK ? NOT OK ?NOT OK ? OK ?
Tools need to be suitable for the people who use it!
27© 2007 Fieldbus Foundation
On-line monitoring
HostComputer
H1 Interface
Device 1 Device 3 Device 2
T
Wiring Block& Terminator
FFPST
FF Power Supply& Conditioner&Terminator
24VDC
DM Diagnostic Instrument
Permanently installed at the fieldbus power supply in the control room.
28© 2007 Fieldbus Foundation
Instrument Management Software (including fieldbus diagnostics)
Fieldbus powersupply system
Host control system
Controller I/O
Fieldbus
wiring components
On-line diagnostic monitoring
On-line Diagnostic Module
29© 2007 Fieldbus Foundation
On-line diagnostic module
Continuously monitors segment and individual instrument parametersMonitors up to 8 fieldbus segmentsDiagnostic software
Integrated in control systems’instrument management software via “DD”No special software required
30© 2007 Fieldbus Foundation
Fieldbus diagnostic module
DI alarm function blocks with individual and
common alarms
Resource block
Segments 1 to 8 transducer blocks
Fieldbus diagnosticmodule
Diagnostic module transducer block
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Example of trending on a DCS– turn data into information
Trending offieldbus segment noise
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Conclusions
Physical layer health is criticalAvoid problems from the start
Select approved and proven devicesUse quality cable, wiring components and power conditionersFollow good installation practicePeriodic and on-line maintenance tools aid diagnosis during start-up and operationOpen-architecture diagnostic monitor is independent of control platform
33© 2007 Fieldbus Foundation
Thank You