Bus diagnostics and troubleshooting - Fieldbus … diagnostics and troubleshooting ... Maintenance Strategies • Failure already occurred ... Follow link to access Fieldbus Forum

Foundation Fieldbus Seminar MalaysiaNovember 20091

Fieldbus FoundationTM

Bus diagnostics and troubleshooting

Andreas AgostinMTL Instruments Pte Ltd Singapore

On behalf ofFieldbus Foundation TM Marketing Committee (Malaysia)


Bus diagnostics and troubleshooting

• Plant life cycle• Costs of diagnosis


Plant life cycle

Which tools for which purpose?

Calculation tools

Engineering

Wiring tools

Installation

Commissioning & troubleshooting tools

Commissioning &Troubleshooting

PredictiveMaintenance

tools

Operation &Maintenance


Plant life cycle


Calculation tools

Engineering

Proper engineering ensures that the plant works as designed.Flaws in engineering will cause the actual plant not to work, and will trigger expensive redesign and re-work.


Plant life cycle


Wiring tools

Installation

According to field experience, approx. 95%1 of the problems occuring in a plant’s lifetime are related to installation.Cause can be:- Wrong ferrule diameter- Wrong crimping tool- Wrong crimping method- Wrong wire cutter- Wrong screw driver- Wrong torque- …

1 Source:http://forums.fieldbus.org/showthread.php?t=1298


Plant life cycle


Commissioning & troubleshooting tools

Commissioning &Troubleshooting

Commissioning should be done one-by-one. There are voices suggesting to connect all instruments and then switch on. However, a fault such as the frequently seen short-to-shield, will be impossible to locate. Connecting devices one-by-one will tell you that the problem occurred at the device you connected last.


Plant life cycle


PredictiveMaintenance

tools

Operation &Maintenance

In large installations with hundreds of bus segments, it can be of help to use physical layer online monitoring (“advanced diagnostics for the physical layer”). Using such tool you can detect degradation in the installation.

There are voices suggesting to use such tool for troubleshooting. However, due to the location of the tool in the control room, accurate measurements are not possible, and some faults are even not detectable (e.g. short to shield on a spur of a fieldbus barrier).


Maintenance Strategies

• Failure already occurred• Failure causes production

loss• Potentially very high

costs

Maintenance

Repair

Time based Condition basedOn a schedule When required

Failure occurred already…



Maintenance

Repair Preventive

Time based Condition basedOn a schedule When required


No failure yet…

• No failure yet• High and regular

maintenance costs



Maintenance

Repair Preventive

Time based Condition based

Predictive

On a schedule When required

In time beforefailure occurs

(Condition: “Warning”)


No failure yet…


Device Maintenance Effort

63% of time is spent investigating “problems” that do not exist. On Fieldbus, the fieldbus diagnostic module will alert you

when maintenance is needed, and will keep quiet if not.

Source: ARC Advisory Group, Intelligent Devices Provide Foundation for Operational Excellence – ARC Strategies, January 2003.

Routine check; 35%

Failure suspect, but no problem found; 28%

Re-ranging; 20%

Zero Drift; 6%

ProcessInterface; 6%

Failure;4% Preventive

Repair

Predictive


Why Predictive Intelligence?

Time to Fail0%

100%C

ondi

tion

of A

sset

s

Too Late



Time to Fail0%

100%C

ondi

tion

of A

sset

s

Prediction gives you enough time to make

proper decision and to prevent abnormal

situations

Too Late

Conditions:(Alarms)

OKNeeds maintenance soon

Needs maintenance now



Time to Fail0%

100%C

ondi

tion

of A

sset

s

Prediction gives you enough time to make

proper decision and to prevent abnormal

situations

Conditions:(Alarms)

OKNeeds maintenance soon

Needs maintenance now


Typical Problems


Case study: faults in operation

Water in junction box, cable or device:

• Increasing number of retransmissions• Indication of shorts to shield• Can be a combination of both


Bend radius too tight, Upward facing gland risks water ingress

Two cables into one glandprevents sealing of gland


Corroded terminals:

• Increasing number of retransmissions• Increase of FF noise• Can be a combination of both



Short to shield on fieldbus trunk:

• Indication of short to shield• Increasing number of retransmissions on all

devices



Short to shield on fieldbus spur (wiring block):

• Indication of short to shield• Increasing number of retransmissions on this

specific device or on the devices of this wiring block



Short to shield on fieldbus barrier spur:

• Indication of short to shield only on Handheld tester (due to galvanic isolation of fieldbus barrier)

• Increasing number of retransmissions on this specific device or on the devices of this fieldbus barrier


Bad wiring technique

Welding, variable frequency drives (VFD), Motors, machinery:

• Increase of HF noise• Increasing number of retransmissions• Can be a combination of both



Cable jacket stripped back too far can cause instrument malfunction:

– Water ingress– Wires shorted to housing– Corrosion– Tearing wires (increasing

resistance)

• Increasing number of retransmissions

• Signal amplitude rises• Increase of FF noise• Can be a combination of

above



Fieldbus terminator missing:

• All signal amplitudes rise (best indicator)• Increased noise in all frequency bands• Increasing number of retransmissions (usually on all

devices)• One or more devices drop off the bus (may or may not

come back)

Note: likely to be the terminator in the field, not on the baseplate (soldered, controlled environment)


Wires coming out of ferrules:

Spur:• Device drops off (may or may not return)• Increasing number of retransmissions

Trunk:• Devices drop off (may or may not return)• Signal amplitude sometimes ok, sometimes high• Increasing number of retransmissions


Problem indicated by Diagnostic Module


Warning or alarm levels exceeded?


On which segment?


What’s the problem on the segment?


……

Device Signal Level Low-Low Alarm

If only one device low: check 1. alarm limits have not been wrongly set, 2. spur cabling, spur and device connections

are tight3. for water in spur cable or device4. device operation. If several/all devices on segment low check: 1. for more than two terminators on

segment, check that terminator switches on the fieldbus barrier are set to “off”.

2. for water in devices, junction boxes and cabling.

Device Signal Level Low Alarm

Device Signal Level High Alarm

If only one device high: check: 1. alarm limits have not been wrongly set, 2. device operation. If several/all devices on segment check: 1. for only one terminator on segment 2. for failed terminator.

Device Signal Level High-High Alarm

Corrective ActionName and Description

And what does that mean, what is the cause of the alarm?

Alarm Identification


In the device manager, you:• Compare actual vs historical data• See information about each device• See alarms of physical layer of device


All data is communicated via FF, allowing fullIntegration into all host software packages.Example: Trending of noise and voltage levels in the historian.


Example: Noise level trendingN

oise

Alarm level (critical)

Warning level

2008 2009 2010 20122011

Warning and alarm levels are set so that there is sufficient time to fix the problem e.g. during a regular shutdown


On-line monitoring

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

DM F809F FieldbusDiagnostic Module

Permanently installed at the fieldbus power supply in the control room.


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.


Typical measured parameters

• DC voltage– Indicates correct function of power supply/conditioner– Instrument supposed to operate from 9V onwards

• Shield short (+ or – connected to shield/ground/screen)– Easy to measure and understand– Further measurements can identify location

• Signal level– Minimum level is specified by Fieldbus specification– Low or high levels on all devices suggests incorrect bus termination– If only one device, suggests problem on single spur


Typical measured parameters

• Noise– Maximum level is specified by Fieldbus specification– Tri-band measurement helps to identify source

• LF: bulk supply• IF: fieldbus device• HF: induction from outside the network

• Retransmissions / Retransmission rate– Good measurement of physical layer health– Measured in absolute retransmissions and in % of total transmissions

(rate)– Re-tries can obscure faulty device or network

http://forums.fieldbus.org/showthread.php?t=1298Follow link to access Fieldbus Forum posting on physical layer problem(see summary on next page)


http://forums.fieldbus.org/showthread.php?t=1298


Amount of diagnostic information

• Fieldbus Diagnostic Modules can provide a multitude of data and information

• Not every maintenance technician is a fieldbus expert

• Tools must match the employee skills


The various solutions


The various solutions

Differentiators:- Physical Interface(FF H1 / FF HSE / RS485 / Contact)

- Measurements- Level of detail- User Interface(H1 Host integration / DTM / OPC)


Conclusion

“Key Three”:• Foundation Fieldbus communication is very

robust• If you do your installation right, you avoid many

problems down the road• Online-diagnostic of the physical layer is an add-

on that can help you to identify problems before they cause a failure


Any Questions?

Andreas Agostin contact:+65 9758 5161

[email protected]


www.fieldbus.org

Documents

Bus diagnostics and troubleshooting - Fieldbus … diagnostics and troubleshooting ... Maintenance Strategies • Failure already occurred ... Follow link to access Fieldbus Forum