Fieldbus Foundation TM Bus diagnostics and troubleshooting Andreas Agostin MTL Instruments Pte Ltd Singapore On behalf of Fieldbus Foundation TM Marketing Committee (Malaysia) 1
Bus diagnostics and troubleshooting Plant life cycle Costs of diagnosis 2
Which tools for which purpose? Plant life cycle Engineering Calculation tools 3 Installation Wiring tools Commissioning & Troubleshooting Operation & Maintenance Commissioning & troubleshooting tools Predictive Maintenance tools
Which tools for which purpose? Plant life cycle 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. Calculation tools 4
Which tools for which purpose? Plant life cycle Installation 5 1 Source: http://forums.fieldbus.org/showthread.php?t=1298 Wiring tools 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 -
Which tools for which purpose? Plant life cycle Commissioning & Troubleshooting 6 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. Commissioning & troubleshooting tools
Which tools for which purpose? Plant life cycle 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. 7 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). Predictive Maintenance tools
Maintenance Strategies Maintenance Failure occurred already Repair Failure already occurred Failure causes production loss Potentially very high costs Time based On a schedule Condition based When required 8
Maintenance Strategies Maintenance Failure occurred already No failure yet Repair Preventive No failure yet High and regular maintenance costs Time based On a schedule Condition based When required 9
Maintenance Strategies Maintenance Failure occurred already No failure yet Repair Preventive Predictive In time before failure occurs (Condition: Warning ) 10 Time based On a schedule Condition based When required
Device Maintenance Effort Zero Drift; 6% Process Interface; 6% Failure; 4% Preventive Re-ranging; 20% Repair Routine check; 35% Failure suspect, but no problem found; 28% 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. Predictive Source: ARC Advisory Group, Intelligent Devices Provide Foundation for Operational Excellence ARC Strategies, January 2003. 11
Why Predictive Intelligence? 100% Condition of Assets Too Late 0% Time to Fail 12
Why Predictive Intelligence? 100% 13 Condition of Assets 0% Conditions: (Alarms) Prediction gives you enough time to make proper decision and to prevent abnormal situations Time to Fail OK Needs maintenance soon Needs maintenance now Too Late
Why Predictive Intelligence? 100% 14 Condition of Assets 0% Conditions: (Alarms) Prediction gives you enough time to make proper decision and to prevent abnormal situations Time to Fail OK Needs maintenance soon Needs maintenance now
Typical Problems 15
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 16
Bend radius too tight, Upward facing gland risks water ingress 17 Two cables into one gland prevents sealing of gland
Corroded terminals: 18 Increasing number of retransmissions Increase of FF noise Can be a combination of both
Case study: faults in operation Short to shield on fieldbus trunk: Indication of short to shield Increasing number of retransmissions on all devices 19
Case study: faults in operation 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 20
Case study: faults in operation 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 21
Bad wiring technique Welding, variable frequency drives (VFD), Motors, machinery: 22 Increase of HF noise Increasing number of retransmissions Can be a combination of both
Case study: faults in operation 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 23
Case study: faults in operation 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) 24
Wires coming out of ferrules: Spur: Device drops off (may or may not return) Increasing number of retransmissions 25 Trunk: Devices drop off (may or may not return) Signal amplitude sometimes ok, sometimes high Increasing number of retransmissions
Problem indicated by Diagnostic Module 26
Warning or alarm levels exceeded? 27
On which segment? 28
What s the problem on the segment? 29
Alarm Identification Name and Description Device Signal Level High-High Alarm Device Signal Level High Alarm Corrective Action 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. 30 Device Signal Level Low Alarm 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 tight 3. for water in spur cable or device 4. 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. And what does that mean, what is the cause of the alarm?
In the device manager, you: Compare actual vs historical data See information about each device See alarms of physical layer of device 31
All data is communicated via FF, allowing full Integration into all host software packages. Example: Trending of noise and voltage levels in the historian. 32
Example: Noise level trending Alarm level (critical) Noise Warning level 2008 2009 2010 2011 2012 Warning and alarm levels are set so that there is sufficient time to fix the problem e.g. during a regular shutdown 33
On-line monitoring 24VDC Host Computer FFPS T FF Power Supply & Conditioner &Terminator Fieldbus barrier & Terminator DM F809F Fieldbus Diagnostic Module Fieldbus Fieldbus barrier T barrier H1 Interface Intrinsically Safe Spurs Device 1 Device 2 Device 3 Permanently installed at the fieldbus power supply in the control room. 34
Portable diagnostic tools 24VDC Host Computer FFPS T FF Power Supply & Conditioner &Terminator Fieldbus barrier & Terminator Fieldbus Fieldbus barrier T barrier H1 Interface PDI Intrinsically Safe Spurs Portable Diagnostic Instrument Device 1 Device 2 Device 3 To measure at fieldbus barrier, PDI needs to be Ex i approved. Important since the galvanic isolation of fieldbus barrier impacts on measurement. 35
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 36
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 37 http://forums.fieldbus.org/showthread.php?t=1298 Follow link to access Fieldbus Forum posting on physical layer problem (see summary on next page)
http://forums.fieldbus.org/showthread.php?t=1298 38
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 39
The various solutions 40
The various solutions Differentiators: - Physical Interface (FF H1 / FF HSE / RS485 / Contact) - Measurements - Level of detail - User Interface (H1 Host integration / DTM / OPC) 41
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 addon that can help you to identify problems before they cause a failure 42
Any Questions? Andreas Agostin contact: +65 9758 5161 aagostin@mtlsing.com.sg 43
44 www.fieldbus.org