vibration monitoring & analysis. what is vibration ? it is motion of mechanical parts back and...
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What is Vibration ?
It is motion of mechanical parts back and forth from its position of rest /neutral position.
Vibration MonitoringVibration Monitoring
Vibration MonitoringVibration Monitoring
What causes Vibration ?
Induced Force &Freedom for Movement
Vibration MonitoringVibration Monitoring
Harmful Effects of Excess vibration
• Increased load on BRGs: Reduced BRG Life• Higher Forces on Mountings:
Foundation Loosening and Damage of Support Structure
• Increased Stresses of M/c : Risk of fatigue
components
Vibration MonitoringVibration Monitoring
Harmful Effects of Excess vibration• Decreased Equipment efficiency.
• Reduced Output Quality.
• Increased Maintenance Cost due to more Component Failures and Unplanned Operations
• Unsafe Operating Environment
Vibration MonitoringVibration MonitoringProblem Identifications
• Unbalance
• Misalignment
• Mechanical Looseness
• Antifriction / Sleeve Bearing Defects
• Gear Defects
Vibration MonitoringVibration MonitoringProblem Identifications
• Belt Defects
• Impeller / Blade Defects
• Bent Shaft
• Electrical Problems
• Resonance
Vibration MonitoringVibration Monitoring
Fundamental Realities• All Machines vibrate.• An increase in vibration level is a sign of
trouble & amplitude of Vibration depends on the extent of defect in the machinery components
• Each trouble will create vibration with different characteristics
VIBRATION FUNDAMENTALS
TIME
Period(T)(1 complete cycle)
Neutral Position
Upper Limit
Lower Limit
90
180
270
Characteristics of VibrationCharacteristics of Vibration
• Vibration characteristics are
Amplitude
Frequency Hz or CPM
Phase Angle or clock face
Displacement
Velocity
Acceleration
Parameter SelectionParameter Selection
• Frequency sensitivity
Displacement <600CPM
Velocity 600-60,000CPM
Acceleration >60,000CPM
Spike Energy/SEE
Ultrasonic range
FFT FAST FOURIER TRANSFORM.
• THE PROCESS OF TRANSFORMING TIME DOMAIN SIGNAL TO FREQUENCY DOMAIN.
• THE TIME DOMAIN SIGNAL MUST
FIRST BE SAMPLED AND
DIGITIZED.
Indian Institute For Production Management
FFT SPECTRUM ANALYSIS
A method of viewing the vibration signal in a way that is more useful for analysis is to apply a Fast Fourier Transformation (FFT). In non-mathematical terms, this means that the signal is broken down into specific amplitudes at various component frequencies.
Time Domain - overall data is the
sum of all exciting and reacting forces
ImbalanceRolling Element Bearing
Coupling chatter
Gearmesh
Time
Resultant Complex Waveform
Fmax, LINES, AVERAGES.
• Fmax REPRESENTS THE MAXIMUM FREQUENCY RANGE IN CPM OR HZ TO BE SCANNED BY THE INSTRUMENT.
• Fmax SHOULD NOT BE SET TOO HIGH SO THAT THE RESOLUTION AND ACCURACY SUFFERS OR IT SHOULD NOT BE TOO LOW SO THAT WE MISS SOME IMPORTANT HIGH FREQUENCIES.
GUIDELINES FOR SETTING Fmax.
• FOR MACHINES HAVING ANTI-FRICTION BEARINGS:- Fmax = 60 x RPM
• FOR MACHINES HAVING SLEEVE BEARINGS:- Fmax = 20 x RPM
• FOR GEAR BOXES:- Fmax = 3.25 x GMF
LINES OF RESOLUTION
• THE RESOLUTION IS THE NUMBER OF LINES
OR CELLS WHICH ARE USED TO CALCULATE AND DISPLAY THE FREQUENCY SPECTRUM.
• THE BANDWIDTH CAN BE CALCULATED BY DIVIDING Fmax BY THE LINES OF RESOLUTION.
• THE GREATER THE NUMBER OF LINES , THE BETTER IS THE ACCURACY.
FREQUENCY RESOLUTION Bandwidth =
F F maxmax
total lines of resolutiontotal lines of resolution
total lines of resolutiontotal lines of resolution
Am
plit
ud
e
Frequency FFmaxmax
lines or bins or cellslines or bins or cellsof resolutionof resolution
• FFT Calculation Time = Time to calculate FFT from Time Waveform [assuming no overlap processing]
Spectrum Data Collection Time
FFT Calculation Time =FFT Calculation Time =(60) ( #FFT Lines) (#Averages)(60) ( #FFT Lines) (#Averages)
Frequency SpanFrequency Span
Where: #FFT = Number of FFT Lines or Bins in Spectrum
# Averages = Number of Averages
Frequency Span measured in CPM
OVERALL VIBRATIONOVERALL VIBRATION
Total summation of all the vibration,with no regard to any particular frequency.
OVERALL VIBRATION
Overall vibration is the total vibration energy measured within a frequency range. Measuring the “overall” vibration of a machine or component, a rotor in relation to a machine, or the structure of a machine, and comparing the overall measurement to its normal value (norm) indicates the current health of the machine. A higher than normal overall vibration reading indicates that “something” is causing the machine or component to vibrate more.
Overall VibrationOverall Vibration
Total summation of all the vibration,with no
regard to any particular frequency.
OA =
OA=Overall level of Vibration Spectrum , Ai = Amplitude of each FFT line
n = No. of FFT Lines of resolution , NBF= Noise Bandwidth for Window chosen
A1 + A2 + ………………………+AnA1 + A2 + ………………………+An22 22 22
NNBFBF
NOTE: Don’t be concerned about the math, the condition monitoring instrument calculates the value. What’s important to remember is when comparing overall vibration signals, it is imperative that both signals be measured on the same frequency range and with the same scale factors.
What is Phase?What is Phase?
• The position of a vibrating part at a given instant with reference to a fixed point or another vibrating part.
• The part of a vibration cycle through which one part or object has moved relative to another part.
The unit of phase is degree where one complete cycle of vibration is 360 degrees.
PhasePhase is a measurement, not a processing method. Phase measures the angular difference between a known mark on a rotating shaft and the shaft’s vibration signal. This relationship provides valuable information on vibration amplitude levels,shaft orbit, and shaft position and is very useful for balancing and analysis purposes.
PHASE AN ILLUSTRATIONPHASE AN ILLUSTRATION
30 Micron10 degrees
32 Micron10 degrees
Shaft centre line moves up and down in a planer fashion
PHASE AN ILLUSTRATIONPHASE AN ILLUSTRATION
30 Micron10 degrees
32 Micron190 degrees
Shaft center line moves up and down in a rocking fashion
MACHINE TRAIN MISALIGNMENTMACHINE TRAIN MISALIGNMENT
Note: All phase readings corrected for pickup direction
TURBINE G/B HP COMP LP COMP
AXIAL PHASE(degrees)
0 5 15 18 198 21510 12 22 24 210 22012 10 20 22 208 218 8 6 16 20 200 210
Comparing Overall Levels Across Comparing Overall Levels Across Mounting InterfacesMounting Interfaces
Phase applicationPhase application
A BC
A 5 Microns, 10 degreesB 7 Microns, 12 degreesC 25 Microns, 175 degrees
Bolt at C is loose
Vibration AnalysisUnbalance
• Amplitude proportional to the amount of unbalance
• Vibration high normally in radial direction (may be also in axial direction incase of overhung and flexible rotors ).
• 1* RPM vibration is greater than 80% (normally) of the overall reading.
Vibration AnalysisUnbalance
• Horizontal and vertical 1* RPM amplitude should be nearly same, although it also depends on system rigidity on the particular direction.
• Other frequency peaks may be less than 5% of the 1*RPM amplitude
• Phase shift of 90 deg. When sensor moves from horizontal to vertical.
UNBALANCE
• Operating conditions such as load, flow condition and temperature effect unbalance– Balance under normal operating conditions
• Changes in track and pitch angle of fan blades can result in “Aerodynamic Unbalance”
MISALIGNMENT
• BIGGEST PROBLEM INITIALLY
• Operating temperature can affect alignment– Machines aligned cold can go out when
warm
• Bases or foundations can settle
• Grouting can shrink or deteriorate
• Increases energy demands
MISALIGNMENT
• Forces shared by driver and driven (not localized)
• Level of misalignment severity is determined by the machines ability to withstand the misalignment– If coupling is stronger than bearing the
bearing can fail with little damage to the coupling
General Characteristics Of Misalignment
• Radial vibration is highly directional
• 1X, 2x, and 3x running speed depending on type and extent of misalignment– Angular 1x rpm axial– Parallel 2x rpm radial (H & V)– Combination 1,2,3x rpm radial and
axial
Vibration AnalysisMisalignment
Angular Misalignment• High axial vibration
( Greater than 50% of the radial vibration)
• 1* , 2*, 3* RPM normally high.
• 180 deg. Out of phase across the coupling
Angular Misalignment
• Produces predominant 1x rpm component• Marked by 180 degree phase shift across the
coupling in the axial direction
Vibration AnalysisMisalignment
Off-Set Misalignment• High Axial vibration. Also shows high radial
vibrations.• 1*, 2*, 3* RPM high. 2* often larger than 1*• In case of severe misalignment, much high
harmonics (4* - 8*) or even a whole series of high frequency harmonics will be generated.
• 180 deg. Out of phase across coupling
Parallel Or Offset Misalignment
• Produces a predominant 2x rpm peak in the spectrum
• Marked by 180 degree phase shift across the coupling in the radial direction.
Vibration AnalysisMechanical Looseness
Caused by structured looseness / weakness of machine feet, base plate or foundation; also by deteriorated grouting, loose base bolts and distortion of the frame or base.
• Radial vibration high• 2* RPM & 1* RPM dominant• 180 deg. Phase differences between mating
surfaces which have looseness between them.
Vibration AnalysisMechanical Looseness
Caused by structured looseness / weakness of machine feet, base plate or foundation; also by deteriorated grouting, loose base bolts and distortion of the frame or base.
• Radial vibration high• 2* RPM & 1* RPM dominant• 180 deg. Phase differences between mating
surfaces which have looseness between them.
Vibration AnalysisMechanical Looseness
Caused by looseness in bearing housing bolts and cracks in the frame structure.
• Radial vibration high• 2* RPM normally dominant. 0.5*, 1* and 3* RPM
may also be present• Substantial Phase difference between mating
surfaces which have looseness between them
LOOSENESS
• Not an exciting force• Allows exciting frequencies already
present to exhibit much higher amplitudes
• Loss or reduction in normal stiffness• Caused by:
– loose mounting bolts– deterioration of grouting– cracked welds
Two Types Of Looseness
• Looseness of Rotating Components– Loose Rotors– Bearings Loose on the Shaft or in Housing– Excessive Sleeve Bearing Clearances
• Looseness of Support System– Loose Mounting Bolts– Grouting Deterioration– Cracks– Poor Support– Frame Distortion
Looseness Of Rotating System
• Rattling condition cause impacts due to excessive clearance in a rolling element or sleeve bearing
• Impacts cause multiple running speed harmonics to appear in the spectra
• Identified by:– multiple harmonics– unstable phase– highly directional radial vibration
Looseness Of Support System
• FFT readings show 1x rpm, 2x rpm, and 3x rpm components
• Structural looseness / weakness will cause high 1xrpm peak in FFT
• Identified by– Highly directional radial vibration– Bouncing– Taking comparative phase readings across
interfaces and look for amplitude variation– Typically loose in vertical direction
Condition MonitoringSystem Integration
SOFTWARE DCS
CMMS
NETWORK
PdM TECHNOLOGIES
ON-LINEANALYSIS
SURVEILLANCE
ON - LINE
PERIODIC
WALKAROUND
OFF- LINE
CENTRALISEDPROTECTION
DISTRIBUTEDPROTECTION
CONTINUOUS
PROTECTION
current value
Overall Data Trends-this is what the DCS records
lo alarm
hi alarm
changes over time
The limitation is that it does not adequately reflect changes at higher frequencies which can increase by
100% but only add 1% to the overall energy level
Vibration Analysis
time waveform
transducer
Vibration Spectrum
Data Collector
Protection Monitor
and / or
Band Trending, the new way forward
lo alarm
hi alarm
changes over time
Trend and alarm the:•Machine unbalance•Alignment•Gear mesh•Bearings etc
Emonitor Odyssey: spectrum band alarming though its diagnostic tools feature for both On & Off line gives advanced machinery analysis and reduces False Alarms
DIAGNOSTICS - the advantage of frequency band trending
• Root cause analysis is a complex machine specific exercise considering all eventualities
• Expert systems are a one off diagnosis and do not show a trend
• Frequency band trending is specific to root cause analysis
• Band alarming also indicates vibration signals that are outside the established norms
• Trending alignment, unbalance, gear meshing and bearing condition condition is more specific
• A complex issue simplified without the need of specialist customisation and regular updates
DCS Limitations - Summary• We have shown that putting total belief in the DCS vibration
trend is highly risky
• Machinery failures still happen with on-line vibration monitoring with 4-20mA data to the DCS. Most causes are due to higher frequency signals swamped by the overall levels.
• Advanced machinery protection through Frequency Band Trending and Alarming - more specific than an Expert system.
• The latest S/w based Analysers incorporates Narrow Band Alarming. They offer machinery protection and narrow band alarming.
• A lower cost solution is periodic manual Data Collection.
ESHAPE: Modal analysis using phase for advanced diagnosis and better understanding of system response
On line Vibration and othermonitors
• Innovative, fully-digital design• Exceeds API 670 specification• Widely-used system• Fully field programmable• Low installation cost• ModBus protocol
TYPICAL APPLICATION
TACHO
TACHO
MONITORVIBRATION
IRD
VIBRATIONMONITOR
IRD
TACHO TACHO TACHO TACHO
VIBRATIONMONITOR
CH.1 CH.2
IRD
VIBRATIONMONITOR
IRD
CH.1 CH.1CH.2 CH.2CH.1
VIBRATIONMONITOR
IRD
MONITORVIBRATION
CH.2 CH.1
IRD
TACHOTACHO TACHO TACHO
CH.2
MONITORVIBRATION
CH.1
IRD
MONITORVIBRATION
IRD
CH.1
VIBRATIONMONITORVIBRATION
CH.2 CH.1 CH.2 CH.1 CH.1CH.2
MONITOR
IRD IRD
HP
DRIVERSDRIVERS DRIVERS DRIVERS
IP
TACHO TACHO
MONITORVIBRATION
IRD
CH.1CH.2 CH.2
VIBRATIONMONITOR
CH.1 CH.2
IRD
TACHO
VIBRATIONMONITOR
IRD
CH.1CH.2
TACHO
CH.2 CH.1 CH.2
VIBRATIONMONITOR
IRD
DRIVERSDRIVERS
LP
DRIVERS
ALT.
FS HP LP GEN EX
TURBINE SUPERVISORY
STATOR END WINDING
CWP
BFP
BFP ID
FD
PA
AUXILIARIES
ENGINEERINGOPERATIONSDCS ODYSSEY SERVER
POWER PLANT INTEGRATION
GATEWAYTO CMMS
VIBRATION ANALYSER
DATA LOGGER
ENGINEERINGDCS ODYSSEY CLIENT SERVER
GATEWAYTO CMMS
ANURAKSHAN
VIBRATION ANALYSER
Plant Integration with LAN or WAN
FS HP LP GEN EX FS HP LP GEN EX FS HP LP GEN EX
CONTROL ROOM No 1 CONTROL ROOM No 2 CONTROL ROOM No 3
TG 1 TG 2 TG 3
ETHERNET
NETWORKING THE INFORATION - LAN / WAN e.g.
NOIDA HQ
CM CELL
VINDHYACHAL
RIHAND
TALCHER
UNCHAHAR KAYAMKULAM
PLANTOPERATIO
NS
GATEWAYTO CMMS
ANURAKSHAN
Using PlantLink
Vibration Trend Plot
Digital Picture of Plant
Hyperlink to equipment Hierarchy
Automatic E-Mail notification on Equipment Alarm Status
Click on Measurement Label to link to plots or other views.
Scenario of Instruments &Sensors & Probes
• Velocity sensors are made in India• Accelerometers range over 150 types
– standard– Low frequency– High temperature (Gas Turbines)– Special application
• Eddy current probes - comprehensive range• Others available for process measurement
Vibration Datacollectors
Many vendors
Select on ‘Fitness for Purpose’
Intrinsic Safety
Dust & Moisture proof
Diagnostic Capability