Vibration Monitoring & Analysis

Vibration Monitoring & Vibration Monitoring & AnalysisAnalysis

What is Vibration ?

It is motion of mechanical parts back and forth from its position of rest /neutral position.

Vibration MonitoringVibration Monitoring


What causes Vibration ?

Induced Force &Freedom for Movement


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


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


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

Frequency sensitivity


Displacement

Velocity

Acceleration

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

Spectrum Analysis

Enables precise evaluation of machinery condition and

prediction

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

FFT SPECTRUM

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.

Vibration PhaseVibration Phase

AdditionalIllustration onPhase

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 Analysis of

Common ProblemsCommon Problems

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”

Typical Spectrum For 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

Three Types of Misalignment

• Combination (most common) • Angular• Parallel or Offset

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

Typical Spectrum for Misalignment

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.

Typical Spectrum for Misalignment

Axial Phase Showing Misalignment

Other Types Of Misalignment

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.


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.

Looseness

• Looseness produces

2X RPM Freq.


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

Typical Spectrum for Looseness of Rotating System

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

Looseness Of Support System

Modern Trend in

Vibration Technology

Condition MonitoringSystem Integration

SOFTWARE DCS

CMMS

NETWORK

PdM TECHNOLOGIES

ON-LINEANALYSIS

SURVEILLANCE

ON - LINE

PERIODIC

WALKAROUND

OFF- LINE

CENTRALISEDPROTECTION

DISTRIBUTEDPROTECTION

CONTINUOUS

PROTECTION

Overall Data Acquistion

time waveform

THE DCSMONITOR

DCS OUTPUT

4-20mA

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 Alarms, associate with each rotating element

frequency bands

hi alarm

lo alarm

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

EMONITOR Odyssey: Frequency Band Trends

Frequency Trend of Single Measurement

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.

Information however you want it !

X-Window Screen Captures

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

Documents

Vibration Monitoring & Analysis