CONDITION MONITORING OF ROTARY EQUIPMENTS

BY VIBRATION ANALYSIS

A Seminar Report

Submitted by

RENJITH M

MECHANICAL ENGINEERING DIVISION

SCHOOL OF ENGINEERING

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

Cochin 682 022

SEPTEMBER 2006

MECHANICAL ENGINEERING DIVISIONSCHOOL OF ENGINEERING

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGYCochin 682 022

CERTIFICATE

This is to certify that the Seminar Report entitled “CONDITION

MONITORING OF ROTARY EQUIPMENTS BY VIBRATION ANALYSIS”

submitted by Mr. RENJITH M to the Mechanical Engineering Division towards the

partial fulfillment of the requirements for the VII Semester of the B. Tech Degree course

in Mechanical Engineering of Cochin University of Science and Technology, is a

bonafide record of the seminar talk presented by him/her on

Seminar Coordinator Seminar Supervisor

ACKNOWLEDGEMENT

I express my deep gratitude to almighty, the supreme guide, for bestowing his blessings

up on me in my entire endeavor.

I would to like to express my sincere thanks to Dr. P.S Sreejith Head of Department of

Mechanical engineering for all his assistance

I wish to express my deep sense of gratitude to Lecturer Mr. Gireesh Kumaran

Thampi. Department of Mechanical Engineering who guided me through out the

seminar. His overall direction and guidance has been responsible for the successful

completion of the seminar.

I would also like to thank Lecturer Mr. Ajith Kumar for his valuable suggestions.

Finally, I would like to thank all the faculty members of the department of mechanical

engineering and my friends for their constant support and encouragement.

ABSTRACT

The main function of condition monitoring is to provide the knowledge of

machine condition and of its rate of change which is essential to the operation of this

method. The knowledge may be obtained by selecting suitable parameters such as

vibration for measuring and reading its value at intervals.

Signals from vibration sensors are measured and then compared with reference

measurements in order that they may be interpreted. This involves some analysis of the

signals ranging from simple RMS amplitude measurement to vibration signature or

spectral analysis, possibly including waveform plots and extending in its most

sophisticated form to data processing and a range of physico-mathematical concepts.

Other techniques such as orbital analysis, time waveform and phase analysis have

signifance as methods for study of particular dynamic characteristics.

CONTENTS

1. Introduction

2. Condition Monitoring

3. Classification of rotary equipments

4. Vibration

5. Transducers

6. Vibration analysis

7. Data acquisition

8. Data interpretation

9. Conclusion

10. Reference

LIST OF TABLES

Table 1: Vibration Severity Range

Table 2: Vibration Range for Diesel Generating set for Diesel Generators

Table 3: Vibration Trouble Shooting Chart

LIST OF FIGURES

Figure 1: Vibration Velocity

Figure 2: Vibration Acceleration

Figure 3: General Machinery Vibration Chart

Figure 4: Vibration Acceleration general severity chart

Figure 5: Moving Coil Type

Figure 6: Direct Prod Transducer

Figure 7: Accelerometer Transducer

Figure 8: Shaft Rider Accessory

Figure 9: Tri-axial Reading

Figure10: Amplitude Vs Frequency

Figure 11: Short term Amplitude Vs Time data

Figure 12: Long term Amplitude Vs Time data

Figure 13: Vibration amplitude Vs frequency data recorder identifies unbalance

Figure 14: Frequency analysis of vibration showing a bad bearing

1. INTRODUCTION

Machinery distress very often manifests itself in vibration or a change in

vibration pattern. Vibration analysis is therefore, a powerful diagnosis tool, and trouble

shooting of major process machinery would be unthinkable without modern vibration

analysis.

It is natural for machines to vibrate. Even machines in the best of operation

condition will have some vibration because of minor defects as a result of

manufacturing tolerances. Therefore each machine will have a level of vibration which

may be regarded as normal or inherent.

When machinery vibration increases or becomes excessive, some mechanical

trouble is usually the reason. Machinery vibration levels just do not increases or become

excessive for no reason at all. Something causes it unbalance, looseness etc.

Each mechanical defect generates vibration in its own unique way. This makes it

possible to positively identify a mechanical problem by simply measuring and studying

its vibration characteristics.

The success of a process industry often depends on the continued, safe and

productive operation of rotating machinery. An effective maintenance programme is

vital to this kind of success. The quality of the company’s maintenance programme

determines how long the machines will run, how safe they are for the people working

around them. The benefits of a good maintenance programme are:

1. Prolonged machinery life.

2. Minimizes unscheduled down time.

3. Eliminates unnecessary overhaul.

4. Eliminates standby equipment.

5. Provides more efficient operations.

6. Increases machinery safety.

7. Improves quality performance.

8. Improves customer satisfaction.

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2. CONDITION MONITORING

The main function of condition monitoring is to provide the knowledge of

machine condition and of its rate of change which is essential to the operation of this

method. The knowledge may be obtained by selecting suitable parameters such as

vibration for measuring and reading its value at intervals. With condition monitoring,

repairs are carried out only when the condition of machine has deteriorated to a

predetermined level. Thus repairs or replacement of parts take place only when it has

definitely been proved that a fault exists and if it left unrepaired would result in

unsatisfactory operation or breakdown with possible damage to other machine parts and

disruption of production.

2.1 Condition Monitoring of Rotary Equipments:

1. Continuous monitoring of vibration and bearing temperature of critical

machines.

2. Vibration and noise measurement and analysis on all rotary equipments.

3. Bearing temperature monitoring by surface thermometers.

4. Condition monitoring of anti-friction bearings using shock pulse meters.

5. Measurement of RPM by stroboscope/tachometer.

6. Measurement of shaft residual magnetism.

7. Detection of cavitations in pumps by SPM.

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3. CLASSIFICATIONS OF ROTARY EQUIPMENTS

Rotary equipment will be classified into three categories depending upon

critically for on-stream condition monitoring as described below.

A) Category-I(Critical Machines)

These are vital machines which will be generally of high cost, high speed, too

large and complex in their design and duties and does not justify the economics of

having another spare set and breakdown of which result in immediate and serious

interruption in production.

These equipments will have continuous on-line vibration and bearing

temperature monitoring systems. These machines will be monitored for vibration on

bearing housings once a week using portable monitoring instruments.

B) Category-II (Semi-critical Machines)

These are essential machines which will be needed for normal operation of the

plant, but having stand by set, and also the running speed of which will not be very

high. Failure of such equipments will not cause immediate production loss as the stand

by set will come in line in case of failure. These machines will be monitored for

vibration on bearing housing once in two weeks. However, some of the important

machines may be monitored once in a week depending upon the requirement and

equipment behavior.

C) Category-III (Non-critical Machines)

These are desirable auxiliary and general purpose machines which, owing to its

function, can be allowed to remain temporarily out of operation without having a

serious effect on operations. These equipments will be normally having spare sets.

These machines will be monitored for vibration housings once in a month.

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4. VIBRATION

Vibration is simply the back and forth movement of an object from its position

of rest. It is like an oscillatory motion. Vibrations in machines above certain limits are

harmful to their functioning.

The most common causes of vibration are:

Unbalance of motor.

Looseness

Misalignment

Bend shaft

Eccentrical

Bad belt drive and drive chains

Electromagnetic forces

Hydraulic forces

4.1) Vibration Characteristics

Machines condition and mechanical problems are identified by simply noting its

vibration characteristics are:

1) Amplitude (Displacement, Velocity, Acceleration)

2) Frequency

3) Phase

4.1.1) Vibration Displacement (peak to peak)

The total distance traveled by the vibrating part from one extreme limit of travel

to the other extreme limit of travel is referred to peak to peak displacement. The

vibration displacement is usually expressed in micrometer where one micrometer equals

one thousandth of a millimeter (0.001mm).

4.1.2) Vibration Velocity

The velocity of the motion is definitely a characteristic of the vibration but since

it is constantly changing throughout the cycle, the highest peak velocity is selected for

measurement. Vibration velocity is expressed in millimeter per second peak.

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Fig 4.1

Vibration velocity

4.1.3) Vibration Acceleration

Vibration acceleration is another important characteristic of vibration.

Technically acceleration is the rate of change of velocity. It is normally expressed in “g”

“s” peak, where one “g” is the acceleration produced by the force of gravity at the

surface of the earth

Fig 4.2

Vibration Acceleration

4.1.4) Vibration Frequency

The amount of time required to complete one cycle of a vibration pattern is

called the period of vibration. Vibration frequency is the measure of complete cycles

that occur in a specified period of time.

Frequency = 1/period

The frequency of vibration is usually expressed as the number of cycles that

occur in each minute or CPM (cycles per minute) or number of cycles per second or

Hertz (Hz).

4.1.5) Vibration Phase

Phase is defined as the position of a vibrating part at a given instance with

reference to a fixed point or another vibrating part. Phase measurements offer a

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convenient way to compare one vibration motion with another or to determine how one

part is vibrating relative to another part.

Vibration Severity

There are no realistic figures for selecting a vibration limit which, if exceeded

will result in immediate machinery failure. The events surrounding the development of

a mechanical failure are too complex to set any reliable limits. On the other hand we

must have some general indications of machinery condition that can be evaluated on the

basis of vibration amplitude.

Fig. 4.3

General machinery vibration severity chart

On the fig 4.3 the horizontal axis is scaled in terms of vibration frequency and

the vertical axis in terms of displacement. The area between the diagonal lines

represents levels of vibration severity from extremely smooth to very rough.

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The fig 4.4 is a severity chart which works much the same way but uses velocity

and acceleration parameters and covers a higher CPM range

Fig.4.4Vibration acceleration general severity chart

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5. TRANSDUCERS

Transducer is a sending device which converts one form of energy into another.

The Vibration Transducer (Pick-Up) converts mechanical vibration into an electrical

signal. There are mainly three types of Vibration Transducers.

1) Velocity Transducers.

2) Accelerometer Transducers.

3) Proximity Transducers.

Velocity Transducer and Accelerometer Transducer are called Seismic

Transducers. Proximity Transducer is called Non-contact Transducer.

5.1) Velocity Transducers

Velocity transducers respond directly to vibration velocity. Most vibration

measurement instruments have provision for processing the electrical signal from a

velocity pick up to show vibration displacement as well. In theory it is also possible to

convert signals from velocity pickups to units of acceleration, however, this is not done

in practice, because the results have been found to be unreliable.

5.1.1) Moving coil type

Fig 5.1

Moving coil type

The fig 5.1 is a simplified diagram of a seismic velocity vibration transducer.

The system consists of a coil of fine wire supported by soft spring. A permanent

magnet, firmly attached to the case of the transducer, provides a strong magnetic field

around the coil. Whenever this transducer is fixed or held tightly against a vibrating

object, this permanent magnet vibrates while the spring suspended coil of wire remains

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stationary in space. When the coil of wire cuts magnet lines of force, a voltage is

generated in that wire. The voltage is proportional to the velocity of motion, the strength

of the magnetic field, and number of turns of wire in the coil. The voltage generated is

transmitted by cable to a vibration meter, monitor or analyzer.

5.1.2) Direct Prod Transducer

Many times it is necessary to measure the vibration of a small light weight part

or structure. However, holding or attaching the standard velocity pickup to a small part

can actually reduce the vibration. We can solve this problem by using a direct prod

pickup such as the one shown in figure.

Fig 5.2

Direct prod transducer

The principle of operation of a direct prod pickup is identical to that of a seismic

velocity pickup. With the direct prod pickup, a thin prod extends through the end cap of

the pickup and is attached directly to the movable coil inside. To measure vibration with

a direct prod pickup, we should fasten the main body of the unit to a rigid structure to

serve as a point of reference. The tip of the prod is then attached to the vibrating part,

using a threaded tip or a special magnetic tip. We should hold the direct prod unit by

hand movements that naturally result; we should use an analyzer whose filter is tuned to

the vibration frequency of interest. The low frequency vibration dye to the hand

movements are thus eliminated from the measurements.

One of the advantages of the advantages of this type pickup is that it adds only

the weight of the weight of the prod and moving coil to the vibrating part. This makes

the pickup especially useful on small, light weight objects where the mass of a standard

seismic velocity pickup can affect the actual vibration. It is often selected for use on

balancing machines where parts may be balanced at speeds as low as 50 RPM with

excellent results.

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5.1.3) Piezoelectric velocity transducer

These transducers have an output that is proportional to velocity, but have no

internal moving parts. Stresses due to vibrational forces applied to the pickup cause a

crystal or special ceramic material to produce an electric charge. These are designed

specifically for low frequency applications. It can measure down to 60 CPM.

5.2) Accelerometer Transducer

An accelerometer is a self generating devise with a voltage charge output

proportional to vibration acceleration. Vibration acceleration is the measure of the rate

of change of velocity and is normally expressed in terms of “g’s”. Acceleration is a

function displacement and frequency. As a result Accelerometer is extremely sensitive

to vibration occurring at high frequencies.

5.2.1) Piezo-electric with built in amplifier

Fig 5.3

Accelerometer Transducer

The figure shows a simplified diagram of piezo-electric with built in amplifier.

When this pickup is fixed or held against a piece of vibrating machinery, the mechanical

vibrations are passed through the frame to a piezo-electric material. This material has

the ability to generate an electrical charge in response to a mechanical force applied to

it. In this instance mechanical vibration producers the force and the piezo-electric

material responds by generating an electrical charge that is proportional to the amount

of vibration acceleration.

5.3) Non-contact (Proximity) Transducers

Many high speed machines consist of relatively light weight motors mounted in

massive cases and rigid bearings. Because of weight and stiffness of the massive

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machine case and bearings, externally mounted vibration and acceleration pickups often

show little outward evidence of motor or shaft vibration. It is necessary to measure the

actual shaft vibration in order to know when bearing clearances are in danger. It is

displacement transducer measuring the shaft displacement relative to it fixing object.

5.4) Shaft Rider Accessory

A shaft stick is usable for periodic vibration checks and some analysis and in-

place balancing operations. When it is necessary to monitor shaft vibration for extended

periods of time, it is recommended that we use a shaft rider.

The figure shows that a shaft rider is permanently installed in the bearing

housing. It consists of a spring loaded probe that is held firmly against the rotating shaft

so that is held firmly against the rotating shaft so that it accurately follows shaft motion.

Fig 5.4

Shaft rider accessory

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6. VIBRATION ANALYSIS

Vibration Analysis is a two step process involving the ACQUISITION and

INTERPRETATION of machinery vibration data. Its purpose is to determine the

mechanical condition of a machine and specific mechanical or operational defects.

The Data Acquisition procedure is a means of systematic measuring and

recording of the vibration characteristics needed to analyze a problem.

The Data Interpretation involves comparing the recorded data with the details of

the machine, like its speed or speeds, its foundations, the construction details etc. then

the characteristic of vibration typical of various defects are compared with the

characteristics that have been measured. By this, one can pinpoint the trouble and take

corrective measures.

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7. DATA ACQUISITION

Data acquisition is the essential first step in vibration analysis, since the right

data must be acquired under the right conditions to completely interpret a machine’s

condition.

Data acquisition can be done in several ways depending on the available

instruments. Apart from data acquisition, additional data acquisition procedure such as

semi-automatic, automatic and real time analysis are employed where the job can be

quicker and more accurate.

In the semi-automatic method, the operator manually adjusts the filter through

the frequency ranges, while the data is automatically recorded in a recorder. These types

of plots are records of vibration amplitudes in the ‘Y’ axis and the frequencies in the

‘X’ axis. Such a plot is called Machinery Vibration Profile (Signature) and the analysis

of the same is called as Signature Analysis.

Automatic data acquisition is the term used to describe the procedure of

obtaining the data, where the instrument automatically plots the vibration profiles. This

type of instrument incorporates and electronically swept filter as well as provisions for

simultaneous plotting of data with the recorders.

7.1) Selection of Measurement Parameters

The various measurement parameters are displacement, velocity, acceleration:-

7.1.1) Displacement

Displacement can be measured with both velocity and acceleration pickups. This

is accomplished by means of integrator circuits that are normally included in the circuit

of vibration meters and analyzers. Pickups that respond directly to vibration

displacement are readily available, but are usually used in the non-contact pickups.

7.1.2) Velocity

Velocity can also be measured with both velocity and acceleration pickups.

Seismic and piezoelectric velocity pickups obtain vibration directly. The output from an

accelerometer can be integrated to produce the equivalent of a velocity measurement,

down to about 3Hz, or 180 CPM.

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7.1.3) Acceleration

Acceleration should be measured only with an accelerometer. It is theoretically

possible to differentiate signals from a velocity transducer to produce acceleration

readings, but this would be needlessly complicated and expensive.

7.2) Common Types of Measurements

The common types of measurements are:-

1) Overall vibration amplitude measurements.

2) Amplitude Vs Frequency measurements.

3) Amplitude Vs Time measurements.

4) Phase measurements.

They are described below:-

7.2.1) Overall vibration amplitude measurements.

Overall vibration amplitude measurements provide a quick check of general

machinery condition. A vibration meter or analyzer can be used for these

measurements. This measurement is generally manually recorded in tabular form, or the

data automatically stored in memory for computer based automated instruments.

7.2.2) Amplitude Vs Frequency measurements.

Amplitude Vs Frequency measurements provide frequency spectrum which is

used to pinpoint the problem to a specific frequency or range of frequencies. Full

capacity or advanced check analyzers are required to take these measurements. Data can

be recorded manually in tabular form, or by semi automatic or automatic swept filter

analysis with tabular or graphic hard copy recording of the data. FFT type analyzer can

also provide tabular/graphic hard copy of visual display of the data.

It is estimated that over 85% of the mechanical problems occurring on rotating

machinery can be identified by displaying the vibration Amplitude Vs Frequency data.

Importance of tri-axial readings

It is common practice to record the Amplitude Vs Frequency data measured in

the horizontal, vertical and axial pickup directions at each bearing of the machines being

analyzed. Obtaining measurements in all the three directions is extremely important for

distinguishing between various mechanical problems. eg. Unbalance, Misalignment,

bend shaft structural weakness (loose parts) will generally cause vibration at a

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frequency 1X RPM. Unbalance will almost always produce high amplitudes in the

horizontal direction while lower amplitudes in the axial direction. Misalignment of

couplings and bearings or a bend shaft will generally show relatively high amplitude of

vibration in the axial direction. Amplitudes due to structural weakness, loose parts are

shown in Vertical direction.

Fig 7.1

Vibration are normally taken in horizontal, vertical and axial directions on a machine bearing

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Fig 7.2

Amplitude Vs Frequency

7.2.3) Amplitude Vs Time measurements.

Time measurements can be made during machine operation to detect vibrations

that would not be apparent from Amplitude Vs Frequency analysis. Amplitude Vs Time

measurements can be made for very fast transient vibrations or for slowly occurring

vibrations. For fast transient vibrations use an oscilloscope with the horizontal axis

scaled in milliseconds. For slowly varying vibrations use a recorder with the horizontal

axis scaled in seconds. It can be taken with a DC recorder connected to an analyzer with

that built-in-capability.

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Fig 7.3

Short term Amplitude Vs Time data.

Fig 7.4

Long term Amplitude Vs Time data

7.2.4) Phase measurement

Phase measurements are important when analyzing mechanical problems in

machinery. Phase is defined as the position of a vibrating part at a given instance with

reference to a fixed point or another vibrating part. Phase measurements offer a

convenient way to determine how one part is vibrating relative to another part.

To obtain phase measurements, an analyzer with a strobe light or remote

reference pickup is required. The use of strobe light necessities visual observation of the

rotating shaft and the capability to fire the strobe light with vibration signal in order to

obtain phase. The remote phase pickup, which is usually an electromagnetic pickup,

non-contact transducer or photocell must be installed so that to observe mechanical

protrusion (depression) or a reflective mark on the shaft.

The strobe light measurement involves observing the angular position of the

reference mark that appears under the strobe light, while the remote reference pickup

provides phase readout (digital or analog) using a meter on the analyzer.

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9. DATA INTERPRETATION

Once the necessary information have been collected by manual, or semi-

automatic or automatic, the next step is to review and compare the reading with the

characteristics of vibration typical of various types of troubles. A key to this comparison

is the frequency. If a machine part has some defect, the frequency of vibration resulting

from this defect will some multiple of the RPM. The multiple is different for different

defects. Also there are some defects which will produce vibration frequencies that are

not related with the RPM.

7.1) Causes Of Vibration

The major causes of vibration on Rotary machines are:-

1) Unbalance

The horizontal, vertical and axial vibration signatures presented in the figure

given below illustrate typical Amplitude Vs Frequency analysis data resulting from an

unbalance condition. It can be noted that, the predominant vibration occurs at 2200

CPM corresponding to the 2200 RPM fan speed. Since the amplitude of vibration in the

axial direction is relatively low compared to the radial amplitudes, a bent shaft or

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misalignment is not indicated. The appearance of small amplitudes at the harmonic

frequencies is common and does not necessarily indicate any unusual problems such as

mechanical looseness.

Fig 7.1

Vibration amplitude Vs frequency data recorder identifies unbalance

2) Mechanical looseness

The vibration may be the result of loose mounting bolts, excessive bearing

clearance, a crack or break in the structure or bearing pedestal, a rotor which is loose on

the shaft, or some other loose machine component. The vibration characteristic of

mechanical looseness will not occur unless there is some other exciting force such as

unbalance or misalignment can result in large amplitudes of looseness vibration. The

vibration due to looseness can be detected from Amplitude Vs Frequency when taking

the reading in vertical direction.

3) Misalignment

Misalignment is an extremely common problem. Misalignment, even with

flexible couplings, results in two forces, axial and radial vibration. The significant

characteristic of misalignment and bent shafts is that vibration will be noted in both the

radial and axial directions. As a result, a comparative axial vibration is the best

indication of misalignment or a bent shaft.

4) Defective antifriction bearing

Flaws on the raceways, balls or rollers of rolling element bearings cause high-

frequency vibrations and the frequency is not the multiple of the shaft RPM. The

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amplitude of vibration depends on the extent of the bearing fault. The natural frequency

vibrations typically occur as vibration peaks in the 10,000 to 100,000CPM. Defects in

the bearing components can generate vibration peaks at frequencies related to the

bearing geometry. The vibration generated by the bearing is not normally transmitted to

other points of the machine.

Fig 7.2

Frequency analysis of vibration showing a bad bearing

The other reasons for the vibration are:-

1) Defective sleeve bearing.

2) Defective gears.

3) Eccentricity.

4) Oil whirl.

5) Bad drive belts or chain.

6) Electrical defects.

7) Rubbing.

8) Bend shaft.

9) Cavitation.

10) Flow turbulence.

7.2) Recommended Method of Vibration Classification (As Per ISO 2372)

The machines are classified into five groups as per ISO 2372.

They are:

Class I

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Individual parts of engines and machines integrally connected with the complete

machine in its normal operating condition (Production electrical motors of up to 15KW

are typical examples of machines in this category).

Class II

Medium sized machines (typically electrical motors of 15-75KW output)

without special foundations rigidly mounted engines or machines (up to 300KW) on

special foundations.

Class III

Large prime movers and other large machines with rotating mass mounted on

rigid and heavy foundations which are relatively stiff in the direction of vibration

measurement.

Class IV

Large prime movers and other large machines with rotating masses mounted on

foundations which are relatively soft in the direction of vibration measurement

(eg.Diesel-generator sets, especially those with light weight substructures).

Class V

Machines and mechanical drive systems with unbalancable inertia effects (due to

reciprocating parts) mounted on foundations which are relatively stiff in the direction of

vibration measurement.

Class VI

Machines and mechanical drive systems with unbalanceable inertia effects (due

to reciprocating parts) mounted on foundations which are relatively stiff in the direction

of vibration measurement. Machines with rotating slack-coupled masses such as beater

shafts in grinding mills, machines like centrifugal machines with varying unbalances

capable of operating as self contained units without connecting components, vibrating

screens, dynamic fatigue-testing machines and vibration exciters used in process plants.

In practice, instead of good/Allowable/Just permissible, the following colloquial

is used to stipulate the health condition of machines.

Good

Satisfactory

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Just satisfactory

Unsatisfactory

Dangerous

VIBRATION SEVERITY RANGE (In accordance with ISO 2372)

Velocity –mm/secClass A-Good B-Usable C-Still acceptable D-Un acceptable

0-15KW Class I 0.71 1.8 4.5 45

15-75KW Class II 1.12 2.8 7.1 45

>75KW Class III 1.8 4.5 11.2 45

Turbocharger

Class IV 2.8 7.1 18 45

Table 7.1Vibration Severity Range

DIESEL GENERATING SET FOR DIESEL GENERATORS

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(WARTSILA,ANMAR,FUJI,DAIHATSHU,MERLESS,BLACKSTONE,SKL,SKODA,CATTERPILLER ETC)

Limit parameter is peak-velocity in mm/sec.Sl. No LOCATION S.LIMIT J.S.LIMIT

1.MACHINE BASE FIXING

LOCATION10 20

2.CRANK CASE CENTRE

LINE10 20

3.CRANK CENTRE LINE

10 20

4.CYLINDER HEADS

10 20

5.TURBOCHARGER

15 30

6.PILLOW BLOCK BEARING

15 25

7.ALTERNATOR BEARING

05 15

8.GENERATOR BEARING

05 15

Table 7.2Vibration Range for Diesel G enerating S et F or D iesel Generators

VIBRATION TROUBLE SHOOTING CHART

Nature of fault

Frequency of

domain vibration

(RPM)

Direction Remarks

Rotating members

out of balance1X RPM Radial

A common cause of excess

vibration in machinery

Misalignment &

Bent shaft

Usually 1X RPM.

Often 2X RPM.

Radial &

AxialA common fault

Damaged Rolling

Element Bearings

(Ball, Roller etc)

Impact rates for the

individual bearing

components.

Radial &

Axial

Uneven vibration level, often

with shocks, impact rates

Journal bearing

loose in housing

Sub harmonics of

shaft rpm,exactly ½

or 1/3 rpm

Radial

Looseness may only develop at

operating speed and high

temperature(eg.turbomachines)

Oil film whirl or Slightly less than Radial Applicable to high speed

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whip in journal

bearinghalf speed machines.

Hysteresis whirl Shaft critical speed Radial

Vibrations exited when

passing through critical speed

are maintained at higher shaft

speeds.

Damaged or worn

gear

Tooth meshing

frequency (shaft

rpm X number of

teeth) and

harmonics

Radial &

Harmonics

Side bands around tooth

meshing frequencies detectable

with very narrow band analysis

and spectrum

Mechanical

looseness2X RPM

Radial &

Axial

Also sub harmonics for loose

journal bearings.

Faulty belt drive 1,2,3,4 X RPM Radial

The precise problem can

usually be identified with the

help of a strobe light.

Unbalanced

reciprocating 1X RPM

Radial &

AxialEasily felt by hand touch

Increased

turbulence or

recirculation

Blade passing

frequencies and

harmonics

Radial &

Axial

Increased level indicate

increasing turbulences

Cavitations 1X RPM Radial No phase difference with

strobe light

Electrical induced

vibrations

1X RPM or 1 or 2

times synchronous

frequency

Radial &

Axial

Disappear immediately when

turn-off the power

Table 7.2Vibration Trouble Shooting Chart

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8 CONCLUSION

Condition monitoring by vibration analysis gives information about the

changing condition of the equipment thus enabling the avoidance of total breakdown

and can have reduced time. Prediction of residual life enables the equipment to be

stopped before they reach critical condition and thus safe operation is ensured.

Improved production quality is achieved through condition monitoring. By condition

monitoring, detection of incipient faults and determination of plant condition enable

forecasting of maintenance demands.

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9 REFERENCE

1. S.S.Rattan, Theory of Machines, Tata McGraw-Hill, New Delhi, 2004.

2. Vibrotech, Training Manual, Chennai.

3. IRD Mechanalysis, Instruction Manual.

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