Vibration Condition Monitoring

Overview of Methods

Maintenance Methods

Method Relative Cost

• Fix when fail 100%

• Preventive Maintenance PM 60%

• Condition Based CM 50%

• CM + Failure analysis & redesign 30%

CM Methods

Method On load Off load • Visual, Hearing, Touching And Smell X X• Crack Detection X• Leak Detection X• Corrosion X X• Performance Evaluation X• Wear Particle Analysis X• Noise X• Acoustic Emission X• Electric Motor Testing X X• Lubrication X X• Thermal X• Vibration Condition Monitoring (VCM) X

Which machine?

• Financial Analysis

• Small power tools not cost effective

• Major plant permanent monitoring?

• Other machines regular screening?

Instrumentation

• Transducer– Eddy Current (displacement)– Piezoelectric Accelerometer– Special: SEE, SPM

• Conditioning Amplifier– to suit transducer– built in to instrument

• Readout/Analyser– Readout, band limited, FFT?

Accelerometer Mounting

Mounting Point

Measurement Location

1H

1V

1A

2H

2V

2A

3H

3V

3A4H

4V

4A

•Measure each vertical position for Trend Analysis

•Measure all positions for full analysis, including Tacho / Phase

•Convention: number starting at driver

Tacho & Phase

Machine Operation

• Consistent operating conditions

• Loaded, speed

• How to detect loading?

OH&S

Operator Safety

• Location of transducers

• Environment while measuring

• Safety moving between machines

• Emergency procedures

• Personal safety equipment

Monitoring

• Vertical vibration at each bearing

• RMS vibration only

• Use trend analysis

• Full measurement at each bearing on fault

Trend Analysis

2 x base level

6 x base level

Time

Vibration Level V RMS

Alarm level

Shutdown level

Repair

Full Measurement, Analysis & Diagnosis

Data, Route, Database

• Record all data for all points

• Regular logical route through plant

• Data storage for maintenance intelligence

• Data feeds back to monitoring/redesign

Vibration Level Assessment

4.5

0.18

0.71

1.8

45

18

7.1

Not permissibleNot permissible

Not permissibleNot permissible

Just tolerable

Just tolerableJust tolerable

Just tolerable

Allowable

Allowable

Allowable

Allowable

Good

GoodGood

Good

Small machines to 15 kWMedium machines

15-75 kW

Large machines withheavy foundations

operating below natural frequency

Large machines withheavy foundations

operating above natural frequency

mm/sRMS velocity

Action at Alarm Level

• CM measurement exceeds criterion

• Fault diagnosis

• Maintenance Plan

• Spares Requisition

19 Apr 2023 16

Rolling Bearings - Geometry

Pitch Diameter

Ball Diameter

Number of Balls

Contact Angle

19 Apr 2023 17

Bearing Defect Frequencies

BPFOnf

BD

PD

BPFInf

BD

PD

BDFPD

BDf

BD

PD

CDFf BD

PD

21

21

1

21

2

( cos )

( cos )

( ( cos ) )

( cos )

19 Apr 2023 18

Characteristic Spectrum

amplitude

frequency

19 Apr 2023 19

Plain Bearings

Oil film

19 Apr 2023 20

Characteristic Spectrum

amplitude

frequency

19 Apr 2023 21

Gear Faults

TMF rpm teeth / 60

19 Apr 2023 22

Characteristic Spectrum - Looseness

amplitude

frequency

19 Apr 2023 23

Characteristic Spectrum - Flow

amplitude

frequency

19 Apr 2023 24

Resonance

• Input vibration that is at or near the natural

frequency causes excessive vibration.

• About 20% of machines show resonance

• May occur with other faults

• Can cause excessive energy use

• Can cause serious damage

25

Diagnostic Case Studies

26

Case Study 1

27

Instrumentation

28

Rotor Details

29

Phase / Amplitude Data

Vertical

Horizontal

2.0 2.0

3.0 2.8

30

Base Spectrum

amplitude

frequency

31

Current Spectrum

amplitude

frequency

25 Hz

32

Case Study 1

• Data analysis confirms likely static

unbalance

• Consider the type of rotor to further

examine the fault

• Static unbalance is rare - fault means

similar loss of mass at each end (eg complete blade from a rotary planer)

33

Case Study 2

34

Machine Layout

Motor

GearboxAxial Compressor

0.7 1.0 2.0 2.1

2.3 2.1 1.5 1.1

35

Base Spectrum (3V)

amplitude

frequency 10kHz

37.5 62.5

162.5 3012.5

36

Current Spectrum (3v)

amplitude

frequency 10kHz

37.5 62.5

162.5

3012.5

37

Current Spectrum – Better Resolution

amplitude

frequency 4kHz

3017.5

47.5

147.5

152.5

38

Probable Fault

• New spectrum bandwidth 5 Hz per line

• Large vibration increase at TMF

• Gear problem - perhaps excessive wear on one

or both gears, failure of tooth hard facing etc.

• Check 3H, 3A, 4V, 4H, 4A, 5V, 5H, 5A, 6V, 6H,

6A to confirm.