basics of vibration analysis

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Balancing andDiagnostic Systems

Welcome to the seminar:Welcome to the seminar:Welcome to the seminar:

Basics of vibration technology– Measurement & Analysis

Basics of vibration technology– Measurement & Analysis

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Lecturer : RolandLecturer : Roland KewitschKewitsch

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Vibration analysis increases knowledge

Provides necessary information for:

Evaluation of machine condition

Recognition of on-going machine damage symptoms

Identification of the cause and the damaged components

Prognosis of remaining service life

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Machine damage in a power station

Total destruction of agenerator

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Rolling-element bearing damage

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Diagnosis methods

Vibration measurement and analysis

Displacement, expansion and process value measurement

Lubricant analysis(e.g. spectroscope, ferroscope, radionuclide)

Temperature, speed and phase measurement

Optical examination(e.g. endoscope, microscope)

Non-destructive testing(e.g. ultra-sound, X-rays)

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Vibration Measurement in the past (& still today)

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Diagnosis methods

Diagnosisby

vibration measurement

Overallmethods

Machineassessment using

Overall measurements

=

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Diagnosis methods

Overallmethods

Machineassessment using

Overall measurements

Fault identificationusing frequency

analysis measurements

Dynamic behaviour

analysis

With self-excitationmethods

With externalexcitation methods

Diagnosisby

vibration measurement

Analytical methods

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Measuring machine conditionin the past

The first portable vibration measuring instrument from the Schenck company

Demonstrated at an exhibition in Leipzig / Germany in 1925

Schenck was founded in 1881

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Modern machine diagnosis

Measuring machine condition with a modern measuring Instrument(VT-60)

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Measurement types for mechanical vibrations

Vibration displacement „s“ in µm or mil= deviation of measured point

from rest position

Vibration velocity „v“ in mm/s or ips= velocity with which measured

point moves about rest position

Vibration acceleration „a“ in m/s2 or g= acceleration with which measured

point moves about rest position

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Characteristics of composite vibrations

• Narrow-band examination- Extraction into harmonic components (e.g. using a frequency analyser or tracking filters)

• Broad-band examination- Through a summing formation in a defined frequency

range (e.g. 10 …. 1,000 Hz)

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Amplitude data for vibration measurement

so = speak = sm

su = speak = sm

speak-peak = spp

srms = seffSaverage

t

s

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Composite vibrationsX

t

f

t

X

+2f

t=

f + 2fX

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Vibration in Time Domain vs. Frequency Domain x

t

1 2 3 4 5 6 7 8 9 10 11

x

fx

tx

f1 2 3 4 5 6 7 8 9 10 11

x

f1 2 3 4 5 6 7 8 9 10 11

x

t

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Influence of integration - Practice

Vibration velocity spectrum

Vibration acceleration spectrum

Vibration displacement spectrum

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Selecting the measurement type

Vibration displacement: Machines with speeds under approx. 600 rpm (10 Hz)

Structural vibrations or

Relative motions (shaft vibrations) in journal bearing machines of any speed

Vibration velocity:

Vibrations in machines with speeds above 600 rpm(10 … 1,000 Hz)

Vibration acceleration:Vibrations with frequencies of interest above 2,000 Hz

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Vibration types in machines

Bearing casing

Absolutebearing vibrations

Relativeshaft vibrations

Rotor

Foundation

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Measuring Absolute Bearing Vibration

Sensor must sit securely and not wobble

Loose paint and rusted surfaces should be cleaned or avoided

Measuring points should be flat, clean and free of grease

Measurement points should be exactly defined and clearly marked

General rules:

Sensor and cable should not move during measurement

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Acceleration sensors

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Vibration velocity sensors

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Measuring Relative Shaft Vibration

45° 45°A B

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Eddy-current sensors

Separate converter (oscillator)

Calibrated extension cable

Sensor with integral cable

Discrete type:

Note:

Cable lengths may not be altered!

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Eddy-current sensors

Integrated type:

Use in temperatures above 110°C is not possible

Cable can be extended up to 1,000m in length

Sensor with built-in oscillator and extension cable

Advice:

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Machine assessment using the Trend

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Machine assessment acc. to Standards and Guidelines

A number of important Standards and Guidelines for rotating masses have been replaced during the last years by:

DIN ISO 10816, parts 1 to 6 (absolute bearing vibrations) and

DIN ISO 7919, parts 1 to 5 (relative shaft vibrations)

Reciprocating machines, including compressors, can be assessed according to

DIN ISO 10816-6 (Reciprocating machines with > 100 kW)

DIN ISO 8528-9 (Reciprocating internal combustion machines)

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Assessment of an electric motor acc. to ISO 10816

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Assessment zones

Assessment zones according to DIN ISO 10816:

Zone A:Vibration in newly-installed machines

Zone B:Machines may be operated for an unlimited time without restriction

Zone C:Machines may be operated for a limited time

Zone D:Vibrations are at a dangerous level and may cause damage to the machines

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DIN ISO 10816 Part 3, Group 2

Medium-sized machines with nominal power from 15 kW to 300 kW;Electrical machines with shaft height 160 mm ≤ H >315 mm

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Vibrations created in damaged bearings

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Impulses from a damaged bearing

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Damage frequencies in a rolling-element bearing

D

ßß Contact angled Rolling-element diametern No. of rolling elementsN Speed of shaft

Outer race damage fo = ( 1 - cos ß )dD

n • N2 60

Inner race damage fi = ( 1 + cos ß )dD

n • N2 60

[ ]²Rolling-element damage fr = ( 1 - cos² ß )D • Nd 60

dD

Cage damage fc = ( 1 - cos ß )dD

N2 60

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Damage frequencies in a rolling-element bearing

Ball-bearing SKF 6211

DimensionsD = 77.5 mmD = 14.3 mmn = 10ß = 0°

N = 3,000 rpm

Damage frequenciesFo = N/60 4.1 = 205 HzFi = N/60 5.9 = 295 HzFr = N/60 5.2 = 260 HzFc = N/60 0.4 = 20 Hz

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BCU signal process

f

t

X

ft

X

t

BCU

t

X

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Trend observation Example:

Damage progress in a rolling-element bearing

Destruction

basics of vibration analysis

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