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Balancing and Diagnostic Systems

Welcome to the seminar: Basics of vibration technology – Measurement & Analysis

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Balancing and Diagnostic Systems

Lecturer :

Roland Kewitsch

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Balancing and Diagnostic Systems

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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Balancing and Diagnostic Systems

Machine damage in a power station Total destruction of a generator

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Balancing and Diagnostic Systems

Rolling-element bearing damage

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Balancing and Diagnostic Systems

Diagnosis methods Vibration measurement and analysis Displacement, expansion and process value measurement Temperature, speed and phase measurement Lubricant analysis (e.g. spectroscope, ferroscope, radionuclide) Optical examination (e.g. endoscope, microscope) Non-destructive testing (e.g. ultra-sound, X-rays) 6

Balancing and Diagnostic Systems

Vibration Measurement in the past (& still today)

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Balancing and Diagnostic Systems

Diagnosis methods Diagnosis by vibration measurement

Overall methods

Machine assessment using Overall measurements

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Balancing and Diagnostic Systems

Diagnosis methods Diagnosis by vibration measurement Analytical methods Overall methods

Machine assessment using Overall measurements

Fault identification using frequency analysis measurements

Dynamic behaviour analysis

With self-excitation methods

With external excitation methods

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Balancing and Diagnostic Systems

Measuring machine condition in 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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Balancing and Diagnostic Systems

Modern machine diagnosis

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

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Balancing and Diagnostic Systems

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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Balancing and Diagnostic Systems

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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Balancing and Diagnostic Systems

Amplitude data for vibration measurement

s

so = speak = sm Saverage

srms = seff t

speak-peak = spp

su = speak = sm

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Balancing and Diagnostic Systems

Composite vibrations X

f t

X

2f

+

t

X

f + 2f

=

t

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Balancing and Diagnostic Systems

Vibration in Time Domain vs. Frequency Domain x

x

t x

1

2

3

4

5

6

7

8

9 10 11

1

2

3

4

5

6

7

8

9

f

x t

x

10 11

f

x t

f 1

2

3

4

5

6

7

8

9

10

1116

Balancing and Diagnostic Systems

Influence of integration - Practice Vibration velocity spectrum

Vibration acceleration spectrum

Vibration displacement spectrum

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Balancing and Diagnostic Systems

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 18

Balancing and Diagnostic Systems

Vibration types in machines

Rotor Relative shaft vibrations

Absolute bearing vibrations

Bearing casing

Foundation 19

Balancing and Diagnostic Systems

Measuring Absolute Bearing Vibration General rules: Measurement points should be exactly defined and clearly marked Measuring points should be flat, clean and free of grease Loose paint and rusted surfaces should be cleaned or avoided Sensor must sit securely and not wobble Sensor and cable should not move during measurement 20

Balancing and Diagnostic Systems

Acceleration sensors

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Balancing and Diagnostic Systems

Vibration velocity sensors

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Balancing and Diagnostic Systems

Measuring Relative Shaft Vibration

A

45°

45°

B

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Balancing and Diagnostic Systems

Eddy-current sensors Discrete type: Sensor with integral cable Calibrated extension cable Separate converter (oscillator)

Note: Cable lengths may not be altered! 24

Balancing and Diagnostic Systems

Eddy-current sensors Integrated type: Sensor with built-in oscillator and extension cable

Advice: Cable can be extended up to 1,000m in length Use in temperatures above 110°C is not possible

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Balancing and Diagnostic Systems

Machine assessment using the Trend

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Balancing and Diagnostic Systems

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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Balancing and Diagnostic Systems

Assessment of an electric motor acc. to ISO 10816

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Balancing and Diagnostic Systems

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 29

Balancing and Diagnostic Systems

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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Balancing and Diagnostic Systems

Vibrations created in damaged bearings

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Balancing and Diagnostic Systems

Impulses from a damaged bearing

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Balancing and Diagnostic Systems

Damage frequencies in a rolling-element bearing ß ß d n N

D

Contact angle Rolling-element diameter No. of rolling elements Speed of shaft

Outer race damage

fo =

n•N 2 60

( 1 - d cos ß ) D

Inner race damage

fi =

n•N 2 60

(1+

Rolling-element damage

fr =

D•N d 60

(1- d D

Cage damage

fc =

N 2 60

( 1 - d cos ß ) D

d cos ß ) D

[ ]² cos² ß ) 33

Balancing and Diagnostic Systems

Damage frequencies in a rolling-element bearing

Ball-bearing SKF 6211 Dimensions

Damage frequencies

D = 77.5 mm

Fo = N/60 4.1 = 205 Hz

D = 14.3 mm

Fi = N/60 5.9 = 295 Hz

n = 10

Fr = N/60 5.2 = 260 Hz

ß = 0°

Fc = N/60 0.4 = 20 Hz

N = 3,000 rpm

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Balancing and Diagnostic Systems

BCU signal process X

t

f

X

t

f BCU

X

t t 35

Balancing and Diagnostic Systems

Trend observation

Destruction

Example: Damage progress in a rolling-element bearing

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