Introduction To Vibration From Caption Data Limited

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Caption Data LimitedIntroduction to Vibration Analysis

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Schedule

Introduction to Vibration measurements Transducers

Acceleration Velocity Displacement Force

Sampling Aliasing Leakage Filtering


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Windows Averaging FFT Analysis

Spectrum Auto Spectrum PSD Cross Spectrum Transfer Function

Coherence Real/Imaginary Nyquist

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Rotating Machinery Analysis Order tracking Synchronous Signal Averaging

Basic Modal Analysis Data Acquisition Windowing Data quality Modeling

Resonant Frequency Non Destructive Testing (NDT)

Machine Health Monitoring (TOMAS)

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Caption Data Limited Introduction to Vibration Analysis

Accelerometers

The Model 353B03 is a quartz shear ICP® accelerometer designed for general purpose measurements. It has a sensitivity of 10 mV/g. The quartz shear-mode sensing elements reduce sensitivity to adverse environmental inputs, such as thermal transients, base strain, and transverse motion. The Model 353B03 features a side-exit, 10-32 coaxial connector. Its frequency range of 1 to 7 000 Hz (±5 %) makes this sensor an ideal candidate for general purpose vibration measurements such as vehicle studies, product qualification studies, structural response tests and vibration control

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http://www.pcb.com/products/svs/images/353b03P.jpg

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Accelerometers

Miniature accelerometers are designed specifically to meet minimum size and weight requirements. Model 352C22 offers a 1 to 8 000 Hz (±5%) frequency range and a sensitivity of 10 mV/g. With a mass of only 0.017 oz (0,5 gm), this sensor excels in testing of lightweight, flexible structures, such as printed circuit boards, disk drives, and those requiring a low-profile unit.

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http://www.pcb.com/products/svs/images2/svs352c22.jpg

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Accelerometers

The Model 356B11 is a miniature, four-gram, hermetically sealed titanium accelerometer. The hermetic titanium case provides a rugged, reliable sensor for minimal mass loading in triaxial vibration measurements. The 10 mV/g output from ceramic shear mode sensing elements provides a wide measurement range from 2 to 10 000 Hz (±5%) in the "Z" axis and 2 to 7 000 Hz (±5%) in the "X" and "Y" axes. The 5 ft integral shielded cable terminates in a four-pin connector.

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Velocity Transducers

Model Numbe

r

Output Sensitiv

ity

Frequency Range (Hz)

Temperature Range

Excitation Source

Mounting Base

Mating Connect

orIntegral Cable Product

Weight

4-102-0001 110 mV/ips 8 - 700+32 to +150°F

0 to +65°C

SELF- GENERATING

2-hole, #8 bolt

1.50" BC

11760 18 inches 14 oz

4-103-0001 110 mV/ips 8 - 700

+150 to +250°F +65 to

+121°C

SELF- GENERATING

2-hole, #8 bolt

1.50" BC

11760 18 inches 14 oz

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Displacement Transducers

Proximity ProbesThese transducers allow direct observation of shaft or target displacement for a variety of vibration, position, speed, and timing (i.e., phase) measurements. Various tip diameters and thread sizes/configurations are offered to allow measurement ranges as small as 200 micro inches to as large as 1 inch (typically used for differential expansion measurements on large steam turbines), and everything in between, including the popular 80 mil range used for the majority of machinery measurements.

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http://www.bentleynevada.com/prod/products/transducers/proxprobes.htm

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What are the Componentsof Vibration?

Amplitude Maximum value of vibration

Frequency Number of events or cycles per unit time

Phase Time relationship between vibrations of the

same frequency

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Vibration SourcesNatural Frequencies / Resonance

Machine Design Induced Machine Structure Mass and Stiffness Damping

Resonance When a forcing frequency excites a

natural frequency In rotating machinery, “Critical

Speed” www.captiondata.com

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Vibration SourcesForcing Frequencies

Machine Design

Universal Joints Asymmetrical

Shafts, Cams Gear Mesh Couplings Bearings Pumps & Fans Reciprocating

Machines Motors /

Generators

Machine Faults

Mass Unbalance Misalignment Bent Shaft Mechanical

Looseness Casing /

Foundation Distortion

Bearing Faults Motor Faults

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How is Vibration Measured?

Primitive, Qualitative Methods / Senses Can you actually SEE movement? Can you HEAR something different? What does it FEEL like? Does it SMELL funny? TASTE, not really recommended!

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How is Vibration Measured?

Better, Quantifiable Methods / Amplitude Movement / Displacement Speed / Velocity Acceleration

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Sensors

Physical Movement / Displacement Proximity Probes

Velocity / Speed Velocity Transducers

Acceleration Accelerometers

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Vibration Units

‘English’ Units Pounds (lb) / Inch (in.) / Second (sec)

Displacement in mils, 1 mil = 1/1000th Inch

Peak-to-peak measure Velocity in Inches per second (in/sec or

ips) Peak or RMS measure

Acceleration in gs, 1 g = 386.1 in/sec 2

Peak or RMS measurewww.captiondata.com

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Frequency / Rotational Units

Vibration Frequencies are expressed as:

Cycles per Minute (CPM) or Cycles per Second (HZ)

Machine or Shaft Speed: Revolutions per Minute (RPM)

Phase is expressed as: Degrees, 360 degrees per revolution. May also be expressed as Leading or

Lagging www.captiondata.com

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Relationship of Amplitude, Velocity & Frequency

Any Quantity can be Calculated

If the remaining two Quantities are Known

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Oh man… MATH??

Mathematical Relationships / Displacement to Velocity

V = (2 π f) D

V = Velocity in Inches per second (ips)

π (pi) = 3.14159 (or, the button on your calculator)

f = Frequency in Hz

D = Displacement in mils peak

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Worse… Algebra!

Mathematical Relationships / Velocity to Displacement

If… V = (2 π f) D

Then… D = V / (2 π f)

Velocity to Acceleration

A = (2 π f) V / 386.1

Acceleration to Velocity

V = A * 386.1 / (2 π f)

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And Finally…

Mathematical Relationships / Acceleration to Displacement

A = D (2 π f)2 / 386.1

D= A * 386.1 / (2 π f)2

(we’re done now… you can all relax!)

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Machine Vibration Measures

MEASURE USEFUL FREQ. SPAN

PHYSICAL PARAMETER APPLICATION

Relative Displacement

(proximity probes)0-1000 Hz Stress / Motion Relative Motion in

bearings / casings

Absolute Displacement

(seismic)0-10 Hz Stress / Motion Machine Condition

Velocity(seismic)

10 – 1000 Hz Energy / Fatigue

General Machine Condition,

medium-high frequency vibrations

Acceleration(seismic)

> 1000 Hz Force

General Machine Condition,

medium-high frequency vibrationswww.captiondata.com

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Machine Design Vibration Sources

Eccentric Shafts / Cams Reciprocating Components Pumps & Fans Gears Bearings Couplings Universal Joints Motors & Generators

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Machine Design Vibration Frequencies

Eccentric Shafts / Cams Shaft Speed (1 X) and Multiples

(Orders)

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Reciprocating Machines ½ and Full Multiples of Shaft Speed

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Pumps & Fans Vane Pass & Blade Pass Frequencies

Shaft Speed X Number of Vanes Shaft Speed X Number of Blades Flow Noise / Cavitations

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Gearboxes Gear Mesh Frequencies

Shaft Speed X Number of Teeth

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Machine Design Vibration Sources

Bearing Frequencies, Rolling Element Bearings BPFI – Ball Pass Freq. Inner Race BPFO -- Ball Pass Freq. Outer Race BSF – Ball Spin Frequency FTF -- Fundamental Train Frequency

Max Range Approximation: Shaft Speed X Number of Elements

X 0.6 www.captiondata.com

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Machine DesignVibration Sources

Bearings, Fluid Film / Sleeve Oil Whirl

0.40 – 0.48 X of Shaft Speed Oil Whip

Machinery Operating at > 2 X Critical Speed Oil Whirl Locks onto 2 X Critical

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Couplings Shaft Speed X Number of Jaws

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Universal Joints 2 X Shaft Speed

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Motors & Generators Synchronous Motor Speed (SMS)

2 X Line Frequency / Number of Poles Slip Frequency

SMS – Actual Speed

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Minimum Acquisition Frequencies

COMPONENT / MACHINE SPAN

Shaft Vibration 10 X RPM

Gearbox 3 X Gear Mesh

Rolling Element Bearings 10 X Ball Pass Freq. Inner

Pumps 3 x Vane Pass

Motors / Generators 3 X Line Freq X 2

Fans 3 X Blade Pass

Sleeve Bearings 10 X RPM

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Applicable Sensors & Limits

Credit: John S. Mitchell, machinery Analysis and Monitoring 2 nd edition

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Sensor Mounting Conventions

Position Referenced from DRIVEN end of Shaft

Horizontal 90˚ CLOCKWISE from Vertical

Direction of Rotation Not Considered

Axial Transducers In the Load Zone

Credit: Ronald L. Eshleman, Basic Machinery Vibration

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Useable Frequency Spans ForAccelerometer Mounting Methods

METHOD FREQUENCY LIMIT

Hand Held (stinger) 500 Hz

Magnetic Mount 2,000 Hz

Adhesives2,500 – 4,000 Hz

(dependent on compound)

Bees Wax5,000 Hz

(watch surface temp!)

Stud Mount 6,000 – 10,000 Hz

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Digital Sampling Amplitude Resolution Effects of under sampling

Aliasing

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Over Sampling

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Minimum Sampling

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Leakage

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Weighting Windows No Window Hanning Blackman Harris Flat Top Exponential Decay Box Car/Rectangular

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Weighting Windows No Window

Transient events Fixed frequency

Cell centered

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Weighting Windows No Window

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Weighting Windows Hanning

Continuous data Good frequency accuracy Most common window May not be suitable for transient data Good for separation of closely spaced

frequencies

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Weighting Windows Hanning

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Weighting Windows Blackman Harris

Similar characteristics to Hanning Continuous data Good frequency accuracy Most common window May not be suitable for transient data Good for separation of closely spaced

frequencies

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Weighting Windows Blackman Harris

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Weighting Windows Flat Top

Best amplitude Accuracy Frequency accuracy is sacrificed Continuous data Common window for order tracking

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Weighting Windows Flat Top

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Weighting Windows Exponential Decay

Used for Bump (impact) testing in Modal Analysis

Used for response channels only Decay is adjustable to eliminate leakage Adds artificial damping

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Weighting Windows Exponential Decay

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Weighting Windows Box Car/Rectangular

Used in Bump (impact) testing in Modal analysis

Used only on the reference channel Adjustable leading and trailing edge Zeros all data outside the window

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Weighting Windows Box Car/Rectangular

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Averaging Linear/Summation Exponential

Variable decay Peak Hold Time Synchronous

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Why do we average Improve statistical confidence Extract signals from noise Smooth random vibration

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Linear/Summation Reduces noise Improves statistical accuracy of repetitive or

stationary signals.

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Exponential Weights the average count New data carries the most weight Decays the old data Smoothes noise Slows rapidly changing signals

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Peak Hold Updates the spectral line value with a

new maximum Holds the maximum until updated

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Time Synchronous Averages in time domain based on a

Synchronous event Reduces effects of other operating equipment

in close proximity Very good for extracting signals from noise

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ZonicBook/618E Hardware Features

8 Vibration Inputs Field expandable to 56 vibration inputs 4 tachometer inputs 8 digital I/O 10/100BaseT Ethernet connection Open ICP and over-range indicators on

front panel Signal conditioned output for each input

channel

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Software configurable ICP®, DC, or AC coupling

9 input voltage ranges 16 bit, 75 dB dynamic range New rugged package with built-in

handle TEDS support

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Expandable up to 56 analog inputs via WBK18 options

Other hardware options DBK34A battery/DC UPS

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eZ-AnalystReal Time Vibration Analysis

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eZ-Analyst

Real-Time Vibration Measurement and Analysis

Two Applications Impact

measurement and structure analysis

Continuous data recording and transient analysis

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eZ-Analyst – Impact Applications

Impact measurements 5 averaging methods Multiple reference

channels Interactive displays Cross-channel

analysis, FRF, transfer functions

Export data to Excel or modal analysis software

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eZ-Analyst – Impact Applications

Measurements for Modal Analysis Effect of mass, stiffness, and damping Operating deflection shapes

Automatically save after averaging Automatically increase

modal locations

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eZ-Analyst – Continuous Data Recording Applications

Record “gap-free” data to PC disk

Stripchart data analysis and reduction

Harmonic, SideBand, and FreeForm Cursors

Export data to Excel or eZ-Rotate

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Rotating Machinery Analysis Order Normalization Order tracking

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eZ-NDTNon Destructive Testing for

Production

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Assumptions If test articles are produced in the same

manner, and have like properties, then they will have the same natural or resonant frequencies.

If the test articles have a change in mass, stiffness or damping, then the resonant or natural frequencies will change.

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What causes the changes? Changes in mass may be caused by void or

missing operation in the test article Changes in stiffness may be caused by a

material or process variation. Changes in damping can be caused by a

material or process variation or a crack in the test article.

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The measurement process The test data is converted into the frequency

domain by the analysis software. Key resonant peaks are identified and their frequencies are noted

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The measurement process Known good and defective test articles are

tested and compared for shifts in fundamental resonant frequencies.

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The measurement process Each resonant frequency of a known good part is examined

and bands are placed around the peak. If the frequency of a tested part is outside of these bands, then the test article fails.

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Caption Data Limited eZ-TOMAS – Applications and Machinery

eZ-TOMAS On line condition monitoring and

analysis

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Caption Data Limited eZ-TOMAS – Applications and Machinery

Petrochemical, Power Utility, Paper and Steel Mill, Pharmaceutical, etc…

Turbines, Compressors, Gearboxes, Pumps, Motors, Generators, etc…

Typically, 1 to 3 machines per system.

10 to 100,000 RPM range

Temporary or Continuous Monitoring

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Vibration Analysis & Monitoring eZ-TOMAS – Gauge Window

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Vibration Analysis & MonitoringeZ-TOMAS – Gauge Window

Current Values & Status

Vertical Amplitude

Circular Phase Limit Checking /

Log Events FIFO Storage High Water

Marks Relay Outputs

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Vibration Analysis & MonitoringeZ-TOMAS - Configuration Setup

Acquisition Fmax: up to 20 KHz Lines: up to 25,600 Hanning / Flat Top FFT Scale Pref: RMS, PK, P-

P Input Channels

D: DC Cplg, +/- 25V A: ICP, AC Cplg, +/- 5V Gap & Runout Ref. Orbit / Tach Pairs

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Vibration Analysis & MonitoringeZ-TOMAS - Configuration Setup

FIFO Storage Up to

200,000 Records/Channel/File

RPM Range Change in

RPM, Time, Vibration

Alarm Condition

User Snapshot

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Vibration Analysis & Monitoring eZ-TOMAS - Configuration Setup

Spectral Bands OAll, Vdc, 1xA &

1xP 6 User Defined Overall, Peak,

Phase Fault Toolkit

Spectral Limits 2 High / 2 Low Delay Text Message www.captiondata.com

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Vibration Analysis & Monitoring Rotating Machinery Analysis

Orbit, Time Waveform w/ or w/o

Filtered N Revolutions

Bode w/ or w/o

Runout OAll, 1x, nX

Waterfall Order Tracks RPM Annotation

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Polar Runout, Limits Annotation

Spectrum Harmonic,

Sideband Peak Cursors

Shaft Center Line Trend

OAll, 1x, nX Cursor to History

Location www.captiondata.com

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Automatic Tach Analog

Inputs Dynamically

adjust trigger levels

Trigger Direction

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Vibration Analysis & Monitoring Learning Limits

Statistical Report Steady State

Condition Min, Avg, Max,

Dev Calculate

Limits based on Normal Operation

Before / After Shutdown comparisons

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Vibration Analysis & Monitoring Configuration Setup – Storage

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Vibration Analysis & Monitoring Edit - Spectral Bands

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Vibration Analysis & Monitoring Edit – Spectral Limits

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Vibration Analysis & Monitoring Gauge Window – Monitor Vibration Levels

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Vibration Analysis & MonitoringGauge Window – Monitor Vibration Levels

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Vibration Analysis & Monitoring Plot Windows – Data Source

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Vibration Analysis & Monitoring Plot Windows – Time Waveform

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Vibration Analysis & Monitoring Plot Windows – Spectrum

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Vibration Analysis & Monitoring Plot Windows – Orbit

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Vibration Analysis & Monitoring Plot Windows – Waterfall

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Vibration Analysis & Monitoring Plot Windows – Bode

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Vibration Analysis & Monitoring Plot Windows – Polar

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Introduction To Vibration From Caption Data Limited

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