What is FFT and Spectrum Analysis? - Windrock Inc.Windrock and RecipTrap Users. Frequency Domain Spectrum analysis is the analysis of frequency domain data. All frequency domain data

What is FFT and

Spectrum

Analysis?

Windrock and RecipTrap Users

Frequency Domain

Spectrum analysis is the analysis of

frequency domain data.

All frequency domain data is collected

with an analyzer as time domain

data…aka waveforms.

Waveform

0 50 100 -3.7

-2.9

-2.1

-1.3

-0.5

0.3

1.1

1.9

2.7

3.5

Time (milliseconds)

g

's (

rms

)

Processed Overall = 0.7983

Raw Overall = 0.9665

Time and Frequency

• Time domain

- shows how the data changes over time

– sine wave on an oscilloscope

– pressure-time curve

– vibration-time curve

• Frequency domain

- data is shown as a function to frequency

- shows the frequencies in the data

• How are they related?

All periodic time domain signals can be represented as the sum

of a bunch of sine waves

Say that again…

• Every periodic time domain data signal is made up of a series of sine waves

• That includes airborne sound, machinery vibration and pressure and pulsations.

• Here’s the magic part…

– we can measure the response of the vibration, isolate all those sine waves and find out what their individual frequencies are, we can tell what caused each one of them

– That’s what spectrum analysis does

Spectrum example

Time

-200

-150

-100

-50

0

50

100

150

Am

pli

tud

e

Frequency domain

Shows that the signal was, in fact composed of two sine waves

0

20

40

60

80

100

120

Frequency

Am

pli

tud

e

FFT

Simple time domain signal

Clearly a bit more complex than a sine wave

How does it work?Time data

»Two sine waves

»Sum (magenta)

-200

-150

-100

-50

0

50

100

150

Time

Am

pli

tud

e

Blue Curve

• Frequency =100

• Amplitude = 100

• Phase angle = 0

Red Curve

• Frequency =200

• Amplitude = 50

• Phase angle = 90

Magenta Curve = Blue + Red

Frequency data

»Shows the components of the time wave forms

0

20

40

60

80

100

120

100 200

Frequency

Am

pli

tud

e

Blue Line

• Frequency =100

• Amplitude = 100

Red Line

• Frequency =200

• Amplitude = 50

FFT

A model of vibration -

sinusoidal motion

• Amplitude indicates how much a component is vibrating

• Frequency identifies the source (forcing function) that is causing the vibration. It is usually the most important parameter

• Phase of the vibration signal to a reference point indicates where the trouble lies within the revolution of a shaft or cycle

UPPER

NEUTRAL

LOWER

0,4

1

2

3

0 4

1

2

3

0, 2 ,4

1

3

PEAK ACCELERATION

PEAK

VELOCITYPEAK TO PEAK

DISPLACEMENT

TIME

PHASE

PERIOD

MASS

Accelerometer to

the Analyzer

The time domain is created by the analog electrical signal that comes from the accelerometer.

The electric signal is a time – varying voltage, proportional to the vibration measured by the accelerometer.

The voltage amplitude in the time waveform is converted to the desired amplitude units based on the sensitivity and conversion factor of the accelerometer.

The accelerometer signal collects data in acceleration. The signal is converted by a single mathematical integration to measure velocity or a double integration to measure displacement.

Waveforms to

Spectrum

Waveforms are viewed as complex sine

waves.

The conversion of the complex sine waves

to frequency domain data is the FFT.

What Is FFT?

FFT is an abbreviation for “Fast Fourier Transform”.

Fourier, whose full name is Baron Jean Baptiste Joseph Fourier, put forth the idea that a complex waveform could be broken down into many different sine waves of frequencies and amplitudes.

FFT is the mathematical conversion from the time domain to the frequency domain.

Time Domain Signal

The time domain signal is dependent on how

fast the data was sampled, the number of

digital samples in the waveform, the total time

in the waveform and the frequencies

generated by the system being examined.

The lines of resolution, maximum frequency,

length of time waveform, the sample size,

aliasing and unit conversion all play a part in

how the spectrum data looks.

Spectral Resolution

The spectrum can mask or hide frequencies and/or even change amplitudes because of the lines of resolution is set to low.

Resolution is the number of parts of the spectrum, usually called bins. The number of lines of resolution selected is divided into the maximum analysis frequency to arrive at the bin width (BW).

BW=Max Frequency/Lines of Resolution

Example #1 - IPS

Testpoint : COBH IPPNo. Of Lines : 801No. Of Averages : 3Calc Overall : N/ATrap Overall : 0.023 Peak At Frequency

1VP 2VP3VP

952.500

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

500 1000 1500 2000 2500 3000

8 Mile Testpoint COBH 5/5/2010 3:22:18 PM

ips (pk)

cpm

0 50000 100000 0

0.1

0.2

0.3

0.4

0.5

0.6

CPM

in

/s (

pe

ak

)

Peaks # Mag. Freq. 01 = 0.174 @ 4248.0

1

02 = 0.106 @ 2636.7

2

03 = 0.087 @ 4687.5

3

04 = 0.061 @ 3222.7

4

05 = 0.060 @ 22119.1

5

06 = 0.052 @ 3662.1

6

07 = 0.048 @ 5273.4

7

08 = 0.042 @ 1025.4

8

09 = 0.039 @ 2050.8

9

10 = 0.033 @ 40722.7

10

Processed Overall = 0.2606 Raw Overall = 0.3363

Example #2 - Mil

Displacement

Testpoint : COBH VIBNo. Of Lines : 401No. Of Averages : 3Calc Overall : N/ATrap Overall : 0.189 Peak At Frequency0.116 at 952.5 0.085 at 1770.00.067 at 1785.00.031 at 2857.50.012 at 240.0

1VP 2VP3VP

952.500

0.000

0.025

0.050

0.075

0.100

0.125

0.150

0.175

0 500 1000 1500 2000 2500 3000


mil (pk-pk)

cpm

0 2000 4000 6000 8000 0

0.1

0.2

0.3

0.4

0.5

CPM

m

ils (

p-p

)

Peaks # Mag. Freq.

01 = 0.467 @ 1042.0

1 02 = 0.184 @ 2084.1

2

03 = 0.079 @ 1572.2

3

04 = 0.072 @ 255.9

4

05 = 0.059 @ 950.6

5

06 = 0.046 @ 182.8

6

07 = 0.033 @ 2614.2

7

08 = 0.025 @ 1901.2

8

09 = 0.024 @ 3126.1

9

10 = 0.022 @ 1425.9

10



Example #3 - G’s

Testpoint : CIBA GPNo. Of Lines : 3201No. Of Averages : 6Calc Overall : N/ATrap Overall : 0.818 Peak At Frequency0.232 at 103012.50.171 at 114450.00.159 at 97275.00.134 at 91575.00.098 at 37.5 0.098 at 80100.00.085 at 34350.00.085 at 74400.00.085 at 11437.50.073 at 68662.5

1.799 -0.010

-0.005

-0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

1 2 3

Acid Gas Booster Testpoint CIBA 5/5/2010 1:16:07 PM

g (pk)

kcpm

0 200000 400000 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

CPM

g

's (

rms)

Peaks # Mag. Freq.

01 = 0.610 @ 96679.7

1 02 = 0.148 @ 151757.8

2

03 = 0.143 @ 99609.4

3

04 = 0.140 @ 107226.6

4

05 = 0.133 @ 160546.9

5

06 = 0.132 @ 86718.8

6

07 = 0.127 @ 162304.7

7

08 = 0.125 @ 184570.3

8

09 = 0.122 @ 159375.0

9

10 = 0.121 @ 104296.9

10



Bins Of Energy

The line for each bin is centered in the bins of energy. Each contains an infinite number of frequencies, and all the energy in the bin is added together and represented by a single amplitude at the center frequency of the bin. The analyzer allows the analyst to set a spectrum maximum frequency and a number of lines of resolution. (100, 200, 400, 800, etc.)

The result is the inability to distinguish closely spaced frequency vibration if the LOR is not set correctly.

Bins

Testpoint : RGIA IPPNo. Of Lines : 801No. Of Averages : 3Calc Overall : N/ATrap Overall : 0.178 Peak At Frequency0.057 at 2100.00.051 at 97.5 0.049 at 67.5 0.043 at 300.0 0.031 at 1500.00.031 at 4800.00.027 at 600.0 0.025 at 2400.00.023 at 4500.00.023 at 165.0

2099.933

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

EDG B Testpoint RGIA 1/25/2010 11:24:27 AM

ips (pk

)

cpm

Just 1 Bin

Testpoint : RGGA GPNo. Of Lines : 1601No. Of Averages : 15Calc Overall : N/ATrap Overall : 2.686 Peak At Frequency0.366 at 19500.00.354 at 19200.00.244 at 20100.00.232 at 22200.00.208 at 15600.00.195 at 52800.00.183 at 18900.00.171 at 44100.00.159 at 100200.00.159 at 20700.0

2.100 0.000

0.005

0.010

0.015

0.020

0.025

2

EDG B Testpoint RGGA 1/25/2010 11:24:27 AM

g (pk)

kcpm

Phase

• Phase – a measure of

the time lead or lag of

one vibration signal to

another or of a vibration

signal to a fixed

reference

• Used for balancing

• A reference point

(trigger location or

keyphasor) is

established by

measuring the point in

time when a keyway

passes a pickup

AMPLITUDE OF TWO IDENTICAL SINE

WAVES (IN PHASE) DOUBLES.

THE SUM OF TWO SINE WAVES, 180 DEG

OUT OF PHASE, IS ZERO.

Forces

• Periodic or oscillatory – rotational forces in machines that repeat over a definable period of time– Unbalance

– Misalignment

– Bent or bowed rotors

– Eccentric gears

• Transient or impact – forces short in duration– Combustion

– Anti-friction bearing defects

– Gear impacts

– Hydraulic hammering

– Mechanical looseness

– Cavitation

– Motor starts

• Random – broad frequency, e.g. pipe turbulence.

Fundamental Frequency

• The spectrum of a periodic signal will consist of a fundamental component at the reciprocal of the period and a series of harmonics of this frequency. The fundamental is also called the "first harmonic". It is possible to have a periodic signal where the fundamental is so low in level that it cannot be seen, but the harmonics will still be spaced apart by the fundamental frequency.

Harmonics

• Harmonics, also called a harmonic series,

are components of a spectrum, which are

integral multiples of fundamental

frequency. A harmonic series in a

spectrum is the result of a periodic signal

in the waveform. Harmonic series are very

common in spectra of machinery vibration.

Sub harmonic

• Sub harmonics are synchronous components in a spectrum that are multiples of 1/2, 1/3, or 1/4 of the frequency of the primary fundamental. They are sometimes called "sub-synchronous" components. In the vibration signature of a rotating machine, there will normally be a component at the turning speed along with several harmonics of the turning speed. If there is sufficient looseness in the machine so that some parts are rattling, the spectrum will usually contain sub harmonics. Harmonics of one-half turning speed are called "one-half order sub harmonics", etc.

Sidebands

• Sidebands are spectral components that are the result of amplitude or frequency modulation. The frequency spacing of the sidebands is equal to the modulating frequency, and this fact is used in diagnosing machine problems by examining sideband families in the vibration spectrum. For instance, a defective gear will exhibit sidebands at the gear rpm around the gearmesh frequency.

Measuring vibration

• Displacement – the distance moved (mil, microns)

• Velocity – rate of change in displacement versus time (ips, mm/s)

• Acceleration – rate of change in velocity versus time (g)Time

ntDisplacemeVelocity

AM

PL

ITU

DE

VELOCITYDISPLACEMENT

ACCELERATION

TIME

ΔTime

ΔVelocityonAccelerati

Frequency,

displacement, velocity

and acceleration

• Velocity is a good “all around” reading.• Displacement readings should be used for low frequency vibration.

– To maintain a 0.3 ips level at high frequency, the displacement is negligible. There’s just no time to build up much displacement in each period.

• Acceleration should be used for high frequency vibration.– To maintain a 0.3 ips level at low frequency, the acceleration is also negligible. There’s so much

time in one period that very little acceleration is needed to get to 0.3 ips.

0.1

0.001

0.01

0.1

1

10

100

1.0 10 100 1000 10000

DISPLACEMENT CORRESPONDING

TO 0.3 ips VELOCITY

ACCELERATION CORRESPONDING

TO 0.3 ips VELOCITY

0.3 ips VELOCITY

VIB

RA

TIO

N A

MP

LIT

UD

E

MIL

S P

K-P

K

IN

/SE

C

G

’S P

K

FREQUENCY IN HERTZ

When to use

displacement, velocity or

acceleration

Displacement

• Measurement of displacement will give the low frequency components most weight. Displacement is often used as an indicator of unbalance in rotating machines parts because relatively large displacements usually occur at the shaft rotational frequency. High amplitudes of vibration displacement that result in stress failures typically occur at very low vibration frequencies, generally below 600 cpm (10 Hz).

Velocity

• It is best to select the parameter that gives the flattest frequency spectrum in order to best use the dynamic range (the difference between the smallest and the largest values that can be measured) of the machine. This is why the velocity reading is normally selected. Velocity readings (IPP) are appropriate when vibration frequencies range between 600 cpm (10 Hz) and 120,000 cpm (2000 Hz). Fatigue failures typically occur in this frequency range.

Acceleration

• Acceleration measurements will weight the level toward high frequency components. Acceleration readings (G’s) are recommended whenever vibration frequencies are expected to exceed 120,000 cpm (2000 Hz). The most common source of such high frequencies are gear mesh frequencies and their multiples or harmonics on high speed gear drives.

When to use displacement,

velocity and acceleration

•Displacement

o Periodic faults

o Misalignment

o Oil whirl

o Unbalance

oVelocity

o General monitoring work

o Periodic faults

o Misalignment

o Oil whirl

o Unbalance

oAcceleration

o Impact faults

o Rolling element

bearings

o Gear mesh

frequencies

o Vane passing

0.1

0.001

0.01

0.1

1

10

100

1.0 10 100 1000 10000

DISPLACEMENT CORRESPONDING

TO 0.3 IN/SEC VELOCITY

ACCELERATION CORRESPONDING

TO 0.3 IN/SEC VELOCITY

0.3 IN/SEC VELOCITY

VIB

RA

TIO

N A

MP

LIT

UD

E

MIL

S P

K-P

K

IN

/SE

C

G

’S P

K

FREQUENCY IN HERTZ

Amplitude units

peak2peaktopeak

peak0.7072

peakRMS

: wavesine aFor

RMS2peakpseudo

SINUSOIDAL MOTION

UPPER

NEUTRAL

LOWER

PEAK

TO

PEAK

RMS

PEAK

RMS22peak-peakpseudo

Peak, RMS, Pseudo

What?

• Peak

– Very sensitive

– Shows the “worst-case” level of vibration in the time sample

• RMS

– Tells about the energy content of the signal

– More realistic measure of vibration energy

• Pseudo-Peak

– Uses the the RMS reading and scales it up so that it is comparable to the peak

– More understandable to most people than RMS

• Peak-Peak

– Normally reserved for displacement readings

• Pseudo-Peak-Peak

– Uses the the RMS reading and scales it up so that it is comparable to the peak-peak

Pseudo-peak

The Trap can measure certain conventional vibration types in four ways: true peak, root mean square (RMS), pseudo-peak, and pseudo peak-to-peak. We recommend you use pseudo-peak types (GP for acceleration, IPP for velocity).

Pseudo peak types are:

• IPP velocity in inches per sec

• GP acceleration in g

The pseudo-peak type is simply the RMS level multiplied by square root of 2. For pure sine waves, it is identical to true peak. For complex signals, it can be significantly different.

The advantages of using pseudo-peak readings:

• commonly used throughout North America

• easier to understand pseudo-peak results, for example, a few of the most significant peaks in the spectrum sum up more closely to the overall value.

• readings tend to be less variable

• readings steady out quickly, making data collection quicker

The disadvantage of using pseudo-peak readings:

• less sensitive to variations in peak vibration than true peak readings

test point types

IMPERIAL METRIC

TYPE UNITS TYPE UNITS

Displacement Pseudo Pk-Pk

Pk-Pk, 700 MV PANEL

Pk-Pk, 200 MV PANEL

Pk-Pk, 100 MV PANEL

PHASED Pk-Pk, PANEL

VIB

MI7

MI2

MIL

PDT

mils

mils

mils

mils

mils

DU

UM2

UM

PUT

MICRONS

MICRONS

MICRONS

MICRONS

Velocity Pseudo-Pk

RMS

True Peak

IPP

IPR

IPS

ips

ips

ips

MMP

MMR

MMS

mm/s

mm/s

mm/s

Acceleration Pseudo-Pk

RMS

True Peak

GP

GR

G

g

g

g

SAME AS IMPERIAL

Spike Energy BEARING DEFECT ENERGY BDE none none

Bearing Defect Energy

• Bearing Defect Energy (BDE) is a

measurement of acceleration in a high-

frequency range, usually to 20 kHz, for the

detection of rolling-element bearing

problems.

Bearing defect energy

• BDE measures vibration above the normal calibrated

operating range of the transducer

• Use the resonant frequency of the transducer to measure

impact faults from rolling element bearings and cavitations.

Accelerometer

• Advantages

– Broad frequency range from approximately 2Hz to

greater than 12 kHz depending upon the mounting

technique

– Small and lightweight

– Easily mounted or could be easily used with a magnet

• Disadvantages

– Poor signal response when used as a hand-held

probe on high frequency components

– Limited signal-to-noise ratio

PiezoVelocity

Transducer

• Velocity is normally used from 100 – 30,000 CPM.

• Out-perform most accels from 90 – 3600 CPM

– Stronger output on slow to moderate speed

machinery

• Essentially an accel with an velocity converter built into it

• Over 3600 CPM has higher signal-to-noise ratio than a

accel

• Can display low frequency noise (ski slope) better than

accels but will cutoff all frequencies below 90 CPM

– The double integration from accels can amplify low frequency

noise

• The internal integration attenuates very high frequencies

before they obscure lower frequencies.

Mounting Response

• The accelerometer and velocity transducer

responds differently depending upon the

mounting technique used for data

collecting.

– The stiffer the contact with the machine, the

higher the natural frequency of the transducer

– The heaver the mass of the accel and mount,

the lower the natural frequency

– The greater the damping of the mount, the

less the vibration becomes amplified

Mounting techniques

• Stud mounted

• Wax mounted

• Side mounted

• Epoxy mounted

• Magnet mount

• Hand-held– Least predictable method but easiest to use.

– The natural frequency of the hand held transducer is around 1600-2000 Hz.

– Data much higher than 2kHz is attenuated

Mounting Methods

• Stud Mounted – Provides a linear response to

approximately 16,000 Hz (960,000 CPM)

• Quick Lock Mount – Provides a linear response to


• Flat Magnet– Provides a linear response to


• Rail Magnet – Provides a linear response on a curved

surface to 3,000 Hz (180,000 CPM)

• Hand-held Accel with 2” Stinger – Provides a linear

response to 800 Hz. Should not be used on high speed

equipment. (48,000 CPM)

Fault frequency chart

Rotor Imbalance

Misalignment

Bent shafts

Spur gear faults

Helical gearing faults

Defective ball bearings

Pump cavitation

Pump impeller problems

Mechanical looseness

Electrical problems

Piping/mounting resonance

Faulty drive belts

Worn journal bearings

Oil whirl

Forced piping/uneven base

Unbalanced pulley

Instrument grounding

Resonance

Instrument noise

Pulsation

Cylinder Stretch

Torque Fluctuations

<1

0 H

z

>1

0 H

z &

< 1

X R

PM

0.4

5X

RP

M

1X

RP

M

1.5

X R

PM

2X

RP

M

3X

- 1

0X

RP

M

1X

LF

2X

LF

1X

GM

F

2X

GM

F

GM

F S

ide

Ban

ds

1X

- 2

X M

F

Be

lt F

req

Ba

ll B

eari

ng

Fre

q

Be

aring

En

erg

y

>1

000

Hz

Bro

adb

and

Nois

e

Ra

dia

l

Axia

l

Very Often

Often

Sometimes

Seldom

Never

Why measure

vibration?

• Machine reliability – identify and correct

problems before downtime or damage

occurs

• Expense – eliminate unexpected

downtime

» Measuring and analyzing vibration allows you to

determine if a problem exists, identify the source and

enable corrective action

Collecting spectrum

data

Collecting spectrum data

pumps and motors

Inboard, outboard bearings

Gearboxes, impellers

• Triaxial (H,V,A) accelerometer

• Displacement, velocity, acceleration

• Free running frequency domain data

• Bearing defect energy

• Overall vibration levels (comparison to

previous)

Foundations and supports

• Triaxial (H,V,A) accelerometer

• Displacement readings only

• Opposite corners of support


• Overall vibration levels (comparison to

previous)

Pressure pulsation in recip compressors

• DC nozzle pressure


Piping vibration, bottles, scrubbers

• Standard accelerometer

• Frequency domain data

Reciprocating

machinery applications

• Engines

– Frame vibration

• Compressors

– Frame vibration

– Cylinder stretch

– Cylinder supports

• Auxiliary Equipment

– Turbo charger

– Gear driven components, blowers

– Water pump

– Oil pump

– Ignition drive shaft

– Bottles, scrubbers, piping

Recommended

locations

MACHINE READING LOCATION

Motor, pump or

compressor with

rolling element

bearings

Velocity or

Acceleration, BDE

One radial at each bearing

One axial, usually on motor to detect thrust wear.

BDE for rolling element bearing defects and cavitation.

Motor, fan with journal

bearings

Displacement or

velocity

1 radial at each bearing, 1 axial displacement to

detect thrust wear.

Turbocharger Acceleration and/or

velocity

1 radial near the bearing. Velocity for looseness,

velocity or acceleration for turbocharger shaft and vain

pass frequencies

Gear box with rolling

element bearings

Acceleration, BDE Transducer mounted as close to each bearing as

possible. BDE for rolling element bearing defects and

cavitation.

Gear box shaft with

fluid film bearings

Displacement Axial, horizontal and vertical at each bearing. The

axial reading to detect thrust wear

Without Speed Saved


0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


ips (pk

)

cpm

0 2000 4000 6000 8000 0

0.4

0.8

1.2

1.6

2.0

CPM

m

ils (

p-p

)


Raw Overall = 2.106

Speed Cursor

(Windrock)

Speed Cursor

(RTWin)


952.500

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


ips (pk)

cpm

Speed Cursor and Shaft

Fault Frequencies


1X 2X 3X 4X 5X 6X

7X 8X 9X 10X 11X 12X 13X

14X 15X

952.500

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


ips (pk

)

cpm

Order Cursor on the

Electric Motor


1C 2C 3C

4C 5C 6C 7C

8C 9C 10C 11C 12C

13C 14C15C

1X

2X

3X 4X 5X 6X

7X 8X 9X 10X 11X 12X 13X

14X 15X

952.500 1786.770

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


ips (pk)

cpm

Order Cursor on the

Electric Motor ¼ of

Run Speed


1C 2C 3C 4C 5C 6C 7C 8C 9C 10C 11C 12C 13C

14C 15C1X

2X 3X 4X 5X 6X

7X 8X 9X 10X 11X 12X 13X

14X 15X

952.500444.647

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000


ips (pk)

cpm

Order Cursor on the

Electric Motor

0 2000 4000 6000 8000 0

0.4

0.8

1.2

1.6

2.0

CPM

m

ils (

p-p

)


Raw Overall = 2.106

X: 530.156

Y: 0.02599

Vane Pass

Testpoint : COBH GPNo. Of Lines : 3201No. Of Averages : 6Calc Overall : N/ATrap Overall : 0.342 Peak At Frequency0.049 at 35212.50.037 at 34275.00.037 at 56175.00.037 at 22837.50.024 at 56962.50.024 at 65587.50.024 at 61462.50.012 at 55200.00.012 at 56625.00.012 at 56062.5

1VP 2VP 3VP

0.952 0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69


g (pk)

kcpm

Resonance Fault

Frequencies

Testpoint : CIBH IPPNo. Of Lines : 801No. Of Averages : 3Calc Overall : N/ATrap Overall : 0.021 Peak At Frequency

1VP

2VP 3VP1FN 2FN 3FN

4FN 5FN

952.500

0.0000

0.0025

0.0050

0.0075

0.0100

0.0125

0.0150

0.0175

0.0200

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

8 Mile Testpoint CIBH 5/5/2010 3:22:18 PM

ips (pk

)

cpm

Band Editor for Windrock

Speed Ratio

Speed ratio is used in setting up bearing locations for rotating equipment (spectrum) analysis. It is the multiplier used to determine the speed at the bearing location. It is used to calculate the changes that belts or gears make on the shaft speed.

• For example: If the nameplate speed of a motor is 1800 rpm, but the speed on the pump that it is driving is reduced to 900 rpm by a gearbox, then the speed ratio at the pump bearing is 0.5 (or half the speed of the driver).

The speed ratio is also used to calculate the machine’s speed when you drag the speed cursor on the Fault Finder graph. The new speed is divided by the speed ratio to determine the machine’s actual run speed. Then, the machine’s speed is multiplied by each component’s speed ratio to determine what speed to put in the snapshot table.

How Do I Set LOR and

Frequency Range?

Frequency range should be set to above the shaft speed. You should

always include at least the 2x.

• Displacement should be left at the default; If the 1 x and the 2x can

not be measured then IPS should be collected.

• IPS should set up to 12x shaft speed. Separate test points in G

should be set up to look for vibration higher than 12x shaft speed if

forcing function vibration exist.

The minimum frequency resolution should be set so that it equals 1% of

the shaft speed.

Analyzer's Preset

Options

• Number of Lines (#Points) 50; 100; 200;

400; 800; 1,600; 3,200; 6,400

• Frequency Range (Freq. Range) CPM

(Hz) 3,000 (50); 6,000 (100); 12,000 (200);

30,000 (500); 60,000 (1,000); 120,000

(2,000); 300,000 (5,000); 600,000

(10,000); 1,200,000 (20,000)

FFT Math Test!

• Compressor running at 1000 RPM would need to have the LOR set

to 800 with the frequency range at 12,000.

– Minimum frequency resolution is 7.5.

– 12,000/800/2= 7.5

• 7.5 divided by 1000 equals 0.0075 which is lower than 1%

• LOR at 400

– 12,000/400/2=15

– 15 divided by 1000 equals 1.5% (Slightly high but would work)

• LOR at 1600

– 12,000/1600/2=3.75

– 3.75 divided by 1000 equals 0.4% (Slightly low but would work)

Why Divide By 2?

• The LOR and Maximum Frequency are

divided and then that number is divided by

2.

– The reason we divide by 2 is because the

analyzer draws the frequency lines in the

center of the bins and not on the LOR. There

is only 1 bin for every two lines of resolution.

Sleeve Bearing

• A good rule of thumb for sleeve bearings is

15xTS with at least 400 LOR• Sub-Synchronous – 0 to 0.8 x TS

• 1 x TS – 0.8 to 1.5 x TS

• 3x through 4 x TS – 2.5 to 4.5 x TS

• Vane/Blade Pass – 4.5 to 15 x TS

• High Frequency – 1 to 20 kHz

Rolling Element

Bearing

• A good rule of thumb for rolling element

bearings is 65xTS with at least 800 LOR• Sub-Synchronous – 0 to 1.5 x TS

• 2 x TS – 1.5 to 2.5 x TS

• 3x through 8 x TS – 2.5 to 8.5 x TS

• 1st bearing band – 8.5 to 35.5 x TS

• 2nd bearing band – 35.5 to 65 x TS


Gears

• A good rule of thumb for gears is a range

of 2x gear mesh plus 5x gear speed with

at least 800 LOR• Shaft speed harmonics – 0 to 2.5 x TS

• 3 through 10 x TS – 2.5 to 10 x TS

• 10 x GM through 5 x TS – 10.5 to [GM minus 5 x

TS]

• 1st Gear mesh – [GM minus 5xTS] to [GM plus 5x

TS]

• 2nd Gear mesh – [GM plus 5xTS] to [2xGM plus

5xTS]


Displacement of Suction

Piping with low end

S pect rum

# Li nes: 401

# Averages: 4

Cal c overal l NA

Trap overal l 6.300

P eak at Frequency

1.276 at 892.5

1.172 at 232.5

1.001 at 195.0

0.574 at 2692.5

0.525 at 285.0

0.427 at 1792.5

0.427 at 337.5

0.379 at 322.5

0.238 at 442.5

0.214 at 397.5

0.00

0.25

0.50

0.75

1.00

1.25

0 500 1000 1500 2000 2500 3000

GIC Z010 - Z010 Suction Piping 4SPH VIB 11/11/2009 6:33:59 AM

mil

cpm

IPS of Suction Piping

S pect rum

# Li nes: 801

# Averages: 5

Cal c overal l NA

Trap overal l 2.813

P eak at Frequency

1.987 at 3585.0

0.432 at 8070.0

0.303 at 7170.0

0.211 at 10755.0

0.160 at 9870.0

0.147 at 5385.0

0.076 at 900.0

0.074 at 2685.0

0.059 at 6270.0

0.055 at 4485.0

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000

GIC Z010 - Z010 Suction Piping 4SPH IPS 11/11/2009 6:33:59 AM

ips

cpm

IPP Spectrum Plot

Sp e c tr u m

# L in e s : 3 2 0 1

# Av e r a g e s : 0

C a lc o v e r a ll N A

Tr a p o v e r a ll 0 .1 4 8

Pe a k a t Fr e q u e n c y

0 .0 6 6 a t 5 4 2 8 .1

0 .0 5 7 a t 5 8 7 8 .1

0 .0 5 1 a t 4 0 6 8 .8

0 .0 4 5 a t 4 9 6 8 .8

0 .0 4 5 a t 4 5 1 8 .8

0 .0 2 1 a t 3 1 6 8 .8

0 .0 1 4 a t 6 3 2 8 .1

0 .0 1 2 a t 2 7 0 9 .4

0 .0 0 0

0 .0 0 5

0 .0 1 0

0 .0 1 5

0 .0 2 0

0 .0 2 5

0 .0 3 0

0 .0 3 5

0 .0 4 0

0 .0 4 5

0 .0 5 0

0 .0 5 5

0 .0 6 0

0 .0 6 5

0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0

4-E - Speed Changer SHIH IPP 7/22/2009 1:43:08 PM

ips

c p m

GP Spectrum Plot( What

is this)

Sp e c tr u m

# L in e s : 6 4 0 1

# Av e r a g e s : 1 2

C a lc o v e r a ll N A

Tr a p o v e r a ll 3 .4 3 1

Pe a k a t Fr e q u e n c y

0 .3 3 0 a t 1 7 0 3 4 3 .8

0 .2 6 9 a t 1 7 0 7 1 8 .8

0 .2 4 4 a t 1 8 6 5 6 2 .5

0 .2 4 4 a t 1 8 5 9 0 6 .3

0 .2 3 2 a t 1 7 6 7 1 8 .8

0 .2 3 2 a t 1 8 5 0 6 2 .5

0 .2 2 0 a t 1 7 2 6 8 7 .5

0 .2 0 8 a t 1 7 2 4 0 6 .3

0 .2 0 8 a t 1 8 4 6 8 7 .5

0 .2 0 8 a t 3 1 8 7 .5

0 .0 0

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .3 0

0 2 0 0 0 04 0 0 0 06 0 0 0 08 0 0 0 01 0 0 0 0 01 2 0 0 0 01 4 0 0 0 01 6 0 0 0 01 8 0 0 0 02 0 0 0 0 02 2 0 0 0 02 4 0 0 0 02 6 0 0 0 02 8 0 0 0 03 0 0 0 0 03 2 0 0 0 03 4 0 0 0 03 6 0 0 0 03 8 0 0 0 04 0 0 0 0 04 2 0 0 0 04 4 0 0 0 04 6 0 0 0 04 8 0 0 0 05 0 0 0 0 05 2 0 0 0 05 4 0 0 0 05 6 0 0 0 05 8 0 0 0 06 0 0 0 0 0

4-E - Left Turbo LAA GP 7/22/2009 1:43:08 PM

g (pk)

c p m

Turbo – Data Collected

with Channel Locks

Tes tpoint : AIRA GPNo. Of Lines : 6401No. Of Averages : 7Calc Overal l : N/ATrap Overal l : 1.392 Peak At Frequency0.464 at 367593.80.256 at 26250.00.147 at 52687.50.134 at 10781.30.134 at 52218.80.122 at 3000.00.122 at 1781.30.110 at 367875.00.110 at 368156.30.098 at 2437.5

1X 2X 3X 4X 5X 6X 7X 8X 9X 10X 11X

12X 13X 14X 15X

1VP

2VP

3VP

52.4820.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

100 200 300 400 500 600

Wilson E 2011 Testpoint AIRA 6/3/2010 2:33:28 PM

g (pk)

k cpm

Printed to PDF

IPP and G readings on

a Turbo

Te s tp o in t : AIR A G PN o . O f L in e s : 6 4 0 1N o . O f Av e r a g e s : 8C a lc O v e r a ll : N /ATr a p O v e r a ll : 2 .7 5 9 Pe a k At F r e q u e n c y0 .2 9 3 a t 2 3 9 0 6 .30 .2 6 9 a t 8 7 0 0 0 .00 .2 6 9 a t 6 4 6 8 7 .50 .2 4 4 a t 9 3 3 7 5 .00 .2 4 4 a t 6 6 2 8 1 .3

Te s tp o in t : AIR A IPPN o . O f L in e s : 6 4 0 1N o . O f Av e r a g e s : 5C a lc O v e r a ll : N /ATr a p O v e r a ll : 0 .3 8 1 Pe a k At F r e q u e n c y0 .1 0 4 a t 1 0 5 0 .00 .0 7 8 a t 2 6 4 3 .80 .0 6 8 a t 1 5 9 3 .80 .0 3 9 a t 3 9 1 6 8 .80 .0 3 9 a t 3 8 6 4 3 .8

1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 C 9 C 1 0 C

1 1 C

1 2 C

1 3 C

1 4 C

1 5 C

1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 C 9 C 1 0 C

1 1 C

1 2 C

1 3 C

1 4 C

1 5 C

7 .3 1 3 1 9 .0 9 5

7 .3 1 3 1 9 .0 9 5

0 .0 0

0 .0 5

0 .1 0

0 .1 5

0 .2 0

0 .2 5

0 .0 0 0

0 .0 2 5

0 .0 5 0

0 .0 7 5

0 .1 0 0

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0

Unit 1 Eng Testpoint AIRA 8/26/2009 9:57:45 AM

g (pk)

ips (pk)

k c p m

Cat Turbo Good and

the Bad

VIB or Mil

Displacement Frame

Te s tp o in t : R FW H VIBN o . O f L in e s : 4 0 1N o . O f Av e r a g e s : 4C a lc O v e r a ll : N /ATr a p O v e r a ll : 3 .4 1 9 Pe a k At F r e q u e n c y1 .5 2 0 a t 4 5 7 .5 1 .0 9 9 a t 1 8 7 .5 0 .7 8 1 a t 9 1 5 .0 0 .7 3 9 a t 2 1 7 .5 0 .6 5 3 a t 3 2 2 .5 0 .5 2 5 a t 2 4 7 .5 0 .5 1 3 a t 2 7 0 .0 0 .3 7 2 a t 4 0 5 .0 0 .3 4 8 a t 3 0 0 .0 0 .3 2 4 a t 3 5 2 .5

1 C 2 C 3 C 4 C 5 C 6 C

7 C 8 C 9 C 1 0 C 1 1 C 1 2 C 1 3 C 1 4 C

1 5 C

4 5 6 .8 0 1

0 .0 0

0 .2 5

0 .5 0

0 .7 5

1 .0 0

1 .2 5

1 .5 0

1 .7 5

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0

4-E Testpoint RFWH 7/22/2009 1:43:08 PM

mil (pk

-pk)

c p m

VIB or Mil

Displacement Plot

Te s tp o in t : R FW H VIBN o . O f L in e s : 4 0 1N o . O f Av e r a g e s : 4C a lc O v e r a ll : N /ATr a p O v e r a ll : 3 .4 1 9 Pe a k At F r e q u e n c y1 .5 2 0 a t 4 5 7 .5 1 .0 9 9 a t 1 8 7 .5 0 .7 8 1 a t 9 1 5 .0 0 .7 3 9 a t 2 1 7 .5 0 .6 5 3 a t 3 2 2 .5 0 .5 2 5 a t 2 4 7 .5 0 .5 1 3 a t 2 7 0 .0 0 .3 7 2 a t 4 0 5 .0 0 .3 4 8 a t 3 0 0 .0 0 .3 2 4 a t 3 5 2 .5

1 C 2 C 3 C 4 C 5 C 6 C

7 C 8 C 9 C 1 0 C 1 1 C 1 2 C 1 3 C 1 4 C

1 5 C1 X 2 X 3 X

4 X 5 X 6 X 7 X

8 X 9 X 1 0 X 1 1 X1 2 X

1 3 X1 4 X1 5 X

9 1 8 .3 4 04 5 9 .5 0 8

0 .0 0

0 .2 5

0 .5 0

0 .7 5

1 .0 0

1 .2 5

1 .5 0

1 .7 5

0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 3 0 0 0

4-E Testpoint RFWH 7/22/2009 1:43:08 PM

mil (pk-

pk)

c p m

Displacement with

wrong settings

1 9 0 .0

0

2500

5000

7500

10000

Spectrum Frequencies in cpm

0

1

2

3

4

mil (pk-

pk)

5/6/2008

5/6/2006

5/5/2004

5/5/2002

5/4/2000

Unit3 movement, Component: Unit3 movement, C1V DSP

Cascade Plot (shows

2x go up)

1 6 1 .0

0

2500

5000


0 .0

2 .5

5 .0

mil (pk-

pk)

4/21/2009

4/1/2008

3/13/2007

2/21/2006

2/1/2005

2 COMPRESSOR, Component: 1, 1H VIB

FFT WaterFall Plot

0 2000 4000 6000 8000 10000 0

0.80

1.60

2.40

3.20

4.00

4.80

Overall Average = 1.681

CPM

m

ils (

p-p

)

Connecting Rod

Bushing Looseness In

Main Bearings

Testpoint : P3H VIBNo. Of Lines : 401No. Of Averages : 4Calc Overall : N/ATrap Overall : 0.653 Peak At Frequency0.446 at 630.0 0.226 at 1882.50.201 at 2505.00.116 at 1252.50.055 at 1567.50.049 at 315.0 0.043 at 2820.0

150.000

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 500 1000 1500 2000 2500 3000

H103-E Testpoint P3H 5/4/2010 12:37:41 PM

mil (pk-

pk)

cpm

1st Order

½ Orders

Trend of Axial and

Vertical Head End

Cylinder

0

5

1 0

1 5

2 0

2 5

3 0

Ap r2 0 0 8

J u l O c t J a n 2 0 0 9 Ap r J u l O c tD a te s

Cascade of Axial

Head End Cylinder

186.0

0

1000200

0

3000


0

5

10

15

20

25

mil (pk

-pk)

11/12/2009

6/4/2009

12/25/2008

7/17/2008

2/7/2008

U-MAKEUP H2 CP0439, Component : 1, 1A VIB

PP4, PP5 and PPP

Testpoint : N1D PP4No. Of Lines : 3201No. Of Averages : 4Calc Overall : N/ATrap Overall : 30.144 Peak At Frequency6.699 at 27900.05.785 at 28931.35.481 at 2062.53.654 at 6196.92.740 at 27871.92.740 at 28903.11.522 at 29962.51.218 at 4134.40.913 at 7228.10.913 at 27928.1

1C 2C 3C 4C 5C 6C 7C 8C 9C 10C 11C 12C 13C 14C

15C

1033.0002062.292

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

0 5000 10000 15000 20000 25000 30000

Limestone South Comp Testpoint N1D 5/20/2010 4:09:16 PM

psig (p

k-pk)

cpm

Normally anything over 12 TS is not an issue

Phased Displacement

(MD)

- 2 0

- 1 0

0

1 0

2 0

- 2 0

- 1 0

0

1 0

2 0

- 2 0

- 1 0

0

1 0

2 0

0 9 0 1 8 0 2 7 0 3 6 0 4 5 0 5 4 0 6 3 0 7 2 0

H 1 0 3 - E 5 / 4 / 2 0 1 0 1 2 : 3 7 : 4 1 P ME n g in e C y lin d e r s : P h a s e d D is p la c e m e n t M D :

P1

(

Me

d

10

)P

2

(M

ed

8

)P

3

(M

ed

4

)

- 2 0

- 1 0

0

1 0

2 0

- 2 0

- 1 0

0

1 0

2 0

- 2 0

- 1 0

0

1 0

2 0

0 9 0 1 8 0 2 7 0 3 6 0 4 5 0 5 4 0 6 3 0 7 2 0

H 1 0 3 - E 5 / 4 / 2 0 1 0 1 2 : 3 7 : 4 1 P ME n g in e C y lin d e r s : P h a s e d D is p la c e m e n t M D :

P4

(

Me

d

10

)P

5

(M

ed

7

)P6

(

Me

d

11

)

Contact Information

• Tracy Wimberly

• 954-319-8386

• [email protected]

Documents

What is FFT and Spectrum Analysis? - Windrock Inc.Windrock and RecipTrap Users. Frequency Domain Spectrum analysis is the analysis of frequency domain data. All frequency domain data