MultiMulti--Channel Channel AnalysisAnalysis

MultiMulti--Channel AnalysisChannel Analysis What is it? What is it good for? How is it done?

Types of MultiTypes of Multi--Channel AnalysisChannel Analysis Simultaneous Measurement

orbits

Comparative Measurement coherence / cross channel phase

Impact Testing frequency response function / transfer function

Orbit PlotsOrbit Plots True Orbit Plot

measure displacement two prox probes at 90

Casing vibration two accel sensors at 90 double integrate

Orbit Plots Identify:Orbit Plots Identify:

Misalignment,Resonance, Wear

Misalignmentand other problems

Misalignment

Misalignment

Shaft rub ormechanical looseness

Sub-synchronous whirl

Ellipse

Inner Loop

Inside Ellipse

Truncation

Figure Eight

Banana

Sample Orbit PlotSample Orbit Plot

Orbit SetOrbit Set--upup

Sample at high frequency

Low number of samples/lines

Low pass or band pass filter

Use Time Synchronous Averaging

Comparative MeasurementsComparative Measurements Cross Channel Phase

Coherence

Cross Channel PhaseCross Channel Phase Check for misalignment

measure across a coupling check phase at running

speed

Cross Channel PhaseCross Channel Phase Check for

looseness/weakness measure across

mechanical interface check phase at running

speed

Cross Channel PhaseCross Channel Phase Verify machine resonance

part of impact testingfull spectrum phaseslow, steady change (ideally over 180)

Machine resonanceverified by 160 shiftin phase spectrum

CoherenceCoherence Compares two sensor signals

Determines: transmission path of vibration quality of measurement

Must be used with averaging (minimum 3-4 averages)

Coherence Case HistoryCoherence Case History

Reoccurring failure on paper machine Unusual vibration present Matched turning speed of pump below

Coherence measurement proved that vibration was related

Fixing pump operation solved paper machine problems

Verify if vibration is related across points

Coherence Case HistoryCoherence Case History

Leased NY penthouse for top dollar

with one condition: noise level in conference room must be below 50 dB

noise level too high, no rent! Landlord hired Art Crawford

checked HVAC fan Coherence measurement

proved vibration was related Balancing HVAC fan

removed sound in conference room Tenant paid top dollar for

penthouse!

Verify if vibration is related across points

Coherence Case HistoryCoherence Case History

Suspect crack in piping

Cross channel measurement one sensor on each side

Check coherence with 3-4 averages high value for good pipe (e.g. > 0.95) low value if crack present (e.g. < 0.85)

Check for cracks in piping

Coherence Case HistoryCoherence Case History

Stud mount sensor A for good reading

Use sensor B as rover measure at several locations

Check coherence with 3-4 averages highest value indicates best location to place

sensor for routine vibration measurements

Establish optimum sensor placement

A

B

CoherenceCoherence

Impact machine with force hammer at least 3-4 averages

Coherence confirms data quality 0.95 or higher desired to confirm diagnosis of

resonance

Determine quality of cross channel measurement

A

Coherence Case HistoryCoherence Case History

Coherence value near 1.0 confirms peak at 42.5 Hz is resonance

Impact TestingImpact Testing

Impact testing measure input (force) with modally tuned hammer measure output (vibration) with accelerometer

Impact Test ApplicationImpact Test Application Structural analysis

Identify resonances Measure stiffness Determine system response Modal analysis

Stiffness with Coherence and PhaseStiffness with Coherence and Phase

MeasurementsMeasurements

RESPONSE IMPACT

Vibration waveform from accelerometer

Force waveform from modal hammer

Measurement WindowsMeasurement Windows

Proper impact measurements require that appropriate windows are applied to the impact and response waveforms. (see dotted line above).

RESPONSE IMPACT

Measurement SetMeasurement Set--upup Conventional systems

have complex set-up

Define values for: % pre-trigger duration of force window

(as % of total time record) half-cosine taper for force

and exponential window exponential decay factor

Menu for custom configuration

Measurement SetMeasurement Set--upup Emerson offers a job template

Easy to use Pre-configured parameters for impact test

user selects impact mode pre-configured parameters for standard impact test parameters may also be customized, if desired

Menu driven guides you through the process

CSI Impact Test FlowCSI Impact Test Flow

1) Select IMPACT mode2) Attach hammer to ch. A, accel to ch. B3) Impact structure with hammer when instructed4) 2130 automatically checks and adjusts scaling5) Review waveform and accept or reject6) Repeat steps 3-5 for additional measurements7) Examine results for evidence of resonances

3 Steps To Locate Resonances3 Steps To Locate Resonances

1. peak in transfer function

2. gradual phase shift3. high coherence (>0.95)

Structural Analysis OptionsStructural Analysis Options Operating Deflection Shape

performed while machine in operation single frequency measurement can be performed with any CSI machinery analyzer measures actual amplitude of deflection shows how machine deflects in normal operation

Modal Analysis requires machine to be shut down analysis across all frequencies requires dual channel 2130 for measurements determines ratio of response to input, no absolute amplitudes detailed model of machine stiffness, resonances, etc.

Single Channel ODSSingle Channel ODS1) Select pre-defined structure2) Load route into machinery analyzer3) Collect Peak/Phase Data (requires phototach for phase)4) Upload route5) Access data from ODS module6) Animate machine to see

deflection during operationB

Moving sensor

Dual Channel ODSDual Channel ODS

Fix one sensor on machine Move second sensor around machine Collect cross channel data Upload data to VibPro Import data to ODS software View animation

operating speed any synchronous freq. all frequencies

A

B

Fixed sensor

Moving sensor

Modal AnalysisModal Analysis

1) Define structure for analysis2) Use ch. A for a fixed sensor

(reference)3) Use ch. B as roving sensor to

other points 4) Transfer cross channel readings

to Modal Analysis software

5) Animate structure- all frequencies- natural resonance

A

B

Moving sensor

Structural AnalysisStructural AnalysisStructural Analysis

Sample results of analysis