2 transducer operation & application
TRANSCRIPT
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VIBRATION MEASURING
INSTRUMENTS
OVERVIEW
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Choosing Your Instrumentation
What do you want to achieve?
What is your present and future.
Budget for equipment & Training?
Person power? Knowledge level?
Number of machines to be monitored?
Type of machines to be monitored?
Environment?
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INSTRUMENT TYPES
Overall Level Meters
Quick Check Analysers
FFT Data Collector/Analysers
Full Feature Analysers
Real Time Spectrum Analysers
Instrument Quality Tape Recorders
Dedicated Balancing instruments
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Real Time Rate
The Highest rate at which
data can be captured anddisplayed without leaving
any gaps in the analysis.
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ON-Line or Permanent Monitors
Due to cable lengths and possible signal
contamination, SNR considerations remain
more important in current permanent / on-line monitoring than they are in a
contemporary data collector context
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Vibration Transducers
Overviewand
Selection
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Transducer TypesSeismic:- Bearing relative to space.
Velocity Pickups Accelerometers
Piezoelectric velocity pickups
Relative:- Shaft relative to bearing. Non-contact Eddy Current Displacement
Probes
Absolute:- Shaft relative to space. Shaft Contact Displacement Probes (including
Shaft Sticks and Shaft Riders)
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Seismic Transducer
VELOCITY
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Velocity Pickups
Note :- There are two types of velocity pickups the aboveadvantages do not apply to piezoelectric velocitytransducers.
ADVANTAGES
Self- Generating
No On-board Electronics Strong signal
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SESMIC TRANSDUCERSACCELEROMETER
AMPAMP
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Accelerometers - advantages
No moving parts, no wear.
Rugged.
Very large dynamic range.
Wide frequency range.
Compact, often low weight.
High stability.
Can be mounted in any orientation.
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Accelerometer Types
The three most common are :-
Compression Type Inverted Compression Type
Shear Type
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Compression type accelerometer
Electric connector
Seismic Mass
Preload Stud
Acoustic Shield
Piezoelectric Material
ICP AmplifierMounting StudReceptacle
Base
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Compression Type Accelerometers
Advantages
Relatively low cost
Disadvantages
Sensitive to base strain
Sensitive to Thermal transients
Can cause over-saturation and
transducer settling problemsWidely used
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Inverted compression type
Piezoelectric MaterialICP Circuit
Mounting stud receptacle
Seismic Mass
Preload Sleeve
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Shear Type Accelerometer
Electric connector
Seismic Mass
Post
Acoustic ShieldPiezoelectric Material
ICP CircuitMounting StudReceptacle
Base
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Advantages - Shear Type
Lower sensitivity to base strain
Large dynamic range
Much less sensitive to temperaturetransients
Stabilizes quickly when takingmeasurements at low frequencies.
Disadvantage: -Generally higher cost due to added
components
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Mounting Methods
BEST GOOD POOR VERY GOOD
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Mounting Methods
Mounting
Maximum
Acceptable
Frequency (cpm)
Rating
Stud 975 000 Best
Adhesive 540 000 Very good
Magnet 450 000 Good
Quick Connect 360 000 Quite good
Hand-held 48 000 Poor
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Piezoelectric Velocity Pickup
Mass
Piezoelectric Disks
Base
Connector
INTEGRATOR
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Non-contact Eddy Current Probe(Relative)
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PICKUPCOIL
MAGNETIC
FIELD
SHAFT
GAP
METER
DC SIGNAL SENSOR
DISPLACEMENT
SIGNAL - TO
ANALYSER ORMONITOR
NON-CONTACT PICKUP
DETECTOROSCILLATOR AMPLIFIER
Non-contact Pickups
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Non-contact Eddy Current
Displacement Probes
USED FOR:-
Relative Shaft Vibration.
Radial & axial shaft position.
Differential expansion between case and rotor.
Especially effective on machinery with high mass
rigid casings and relatively low mass rotorssupported in journal type bearings.
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N.C.P.
Problems & precautions
Only Measures Displacement - SensitiveOnly to low frequency defects.
Subject to Mechanical and Electrical Run-out.
Units must be pre calibrated for specific shaftmaterials.
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Shaft Contact Displacement Probes
(Absolute)
Shaft Sticks
Hardwood, fish-tail, fixed toaccelerometer or velocity pickup
Measures vibration amplitude &
phase Shaft Riders
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SHAFT SURFACE
NON-METALLIC TIP
MACHINE HOUSING
SHAFT RIDER ASSEMBLY
PICKUP MOUNTING STUD
Shaft Rider
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Direct Contact : Absolute Measurements
Shaft Riders (permanently installed) Shaft Sticks or Fishtails
safety issue
VERY useful below coupling of vertical pumps