week 13 vibration measurements
TRANSCRIPT
![Page 1: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/1.jpg)
Week 13
1
Vibration Measurement
![Page 2: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/2.jpg)
Week 13
2
Vibration Measurement Schemex, v, a, F
electrical signal
amplified signal
signal data
The type of vibration measuring instrument used will depend on:
- The expected range of frequencies and amplitudes
- The size of machine / structure involved
- Conditions of operation of the machine / structure
- Type of data processing used
![Page 3: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/3.jpg)
Week 13
3
Dynamic Testing of Machine/Structure
� Dynamic testing is a valuable complement to dynamic analysis
� Modal testing:
� Natural frequencies
� Damping
� Mode shapes
� Operational testing:
� In-service loads
� Various cases
� Often random
![Page 4: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/4.jpg)
Week 13
4
Dynamic Testing of Machine/Structure
Measurement Hardware
![Page 5: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/5.jpg)
Week 13
5
Transducer
� A transducer translates changes in mechanical quantities (such as displacement, velocity, acceleration or force) into electrical signals (such as voltage or current).
� The size of the transducer is importatn
� Especially when measuring small structures
� Ideally should not influence the structure’s dynamics through added mass or stiffness
� Analytical models often include effects of transducer mass
![Page 6: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/6.jpg)
Week 13
6
Variable Resistance Transducer
Mechanical motion produces a change in electrical resistance of the strain gage, which in turn causes a change in the output voltage or current.
R ∞ ε ∞ x(t)
![Page 7: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/7.jpg)
Week 13
7
Variable Resistance Transducer
R ∞ ε ∞ x(t) Wheatstone bridge, sensitive to small changes in R
![Page 8: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/8.jpg)
Week 13
8
Piezoelectric Transducer
E
Piezoelectric material, such as quartz and Rochelle salt, generate electrical charge when given deformation or mechanical stress.
crystal
Piezoelectric accelerometer
![Page 9: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/9.jpg)
Week 13
9
Electrodynamic Transducer
The movement of the coil in a magnetic field produces a voltage Vout.
Voltage ~ Velocity
Current ~ Force
![Page 10: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/10.jpg)
Week 13
10
LVDT
Linear Variable Differential Transformers:
- coils and magnetic core
- output voltage depends on the axial displacement of the core
- Displacement transducer
- Insensitivity to temperature
- Mass of core restricts application
- Best for low frequency, high displacement application
![Page 11: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/11.jpg)
Week 13
11
Vibration Pick-ups
� Instruments that measure vibrations, e.g. vibrometer, accelerometer.
Most commonly used pick-ups are known as seismic instruments
- a mass-spring-damper system in a cage � inertial sensor
- a certain type of transducer is integrated in the instrument.
- fastened onto the vibrating body
![Page 12: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/12.jpg)
Week 13
12
Vibration Pick-ups
![Page 13: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/13.jpg)
Week 13
13
Vibrometer
- Measures the displacement of a vibrating body
- Works in the right (blue) range where r >= 3 � Z/Y = 1
if
Recorded z(t) lags from measured y(t)
![Page 14: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/14.jpg)
Week 13
14
Accelerometer
Measures the acceleration of a vibrating body, from which the velocity and displacement are obtained by integration.
recorded z(t)ωn2 lags from the
acceleration of the base ytt(t)
![Page 15: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/15.jpg)
Week 13
15
Accelerometer
Works in this range
![Page 16: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/16.jpg)
Week 13
16
Vibration Exciter
Application:
- in the determination of the dynamic characteristics of machines and structures;
- In fatigue testing of material.
Types: mechanical, electromagnetic/electrodynamic, hydraulic.
Also known as ‘shakers’.
![Page 17: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/17.jpg)
Week 13
17
Mechanical Exciter
![Page 18: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/18.jpg)
Week 13
18
Mechanical Exciter
![Page 19: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/19.jpg)
Week 13
19
Electrodynamic Shaker
Also known as electromagnetic exciter.
A reverse of the electrodynamic transducer.
Apply a force through a range of frequencies (harmonic or random input)
![Page 20: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/20.jpg)
Week 13
20
Electrodynamic Shaker
- Current (A) passes through coil
- Generates force F (N) ~ I (A)
- Generates magnetic flux intensity B (Tesla)
F = BIl
l : length of coil
This accelerates the component on the shaker table.
AC: F harmonic
DC: F constant
![Page 21: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/21.jpg)
Week 13
21
Signal Conditioning
![Page 22: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/22.jpg)
Week 13
22
Signal Analyzer
![Page 23: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/23.jpg)
Week 13
23
Signal Analyzer
![Page 24: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/24.jpg)
Week 13
24
Impulse Testing
![Page 25: Week 13 vibration measurements](https://reader034.vdocuments.net/reader034/viewer/2022052618/554a5c8fb4c905572f8b505b/html5/thumbnails/25.jpg)
Week 13
25
Relationship between components and vibration spectrum