Shock & Vibration Testing - Overview

Shock and Vibration Testing Overview
- From Sensor Selection to Analysis -
Stephen Hanly
Midé Technology Corporation
1© 2016 Midé Technology – All Rights Reserved GENERAL

Agenda
Introduction
Shock and Vibration Testing: What, Why, Who, When and Where?
Hardware Selection
• Sensor Selection
• Data Acquisition (DAQ) Selection
Equipment Setup
Analysis
• Spectrum Analysis
• Vibration and Shock Response Spectrum
• Software Packages Available
Resources
Wrap Up, and Q&A
© 2016 Midé Technology – All Rights Reserved GENERAL 2

Shock and Vibration Testing:
What, Why, Who, When and Where?

Shock and Vibration Testing Introduction
Shock and vibration measurement is the art and science of
measuring and understanding a structure's response to a dynamic
event.
• Anything you see and touch can vibrate
• More automated world, powerful machinery
Key terms
• Frequency
• Amplitude
• Stiffness
• Damping

Shock and Vibration Testing Introduction
1. What frequency range do you care about?
2. What amplitude range is of interest?
3. Who needs the data and why?
4. Where is the test environment?
5. When is the test date?
6. When will the vibration analysis need to be completed by?
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2
3
4
5
6

Hardware Setup

Sensor Selection: Accelerometers
Piezoelectric
• Good all purpose
• AC coupled
Capacitive MEMS Accelerometer
• Cheap and easy to get
• Lower frequency and amplitude
Piezoresistive
• Premier for shock testing
• DC coupled
http://blog.mide.com

Alternatives to Accelerometers
Vibration meters
• Good for go, no-go testing of equipment
• RMS, resonant frequency and amplitude, not much time domain data
Vibration data loggers
• Cheap options (including smart phone) for low value testing
• Higher end options like Slam Stick bridge the gap to wired accelerometers
Non-contact displacement sensors
• Great for rotating equipment or small mass
• Measures relative displacement, not absolute
Microphones
• Sound is vibration in the form of pressure waves

DAQ Selection: Sensor Mating
Digital or analog output?
If analog,
• Voltage range?
• Do I need an amplifier?
How to power the sensor?
1
2
3

DAQ Selection: Sample Rate
Sample 10x greater than max frequency
• Under sampling can miss important data
Digital sensors will have fixed output data rates
General guidelines
• Shock: >10,000 Hz
• Typical vibration: >5,000 Hz
• Human motion: ~1,000 Hz

DAQ Selection: Resolution
Resolution specified as bits
• N = number of bits
• 2N = number of measurement bins
Good DAQ systems have >16-bit resolution
Be wary of <12-bit resolution

DAQ Selection: Anti-Aliasing
Need filtering to prevent aliasing
• Analog lowpass filter
• Removes high frequency content
• Once converted to digital, it can’t be filtered
out
Avoid systems without hardware low-pass filters

DAQ Selection: Types of Filters
Ideal filter:
• Uniformly passes all frequencies below limit,
and eliminate all above
• Perfectly linear phase response
• Ideal filters don’t exist…
Filter types:
• Butterworth
• Bessel
• Chebyshev
• Elliptic

Equipment Setup

Accelerometer Mounting 1

Accelerometer Mounting 2

Sensor Wiring
Ground Loop
Electromagnetic Noise
Mechanical Noise
Risk of Losing Connection
1
2
3
4
Best practice: keep them short

Environmental Concerns
Piezoelectrics are temperature dependent
• Need compensation
Influences
• Base strains
• Acoustic Noise
• Transverse Vibration
• Magnetic Fields
• Humidity
• Corrosive
Exposure of DAQ Electronics
• Survive shock/vibration?
• Other environmental concerns

Shock and Vibration Analysis

Simple Analysis in the Time Domain

Spectrum Analysis and FFT Basics
Time doesn’t tell the full story of vibration
Compute frequency spectrum with Fourier
Transform
• Discrete Fourier Transform (DFT)
• Fast Fourier Transform (FFT)
FFT depends on number of samples

Spectrogram

Power Spectral Density

Transmissibility - SDOF

Vibration Response Spectrum
Use VRS as design criteria
• Military standards (or customer) provide
PSD of environment
 You may need to get this data yourself
• Calculate vibration response spectrum
• Avoid natural frequency range with high
acceleration levels
Use VRS to check test standard
• If no PSD exists, use test data to build
one
https://vibrationdata.wordpress.com/

Shock Response Spectrum
Use SRS as design criteria
• Use known input levels to determine
Avoid worst case fn to survive base input
• Must decide to go stiff or damper
• Lower fn (damper) needs relative
displacement

Shock and Vibration Analysis Software
Write your own analysis code
• MATLAB vs Python
 MATLAB is $2,150 for commercial license
 Python is open source
• Block Diagram Environment – Best for data streaming
 MathWorks Simulink ($3,250)
 National Instruments LabVIEW ($2,999 for one year)
o Sound and Vibration Toolkit ($1,999)
Standalone GUI Software
• Tom Irvine’s vibrationdata (MATLAB and Python packages)
• Slam Stick Lab – currently only works with Slam Stick recorders
• Software available to buy
 m+p Analyzer, VibrationVIEW, Brüel & Kjaer, ProAnalyst (from video)

Wrap Up

Summary
Shock and vibration measurement is an art and a science
What, Why, Who, When and Where?
• Types of accelerometers
• Alternatives to wired accelerometers
• DAQ selection
• Analysis
Analysis is the best; but most critical part
• Explore the software options available
Utilize online resources to learn!

Resources
https://vibrationdata.wordpress.com/
http://blog.mide.com/
MEGGITT (Endevco) Technical Papers
PCB Piezotronics Technical Papers
Books
• Mechanical Vibration and Shock Measurements by Brüel and Kjaer
• Vibration Testing – Theory and Practice by Kenneth McConnell
• Shock and Vibration Handbook by Cyril Harris
Download eBook:
mide.com/vibration-ebook

Thank You
Questions?

Shock & Vibration Testing - Overview

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