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What’s up with Bump Testing ?
By: Jack D. PetersConnection Technology Center, Inc
590 Fishers Station DriveVictor, New York 14564
(585) 924-5900 x834
www.ctconline.com
Jack D. Peters
Bump Testing
2
What is a bump test ?
A bump test is the measured response of an impact to an object.The force of the impact is not controlled or measured.The response of the object is not controlled, BUT IS MEASURED.A single channel response measurement.
Jack D. Peters
Bump Testing
3
Why do a bump test ?
To excite and measure the natural frequency(s) of an object.
To identify a resonanceTo understand a change in massTo understand a change in stiffnessTo understand a change in damping
Jack D. Peters
Bump Testing
4
How does it work ?
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1
8V
-8
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
5
Sine Waves ?
EmptyEmptyEmptyEmptyEmptyEmptyEmptyEmptyEmpty
0.1V
-0.1
Real
s1.999023 0 s
Fundamental 1
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Bump Testing
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Bumps from Sine Waves ?
0.1V
-0.1
Real
s1.999023 0 s
Time Record 1
8V
-8
Real
s1.999023 0 s
Time Record 1
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Bump Testing
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100th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1
8V
-8
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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50th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1Bump 1
4V
-4
Real
s1.999023 0 s
Fundamental 1
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Bump Testing
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20th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 1
EmptyEmpty
2V
-2
Real
s1.999023 0 s
Bump 1
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Bump Testing
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10th Harmonic
5th Harmonic 110th Harmonic 1
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1
EmptyEmptyEmpty
1V
-1
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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5th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 1
EmptyEmptyEmptyEmpty
0.5V
-0.5
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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4th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1
EmptyEmptyEmptyEmptyEmpty
0.4V
-0.4
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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3rd Harmonic
Fundametal 12nd Harmonic 13rd harmonic 1
EmptyEmptyEmptyEmptyEmptyEmpty
0.3V
-0.3
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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2nd Harmonic
Fundamental 12nd Harmonic 1
EmptyEmptyEmptyEmptyEmptyEmptyEmpty
0.2V
-0.2
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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Fundamental
EmptyEmptyEmptyEmptyEmptyEmptyEmptyEmptyEmpty
0.1V
-0.1
Real
s1.999023 0 s
Fundamental 1
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Bump Testing
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2nd Harmonic
Fundamental 12nd Harmonic 1
EmptyEmptyEmptyEmptyEmptyEmptyEmpty
0.2V
-0.2
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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3rd Harmonic
Fundametal 12nd Harmonic 13rd harmonic 1
EmptyEmptyEmptyEmptyEmptyEmpty
0.3V
-0.3
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
18
4th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1
EmptyEmptyEmptyEmptyEmpty
0.4V
-0.4
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
19
5th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 1
EmptyEmptyEmptyEmpty
0.5V
-0.5
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
20
10th Harmonic
5th Harmonic 110th Harmonic 1
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1
EmptyEmptyEmpty
1V
-1
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
21
20th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 1
EmptyEmpty
2V
-2
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
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50th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1Bump 1
4V
-4
Real
s1.999023 0 s
Fundamental 1
Jack D. Peters
Bump Testing
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100th Harmonic
Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1
8V
-8
Real
s1.999023 0 s
Bump 1
Jack D. Peters
Bump Testing
24
How does it work ?
Bump testing or impact testing works because the bump or impact contains all of the individual frequencies or sign waves.When you bump or impact the object under test, you will excite all of the natural frequencies of that object.
Jack D. Peters
Bump Testing
25
What do you impact with ?
Pin Drops !High frequency contentLow energy value
Cow Plops !Low frequency contentHigh energy value
Jack D. Peters
Bump Testing
26
Energy Value vs. Frequency
The item used to deliver the impact to the object under test will determine the energy that is delivered to the object.
Large objects with considerable mass should be impacted with rubber or wood. This will generate high energy low frequency responses. (cow plops)Small objects with considerable stiffness should be impacted with metal or hard plastics. This will generate low energy high frequency responses. (pin drops)
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Bump Testing
27
Set-up
UNIFORM WINDOWTake your time – Bump aroundDo not over range or clip the input signal800 – 1600 lines of resolutionTry some different frequency spansOnly 1 bump for each time recordAbout 4 averages (depends on noise)
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Bump Testing
28
Why the Uniform Window ?
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Bump Testing
29
What to Bump ?
1” diameter steel round stock
36” length
Clamped in “V” blocks at each end
CTC AC140 accelerometer stud mounted on center (100 mV/g)
Jack D. Peters
Bump Testing
30
Bump It ! Two Responses !
2G
-2
Real
s1 0 s
Time Record 1 TIME4.63
0.015G
rms
0
Real
Hz100 0 Hz
Auto Pwr Spec 1 HZ4.63
dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G
X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG
Time Waveform
Frequency Spectrum
Jack D. Peters
Bump Testing
31
Mental Health Check !
2G
-2
Real
s1 0 s
Time Record 1 TIME4.63
0.015G
rms
0
Real
Hz100 0 Hz
Auto Pwr Spec 1 HZ4.63
dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G
X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG
Time Waveform
Frequency Spectrum
76.17 msec/5 = 15.23 msec
F = 1/0.01523 sec = 65.64 Hz
65.5 Hz
Jack D. Peters
Case History
32
CASE HISTORY
Bumps in the Road !
Jack D. Peters
Case History
33
So Easy !!!!!!
0.6G
rms
0
Real
Hz200 0 Hz
Auto Pwr Spec 1 HZ3.63
4.5G
-4.5
Real
s3.998047 0 s
Time Record 1 TIME3.63
X:109 Hz Y:539.6552 mG
Time Waveform
Frequency Spectrum
109 Hz
Jack D. Peters
Case History
34
Zoom
0.3G
rms
0
Real
Hz150 50.00001 Hz
Auto Pwr Spec 1 HZ1.63
2G
-2
Real
s8 0 s
Time Record 1 TIME1.63
X:109.125 Hz Y:214.7374 mG
dX:554.6875 ms dY:-729.2974 mGX:164.0625 ms Y:1.379613 G
Time Waveform
Frequency Spectrum
109.125 Hz
Jack D. Peters
Case History
35
Zoom & Mental Health Check
0.3G
rms
0
Real
Hz150 50.00001 Hz
Auto Pwr Spec 1 HZ1.63
2G
-2
Real
s8 0 s
Time Record 1 TIME1.63
X:109.125 Hz Y:214.7374 mG
dX:554.6875 ms dY:-729.2974 mGX:164.0625 ms Y:1.379613 G
Time Waveform
Frequency Spectrum
109.125 Hz
554 msec/5 = 110.8 msec
F = 1/0.1108 sec = 9.02 Hz What
the
He_ _ !
Jack D. Peters
Case History
36
So Easy ??????
0.6G
rms
0
Real
Hz200 0 Hz
Auto Pwr Spec 1 HZ3.63
4.5G
-4.5
Real
s3.998047 0 s
Time Record 1 TIME3.63
X:109 Hz Y:539.6552 mG
Time Waveform
Frequency Spectrum
109 Hz
Jack D. Peters
Case History
37
What’s This ?
0.6G
rms
0
Real
Hz200 0 Hz
Auto Pwr Spec 1 HZ3.63
4.5G
-4.5
Real
s3.998047 0 s
Time Record 1 TIME3.63
X:109 Hz Y:539.6552 mG
Time Waveform
Frequency Spectrum
109 Hz????
Jack D. Peters
Case History
38
Log – Can’t Live With It, Can’t Live Without It !
4.5G
-4.5
Real
s3.998047 0 s
Time Record 1 TIME3.63
1G
rms
1E-05
Mag (Log)
Hz200 0 Hz
Auto Pwr Spec 1 HZ3.63X:109 Hz Y:539.6552 mGX:11 Hz Y:12.05162 mG
Time Waveform
Frequency Spectrum
Log "Y" Scale
109 Hz11 Hz
Jack D. Peters
Case History
39
0 – 50 Hz Span
0.008G
rms
0
Magnitude
Hz50 0 Hz
Auto Pwr Spec 1 HZ2.63
0.4G
-0.4
Real
s15.99219 0 s
Time Record 1 TIME2.63
X:10.8125 Hz Y:2.774957 mG
Time Waveform
Frequency Spectrum
10.81 Hz
Jack D. Peters
Case History
40
0 - 50 Hz (expanded “x” scale)
0.008G
rms
0
Magnitude
Hz50 0 Hz
Auto Pwr Spec 1 HZ2.63
0.4G
-0.4
Real
s4 0 s
Time Record 1 TIME2.63
X:10.8125 Hz Y:2.774957 mG
dX:460.9375 ms dY:-131.8069 mGX:148.4375 ms Y:152.3216 mG Time Waveform
Frequency Spectrum
10.81 Hz
460.9 msec/5 = 92.18 msec
F = 1/0.09218 sec = 10.84 Hz
Jack D. Peters
Bump Testing
41
Back to Bump Testing
2G
-2
Real
s1 0 s
Time Record 1 TIME4.63
0.015G
rms
0
Real
Hz100 0 Hz
Auto Pwr Spec 1 HZ4.63
dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G
X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG
Time Waveform
Frequency Spectrum
76.17 msec/5 = 15.23 msec
F = 1/0.01523 sec = 65.64 Hz
65.5 Hz
Jack D. Peters
Amplification Factor
42
Using the Time Waveform
Log decrement = [1/n[LN(A0/An)]] = [1/5[LN(1.633/0.268)]] = 0.36
Damping ratio = Log dec/2Pi = 0.36/2Pi = 0.36/6.28 = 0.057
Amplification factor = 1/(2*Damping) = 1/(2*0.057) = 8.68
2G
-2
Real
s1 0 s
Time Record 1 TIME4.63X:99.60938 ms Y:268.2297 mGX:23.4375 ms Y:1.63297 G Time Waveform
A0 = 1.633 GAn = 0.268 G
n = 5 cyclesLN = natural log
F = 1/0.01523 sec = 65.64 Hz
Jack D. Peters
Amplification Factor
43
Using the Spectrum
0.015G
rms
0
Real
Hz100 0 Hz
Auto Pwr Spec 1 HZ4.63X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG Frequency Spectrum
F = 65.5 Hzf2 = 70.75 Hzf1 = 58.75 Hz
-3dB
Find the –3dB points = AF * .707 = 12.24 mG * .707 = 8.65 mG
Find the frequencies at the –3dB points (f1 and f2)
Amplification factor = F/ (f2 - f1) = 65.5/(70.75 – 58.75) = 5.46
Jack D. Peters
Mass & Stiffness
44
Fn = 1/2Pi k/m
INCREASE the stiffness ( k )
INCREASE the frequency (F)
INCREASE the mass ( m )
DECREASE the frequency ( F )
Jack D. Peters
Damping
45
Control the Response
Un-Damped
Damped
Jack D. Peters
Bump Testing
46
Summary
Take your timeChoose your weaponBump aroundUniform WindowLook at the time waveformLook at the frequency spectrum
Do a mental health checkCalculate the amplification factorChange the massChange the stiffnessAdd dampingBump around
Jack D. Peters
Thank You !
47
Thank You !
You can find technical papers onthis and other subjects atwww.ctconline.com
in the “TechnicalResources” section
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