Vibration Testing Fixtures - The vibration testing blindspot

Vibration Testing Fixtures The Vibration Testing Blindspot Tony Araujo – Paragon Systems Testing August 2, 2021

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Agenda Why do we perform vibration testing?

What do we need to perform a vibration test?

ISO 17025 definition of “Equipment” Can a vibration fixture affect a vibration test result?

• The vibration fixture blind spot • Conclusions • Questions/Comments • • • •

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Agenda Why do we perform vibration testing?

What do we need to perform a vibration test?

ISO 17025 definition of “Equipment” Can a vibration fixture affect a vibration test result?

• The vibration fixture blind spot • Conclusions • Questions/Comments • • • •

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Why Do We Perform Vibration Testing?

“The vibration test is designed to simulate the vibration damage that the DUT will experience during its life time.”* *Hunter, N.F., “Vibration Testing – Reviewing the State of The Art-Prospects and Challenges”, Proceedings of the SD 2000 Conference LA-UR-993413 06/23/99

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Why Do We Perform Vibration Testing?  Engineering development  Component selection  Design verification  Failure modes  Reliability qualification  Warranty  Recalls  Liability

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ISO 17025 Definition of “Equipment”

0.1 PSD (g²/Hz)

What “specified requirements” or “measurement accuracy” are we trying to achieve?  Typically +/- 3dB allowing for the instrument error*

1

0.01

0.001

0.0001

*IEC 60068-2-64 Part 2, Environmental Testing, Test Fh: Vibration, broad-band random (digital control) and guidance, Section 4.3.4 Vibration Tolerance

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100 Frequency (Hz)

1000

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What’s Required to Perform a Vibration Test?

• Test method • What is the test environment?

• Tolerances?

• The device which requires a vibration test (DUT)

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ISO 17025 Definition of “Equipment”  6.4.1 The laboratory shall have access to equipment (including, but not limited to, measuring instruments, software, measurement standards, reference materials, that is required for the correct performance of laboratory activities and that can influence the results.

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Can a vibration fixture affect a vibration test?  Absolutely!  All vibration energy enters the DUT through the vibration fixture.  Depending on the fixture resonant performance or the vibration control method used, the DUT can be tested well outside of the control profile tolerance.  The DUT “shall be mechanically connected to the mounting surface either directly or by means of a rigid test fixture… or as stated in the relevant specification.”* *IEC 60068-2-47 Tests – Mounting of specimens for Vibration, Impact and Similar Dynamic Tests, Section 6 Mounting, where the specimen is equipment and other articles.

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment DUT 4U Rackmount chassis (19” rack) Test Profile ISO 16750-3 Test IV – Passenger Car, Sprung Masses (Vehicle Body) reduced to -6 dB (10 Hz to 1,000 Hz) to 1.5grms; Z-axis only tested for brevity Vibration Monitoring Locations External - Vibration table surface, DUT Mounting Flange, Internal - HDD and Power Supply

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment DUT Mounting Methods 1. Simple sandwich clamp to vibration table surface (Condition 1) 2. Qualified vibration fixture simulating actual DUT installation method Condition 2A & 2B)

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ISO 17025 Definition of “Equipment” Frequently confirmation of the +/- 3dB tolerance is interpreted as having being achieved if the vibration test level is within this tolerance on the shaker test surface

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Can a vibration fixture affect a vibration test?

Vibration fixture resonant performance

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Acceleration (g)

• Control on vibration table surface; fixture monitored adjacent to flange mount.

• 0.5g sine sweep • Two resonances evident, one at 444 Hz and a second at 489 Hz. • Presence of a third resonance just beyond 1,000 Hz

6.0 5.0

Control (g)

4.0

Fixture (g)

3.0 2.0 1.0 0.0 10

100

1000

Frequency (Hz)

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Can a vibration fixture affect a vibration test?

Test Condition 1 • DUT ‘sandwich” clamped to vibration table surface • Does not reflect design intent mounting • Control on vibration table surface

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Flange

Control

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment DUT 4U Rackmount chassis (19” rack) Test Profile ISO 16750-3 Test IV – Passenger Car, Sprung Masses (Vehicle Body) reduced to -6 dB (10 Hz to 1,000 Hz) to 1.5grms; Z-axis only tested for brevity Vibration Monitoring Locations External - Vibration table surface, DUT Mounting Flange, Internal - HDD and Power Supply

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment DUT Mounting Methods 1. Simple sandwich clamp to vibration table surface (Condition 1) 2. Qualified vibration fixture simulating actual DUT installation method Condition 2A & 2B)

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment DUT Mounting Methods 1. Simple sandwich clamp to vibration table surface (Condition 1) 2. Qualified vibration fixture simulating actual DUT installation method Condition 2A & 2B)

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment Control Strategies 1. Accelerometer mounted to vibration table surface (Condition 1 & 2A) 2. Multi-point averaging with accelerometers mounted to vibration table surface + mounting flange of DUT (Condition 2B) Navigating the waters of accreditation

Vibration Table Surface

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Can a vibration fixture affect a vibration test?

Vibration fixture experiment Control Strategies 1. Accelerometer mounted to vibration table surface (Condition 1 & 2A) 2. Multi-point averaging with accelerometers mounted to vibration table surface + mounting flange of DUT (Condition 2B) Navigating the waters of accreditation

DUT Mounting Flange

Vibration Table Surface

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Can a vibration fixture affect a vibration test?

Experiment Setup (Fixtured)

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Can a vibration fixture affect a vibration test?

External results (Mounting Flange and Vibration Table surface) appear even closer together Regardless of mounting method the overall grms (area under the PSD curve) for the Control location is the same as the Mounting Flange location??

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Location (Overall grms) Test Condition

Control

Mounting Flange

1

1.5

1.5

2A

1.5

1.5

2B

1.5

1.5

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Can a vibration fixture affect a vibration test?

Test level at the Mounting Flange

10

Even though all three mounting methods have the same overall grms level (area under the PSD curve), noticeable out-of-tolerance conditions are evident for Condition 1 and 2A

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PSD (g²/Hz)

1

Condition 1 Condition 2A Condition 2B

0.1 0.01 0.001 0.0001 0.00001 10

100 Frequency (Hz)

1000

31

Can a vibration fixture affect a vibration test?

Test Condition 1 Results

10 HDD Power Supply

1

PSD (g²/Hz)

Tolerance bands at +/- 3dB

0.1 0.01 0.001 0.0001 0.00001 10

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100 Frequency (Hz)

1000

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Can a vibration fixture affect a vibration test?

Test Condition 2A • DUT attached to vibration fixture using chassis flanges • Design intent mounting • Control on vibration table surface

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Flange Control

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Can a vibration fixture affect a vibration test?

Test Condition 2A Results

10 HDD Power Supply

Tolerance bands at +/- 3dB

PSD (g²/Hz)

1 0.1 0.01 0.001 0.0001 0.00001 10

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100 Frequency (Hz)

1000

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Can a vibration fixture affect a vibration test?

What’s happening inside of the DUT? Test Condition

PSD In Tolerance?

HDD (Peak g2/Hz at 20 Hz)

%*

1

NO

7.1

97.2

2A

NO

3.4

5.5

2B

YES

3.6

N/A

*% over or under the peak g2/Hz value at 20 Hz for Test Condition 2B

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The Vibration Fixture Blind Spot  Equipment that can “influence results” is commonly understood to mean  Controller accuracy  Accelerometer accuracy  The vibration fixture can also significantly influence test results

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10 0.1 0.001 0.00001 10

100 1000 Frequency (Hz)

Condition 1

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10 0.1 0.001 0.00001 10

100 Frequency (Hz)

1000

Condition 2A PSD (g²/Hz)

PSD (g²/Hz)

Internal results on the HDD and Power Supply appear similar, but are they?

PSD (g²/Hz)

Can a vibration fixture affect a vibration test?

10 0.1 0.001 0.00001 10

100 Frequency (Hz)

1000

Condition 2B

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Can a vibration fixture affect a vibration test?

External results (Mounting Flange and Vibration Table surface) appear even closer together Regardless of mounting method the overall grms (area under the PSD curve) for the Control location is the same as the Mounting Flange location??

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Location (Overall grms) Test Condition

Control

Mounting Flange

1

1.5

1.5

2A

1.5

1.5

2B

1.5

1.5

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Can a vibration fixture affect a vibration test?

Test level at the Mounting Flange

10

Even though all three mounting methods have the same overall grms level (area under the PSD curve), noticeable out-of-tolerance conditions are evident for Condition 1 and 2A

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PSD (g²/Hz)

1

Condition 1 Condition 2A Condition 2B

0.1 0.01 0.001 0.0001 0.00001 10

100 Frequency (Hz)

1000

31

Can a vibration fixture affect a vibration test?

Test level at the Mounting Flange

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PSD (g²/Hz)

Condition 1 – Sandwich Clamp w/Table Control - Out of tolerance Condition 2A – Fixture mount w/Table Control - Out of tolerance Condition 2B - Fixture mount w/Multi-point avg.

Control - In tolerance

0.01

0.001

0.0001

Condition 1 Condition 2A Condition 2B

0.00001 100

1000 Frequency (Hz)

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Can a vibration fixture affect a vibration test?

What’s happening inside of the DUT? Location Test Condition

PSD In Tolerance?

HDD

Power Supply

Overall grms

%*

Overall grms

%*

1

NO

5.5

-5.2

2.6

-21.2

2A

NO

4.5

-22.4

4.4

+33.3

2B

YES

5.8

N/A

3.3

N/A

*% over or under the grms value for Test Condition 2B

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Can a vibration fixture affect a vibration test?

What’s happening inside of the DUT? Test Condition

PSD In Tolerance?

HDD (Peak g2/Hz at 20 Hz)

%*

1

NO

7.1

97.2

2A

NO

3.4

5.5

2B

YES

3.6

N/A

*% over or under the peak g2/Hz value at 20 Hz for Test Condition 2B

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The Vibration Fixture Blind Spot  Equipment that can “influence results” is commonly understood to mean  Controller accuracy  Accelerometer accuracy  The vibration fixture can also significantly influence test results

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The Vibration Fixture Blind Spot  Equipment must conform to specified requirements and be capable of achieving measurement accuracy to provide a valid result  Typically +/- 3dB allowing for the instrument error  The vibration fixture can significantly influence test results

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The Vibration Fixture Blind Spot IEC 60068-2-47 Tests – Mounting of specimens for vibration, impact and similar dynamic tests  The purpose of a vibration fixture is: “… to transmit faithfully the mechanical stimulation from the test apparatus to the specimen, and to ensure that the specification requirements can be met at the fixing points of the specimen”

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The Vibration Fixture Blind Spot Consider how we normally perform a high temperature exposure test on electronic components Tolerance: 120C +/-2C

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The Vibration Fixture Blind Spot  Can we achieve + at the fixing points?/- 3dB And…  Is the vibration energy entering the DUT in the manner the DUT was intended to receive it?

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The Vibration Fixture Blind Spot Then consider…

Tolerance: 120C +/-2C Will this approach influence results?

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Conclusions  The laboratory should consider the method of attachment of the DUT to the shaker when planning a vibration test  The DUT attachment method should be representative of the manner the DUT is designed to receive vibration unless the specification specifies otherwise  The dynamic performance of the attachment method can influence the control strategy employed

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Conclusions  Vibration fixtures correspond with the ISO 17025 definition of equipment, accordingly…

The laboratory must treat the attachment method of the DUT in the same manner as all other equipment

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Questions?

Tony Araujo Vice President – Business Development Paragon Systems Testing tonya@paragonsystems.ca

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Contact Us

Thank You!

Contact Us A2LA 5202 Presidents Court, Suite 220 Frederick, MD 21703 301 644 3248 Main 301 662 2974 Fax info@A2LA.org www.A2LA.org

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