Sine sweep vs. random vibration test

[izax1]

We are discussing with a customer the usefulness of a Sine sweep test as an addition to a Random Vibration test. The customer is intending to set an acceptance criteria of some value for unwanted amplification on the resonances. I can see the usefulnes of a sine sweep test as a check for a pre- and post-random vibration test, but I would think that any execcesive amplifications would lead to failure in the random vibration test. Is it really unwanted amplifications if the random vibration test passes without failures???

What do you think??

 

[tomirvine]

The answer depends on several factors.

What is the purpose of the test?
Three possiblities are:
1. Simulated expected field environment
2. Expose latent workmanship defects, part flaws, bad solder joints, etc.
3. Verify design integrity
4. Identify natural frequencies and damping ratios.

What is the expected field environment for the test item? Is this environment best represtented by sine or random vibration?

Note that random vibration has proven to be a more effective screen of workmanship than sine vibration. This is documented in NAVMAT P-9492.

Tom Irvine

http://www.vibrationdata.com

 

[izax1]

The random vibration test is supposed to simulate the expected environment. The sine sweep test is only a 1G sweep through 0-500 Hz. As I explained, this 1g sine sweep will be done before and after the random vibration test. So natural frequencies and damping ratios will be recorded. But will a requirement for a max. amplification for the sine sweep do me any good if the random vibration test pass without malfunctions or failures?

 

[tomirvine]

I do not see a compelling reason for an amplification criteria, as long as the unit functions before, during, and after the random vibration test.

Measurement of the amplification factor should be for reference only.

Tom Irvine

http://www.vibrationdata.com

 

[IRstuff]

The primary reason for running sine sweep is to find resonances. It may well be that the environment that the equipment is going into is characterized by a particular frequency vibration as opposed to a random vibration.

Some of the systems that we buy are required to have no resonance greater than 10% of total mass to ensure that our stabilization system does not freak out.

TTFN