Vibe Input, Random or Sine?

[TomFin]

The following vibration spec came across my desk almost on a cocktail napkin.

Vibration/ Shock Spec:
Frequency Range: 10Hz to 40Hz; amplitude = 0.1” p-p
40Hz to 2000Hz; acceleration = 4g RMS
Frequency Period: 30 minutes; 10Hz to 2000Hz and return
Test Time: 3 hours per axis


My job is to work with a test house to carryout this test. I’m assuming this is not a Random Vibe Test as the Amplitude is not specified in g^2/Hz, am I correct?

Thank you in advance for any advice.
-Tom


Failure is a prerequisite of successful design

 

[IRstuff]

4g RMS sounds like random to me.

TTFN

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[GregLocock]

"30 minutes; 10Hz to 2000Hz and return"

sounds like poorly defined swept sine to me.

better go and ask them what they really want!

Cheers

Greg Locock


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[Twoballcane]

If it is random vib, be safe and just ask for the break point table.

Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”

 

[TomFin]

This is a situation where the customer did not require a spec, but the sales engineer wanted some piece of mind that the product would endure application environment. This aforementioned vibe spec is a spec that he used a while back to test another product for a seperate,but similar type of customer (heavy outdoor vehicle equipment e.g cranes).

With the minimal experience/knowledge I have of vibration testing I would agree with GregLocock and figured that it was a Sine Sweep from this part of the spec:
"Frequency Period: 30 minutes; 10Hz to 2000Hz and return", Random vibe excites all frequencies at once, right?

"40Hz to 2000Hz; acceleration = 4g RMS"
Are the amplitudes of Sine Sweeps typically given in g RMS?



Failure is a prerequisite of successful design

 

[GregLocock]

They certainly can be. My accelerometer calibrator has a label on it proclaiming 1g RMS at 80 Hz.

Cheers

Greg Locock


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[MikeyP]

We see a lot of questions like this here and I just don't get it. If the spec is ambiguous then do a sanity check yourself (just to make sure you aren't being stupid), ask a colleague to do the same (or ask here if there is no-one else); then go back to the specifier and get clarification.

Simples

M.

--
Dr Michael F Platten