Shaker load question

[sorin84]

Hello, I am new in vibration domain and I am looking for some information.

I have to perform a random vibration test:
Hz (m/s^2)^2
10 10
100 10
300 0,51
500 5
2000 5
R.M.S. acceleration 96,59(m/s^2)^2
Sigma clipping 3
Necessary force to perform this test is: 66938 N (for 3sigma and my test setup load - it was calculated by the vibration control software).
Available shaker force: 90000N.
I start the test at -6 dB, after that at -3 dB and after at 0 dB. When the acceleration level is at 0 dB I hear some sounds from inside of power modules of shaker amplifier. The sounds is like when a switch is turned on and off, on and off - or a non engineering description- the sound is like when pop-corn is donne. I take a look inside of a power module and I didn’t see any switch.
Can somebody tell me:
- if this sounds are the effect of the acceleration clipping;
- if this sounds are the effect of the test setup load ;
- if a test require 75% or more (but less than 100%) of shaker availability for one of the following parameters: displacement, velocity, acceleration, force, for how many hours the shaker can work in this conditions?

 

[GregLocock]

My guess is your shaker amp has a whole bunch of error LEDs on it, do these light up? Incidentally you don't need to be coy about which shaker/ amp setup you are using.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[sorin84]

Each power module of the amplifier have a green (OK) and a red (not OK) LED. For the vibration test described above the green LED was ON permanent.

 

[GregLocock]

Give the manufacturer a ring. My gut feel is that you are just working it hard, but it is a reasonably expensive bit of gear so better safe than sorry.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[IRstuff]

It's only 1 g rms, which should be within the range of any reasonable shaker. How heavy is the UUT?

TTFN
faq731-376

 

[btrueblood]

Closer to 10 g rms.

 

[IRstuff]

But his units were (m/s^2)^2

TTFN
faq731-376

 

[btrueblood]

Errr...then 3.3 grms? Agree hard to figure out with the units as written.

 

[IRstuff]

Given his stated force requirement, it seems likely that someone glitched a decimal place. 22300N/10g = 227kg, which seems like a plausible number, but it's shouldn't be anywhere near 10g, unless they doing some sort of accelerated life test.

TTFN
faq731-376

 

[sorin84]

The test has to be perform on the slip table. Total weight of all test setup - including moving element of the shaker is aprox. 230 kg.

 

[IRstuff]

OK, someone needs to check the units, the numbers given are not consistent with each other nor with reality. The PSD given, if the units are correct, result in about 98 m/s^2 rms, not 98 (m/s^2)^2, or about 10g rms, which is consistent with the loading on the shaker

Again, 22300N/230kg = 9.9g rms, which is a very severe vibration level.


Is your UUT top-heavy?

TTFN
faq731-376

 

[sorin84]

I'm sorry! The unit for rms value is (m/s^2).
Slip table + copling element + thermal barrier + moving elemet + fixture + screws + UUT's = 230kg

 

[IRstuff]

But, is it top heavy? A standard slip table is prone to rocking if the UUT pushes the CG too high

Have you contacted the manufacturer?

TTFN
faq731-376