Random vibration test -IEC standard 2

[elogesh]

In our company, we need to carry out Random vibration test according to IEC standard for few of our assemblies. The specification is acceleration spectral density = 0.05 g2 /Hz , Frequency range 10-500 Hz

Earlier, we used to carryout constant vibration level frequency sweep. (Acceleration level =10 ‘g’ and frequency range 10-500 Hz).

For this random vibration test in the vibration shaker, we are planning to acquire additional software.

To better understand the random vibration test, I have following questions,

1) How to calculate the acceleration level (g) with frequency?

I tried to do like this
Acceleration spectral density = 0.05 g2 /Hz. Frequency range 10-500 Hz
Mean square acceleration spectral density = 24.5 g2 (0.05*490)

Then RMS acceleration level = 4.97 g =5g (approx) for frequency range between
10-500 Hz.

Later, I have understood that individual bandwidth is not accounted in the calculation. If octave bandwidth is accounted then, whether the RMS acceleration level increases with frequency.


2) In random vibration test both amplitude and frequency has to vary.

Does this mean that for any given frequency the amplitude will vary?

Regards,
Logesh.E

 

[CESSNA1]

ELOGESH:
1. Usiing the G^2rms/hz which is the Power Spectral Density (PSD) the G-level can be obtained for each frequency by reading the G^2rms/hz level at a particular frequency and taking the square root of it. For example assume at 100 Hz the PSD level is .05 G^2rms/Hz. The square root of this is .223. This means that, in this case, at 100 Hz the level is .223 Grms. To find the overall G level of the spectrum you must integrate the spectrum. This is not as easy as it seems since the spectrum is a log-log plot there are special equations for the integration. If you reply with a E-mail I will send them to you.

2. The amplitude and frequency will vary with your profile. Where the profile is flat the frequency will vary and the amplitude will be constant. Where the amplitude slopes up or down the amplitude will vary with frequency.

I suggest you take some short courses to fully understand this. Try "

http://www.ttiedu.com"

for their course list. TTI is probably the best kept secret in engineering. They offer high quality short courses from seasoned instructors.

Regards
Dave

 

[Heckler]

If you're still looking for a step by step on the integration of the PSD function. I have a document that I found on the web. I tried to find it but they must have removed it. Let me know I will be more than happy to help out.

http://www.vibrationdata.com/

 

[elogesh]

Hai,

Thanks to Dave and Heckler......

We bought the random vibration software for carrying out random vibration test in Ling dynamic system shaker with Dactron controller.....

From local testing support personnel,We understood that the software automatically indicates input overall 'Grms' level(on shaker table) and output overall 'Grms' level(on component).

About the short courses,I forwarded to our vibration testing person, who works full time in NVH....

Regards,
Loganathan.E

 

[tomirvine]

The PSD tutorials are given at:

http://www.vibrationdata.com/random.htm

Username: vibration
Password: quake

Please contact me if you would like onsite training and test support.

Thank you,
Tom Irvine

http://www.vibrationdata.com

 

[Tunalover]

Ah yes, the preeminent Tom Irvine. Always there to lend a hand and to educate! The world needs more of you.



Tunalover