Why do all vibration /sine sweep testing are done at the range of 20 - 2000Hz?

Question

I wanna do a physical product testing. And this Lab give me aprofile for a vibration and sine sweep test. The frequency range is at 20 - 2000Hz. My question is, why at that frequency range why not at other range. What the difference between random vibration and sine sweep?

Answer 1

The 20-2000 Hz test band is a long established norm for random vibration that was mostly based on shaker capability. The foundation for most vibration testing was laid in the 50's and 60's when there were significantly less computer capability than a current test lab has. Think vacuum electronic tubes and solenoid switching. The shakers had power limitation and were unable to produce the energy to run beyond 2000 Hz. Most started to roll off significantly after 1000 Hz. On the low end (20 Hz) the limitation was and still is usually stroke on the shaker armature. To maintain an acceleration at low frequency a large displacement is require. Most shakers only have 1 to 2 inch stroke that limits capability at low frequency.

On the Sine vs Random question, both represent different risks to your test hardware. The Sine gives a strong input at a single frequency. If that frequency is the vulnerable frequency of the hardware a prolonged dwell results in significant damage. The Random gives all the frequencies all at one. As a result, if there are interactions between different frequencies in the hardware the random induces them. A noted above in most cases the random is much more representative of the real world. The exception is equipment that goes on or near rotary machinery. This type of machinery tends to induce a strung vibration at a single frequency, similar to a sine.

Answer 2

There is no clear reason for that particular frequency range for vibration testing. I have done vibration testing at frequencies as low as 0.5Hz (rocket engine test stands) and as high as 10,000Hz (sensors for rocket engines). The lab must have known what you are testing and why, and provided equipment for that. Random vibrations are a better simulation of real environments than sine wave testing. Both are useful. Sinewave testing reveals dangerous resonances and will provide an answer to the maximum acceleration the object will withstand. Random vibrations with a realistic frequency spectrum is useful for MTF (mean time to failure) estimations. Even if the frequency spectrum is uniform, certain acceleration amounts may occur more frequently than others, and you can program random vibrations to give different statistical distributions of acceleration magnitudes to more closely simulate real-world conditions.

Answer 3

well 20 hz is below the limit of human hearing and 22 khz is the highest we hear so those limits are good