When preparing to run a vibration test, a test engineer is faced with the question of what kind of test should be run with any particular set-up. One option is a RANDOM vibration test.
What is RANDOM?
A RANDOM vibration test is a test that simultaneously sends random vibrations that over time include the entire vibration test’s frequency range. For example, consider Figure 1, in which a test profile is displayed that tests an item from 50 Hz to 4000 Hz. In Figure 2, the acceleration waveform for that test is displayed. The display shows a “ragged” plot, in which random amplitude vibrations are being used to test the DUT (Device Under Test).
Figure 1: A RANDOM test profile from 50 to 4000 Hz.
Figure 2: The acceleration waveform for a RANDOM vibration test. Note the random amplitudes of the accelerations experienced by the DUT.
Why Should I Use RANDOM?
Random vibration testing is beneficial for several reasons:
- The “real-world” is less synthetic than a single sine wave. Exciting all the frequencies makes a random test a more realistic representation of what occurs in the “real-world”.
- A random test can be created to represent multiple environments under which the DUT may be used in the “real-world”
- A random test can be accelerated to create a test representative of a longer field life than may be practically run in a lab.
- A DUT may have multiple resonances. Sine testing can only test one resonance at a time and cannot test the interactions of multiple resonances. By exciting all resonances at the same time, random vibration gets a glimpse of the interaction between these multiple resonances.
When Should I Use RANDOM?
Vibration test engineers should use random vibration testing when:
- Looking to test a product for “real-life” vibrations.
- Looking to see how a product will respond to multiple resonances being excited at the same time.
Testing a product to failure. Bringing the product to failure using a sine-track-and-dwell at one frequency ignores how vibrations at other frequencies affect the failure rate. Random vibration testing will result in a faster failure mode since all frequencies in the test profile are tested simultaneously.
