Vibration Testing Methods: Which Should You Perform?
The decision to select the ideal method to perform a vibration test should be depending on the environment and the goal of the test program.
There are four types vibration testing methods; each designed to simulate the vibration energy observed on each unique system.
1. Sinusoidal or Sine vibration testing
2. Random vibration testing
3. SOR Sine on Random
4. ROR Random on Random
Sinusoidal or Sine Vibration Testing
Sinusoidal vibration testing, also known as sine vibration testing, uses the vibration shaker to input the vibration energy in a sinusoidal wave form. The amplitude and frequency of the sinusoidal wave form is changed depending on the testing condition.
Sine-on-Random (SOR) Vibration Testing
In this test, sinusoidal tones are specifically placed over a random vibration profile. SOR test typically simulates environments for propeller driven airplanes and helicopters. Sine-on-Random Vibration Testing is also known as Mixed Mode Vibration Testing.
In summary, Sine testing is used in identifying resonant conditions within a device under test (DUT). For example, on an electronic module the circuit boards are often the main resonant structures and typically their fatigue conditions are most important to understand. However, the components themselves mounted on the PCB as well as the electronics housing also have their own unique natural resonant conditions which are usually different than the circuit boards.
We can use sine vibration to identify these resonant conditions on the PCB or on other test item structures in an effective way to understand the flow of mechanical vibration through a device which will help product owners to stiffen or dampen elements of the product to reduce the probability of a fatigue failure.
Random Vibration Testing
In real life situation, vibrations are usually in random form. Random vibrations can be found in automobiles, aircraft, rockets etc.
Random vibration testing involves running of vibration energy at all frequencies over a specified range on a device under test (DUT) simultaneously.
This is the most effective when the test is based on actual field measurements of the specific environment where a product will be operated.
Due to this (the process of conducting random vibration testing) and the statistical nature of random data, random vibration testing is most suited for vibration qualification tests.
Using an accelerometer or multiple accelerometers to capture the in-situ vibration environment, a random power spectral density plot can be created. This will allow the test to run at the level recorded or at increased levels.
By increasing the levels, it accelerates fatigue and reduces test time.
On a random vibration power spectral density plot, the acceleration amplitude is scaled on the y-axis in units of g2/Hz and the x-axis in units of frequency (Hz).
ROR Random on Random
When the vibration environment has two unique random vibration characteristics, then the random vibration profile can also be tailored to include random vibration applied over another random vibration background.
This type of test is the most common type of validation and qualification test performed for electronic components. This can perform tests including components production stress, screening to prototype testing, and qualification of products to military standards.