Product Testing Services

Have you ever considered the vibration that is experienced by a package in transit?  What about the vibration that you feel while driving in a car down a country road?  Both of these are examples of random vibration.  As opposed to limiting vibration to a single frequency, all frequencies within a given range are applied at the same time (relatively speaking) at an intensity that you specify.  This intensity profile is designed to mimic those vibrational forces that the product would experience in actual operation or use.

So what are the variables associated with such a profile?  A sample of such a profile is given below.  You will note that it is a series of frequency breakpoints.  For each frequency, there is a corresponding intensity value known as Power Spectral Density (PSD) measured in g²/Hz.  Additionally there may be a third column of information for slope measured in dB/octave (not shown).

Sometimes this information is represented graphically:

The breakpoints define a profile within which the vibrational energy must be controlled.  It does not mean that vibration is only applied at the breakpoint frequencies.

So where do these profiles come from?  The most common source is the real world.  If you want to test a product for a vehicular application, go instrument a vehicle with accelerometers and record the actual vibration.  This information is used to develop a simplified profile that encompasses the original vibration patterns, perhaps with a little extra energy to ensure safety or design margin.

If you don't have real world vibration data, but do have some idea of what frequency range and acceleration you expect your product to experience, you can create a simple profile using the following conversion.  As noted previously, PSD is expressed in g²/Hz.

The final profile would be:

Which would provide approximately 3 g's of acceleration across the defined frequency band.

Test Specification Template (Random Vibration)