Random Testing and the Power Spectral Density (PSD)

Back to: Random Testing

Vibrations in the world around us are not repetitive or predictable like sinusoidal waveforms. They are random, so engineers often use random waveforms in vibration testing to ensure their products can withstand a realistic environment.

The main purpose of random vibration testing is to bring a device under test (DUT) to failure. Testing the DUT to failure will expose important details about the device’s weaknesses and indicate ways to improve the design.

Power Spectral Density

The power spectral density (PSD) is the most common tool for analyzing random vibration. Resonances and harmonics hidden in a time-history graph are visible in a PSD graph. In practice, generating a PSD is usually the first step in examining and analyzing a random waveform.

Generating a useful PSD is not as simple as pushing a button. Test engineers and technicians set various parameters to tailor the PSD calculations to specific test requirements. For the parameter settings to be effective, however, the engineer must understand the PSD.

How to Calculate the PSD

The subsequent lessons provide the steps to calculate the PSD. The lessons will communicate critical concepts without equations first and then move into a mathematically rigorous description of the PSD and related calculations.