WHITE PAPER: Normalized PSD Difference Method

In HALT & HASS testing (Highly Accelerated Life Test & Highly Accelerated Stress Screen), the PSD (Power Spectral Density) of input energy into a tested component is important, as it measures which frequencies of the product under test have become stimulated. Coinciding, there is a need to compare the similarity of two PSD curves, yet no commonly accepted metric exists for comparing the similarity or dissimilarity of two PSD curves. Fulfilling this void, a new method of PSD comparisons was created at Qualmark, now making it possible to answer the question of “how different are these PSD’s?”. This new method normalizes two samples, plots the difference, and shows energy shifts across the frequency spectrum. With an improved metric to effectively compare these differences, deeper analysis can be performed to move PSD comparisons from subjective to objective. This method will assist HALT & HASS users to monitor PSD changes over time, develop PSD tolerances, evaluate variability between products in HASS, and also provide an effective tool to assess table performance. Continue reading to dive in to the science …