How Well Does 3 Approximate ∞? : Understanding ±3σ Clipping in Random Shake Tests

Random vibration testing presents a host of new and often confusing concepts to the test engineer. Among these, the notion of "clipping" or limiting the excitation signal to ±3 standard deviations has caused undue confusion. This article attempts to explain what 3σ clipping is all about and how it came to haunt us. Given the erosion of written history with time, we will do better at the former objective than the latter.