On the Use of Tracking Filters During Sine Vibration Testing

35th ANNIVERSARY ISSUE Sinusoidal vibration testing has evolved over the years for many good reasons. Initially, from a military standpoint, a predominant part of vibration excitation was from propeller driven aircraft. Here, system resonances could easily be excited during runup, or in the more unfortunate circumstance, during sustained operation at flight speed. Although there initially was only rudimentary instrumentation to measure and analyze field and test data, the approaches have been relatively consistent for over 40 years. In the mid to late 50s and throughout most of the 60s swept spectrum analyzers and then tracking filters were used to measure the ‘sine’ values of signals. When real-time analyzers and FFT analyzers were introduced in the late 60s and early 70s, attempts were still made to quantify the peak sinusoidal signals present. Through the addition of several “safety factors” a series of MIL-STD sine criteria, such as MIL-STD-202, was developed. Early shaker designs were aimed at sine testing as well. It was only in the early 60s that shaker manufacturers introduced designs with flexures aimed at random vibration testing in addition to swept sine testing. Several other advances in testing and analysis led to additional requirements for analyzing and testing with sine components. Thus today’s sine requirements include satellite shakedown, phase resonant dwell and MIL-STD-810’s sine-on-random definitions as well as swept sine testing.