Historically, acceptance of electronic equipment was originally limited to a form, fit and function appraisal through visual inspections and a functional "smoke" test conducted under room environments. In 1957 the Advisory Group on Reliability of Electronic Equipment (AGREE), created in 1952 by the Department of Defense Research and Development Board to "monitor and stimulate interest in reliability and recommend measures that would result in more reliable equipment," published its recommendations. These included specific requirements for establishing environmental test profiles to be used during reliability demonstration testing. It was also suggested that these same conditions be utilized for acceptance testing of electronic hardware. Vibration was established as one of the environments and was limited to a sinusoidal excitation of ±2g at a fixed non-resonant frequency between 20 and 60 Hertz. This form of vibration persisted for years and was used, with few exceptions, in the majority of electronics and avionic equipment acceptance tests conducted.
Evolving from the McDonnell Douglas Mercury and Gemini
manned spacecraft programs, random vibration was utilized to more effectively
screen workmanship defects. The unprecedented success of the Apollo manned
space program, attributable in large measure to the intensive test program (Reference 2), generated some new thinking
in industry and the military concerning the utilization of effective testing
(including random vibration) in achieving reliability requirements. Skeptics
still maintained that, while those techniques might work for Apollo whose
vehicles were essentially "one shot" devices, they probably would not be
effective for hardware (such as aircraft avionics) which had to survive
thousands of takeoff, flight, and landing hours. The Grumman Aerospace
Corporation decided at this time to investigate the merits of sine and random
vibration testing. Intuitively, it appeared that random vibration, which
provides simultaneous excitation of many modes in contrast to the single
frequency sine test, must be more effective in disclosing manufacturing
defects. Dr. John Dreher of Wright-Patterson Air Force Base supported this
intuition in his paper (Reference 3)
where he stated:
"While it is true that the associated sine sweeps do excite most of these
other resonances, one must consider the short time period spent in any one
resonance bandwidth and the fact that many of these resonances aren't excited
long enough to peak out. In contrast, the random test excites every resonance
for the duration of the test.
It appears, then, that the random test proposed is a less severe but more
thorough test."
