Write the one sentence the report needs if the source cannot be found
How a Random Profile Is Written
An ASD: acceleration spectral density, in g squared per hertz
Often called PSD on the test floor
The overall level, grms, is the square root of the area under it
From the Sequence to the Profile
1. The step
One step of the sequence from Figure 1.2: carriage, tonal on broadband, hours at a time.
2. What the sensor saw
One record of many, half a second of it, level normalized.
3. Sorted by frequency
The same signal as an ASD (acceleration spectral density, the standards' word; often called PSD on the test floor), with two sibling records (dashed, dotted) behind it. The step from the record to this curve is the autospectrum, and how the controller averages it is Volume 2's subject.
4. Enveloped into a spec
Drag the amber breakpoints. Shaded: where the envelope sits above every record, the over-test.
breakpoint
level
Figure 1.5. From the sequence to the profile, in four panels: a step from the timeline; what the sensor saw during it; the same record sorted by frequency as an ASD, with its sibling records behind it; and the envelope drawn over them with the breakpoint table the lab actually receives. VD
Measured and Enveloped
Measured: sensors on the real article in the real step; the best case and the rarest
Enveloped: a smooth line over measured data, so one test covers many conditions
The lab receives a breakpoint table: frequency and level at each corner, slope in dB per octave
Every envelope over-tests somewhere, on purpose: one test is cheaper than ten
Tailored, Inherited, Predicted
Tailored: a standard's default adjusted to the platform and the step
A default curve with a program name typed on it is not tailoring
Inherited: the last program's profile; the most common source and the least examined
Predicted: a model driven by what a similar vehicle does to its payload
The Five Sources as a Ladder
Figure 1.6. The five sources as a ladder, ranked by how close each stays to the real step, measured at the top, with what is lost at each step down.
Margin and Duration Ride on Top
Margin is added on purpose, and should show as its own step in the derivation
Duration is scaled: a long exposure at a low level becomes a shorter, hotter test
That exchange is never free
Decide
Ask where the numbers came from before the test is scheduled
A document number and nothing else: find what is behind it
Or write down that it could not be found; the report needs that sentence either way
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