Random equalization (para. 1-3.1.1 ) is accomplished synthetically using
the results of a 1.0g(peak) sinusoidal frequency sweep. The sine data in the
form of transfer functions (Power Amplifier Input Voltage ÷ peak acceleration -
E/g) provides the basis for the random equalization process. Since the
accurate determination of the transfer functions require a real time analyzer
or equivalent, for data analysis, a tape recording of the two required
parameters is made for transmittal to the agency which will prepare the
synthetic random tape.
This tape recording of the 1.09 (peak) sine frequency sweep will serve
another important function besides providing the transfer function data. It
will provide a means of verifying the test setup prior to performing the
random vibration test. In this sense, it substitutes for a spectrum analysis
of the random test for which the target test laboratory is not equipped.
The utilization of this recording of the 1.0g (peak) sine frequency sweep
to verify the test setup by playback through the shaker system necessitated
two special requirements for the frequency sweep:
a. Frequency is swept from upper limit (2000 Hz) to lower limit (20 Hz)
to minimize the potential for structural damage due to incorrect system gain
adjustment at the start of the sweep.
b. A one minute single frequency dwell at 1.0g (peak) is provided on the
tape prior to the start of this frequency sweep. This serves as a reference
for setting the system gain for 1.0g (peak) amplitude during
Another important consideration in recording the sine sweep is the
configuration of the vibration system. Since this frequency sweep will serve
as the random equalization reference for all subsequent tests, the vibration
system must be identical to that anticipated for subsequent production
testing. A prototype or mockup of the test article CANNOT be substituted for
the actual production unit. All test support equipment such as cooling air
hoses, electrical checkout cables, etc., which will be used on the production
units, must be installed for this test run.