As indicated in Chapter 2, Theory of
Operation, the purpose of the sine sweep is to replace the random noise
spectrum analysis normally required to verify the input spectrum applied to
the test article. This is accomplished by accurately monitoring the control
accelerometer for deviations about the required 1.0g (peak) input during the
application of the sine sweep discussed in Chapter 3, paragraph
5-3.1.1 Prior to test, verify, that the tape cassette
title description corresponds to the test article and setup. Insert the tape
cassette into the deck such that the side designation which corresponds to the
required test axis or condition, faces outward.
5-3.1.2 Utilizing the electrical configuration described
in paragraph 5-2 1 , verify that the amplitude or master gain control of the shaker system
is in the zero or off position.
5-3.1.3 Rewind the tape cassette to the start position and
set the tape deck counter to 000.
5-3.1.4 From the
Tape Data Sheet Chapter 3, (see Figure 3-3 ) determine the
tape deck counter reading locating the recorded Gain Reference Signal.
5-3.1.5 Prior to test, switch the left channel tape deck VU meter to output
if manual switching is required If the tape deck utilized has an output level
control, move it to the full output position
5-3.1.6 Advance the tape using the fast-forward control the tape deck
counter reads two to three counts beyond the start of the recorded Gain
5-3.1.7 Verify that the shaker system is in a "run" or operate mode and
activate the playback control on the tape deck.
5-3 1 8 Observe the left channel VU meter for a positive reading (above 20
dB) when the tape reaches the Gain Reference Signal. When a positive reading
is observed slowly increase the amplitude or master-gain control of the shaker
system until a 1.0g (peak) or its equivalent rms voltage is read on the rms
voltmeter or servo-controller "g" meter
5-3.1.9 The tape deck will run continuously from that point until the end
of the sine sweep. The tape is programmed to initiate the following sequential
a. One minute of dwell at 1.0g (peak) at the gain reference
b. Twenty second drop in level while frequency is reset to 2000 Hz
c. Ten second increase in level at 2000 Hz to approximately 1.0 g
d. Seven minute frequency sweep from 2000 to 20 Hz.
e. Ten second decrease in level at 20 Hz.
During the frequency sweep from 2000 to 20 Hz, the control acceleration
amplitude shall be monitored continuously with the RMS voltmeter or
servo-controller "g" meter. Deviations from the nominal 1.0g (peak) level or
the rms voltage equivalent, shall be recorded when the value exceeds the
tolerance band specified in Table 5-1. The tape deck counter time shall also
be recorded on the Acceptance Test Data Sheet (see Figure
5-3.1.11 It should not be necessary to change the
amplitude or master-gain setting during the sweep once it is set during the
gain reference recording portion of the tape If a variation does exist, i e.,
the amplitude consistently averages higher than the upper tolerance band (see
Table 5-1) the master-gain shall be reduced to an average amplitude closer to
the 1 0g (peak) level and the change noted on the Acceptance Test Data Sheet
5-3.1.12 At the conclusion of the
frequency sweep portion of the tape, as evidenced by a drop in amplitude on
the RMS voltmeter and left channel VU meter, the amplitude or master gain
control be reduced to zero and the tape deck stopped.
If amplitude variations during the test run exceeded
the tolerance bands, in Table 5-1, proceed to Chapter 6,