A preliminary test run shall be conducted before the actual sine tape
recording run. The objectives of this initial run are:
a. To measure the maximum power amplifier input voltage required during
the sine sweep.
b. To determine the frequency of the gain reference which will be
recorded on the tape.
The power amplifier input voltage measurement
will be used to set the recording level of the left tape channel. The gain
reference (see Chapter 1, Theory
) is required to provide the operator with a stationary
taped signal which will permit adjustment of system gains necessary to obtain
a 1.0g (peak) sine level.
Set up the sinusoidal oscillator and servo control equipment for a 1.0g (peak)
sine sweep from 2,000 to 20 Hz at a logarithmic rate of one octave per minute.
Connect the control accelerometer to the accelerometer input of the servo
controller to complete the servo loop (see Figure
Connect an RMS voltmeter or equivalent in parallel with the input to the
shaker power amplifier to monitor voltage during the sine sweep (see Figure
3-3.1.3 Energize the shaker system using the
nominal values of the parameters discussed in para. 3-2.2.1. Perform the
1.0g (peak) sinusoidal sweep described above. Monitor and record the power
amplifier input voltage during the frequency sweep to determine the following
a. Maximum power amplifier input voltage and the frequency of
b. Gain reference frequency. The choice of this frequency is
arbitrary but should be guided by the following ground rules.
(1) The frequency should be above 300 Hz to minimize the
potential for structural damage from potential mistakes made during
initial adjustment of the shaker system gain.
(2) The frequency should be at the center of a 100 Hz or wider
frequency band in which the power amplifier input voltage remains
relatively constant. This will avoid resonant peaks whose frequency may
shift slightly from setup to setup.
(3) In cases where several non-resonant bands are available,
the frequency selected shall be one in which the amplitude of the power
amplifier input voltage is close to the average for the various bands.
(4) Frequencies above 1500 Hz should be avoided since this
region is most sensitive to minor variations in the test
Record the gain frequency on the Tape Data
Sheet. (Figure 3-3 )