Recording a calibration signal of known frequency and voltage on both tape
channels serves the following purposes:
a. It provides a known reference for verifying tape system validity
during troubleshooting operations.
b. It is used to set the tape deck input level to provide maximum dynamic
range during subsequent recordings. This is especially important for the
power amplifier input voltage recording when the full 40 dB usable recorder
range is often required.
3-3.2.1 Apply a 3.0g (peak) signal at approximately 1000 Hz to the
right (control accelerometer) channel of the tape deck (a charge amplifier
output sensitivity of 100 mv/g is recommended for the sine tests to minimize
noise and provide higher recording level to the tape deck). The output
calibration signal of the accelerometer charge amplifier may be used for this
purpose. Adjust the tape deck input level to obtain a 0 dB reading on the
right channel VU meter.
Apply a voltage signal at 1000 Hz to the left (power amplifier input voltage)
channel of the tape deck. This shall be accomplished by turning off the power
to the shaker system and using the compressor-off mode of the servo-controller
to provide the required 1000 Hz signal. Adjust the output level of the
servo-controller to approximately 10% higher amplitude than that measured in
the preliminary test run (reference paragraph 3-3.1.3
Then, adjust the tape deck input level to obtain a 0 dB reading on the left
channel VU meter. This will provide an undistorted recording range of +4 dB/
-40 with respect to the maximum level required for the sine sweep.
3-3.2.3 Set the tape counter at zero and then advance the tape
(without recording) for one minute of elapsed time. Stop the recorder at the
conclusion of one minute.
3-3.2.4 Place the tape deck in the record mode and record the two
calibration signals for one minute of elapsed time. Stop the tape deck at the
conclusion of the one minute.
3-3.2.5 Record all significant
parameter measurements, including tape counter readings, in the appropriate
box on the Tape Data Sheet (Figure