Any distortion of the fundamental signal, regardless of source, shall
not be allowed to affect the measurement of displacement or acceleration
amplitude of the fundamental input frequency to the vibration machine.
Such distortion shall be eliminated from the input control signal by
use of a tracking band pass filter between the input control circuit
and the amplitude servo system.
22.214.171.124.3.2 Vibration pickups. During tests specified in 126.96.36.199
the output of the vibration machine shall be controlled and monitored
by three piezoelectric accelerometers mounted in the vicinity of the
programmer so as to indicate the greatest motion of the supporting
fixture on which the programmer is directly mounted. The accelero-
meters shall be positioned in three mutually orthogonal axes. One
accelerometer, mounted with its axis parallel to the axis of motion,
shall be used to control power to the vibration machine. The remain-
ing two accelerometers, mounted parallel and perpendicular to the
vibration machine trunnion axis, shall be used to monitor cross-axis
motion. Unfiltered cross-axis motion as indicated by either accelero-
meter shall not exceed the filtered input to the vibration machine.
Motion transducers other than piezoelectric accelerometers shall not
be used for input control or monitoring.
188.8.131.52.3.3 Control and monitor circuits. Circuits used to control
and monitor the vibration system for tests specified in 184.108.40.206 shall
meet the following requirements:
(a) Displacement circuits shall indicate amplitude of input
displacement to the programmer over the range of 0.010-inch double
amplitude to the upper limit of the equipment to an accuracy of plus
or minus 10 percent from 10 to 100 cps.
(b) Acceleration circuits shall indicate amplitude of input ac-
celeration to the programmer to an accuracy of plus or minus 10 per-
cent over the range of 17 to 2040 cps. The circuits shall be capable
of indicating the amplitude of both the fundamental and. unfiltered
signal. It shall not be necessary, however, to indicate these signals
Page 15, paragraph 220.127.116.11, last sentence: Delete "an indicated" and
substitute "as indicated".
Project No. 1340-N268