roswell

(b)
gears or poor alignment of the rotating cy-
linder. The motor gears may be cleaned with
carbon tetrachloride and a small clean brush.
If the trouble is due to misalignment, the in-
strument should not be used since this will
affect the rotation at a non-uniform rate and
thus destroy the entire accuracy of the record..
Calibrate the instrument. The following equip-
ment is required for the calibration: ·
Vacuum pump
Bell jar
Base plate with at lest 4 electrical leads
Manometer
Tape recorder
The vacuum pump should be capable of evacuating
the bell jar to a pressure lower than that to
be reached by the balloon in flight. A pressure
of ten millibars. corresponding to about
100.000 feet elevation is usually a good minimum.
Four wires are necessary to conduct the six
volts to the motor and to transmit the reference
and pressure signals. The wires must pass out
of the bell jar through an air-tight seal in
the base plate. The base plate also needs a
tube leading to the manometer and a tube to the
vacuum pump. It is advisable to use two sepa-
rate tubes rather than placing the manometer
lead in the same line as the pump lead in order
to obtain the pressure in the bell jar rather
than that in the pumping line.
In operation the negative line of the battery
leads is used as the ground connection of the
output signal.
A tape recorder such as the Brush Development
Co. model BL-902 oscillograph and amplifier
BL-905. is needed to record the signal both
during calibration and during the balloon flight.
The Brush recorder is used at present and the
discussion of the operation will be made in terms
of the characteristics of this instrument. When
using the slow speed of the recorder, which
feeds the paper at the rate of 30 centimeters
per minute, the distance between successive re-
ference marks will be 30 to 40 centimeters de-
-56-