roswell

will cause an overshoot, hence the unnecessary exhaust of some
lifting gas.
The effects of temperature on the aneroid capsule of the auto-
matic ballast valving system wereeliminated by the use of a
ballast ~itch which uses a vacuum-sealed aneroid, set to per-
mit ballast flow through a valve whenever the balloon is below
a given pressure altitude. In this system the minimum pressure
switch and the lag caused by its usecre eliminated. This dis-
placement-switch control has the disadvantage that the flow
which it permits is not proportional to the displacement of the
balloon below a datum plane but is constant through the valve.
Normally this flow is large to permit rapid restoration of equi-
librium. A second disadvantage is the requirement of batteries
to supply power to the electrically operated valve. However,
the advantage of eliminating the temperature effects on the
aneroid compensate for these two comparatively minor disadvan•
tages.
In practice, the displacement switch has consisted of a modified.
radiosonde modulator in which the standard commutator is re-
placed by a special bar which is an insubtor above a certain
point and e. conductor at lower levels (higher pressures). When
the aneroid pen arm is on the conducting section of the commu-
tator, a relay opens the ballast valve. To prevent excessive
flow on ascent, the pen arm rides on an insule.ted shelf above
most of the contact segment of the commutator (Figure 11).
Figure 11. Pressure displacement switch.
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