The following statistics for a given pressure (1001.8 ~il!ibars)
were computed:
on the mean
within 0.1% or mean
" o.2% " II
" 0.3% " "
" 0.4% " "
" 0.5% " "
N .Y .'J. Shop Model
L-416
12.5%
25 %
41.5%
62.5%
75 %
95.6%
Bra:Dsford Model
B-501
34 %
50 %
70.5%
85.5%
91 %
100 %
Other conclusions arrived at as a result of this test were:
(a) Since changes of speed of the motors did not occur simul-
taneously in the two instruments, the speed changes probably
are not due to slight changes in pressure or temperature.
(b) Sensitivity varied from 0.1 to 0.9 millibars.
(c) Sensitivity increased with increase of rate of pressure change.
It was recommended as a result of these tests that the records
of flights when the balloon is floating be read to the nearest
two-tenths of a percent of a oycle,or approximately two-tenths
of a millibar, for high accuracy. ~ben using the instruments
manufactured by Brailsford and Co., satisfactory accuracy will
be attained, if necessary, when the record is read to the
nearest one-tenth of a percent of a cycle.
In the second group of tests the pressure was reduced slowly
to about 20 millibars and increased to sea-level pressure at
different temperatures.
The most comprehensive series of calibrations wes made with the
first instrument made by Brailsford and Co. Two runs were made
at room temperature ( 22_10 C), one at -lOOC, one at -30 to 37°C
and one at -56 to -620C. On the last test at the lowest tempera-
ture, the unit was found to be completely unreliable. The
cause of failure was the erratic· motor operation at extremely
low temperatures. This had been observed previously during
flights when the Olland-cycle was not thermally insulated.
The other curves were plotted on a single chart in order to
study their spread (see Figure 31). The envelope of curves
thus obtained showed no regular temperature effect over the
range +2,°C to -370C. In general, the envelope was less than
10 millibars wide although at some higher pressures it was as
much as 12 millibars wide. The curves at low pressures fell
closest together and were all within 3 to 4 millibars apart
between 50 and 150 millibars and 6 millibars apart between
150 to 200 millibars.
-70-