Figure 2-7. Schematic of Compensating Baths
during compensation testing must be taken into account.
openings in each bath are opposite center of diaphragm.
These changes in pressure may be noted in terms of
Insure baths are on a level plane. Fill vessels with
feet of altitude from another standard altimeter. For
enough liquid to cover pointer of mechanism.
instance, if standard altimeter indicates 140 feet at start
of compensation test and 170 feet when test is
Avoid fires. Do not heat bath with an
completed, mechanism undergoing compensation test
open flame or permit smoking or any
will have changed plus 30 feet during same time. This
spark of flame in same room. Bath is
error must be subtracted algebraically from reading
heated to a temperature well above
obtained from test instrument in order to arrive at true
flashing and burning points in case
compensation. In short period of bath test, atmospheric
kerosene and certain volatile and
pressure variations may or may not occur. Generally,
inflammable constituents of liquid are
variations are of such slight magnitude as to be
distilled off during heating. Work in a
negligible. During a 2-hour ice box test, however,
place with good ventilation and safe
appreciable changes in atmospheric pressure may take
exits. Keep extinguisher, for oil fires,
m. Bring baths to their proper temperatures, usually
i. Liquid in hot bath can be heated safely by using
+40C (140F) and --40C (--40F), and stir liquid in
one or more electric immersion heaters or by coil in
each bath to insure uniform temperature throughout.
bath, through which hot water or steam is circulated.
Table 2-1. Temperature Compensation
j. Liquid in cold bath can be cooled in a refrigerator,
by a coil in bath through which a refrigerant is circulated,
For 35,000 ft
or by placing in bath one or more open metal vessels
containing carbon dioxide, d ice. If temperature cannot
be lowered to -40 C (-40F) and held during test period,
raise temperature of hot bath until it is 80C (144F)
above that of the cold bath.
k. If it is not possible to have a difference of 80C
(144F) between hot and cold baths, a smaller
difference may be used, but allowable change of reading
shown in table 2-1 will be proportionately reduced. If
temperature difference is 40C (72F), allowable
n. Place altimeter mechanism in stand assembly,
change of reading is half the allowable change with 80C
part no. TE1357-5003.
(144F) temperature change.
o. With hand at 0. Immerse mechanism in
l. Fluctuations in atmospheric pressure