TM
5-6675-270-15
Section V. OPERATION UNDER UNUSUAL CONDITIONS
inaccurate or inoperable. Brush the theodolite
2-11. Operation in Extreme Cold
frequently, and carefully wipe it clean. Take care
(Below OF)
not to scratch lens and prism surfaces while clean-
With proper precautions and servicing, the the-
ing. Protect the instrument from blowing dust
odolite can be used in extreme cold. Its use is
and sand. Place a protective cover over the the-
limited only by the endurance of operating per-
odolite when it is not in use.
sonnel and by conditions affecting visibility. The
instrument should be kept out-of-doors or in
2-14. Operations Under Rainy or Humid
unheated buildings for short periods of non-use.
Conditions
Extreme changes in temperature will cause in-
In humid areas, a slight lowering of the ambient
ternal stresses affecting accuracy, and lenses and
temperature will cause condensation of moisture.
prisms may become fogged. Theodolites should
The result will be fogging of lenses and prisms.
be cleaned and all lubricants removed before be-
To avoid this condition, keep the theodolite
ing put to use under extremely cold conditions.
warmer than the surrounding air. Internal
Snowfall, winds, and refraction of light are some
fogging can usually be removed by putting the
of the adverse conditions encountered at low
theodolite in a warm dry place. Corrosion result-
temperatures.
ing from high humidity can be minimized by
CAUTION
utilizing warm, dry storage areas and by using
Avoid subjecting the theodolite to sudden
dessicants. After using the theodolite, dry the
changes in temperature.
instrument thoroughly and wipe all metal parts
2-12. Operation in Extreme Heat
with a soft cloth lightly impregnated with watch
oil. Do not get any oil on the lens, prisms, or
Both theodolite and operator should be protected
level vial surfaces.
by a surveyor's umbrella when sightings must be
taken in strong sunlight. Direct rays of the sun
2-15. Operation in Salt Water Areas
may cause internal stresses and distortion in the
Salt air is highly corrosive to metals and espe-
instrument. Heat ripples in the air near ground
cially to brass, from which many theodolites are
level create poor sightings condition. When such
made. Salt reacts with brass to produce a green
conditions prevail, taking shorter sightings will
deposit (verdigris), which must be guarded
reduce sighting errors. Also, taking sightings in
against and removed as soon as it is noticed. Wipe
the early morning or late evening will reduce
the instrument frequently with a soft cloth and
error magnitude. Operator error resulting from
dry thoroughly. Clean the instrument daily and
eyestrain and fatigue can be lowered if the opera-
apply a light film of watch oil to metal parts. If
tor wears suitable dark glasses. If the theodolite
the theodolite is exposed to direct salt spray, it
is stored in a cool place, it should be removed
should be cleaned thoroughly and returned to an
from storage long enought before use to allow the
instrument shop for overhauling as soon as pos-
instrument temperature to approach that of the
sible.
outside air.
2-13. Operation in Dusty or Sandy
2-16. Operation at High Altitudes
Areas
No special operating procedures are required
An instrument used in dusty or sandy areas re-
at high altitudes.
quires special care because both dust and sand are
highly abrasive. The theodolite's moving parts
will soon bind if they remain on threaded or slid-
No special operating procedures are required
ing surfaces, and the instrument will become
below sea level.
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