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TM 9-254
10-4.
Dioptometer - Continued
b.
Use. The dioptometer can be used for accurately setting and checking the diopter setting of fire control
sighting instruments. It can also be used for checking definition of field-of-view, parallax, and astigmatism in an
instruments optical system. The dioptometer is placed between the eye and the instrument to be checked and the
focusing sleeve is adjusted until the field-of-view is in sharp focus. The diopter setting of the instrument is then read on
the objective diopter scale at the focusing sleeve. When the fixed focus eyepiece of an instrument is properly adjusted,
the indication on the dioptometer should be -3/4 to -1 diopter, as read on the objective diopter scale (fig. 10-4).
Section II. TEST FIXTURES
10-5.
General.
The test fixtures listed in this section are those most commonly used in the rebuild and inspection of fire control
instruments. These particular test fixtures are of a universal type and with the use of special adapters each test fixture can
accommodate many different fire control instruments.
10-6.
Azimuth Test Fixture.
a.
Description. The azimuth test fixture (fig. 10-5) consists of a base, azimuth ring, vernier scale, adapter
support plate, and column. It uses various mounting adapters to accommodate different fire control instruments and uses
a projector collimator for a test target.
(1)
The base is cast iron having three leveling screws. It mounts and supports the other components of the
fixture.
(2)
The azimuth ring is precisely machined and graduated into 6400 mils by six hundred forty engraved
lines, each of which represents 10 mils. The ring can be set at any position and locked in place with a
clamping arm which is mounted under the base. A spring loaded plunger and adjustment screw
provides for fine adjustment of the azimuth ring.
(3)
The vernier scale mounts on the base in a machined track. It has an engraved scale consisting of fifty-
one graduations. Each graduation represents 0.2 mil. Every tenth line is numbered progressively by
increments of two from 0 to 10. It is possible to estimate readings as small as 0.1 mil on the vernier
scale.
(4)
The column clamps to the base and supports the projector collimator.
(5)
The adapter support plate is fastened to the spindle of the azimuth ring, concentric to the ring. A
machined surface perpendicular to the axis of the spindle, provides the mounting surface for the test
fixture adapters. Three cam-head screws in the plate permits easy clamping of the adapters on this
surface.
b.
Use. The azimuth test fixture is used for adjusting and inspecting panoramic and azimuth indicating, fire
control instruments such as the M-2 Aiming Circle, M117 Panoramic Telescope and the M12A7 Panoramic Telescope.
Parameters that can be checked with this test fixture are; backlash in azimuth and elevation gears, level travel, azimuth
and micrometer scale accuracy, and counter accuracy.
Change 2 10-4
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